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21 306 marine design

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  • 1. 21 306 Marine Design © Mr D. L. Smith Universities of Glasgow & Strathclyde2006
  • 2. Marine Design 2_____________________________________________________________________________________________________________________________________________________________________ September 2005
  • 3. Marine Design 3__________________________________________________________________________________________TOPIC OUTLINES .............................................................................................................................................. 51. PHILOSOPHY OF DESIGN ....................................................................................................................... 6 1.1 WHAT IS DESIGN?.................................................................................................................................... 6 1.2 THE DESIGN TEAM................................................................................................................................... 6 1.3 WHAT IS A DESIGN PHILOSOPHY?............................................................................................................ 72 PRELIMINARY, CONTRACT & DETAILED DESIGN......................................................................... 9 2.1 MARINE DESIGN PROCESS ....................................................................................................................... 9 2.2 DETAILED DEFINITION OF PHASES OF SHIP DESIGN ............................................................................... 11 2.3 BASIC OR PRELIMINARY DESIGN ........................................................................................................... 12 2.4 CONTRACT DESIGN ................................................................................................................................ 12 2.5 DETAILED DESIGN ................................................................................................................................. 133 ELEMENTS OF SHIPPING – TYPES OF SHIP .................................................................................... 14 3.1 GENERAL ............................................................................................................................................... 14 3.2 SHIPS ..................................................................................................................................................... 14 3.3 SHIP SIZE AND DIMENSIONS ................................................................................................................... 17 3.4 CARGO CONSIDERATIONS ...................................................................................................................... 17 3.5 SIZE AND SPEED ..................................................................................................................................... 18 3.6 STRUCTURAL ARRANGEMENTS .............................................................................................................. 18 3.7 WORKED EXAMPLE - DEADWEIGHT CARRIER ....................................................................................... 21 3.8 SECOND WORKED EXAMPLE - DEADWEIGHT CARRIER.......................................................................... 224 OWNERS REQUIREMENTS & THE FORMULATION OF THE DESIGN...................................... 25 4.1 INTRODUCTION ...................................................................................................................................... 25 4.2 THE OWNERS REQUIREMENTS............................................................................................................... 25 4.3 SHIP TYPE .............................................................................................................................................. 27 4.4 DEADWEIGHT OR VOLUME?................................................................................................................... 275 ESTIMATING PRINCIPAL DIMENSIONS ........................................................................................... 29 5.1 DISPLACEMENT, LIGHTWEIGHT AND DEADWEIGHT ............................................................................... 29 5.2 DEADWEIGHT/DISPLACEMENT RATIO .................................................................................................... 30 5.3 LENGTH ................................................................................................................................................. 32 5.4 BREADTH, DRAUGHT AND DEPTH .......................................................................................................... 32 5.5 OVERALL LIMITS ON DIMENSIONS ......................................................................................................... 32 5.6 FORMULAE FOR LENGTH ........................................................................................................................ 33 5.7 BLOCK COEFFICIENT.............................................................................................................................. 34 5.8 LENGTH/BREADTH RATIO ...................................................................................................................... 356 WEIGHT ESTIMATION........................................................................................................................... 42 6.1 BASIC APPROACH .................................................................................................................................. 42 6.2 STEEL WEIGHT ...................................................................................................................................... 42 6.3 OUTFIT WEIGHT..................................................................................................................................... 46 6.4 MACHINERY WEIGHT............................................................................................................................. 48 6.5 WEIGHTS OF CONSUMABLES .................................................................................................................. 49 6.6 CENTRE OF GRAVITY ESTIMATION ........................................................................................................ 51 6.7 PRINCIPAL ITEMS OF MACHINERY WEIGHT ........................................................................................... 53 6.8 PRINCIPAL ITEMS OF OUTFIT WEIGHT.................................................................................................... 547 POWER ESTIMATION AND SERVICE MARGINS ............................................................................ 56 7.1 GENERAL ............................................................................................................................................... 56 7.2 DEFINITIONS OF POWER ......................................................................................................................... 56 7.3 STANDARD SERIES ................................................................................................................................. 57 7.4 COMPONENTS OF RESISTANCE ............................................................................................................... 57___________________________________________________________________________ September 2005
  • 4. Marine Design 4__________________________________________________________________________________________ 7.5 FRICTIONAL RESISTANCE....................................................................................................................... 59 7.6 RESIDUARY RESISTANCE ....................................................................................................................... 60 7.7 RAPID POWER ESTIMATES FOR NEW SHIP DESIGNS ............................................................................... 61 7.8 TRIAL AND SERVICE MARGINS .............................................................................................................. 61 7.9 SPEED MARGINS .................................................................................................................................... 628 SELECTION OF MAIN MACHINERY .................................................................................................. 66 8.1 FACTORS IN THE CHOICE OF MAIN MACHINERY..................................................................................... 66 8.2 TYPES OF DIESEL ENGINE ...................................................................................................................... 66 8.3 AUXILIARY MACHINERY........................................................................................................................ 66 8.4 PRINCIPAL MAIN ENGINE SYSTEMS ....................................................................................................... 67 8.5 ELECTRIC POWER GENERATION ............................................................................................................. 67 8.6 FUEL SYSTEM FUNCTIONS ..................................................................................................................... 68 8.7 PRELIMINARY ESTIMATION OF PROPELLER DIAMETER .......................................................................... 689 ESTIMATING HYDROSTATIC PROPERTIES AND INITIAL STABILITY ................................... 71 9.X UNDAMPED ROLL MOTION IN STILL WATER ......................................................................................... 77 9.Y WORKED EXAMPLE - CAPACITY CARRIER ............................................................................................. 7810 GENERAL ARRANGEMENT.............................................................................................................. 83 10.1 INTRODUCTION ...................................................................................................................................... 83 10.2 TRIM ...................................................................................................................................................... 83 10.3 LOCATION OF THE MACHINERY SPACE .................................................................................................. 83 10.4 LENGTH OF MACHINERY SPACE............................................................................................................. 84 10.5 STORAGE OF LIQUIDS............................................................................................................................. 84 10.6 CARGO HOLDS ....................................................................................................................................... 85 10.7 HATCHWAYS .......................................................................................................................................... 85 10.8 ACCOMMODATION ARRANGEMENT ....................................................................................................... 86 10.9 MINIMUM REQUIREMENTS FOR CREW ACCOMMODATION ..................................................................... 86 10.9 MORE COMPLEX GENERAL ARRANGEMENT PROBLEMS ........................................................................ 8711 CAPACITY AND CENTRE OF VOLUME ESTIMATES ................................................................. 9312 THE REGULATION OF SHIPPING ................................................................................................... 98 12.1 THE ROLE OF THE CLASSIFICATION SOCIETY ........................................................................................ 98 12.2 STATUTORY REGULATIONS ................................................................................................................. 101 12.3 INTERNATIONAL MARITIME ORGANISATION (IMO)............................................................................ 10513 TONNAGE ............................................................................................................................................ 111 13.1 INTRODUCTION .................................................................................................................................... 111 13.2 PRESENT TONNAGE REGULATIONS ...................................................................................................... 111 13.3 THE MOORSOM TONNAGE MEASUREMENT SYSTEM ............................................................................ 11414 THE ASSIGNMENT OF FREEBOARD ............................................................................................ 116 14.1 WHAT IS FREEBOARD?......................................................................................................................... 116 14.2 WHAT IS THE PURPOSE OF FREEBOARD?.............................................................................................. 116 14.3 THE DEVELOPMENT OF FREEBOARD RULES ......................................................................................... 116 14.4 CURRENT REQUIREMENTS FOR FREEBOARD ......................................................................................... 117 14.5 DETERMINATION OF MINIMUM FREEBOARD ........................................................................................ 119 14.6 GENERAL CONDITIONS OF ASSIGNMENT OF FREEBOARD ..................................................................... 11915 FURTHER READING ......................................................................................................................... 121 15.1 BOOKS ................................................................................................................................................. 121 15.2 TECHNICAL PAPERS ............................................................................................................................. 121___________________________________________________________________________ September 2005
  • 5. Marine Design 5__________________________________________________________________________________________Topic Outlines Examinable Material 1 Philosophy of Design 2 Preliminary, Contract & Detailed Design 3 Elements of Shipping – Types of Ship 4 Owners Requirements 5 Displacement, Dimensions & Form Relationships 6 Weight Estimation 7 Powering Calculations 8 Machinery Selection 9 Approximate Hydrostatics 10 General Arrangement For Information (Relevant to Ship Design Project) 11 Capacity Calculations 12 Maritime Organisations & Regulation 13 Tonnage 14 Introduction to Freeboard___________________________________________________________________________ September 2005
  • 6. Marine Design 6__________________________________________________________________________________________1. Philosophy of Design1.1 What is Design? Design and Designer tend to be overused words for which there are many definitions.However it is not always easy to agree on the right definition. Here are some candidates forthe position:- a) Design is the visualisation and depiction of form. b) Design is the mental process which must intervene between the conception of a specific engineering intention and the issue of drawings to the workshop. c) Design is the optimum solution to the sum of the true needs of a particular set of circumstances. d) Design is a creative, iterative process serving a bounded objective. e) Mechanical Engineering Design is the use of scientific principles, technical information and imagination in the definition of a mechanical structure, machine or system to perform pre-specified functions with the maximum economy and efficiency. The Designer is clearly the paragon who carries out such tasks. His/her work can be split into three areas of activity:- a) Decision-making regarding the physical form and dimensions of the product. b) Communication to the builder, mainly in the form of drawings and specifications (Graphics, Text and Computer Files). c) Responsibility for the achievement of the original requirements. Often the designer must guide the original requirements to limit them to the possible.1.2 The Design Team In this class we are concerned with ships and other marine structures which aresufficiently large that they are unlikely to be designed by one person acting alone. The workmust be shared by a team, many of whose members will be specialists in one sub-section ofthe work. The main duty of the chief designer is then to ensure proper co-ordination of theteam members and to maintain a balanced overall view of the design. This may involve takingall important decisions and examining the associated plans. For peace of mind the successfulchief designer must have an almost instinctive ability to notice errors and query impossibleassumptions. In this Class and the associated Design Projects Classes you will be largely working asindividual designers practising the basic technical skills. In later years of the course you canexpect to work as Design Teams where some of the wider skills will be developed and tested.___________________________________________________________________________ September 2005
  • 7. Marine Design 7__________________________________________________________________________________________ It is important always to be aware of these wider skills and to remember that when youmake a decision you should record it and, what is often more important, why you made it, sothat you can communicate it to someone else or accept responsibility for it at a later time andbe able to justify it.1.3 What is a Design Philosophy? Philosophy might seem a somewhat grand word to use in the context of design but, inthe sense of a body of broad principles, concepts and methods which underpin a given branchof learning, it is a meaningful one to use. A philosophy does not determine the detailed actionto be taken in particular applications, but it does lead to the development of theories, rules andlaws and to detailed methods of applying them. These form the discipline of design. There is no single philosophy which satisfies all situations so the aim must be todevelop a philosophy which leads to a consistent set of general principles on which thediscipline can be based. This pragmatic approach requires that the outcome of applying thegeneral principles in a particular situation must be evaluated against some appropriate criteriaof success so that the principles and the associated discipline can, if necessary, be modifiedfor future applications. The feed-back mechanism is an essential component of both thephilosophy and the discipline. The following is a list of terms, aspects and concepts which reveal some of the generalprinciples arising in design:- a) Morphology. There is a pattern of events and activities which, by and large, are common to all projects. b) Design Process. Iteration to solve problems followed by feedback of information from a later stage to review decisions made earlier. c) Stratification. As the solution to one problem emerges, a sub-stratum of lesser problems is uncovered. Solutions to these must be found before the original problem can be solved. d) Convergence. Many possible solutions may be processed in search of the one correct solution. e) Decision-making. Choosing between alternatives. f) Analysis. Used to establish the characteristics of the product which is the subject of the design. This is a fundamental design tool because it forms the basis on which decisions can be made but it is not the starting point for a design. A first shot must have been made at what the whole product will be like. g) Synthesis. This is the truly creative part of design - putting together separate elements into a coherent whole. Probably this is the most characteristic part of design. h) Creativity. Inventiveness - obviously a highly desirable facility in a designer.___________________________________________________________________________ September 2005
  • 8. Marine Design 8__________________________________________________________________________________________ i) Practicability. What can be achieved in design is determined not only by what is technologically practicable but also by the capabilities of the design team. j) Communication. A design is a description of a product and the instructions for its manufacture. The quality of the end product depends critically on how well these two aspects are communicated. k) Dynamics. Design is not a static process, especially with a large and complex product. Change in requirements or solution is almost unavoidable. l) Need. The need for the product must be clearly established before starting design work. m) Economic Worth. The owner of the end product must feel that it is worth the true cost of its acquisition. n) Optimisation. In design terms it may not be possible to devise the optimum solution, where the optimum is determined relative to many disparate constraints and on the basis of incomplete data. The best available solution may be no more than the best compromise that can be made between conflicting qualities within the constraints. o) Criteria. The objective and quantitative measure of how successful or how near the optimum the design is. Sometimes the criteria are subjective and qualitative - the result of value judgements by those involved in the process. p) Systems Approach. When a product is part of a broader system (and very few exist in complete isolation) its design must take account of the impact of the rest of the system on it and vice versa.___________________________________________________________________________ September 2005
  • 9. Marine Design 9__________________________________________________________________________________________2 Preliminary, Contract & Detailed Design2.1 Marine Design Process The life of a ship may be divided into two distinct parts: - The period of Construction The period of Operation. The owner is most concerned with the second period but the Naval Architect is moreconcerned with the first. The first period can be further divided into two stages: - Design Build. Naval Architects are concerned in both stages but the Designer is most involved in thefirst stage. The actual design process is not a single activity but for most ships consists of three orfour distinct phases: - Basic Design ( Concept Design ( Feasibility Design Contract Design Contract Design Detailed Design Detailed Design The three or four phases are conveniently illustrated in the Design Spiral as aniterative process working from owners requirements to a detailed design. Three sampledesign spirals are shown (Buxton, Taggart and Rawson & Tupper). Taggart shows the processstarting at the outside of the spiral, where many concept designs may exist, and converging into the single, final, detailed design. Rawson & Tupper and Buxton show the process startingat the centre of the spiral where very little information is known and proceeding outwards torepresent the ever increasing amount of information generated by the design process. In eitherrepresentation it is clear that a series of characteristics of the ship are guessed, estimated,calculated, checked, revised etc. on a number of occasions throughout the design process inthe light of the increased knowledge the designer(s) have about the ship. The analogy of the Design Spiral can be extended to demonstrate the passage of timeas the design progresses. If a time axis is constructed at the centre of one of the figuresperpendicular to the plane of the paper then as time passes between successive activities sothe spiral is traced out on the surface of a cone. This class deals essentially with only the basic (or preliminary) design process whichis considered to be completed when the characteristics of the ship which will satisfy therequirements given by the owner have been determined.___________________________________________________________________________ September 2005
  • 10. Marine Design 10_____________________________________________________________________________________________________________________________________________________________________ September 2005
  • 11. Marine Design 11__________________________________________________________________________________________ Contract design involves the preparation of contract plans and specifications insufficient detail to allow an accurate estimate of the cost and time of building the ship to bedeveloped. It is at this point that the decision to go ahead and build the ship can be taken. The detailed design stage is devoted to the preparation of detailed working drawings,planning schedules, material and equipment lists etc. from which the production workforceactually build the ship. Detailed design, itself, is often broken down into three parts -Functional Design where each of the systems which contribute to the operation of the vesselare designed for function and performance on a ship-wide basis, Transition Design whichgroups all the systems present in a single constructional zone of the ship and integrates themto develop the most efficient manufacturing approach and Detailing or Work InstructionDesign which translates the design intent into clear, complete and accurate ordering ormanufacturing information in the format and timescale required by the shipbuilding process.2.2 Detailed Definition of Phases of Ship Design Before looking at the specific features of preliminary design, it is expedient to re-examine the fundamental requirements for every ship. Every ship designer, no matter howlogical and realistic they may be, needs to get back to first principles every so often in thesearch to make nature serve. It is not in the least beneath the designers dignity or intelligenceto write down, in a few lines, as did the renowned W J M Rankine in the middle of the 19thCentury, the following simple requirements for every ship: - i) To float on or in water ii) To move itself or to be moved with handiness in any manner desired iii) To transport passengers or cargo or any other useful load, from one place to another iv) To steer and to turn in all kinds of waters v) To be safe, strong and comfortable in waves vi) To travel or to be towed swiftly and economically, under control at all times vii) To remain afloat and upright when not too severely damaged.___________________________________________________________________________ September 2005
  • 12. Marine Design 12__________________________________________________________________________________________2.3 Basic or Preliminary Design Basic or preliminary design is the process of finding the set of principal characteristicsof a ship which satisfies the requirements in the ship owners proposal document. Severalpreliminary designs may be worked up, each satisfying the requirements but differing incharacteristics not specifically set out in the proposal such as type of propelling machineryThese alternative designs or some of them may be taken as far as the contract design stage toascertain the difference in cost and build time or the ability of particular shipbuilders tosupply ships of the given characteristics. Indeed contracts may be placed with differentdesigners for several different designs all satisfying the same commercial or militaryrequirements. Thus basic design includes the selection of ship dimensions, hull form, power (amountand type), preliminary arrangement of hull and machinery, and main structure. The correctselection will ensure the attainment of the owners requirements such as deadweight, cargocapacity, speed and endurance as well as good stability (both intact and damaged), seakeepingand manoeuvrability. In addition there must be checks of, and the opportunity to modify,cargo handling capability, crew accommodation, hotel services, freeboard and tonnagemeasurement. All of this must be done while remembering that the ship is but part of atransportation, industrial or service system which is expected to be profitable. Basic design includes both Concept design and Feasibility design In Concept design the aim is to explore both a basic design and systematic variationsof it in order to find the effect of a small change in Length, Beam etc. with the objective offinding the most effective or most economic solution. Much of the background data used willbe in the form of curves and formulae which allow simple methods to be used in theevaluation of the effects of variation. A design variation which would not be economic inservice or would not be profitable to build would be discarded while further variations mightbe applied to a design which survived this stage. In Feasibility design (Preliminary design for Taggart) the most successful conceptdesign is developed further to ensure that it can be turned into a real ship. The effect ofchoosing "real" engines, "real" plate thicknesses will inevitably induce minor but significantchanges to layout, weights and dimensions. The completion of this phase should provide aprecise definition of a vessel that will meet the owners requirements and hence the basis forthe development of the plans and specifications necessary for the agreement of a contract.2.4 Contract Design This involves one or more subsequent loops around the design spiral to further refinethe basic design. The work has expanded to the extent that it can no longer be progressed byone person or a handful of people. It now involves large teams representing all the maindisciplines - Naval Architecture, Ship Structures, Marine Engineering, Electrical Engineeringand Systems Engineering - all hopefully under the control of a Naval Architect. The hull formcan be based on a faired lines plan, and powering, seakeeping and manoeuvring may be basedon model test results. The structural design will have taken account of structural details, theuse of different types of steel and the spacing and type of framing.___________________________________________________________________________ September 2005
  • 13. Marine Design 13__________________________________________________________________________________________ A firm and reliable estimate of the weight and position of the centre of gravity of theLightship, taking account of major items in the ship is a clear requirement at this stage. Thefinal General Arrangement is also developed now. It fixes the volumes given over to cargo,fuel, water and store spaces and the areas devoted to crew accommodation, machinery andcargo handling equipment. The specification of the performance of every aspect of the ship, its outfit, machineryand equipment is determined along with the necessary quality standards and the tests andtrials needed to demonstrate the successful build of the ship. It is only at this stage that the prudent owner will become committed to buying theship by the act of signing the contract2.5 Detailed Design The final stage of ship design is the development of detailed working drawings. Theseform the detailed instructions for construction and installation that will be issued toshipwrights, platers, welders, fitters, turners, plumbers, coppersmiths, electricians and all theother trades without whom the ship could not be built. This work is not really the province ofthe Naval Architect although a Naval Architect may well control the work of those whoproduce the drawings and instructions. There is of course a clear role for the Naval Architect in assuring the quality of thedetailed definition of the ship and in ensuring that the design intent of the concept has beencarried through to the final stage. This means for example, checking that the routes for criticalpiping systems do not clash or that high power electric cables do run alongside sensitivecircuits carrying digital electronic control signals. Other checks would include ensuring thatthe correct structural detailing of cut outs, brackets and compensation have always beenemployed, that continuity of structure has been maintained and that doorways toaccommodation do not have pillars or similar obstructions directly in front of them. In traditional shipbuilding no thought was given as to how best to build the ship untilall the drawings were complete by which time it was too late to make any changes. In modernshipbuilding, partly but not exclusively, assisted by computer it is practical to considerplanning the build process alongside the design process to ensure that the detailed designinformation is made available to match the production process both in timescale and inmethod. This gives rise to the Transition Design phase of Detailed Design where themanufacturing information for all the systems in a single constructional block or zone isextracted from the design information prepared or being prepared on a ship-wide basis foreach individual system. With functional requirements and component positions defined by thepreceding design processes, Work Instruction Design finalises details and materialrequirements on work instruction plans. These are organised to suit the production process byproviding manufacturing (part fabrication) and fitting (assembly) instructions which matchthe way the work is to be carried out. This concept and the benefits it brings were more fully developed in the class MarineManufacturing.___________________________________________________________________________ September 2005
  • 14. Marine Design 14__________________________________________________________________________________________3 Elements of Shipping – Types of Ship3.1 General Ships are a sub-set of the set of transport vehicles which have the feature that theycarry their cargo over water. The different characteristics of the various types of transportvehicle can be illustrated in many ways. One, rather elderly, figure “Specific Resistance ofSingle Vehicles” shows one such illustration - the domain of each vehicle is shown, as are thegaps between vehicles. The gaps may be caused by economic factors as well as technical onesbut developments tend to remove them, either by adjustments to existing vehicles, or byproducing new ones. For a new type of vehicle to prosper it must either fill a gap on such adiagram or have an economic advantage over the existing vehicle.3.2 Ships Ships are the main type of sea transport vehicle. The figure “World Fleet of MarineVehicles” shows a breakdown of all seagoing self-propelled marine vehicles into a variety ofcategories. Ships for transport make up just under half of the world fleet by number but nearly90% by gross tonnage. The contribution of sea transport to the world economy is clearly vastwhen we take gross tonnage as a measure of the relative size of ships. Care does have to betaken over what is meant by the size of a ship and some key definitions are also given.___________________________________________________________________________ September 2005
  • 15. Marine Design 15__________________________________________________________________________________________ Most ships for transport are displacement craft and support the weight of theirstructure and contents by displacing a volume of water of equal weight. Thus the weightcarried is not a function of the speed of the ship, but none the less displacement and speed arethe basic characteristics of any ship. They complement one another to produce the tonne-miles which can be moved in a given time. Speed may also be interpreted as the rapidity ofturn round in port as well as the more obvious rate of crossing the sea. A Table of Particularsof Some Sea Transport Vehicles is included to indicate the size and range of size of merchantships.___________________________________________________________________________ September 2005
  • 16. Marine Design 16__________________________________________________________________________________________ The displacement of a ship reflects its size for all ship types but a simple visualcomparison of size between different types is often misleading. The Oil Tanker andSubmarine, like the iceberg, when laden are mainly below the water surface; the Ferry and theWarship, in contrast, are mainly above the water surface. All cargoes (including passengers)have a certain density as does the seawater in which the ship floats. When the cargo is densethen it demands a considerable displacement for its support and most of the ship is belowwater. Passengers, on the other hand, like weapons on a warship, demand a lot of space anddo not like it to be below the waterline.Oil TankerCruise Ship Cargo is usually assessed by its Stowage Rate - the inverse of density - in units ofm3/tonne. Ore represents a dense cargo with a stowage rate of about 0.5 m3/tonne. Thestowage rate for passengers is much more variable, depending as it does on the nature of thevoyage, its length, its cost and so on. Typical values range between 6 and 30 m3/tonne. Thus agreat deal of a passenger ship is above water. Outline General Arrangement drawings of a number of ship types are shown toillustrate the relative distribution of volume above and below the design waterline.___________________________________________________________________________ September 2005
  • 17. Marine Design 17__________________________________________________________________________________________ Safety demands that some part of the ship shall project above the water. The amountthat does project must fulfil at least the minimum international standards for reserve ofbuoyancy. However it cannot be assumed that the more of a ship that projects above the waterthe safer it is because not all of the superstructure may be strong enough or well enoughsubdivided to provide such buoyancy. For many years a class of cargo ship – the Open ShelterDecker – deliberately avoided such subdivision to minimise its tonnage – used as a measureof its earning capacity – and this philosophy was also applied to Ro-Ro ships with the seriousconsequences which are now familiar to all.3.3 Ship Size and Dimensions The principal dimensions of a ship are Length, Breadth, Draught and Depth (L, B, Tand D). Long experience, together with scientific effort and a good deal of experimental work,shows that these dimensions must bear appropriate relationships to each other if a successfulship is to emerge. Among the factors which influence the relationships are Propulsion,Stability, Seaworthiness, Cargo Considerations and Geography, including Port Development. A set of relationships between the principal dimensions for the main types of merchantships have been derived and show significant differences between ship types - especiallybetween “Deadweight” carriers and “Capacity” carriers Physical restrictions are important and may affect any dimension but in merchantships draught is usually the one first affected. Older port restrictions may affect draught atabout 10 metres or 15000 tonnes deadweight. Breadth and length may not indicate asignificantly larger vessel before restriction is imposed on them too. No port limitation ispermanent - they alter as time passes or the port goes out of business. Restrictions imposed by the Suez and Panama Canals and perhaps by such secondarychannels as the St Lawrence Seaway come into effect next. At present the "Suezmax" limit isabout 180,000 tonnes deadweight and the "Panamax" limit is about 75,000 tonnesdeadweight. Changes to the Panama Canal would be almost prohibitively expensive and so theships must remain within the canal limits or accept that the only way of getting from the EastCoast of the American Continent to the West Coast is the long way round by Cape Horn. The ultimate limits are set by the main sea-lanes of the world. In some of them, suchas the English Channel, draught restrictions begin at about 25 metres corresponding to350,000 tonnes deadweight. These limits are hard to overcome but dredging and blasting canbe used. At present this is the largest economic size of vessel built and it may be that the costsof developing all the facilities for even larger vessels, - say up to 1,000,000 tonnesdeadweight - are not outweighed by the improved operating costs.3.4 Cargo Considerations Cargo has an important bearing on ship design, especially on the size of ships. Thesize of the ship must match the size of the consignment in which the cargo can be produced,collected, stored, marketed and distributed. Part loads are now seen as uneconomic.___________________________________________________________________________ September 2005
  • 18. Marine Design 18__________________________________________________________________________________________ Only non-perishable bulk commodities can be gathered together in large enoughquantities to take advantage of the economies of scale possible with very large ships. Thecontainer ship secures the economies of scale for the small consignment and provides ameasure of security for those of relatively high value.3.5 Size and Speed Total resistance to the forward motion of a ship is a complicated function of size,shape and speed among other quantities but resistance per unit of displacement remains fairlyconstant if the Froude Number v//gL is constant. Hence an increase in size makes possible a corresponding increase in speed withoutparticular change in specific resistance although the total resistance will naturally rise.3.6 Structural Arrangements It is clear that in much of ship design “form follows Function”. Low value, non-perishable cargoes travel slowly, in large quantities in simple, almost box shaped vessels,while high value or time dependent cargoes travel much faster, in small quantities in muchmore complex vessels. Similar considerations apply to the structure of ships, typified by their midshipsections. Representations of the most common types – General Cargo, Bulk Carrier, OilTanker and Container ship are given. The General Cargo ship and the Container ship both need large hatch openings in theupper deck to load/unload their cargo and also require holds of reasonably rectangular crosssection to stow the cargo. Bulk carriers have similarly large hatch openings but a differenthold cross section to restrain their cargoes from movement in a seaway and to ensure thatmost of it can be removed by grab descending through the hatchway.___________________________________________________________________________ September 2005
  • 19. Marine Design 19__________________________________________________________________________________________ The Oil Tanker needs no significant hatch opening since its cargo is pumped in andout. Shown here is a traditional “single skin” tanker. Most newly built Tankers now have adouble skin (and the cross section looks like a container ship with the deck entirely platedover) to protect the environment in case of collision or grounding.___________________________________________________________________________ September 2005
  • 20. Marine Design 20__________________________________________________________________________________________From ‘Basic Ship Theory’ by Rawson & Tupper(Note that in Col 3 (Tanker) of Table 15.3, the percentages for Crew, Fuel & Fresh Waterwould be more realistic if taken as 0.1; 4.8; 0.6 and not as shown.)___________________________________________________________________________ September 2005
  • 21. Marine Design 21__________________________________________________________________________________________3.7 Worked Example - Deadweight CarrierUsing the data in Figures 15.8, 15.9 and in Table 15.3 of this section, estimate the principaldimensions of a general cargo ship of 14,500 tonnes deadweight and 14 knots service speed.From Table A , Deadmass Ratio (D.R.) = 0.675∴ Design Displacement = 14500/0.675 = 21481 tonnesFrom Figure A, Take CB = 0.77 and corresponding Fn = 0.2 14 knots = 0.5144 * 14 = 7.2 m/sec Fn = v/√(gL) ∴ L = v2/g*Fn2 = 7.22/9.81*0.202 = 132 m v in m/sec; g in m/sec2; L in mFrom Figure C, Take L/B = 6.2 (the middle of the range of 14500 t ships) Hence B = 132/6.2 = 21.29 mSimilarly, Take B/T = 2.2 Hence T = 21.29/2.2 = 9.68 mNow check ∆ = ρLBTCB = 1.025*132*21.29*9.68*0.77 = 21470 tonnes (A close result!)If you are not so fortunate with your first choice then select two further values of CB andcorresponding Fn from the figures; then find the dimensions and displacement of your twoadditional trial ships as above. Then plot displacement against Length and pick off the Lengthwhich gives the desired displacement. Fn (design) = v/√ (gLdesign)and so the correct CB can be read from Figure A anda check made on displacement. ∆ = ρLBTCB = ρL3CB/(L/B)2(B/T)Alternatively, displacement may be plotted against CB,in a similar way to the plot against Length shown above,and the design value found.___________________________________________________________________________ September 2005
  • 22. Marine Design 22__________________________________________________________________________________________3.8 Second Worked Example - Deadweight CarrierEstimate the dimensions of a dry cargo ship of 13,000 tonnes deadweight at a maximumdraught of 8 metres and with a service speed of 15 knots. Assume Deadweight/Displacement Ratio (DWR) = 0.67 and B = 6 + (L/9) mDisplacement (∆) = 13000/0.67 = 19403 t ∆ = ρLBTCB = ρL(6 + (L/9))TCB∴ CB = ∆/(ρL(6 + (L/9)T) = 19403/(1.025*L*(6 + (L/9))*8) (1)Also, CB = 1.08 - 1.68 Fn = 1.08 - 1.68v/√(gL) (2) For L (m) CB (from 1) CB (from 2) 140 0.784 0.705 150 0.696 0.718 160 0.622 0.729Hence, L = 147.6 m and CB = 0.715 B = 6 + (L/9) = 22.4 m ∆ = ρLBTCB = 1.025 * 147.6 * 22.4 * 8 * 0.715 = 19384 tonnes Sufficiently close!___________________________________________________________________________ September 2005
  • 23. Marine Design 23_____________________________________________________________________________________________________________________________________________________________________ September 2005
  • 24. Marine Design 24_____________________________________________________________________________________________________________________________________________________________________ September 2005
  • 25. Marine Design 25__________________________________________________________________________________________4 Owners Requirements & the Formulation of the Design4.1 Introduction A design begins with the preparation of a set of "Owners Requirements" for amerchant ship or "Staff Requirements" for a warship. In general the stages leading up to therequest for a new design are the same for merchant ships as for warships with the importantdifference that warships are built for a government whereas merchant ships are normally builtfor a private owner. The preparation of these requirements, especially for merchant ships,remains an inexact science. It is based on future expectation of demand in the trade underconsideration and chance is often as likely to make the forecast correct as foresight. In commercial ship design the demand for a new design usually originates with thechief executive responsible for the operation of a companys ships. From information whichbecomes available on such matters as the economics of operating the existing fleet, the stateof their part of the shipping market, developments in international trade etc, he/she arrives atthe conclusion that new ships are required either now or very shortly for the satisfactoryconduct of the business. With the aid of his/her staff, sometimes supplemented by technicaladvice from a naval architecture consultancy, he/she arrives at the operating characteristics ofthe proposed ships and the number required. These characteristics will be set out in the formof a statement of requirements which will form the basis of the preliminary design. Once the Requirements are drawn up the Naval Architect can start to prepare apreliminary design which aims to fix displacement, main dimensions, powering, an outlinearrangement and specification. An owner’s naval architect, a consultant or a shipbuilder maycarry out this stage of the process. If the shipowner is happy with the design it may be put outto tender - offered to a number of shipbuilders - or simply given to a preferred shipbuilder forcosting. Once the cost is agreed the builder will progress the design to produce a package ofmanufacturing information which suits his building methods.4.2 The Owners Requirements The practice followed by owners in stating their requirements for a new ship varieswidely and statements of requirements can range between the briefest outline and the mostdetailed specification (sometimes so restrictive as apparently leaving the ship designer littlescope to apply his/her skills). The most forward looking owners will have based theirrequirements on a careful analysis of their needs or on market research but this cannot alwaysbe taken for granted. Ideally, the requirements should lay down what the owner wants in thefollowing categories, namely, the performance, availability and utility of the ship; it wouldalso be helpful for an opinion to be included on the aspect of cost. The Performance category includes such aspects as: - Amount and type of cargo to be carried How the cargo is to be handled Turn-round times Trade Routes and Trading Pattern Ship Speed required at sea Distance between fuelling and storing ports___________________________________________________________________________ September 2005
  • 26. Marine Design 26__________________________________________________________________________________________ The Availability category includes such aspects as: - Maintenance Policy - How much afloat? How much ashore? Standard or Extended periods between Dockings? What emphasis is to be placed on reliability - is any redundancy required in machinery and systems? The evaluation of availability is a recent development in the field of shipping andrequires access to a database of information on the performance of machinery, systems andequipment already at sea in ships. Although few shipowners or shipbuilders have suchinformation, it is clear that improved reliability is an essential step in maintaining aneconomic and competitive fleet. The Utility category includes such aspects as: - Flexibility - ability to change role as in the O.B.O. or Ro-Ro Ship Ability to load/discharge cargo using on-board equipment Ability to use canals or waterways without restriction The Cost category includes the aspects of: - Initial Cost Running Costs Maintenance Costs Finance Depreciation All of these form part of the Life-cycle Cost and a common overall objective is toreduce them to a minimum consistent with meeting the Performance, Availability and Utilityrequirements. The fundamental explicit requirements which should be addressed in preliminary design are: - Cargo Deadweight Cargo Capacity Speed at Sea EnduranceThe first two are related by the Cargo Stowage Factor = Cargo Capacity/Cargo Deadweight,and together they fix the type of ship that must be used. Stability and Safety are requirements which must also be addressed during preliminarydesign. They are traditionally regarded as being implicit to the process - whatever choice theowner makes about Deadweight or Speed he/she wants the ship to survive for a reasonablelength of economic life and no-one deliberately designs an unsafe ship. However, publicconcern is leading to a greater pressure for these to become explicit requirements as well.___________________________________________________________________________ September 2005
  • 27. Marine Design 27__________________________________________________________________________________________4.3 Ship Type The best known subdivision of Ship type is by its obvious function such as BulkCarrier, Tanker, General Cargo, Container Ship, Cruise Liner, Ferry and so on. However in Design it can also refer to the more fundamental distinction between theDeadweight Carrier and the Volume (or Capacity) Carrier. Any given ship type aims to be best in its own trade. A widely accepted measure ofefficiency is that the ship should be "full and down". That means that the cargo capacity andcargo deadweight are both at their limits when the ship is at its load draught. Depending onthe range of stowage factor of the cargo on offer this yardstick may be of some value but aswe shall see it cannot be applied sensibly in all cases. A third fundamental ship type is the "Linear Dimension" ship where the designprocess proceeds directly from the linear dimensions of the cargo, an item or items ofequipment, or from restrictions set by canals, ports etc. and for which the deadweight,capacity and sometimes the speed are the outcome of the design instead of the main factorswhich determine it. The Container Ship is an example of this kind of vessel as neither thedeadweight nor the capacity are directly related to the dimensions, nor are the dimensionscapable of continuous variation - rather the main dimensions must be close to discrete valuesrelated to multiples of the dimensions of the containers which are to be carried. The vehicle-carrying Ferry is another example of this type.4.4 Deadweight or Volume? 3 Seawater has a stowage factor of 0.9754 m /tonne. A minimum reserve of buoyancy isrequired when laden. Hence the least overall stowage factor for a ship i.e. Total Enclosed 3Volume/Displacement is about 1.5 m /tonne. The separate stowage factors for cargo and theremainder of the ship are close to this figure. Hence if the cargo to be carried is more densethan (stows closer than) this figure then empty space in the hold is inevitable. Many cargoes 3 3fall into this category. They range from ore at 0.5 m /tonne to oil at about 1.25 m /tonne. Theempty space can be put to some use as it allows the cargo to be distributed within the ship insuch a way as to minimise problems of strength and stability and perhaps segregate cargo andballast spaces. However convenience in working cargo may demand that it be concentratedand the strength advantages can be lost. If draught is restricted but economy of scale demandsa large ship and depth remains proportional to length because of strength considerations thenspare space will be automatic. In the normal manner however as the average cargo density decreases the ship will 3become full and down with cargo stowing at about 1.6 m /tonne. If the cargo density is so lowthat the vessel has unused deadweight remaining then deck cargo could be carried but itwould not be protected from the weather or the sea. This is where the container shipdemonstrates one of its advantages - its deck cargo is reasonably well protected because it isinside a container. The modern bulk cargo ships – Dry Bulk Carrier and Oil Tanker – are designed tocarry a range of cargoes with a stowage factor of less than 1.5 or 1.6 m3/tonne so that the___________________________________________________________________________ September 2005
  • 28. Marine Design 28__________________________________________________________________________________________amount of cargo they can carry is solely determined by their deadweight. As a consequencethey are box like single deck ships with a relatively simple structural arrangement. In the case of the traditional general cargo ship or high speed cargo liner (nowobsolete) erections were added - typically in the form of Poop, Bridge and Forecastle - butmore commonly recently simply a shelter deck. The presence of this first tier of erections onthe freeboard deck allowed the carriage of additional deadweight but enclosed volume(capacity) increased faster and the cargo stowage factor rose. The volume generated byadopting a satisfactory height of tween deck tended to cause a jump in the stowage factor to 3about 1.9 m /tonne although an intermediate value could be obtained by covering less than thefull length of the ship. The cargo liner whose trade has been extensively taken over by the container shipoften carried cargoes of high value but low density (including passengers). This type of shipwas designed with several tween decks above each hold to ensure that adequate volume(capacity) was available to protect from the weather all the cargo carried. 3 If the cargo stowage factor exceeds 2.3 m /tonne an additional tier of erections isusually required. Such a cargo is rare but one example is Bananas with a factor of 4.0 3m /tonne and another is the car - either on a ferry or on a "Bulk Car Carrier". Passengers toohave a high stowage factor as is made obvious by the extensive superstructures to be found oncross-channel ferries and cruise liners. An exact estimate of cargo stowage factor is hard to make, especially as it will varyover the vessels life due to alterations in trading patterns. However it is worth noting thatcargo deadweight can always be gained in the short term at the expense of carrying less fueland bunkering more frequently while additional covered capacity is expensive to provide.___________________________________________________________________________ September 2005
  • 29. Marine Design 29__________________________________________________________________________________________5 Estimating Principal Dimensions5.1 Displacement, Lightweight and Deadweight The load displacement of a ship is made up of two components - lightweight anddeadweight. Each of these can in turn be subdivided for analysis and control. In naval practicethe subdivisions are set out in great detail but for merchant ships there is no commonly agreedbreakdown other than the large groups associated with preliminary design. The difficulty increating clear-cut definitions of weight groups can make comparison of figures from differentsources difficult and often dangerous. In this respect large groups are likely to provide betteragreement than small ones but they will be less amenable to analysis and control. In Preliminary Design the following definitions and subdivisions are customarily used: Design Displacement or Full Load Displacement is the displacement of the ship at 3its Summer Load Draught in salt water of density 1.025 tonne/m Lightweight is the weight of the vessel complete and ready for sea with fluids insystems, settling tanks and ready-use tanks at their working levels. No cargo, crew,passengers, baggage, consumable stores, water or fuel in storage tanks is on board. (The Lightweight represents the fixed part of the displacement.) Lightweight = Steel Weight + Outfit Weight (Including Refrigeration & Insulation) + Machinery Weight (Refrigeration & Insulation Weight may be taken with Outfit, as above, or may be made a separate group) Deadweight is the difference between the Displacement at any draught and the Lightweight i.e. Deadweight is the variable part of the displacement. Design Deadweight (Total Deadweight) is the difference between the Design Displacement and the LightweightIn general, Displacement = Lightweight + DeadweightIn particular, Design Displacement = Lightweight + Design Deadweight Deadweight = Cargo Deadweight (Payload) + Fuel Oil + Diesel Oil + Lubricating Oil + Hydraulic Fluid + Boiler Feed Water + Fresh Water + Crew & Effects + Stores___________________________________________________________________________ September 2005
  • 30. Marine Design 30__________________________________________________________________________________________ + Spare Gear + Water Ballast * * Water ballast is only carried if required to achieve a particular trim or draught/trim combination. It is not normally carried in the Full Load Condition. Cargo Deadweight will include passengers and their effects if they are carried. Cargo Deadweight is sometimes referred to as Payload.5.2 Deadweight/Displacement Ratio This ratio is a common starting point for a design although an immediate choice ofmain dimensions based on past practice is sometimes taken as a short cut. TheDeadweight/Displacement Ratio is used to obtain the first approximation to Displacement fora given Deadweight. It is often based on total deadweight rather than the more logical choiceof cargo deadweight because total deadweight is a more readily available figure beingindependent of the amount of fuel etc. carried. If cargo deadweight is available then it may beused but as the value will be taken from data on existing ships the designer must be sure of thefigures being used. The data would normally be recorded as a graph of Deadweight Ratioagainst Deadweight. The Ratio will vary with the type of ship, its speed, endurance andquality. Generally speaking, the larger, slower and more basic the ship the higher the value ofthe ratio.DWR = Deadweight/DisplacementTypical values of DWR for a range of ship types are as follow- Reefer 0.58 - 0.60 General Cargo 0.62 - 0.72 Ore Carrier 0.72 - 0.77 Bulk Carrier 0.78 - 0.84 Tanker 0.80 - 0.86 In a preliminary design it is wise to consider how the ratio may vary from the chosentype ship and be prepared to correct the resulting displacement at a later stage of the designprocess if necessary. The quoted figures indicate considerable variation in the value of DWR for similarships. Among the factors which account for this variation are: - 1) Ship Speed and Block Coefficient. These factors partly account for the variation inDWR between different ship types as well as within any one ship type. For a given set ofdimensions, an increase in speed will call for an increase in power. The increased power willincrease the machinery weight and so decrease the available deadweight. It may decrease theCargo Deadweight even further if there is, in addition, an increase required in the amount offuel to be carried. If, on the other hand, the Block Coefficient is reduced to allow a slightincrease in speed for no increase in power then the displacement is reduced but there isscarcely any decrease in Lightweight and again the deadweight is reduced.___________________________________________________________________________ September 2005
  • 31. Marine Design 31__________________________________________________________________________________________ 2) Voluntary reduction of draught. The operating draught may be less than themaximum allowed by freeboard rules or by the choice of scantlings. Thus the vessel, inservice, is carrying less deadweight than it might theoretically be able to 3) Variations in propulsion machinery. There can be a significant difference inmachinery weight between an installation using a slow speed diesel engine and one usingmedium or high-speed engines. 4) Variations in construction method. For example the Ore Carrier requires to have amuch heavier bottom structure than a non-ore carrying Bulk Carrier because of the localintensity of loading arising from the very dense ore. 5) Variations in Outfit Specification. A Refrigerated Cargo Ship (or Reefer) will havea greater outfit weight than the equivalent General Cargo Ship and so carry less Deadweighton a given Load Displacement. Similarly a Bulk Carrier with cargo handling gear is likely tohave reduced deadweight when compared with a gearless vessel (one without cargo handlinggear). Once the displacement has been derived then each of the principal dimensions can beconsidered in turn.(From Watson, Practical Ship Design, 1998)___________________________________________________________________________ September 2005
  • 32. Marine Design 32__________________________________________________________________________________________5.3 Length Length is probably the most expensive dimension to provide and is governed in partby size and in part by speed. It is expensive in terms of steel weight and building costs andwere it not for hydrodynamic considerations the ideal length might well be taken to be thecube root of the volume of displacement. However that is not the case and ship size associated with desirable characteristics forresistance and propulsion is used to fix a first approximation to the length. Adjustments arethen made above or below this value to account for the relative importance of frictional andwavemaking resistance and to meet any physical restrictions imposed by canals, ports, docksand ship handling. The choice of Length and Block Coefficient (CB) are closely related and are dependenton Speed and Froude Number. A number of formulae for the initial determination of Lengthwill be given later.5.4 Breadth, Draught and Depth Given the Volume of Displacement, Length (L) and CB, then the value of the productof Breadth (B) and Draught (T) is determined. Unless there are over-riding dimensionalconstraints such as the width of a dock entrance or the water depth at a harbour mouth thenboth B and T can be determined knowing a typical value of the ratio between them, B/T.Alternatively B may be determined from a typical value of L/B and hence T can be found. Depth (D) may be determined in a similar way if a requirement for total internalvolume is known and an estimate is made of CBD, the Block Coefficient of the ship up to theupper deck. Depth is also constrained by the need for a minimum freeboard over the draught.A good first approximation is to take T = 0.70 D. The final choice of Breadth, Draught and Depth is also influenced by stabilityconsiderations where increasing Breadth and/or reducing Depth will lead to an increase ininitial stability. On the other hand, increasing Breadth and reducing Draught may have anadverse effect on the resistance and propulsion characteristics of the vessel.5.5 Overall Limits on Dimensions For many ships the maximum dimensions are restricted by navigational features of theroutes they must use: - Depth of Channels; Size of Canals or Seaways and their associated Locks Clear Height under Bridges The limiting dimensions for some of the worlds most significant canals are given inthe following table: -___________________________________________________________________________ September 2005
  • 33. Marine Design 33__________________________________________________________________________________________ Length Breadth Draught (m) (m) (m)St Lawrence Seaway 222.5 23.16 7.92Kiel Canal 235.0 32.5 9.5Panama Canal 289.5 32.3 12.0Suez Canal No Limit 71.0 (Ballast) 12.8 50.0 (Loaded) 16.15.6 Formulae for Length The following empirical formulae have been developed over the years to help in theinitial estimation of Length. They all come with "standard" values of their constants, but eachcan (and should) be fine tuned to match modern design practice by using a particularprototype or basis ship to derive a new value for the constant. Posdunine LBP = C ( Vt / (Vt+2) ) 2 1/3 Where Vt is the Trial Speed of the vessel in knots and is the Volume of Displacement in cubic metres. C = 7.25 is applicable to cargo ships where 15.5 < Vt < 18.5 C can also be determined from a basis ship Schneekluth Professor Schneekluth of Aachen University of Technology derived the followingfrom economic considerations. LBP = ∆0.3 Vt0.3 C Where ∆ is the Displacement in tonnes Vt is the Trial Speed in knots and C is a constant = 3.2 if the block coefficient has the approximate value of CB = 0.145/Fn within the range 0.4 < CB < 0.85 C can also be determined from a basis ship. In the course of his research, Professor Schneekluth discovered that ships which areoptimum in meeting shipping company requirements are about 10% longer than thosedesigned for minimum production cost. Ayre 1/3 LBP / = 3.33 + 1.67 Vt / √LBP Where Vt is the Trial Speed of the vessel in knots and is the Volume of Displacement in cubic metres.___________________________________________________________________________ September 2005
  • 34. Marine Design 34__________________________________________________________________________________________ This relation must be solved iteratively. Assume a value for LBP and put it into theRHS. Hence evaluate the LHS and arrive at a value for LBP say LBP. Put this value into theRHS and find a new value for LBP say LBP. Compare LBP with LBP. When the differencebetween the two values is sufficiently small then take LBP = LBP. It must be said that it is not so easy to "fine tune" the Ayre formula to a particularbasis ship because it uses two numeric coefficients and it is not obvious whether one aloneshould be adjusted, or both. However it appears to give initial estimates of length which areconsistent with modern practice despite its age. It is therefore still quite useful to the designer.5.7 Block Coefficient The variation of Block Coefficient, CB, with Speed and Length is shown in a diagramtaken from ‘Practical Ship Design’ by D. G. M. Watson (based on a Figure in the1977 RINAPaper by Watson & Gilfillan). Over the years segments of the curve appropriate to particularship types have been presented as linear relationships known as "Alexander Formulae" of theform: - CB = K - 0.5 V/ √Lf or CB = K - 1.68 Fn where K varies from 1.12 to 1.03 depending on V/ √Lf or Fn and V is speed in knots, Lf is length in feet v is speed in metres/second, L is length in metres 2 g is acceleration due to gravity in metres/secondThe mean line shown in the diagram can be approximated by the equation:- CB = 0.7 + 0.125 tan-1((23-100Fn)/4) where the term in brackets is taken in radians.___________________________________________________________________________ September 2005
  • 35. Marine Design 35__________________________________________________________________________________________5.8 Length/Breadth Ratio In another diagram taken from the same paper the variation of L/B ratio with length isshown. Small craft (under 30 m in length) remain reasonably directionally stable and steerablewith L/B = 4.0, probably because they have little or no parallel body and generally low valuesof CB. The typical value of L/B increases to about 6.5 at 130 m and maintains that value aslength increases further. For vessels with lengths between 30 m and 130 m the formula: - L/B = 4 + 0.025 ( L - 30 ) reasonably represents the available data. A small number of the largest VLCC’s find their maximum draught limited by theneed to pass through some of the shallower of the world’s “Deep Water Channels” such as theEnglish Channel or the Malacca Straits. In consequence these ships have accepted a largerB/T ratio giving them a smaller than usual L/B ratio but they appear to run into directionalstability problems at L/B slightly above 5.___________________________________________________________________________ September 2005
  • 36. Marine Design 36__________________________________________________________________________________________(Based on Fisher, RINA 1972, Fig 4)___________________________________________________________________________ September 2005
  • 37. Marine Design 37_____________________________________________________________________________________________________________________________________________________________________ September 2005
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  • 39. Marine Design 39_____________________________________________________________________________________________________________________________________________________________________ September 2005
  • 40. Marine Design 40_____________________________________________________________________________________________________________________________________________________________________ September 2005
  • 41. Marine Design 41_____________________________________________________________________________________________________________________________________________________________________ September 2005
  • 42. Marine Design 42__________________________________________________________________________________________6 Weight Estimation6.1 Basic Approach There are two basic approaches to estimating the weight of a ship. The first is to sumthe weights of all the items built into the ship. The second is to employ a system of scaling orproportioning from the weights of a known basis ship to the new design based on the ratiosbetween principal characteristics of the two vessels. The first approach will only give an answer when the ship is complete and so is toolate to be of value to the designer. The second approach is thus the one we will consider here.Once the first choice of main dimensions has been made these are used to make weightestimates for each group weight of the design displacement. Naturally the total must equal thedesign displacement. If it does not the required cargo deadweight will not be obtained andeither a larger or a smaller ship is required. Iteration may be necessary to arrive at a set ofdimensions which ensure that the sum of the weights making up the ship (its designdisplacement) exactly * equals the buoyancy offered by the hull at its design draught.(* Exactly in preliminary design means Displacement = Buoyancy ± Errorwhere Error is approximately ½ of the tonnes per cm immersion of the vessel at its designwaterline. This is because it is practically impossible to determine the draught of a ship tobetter than ± 0.5 cm thus limiting the accuracy of any weight.) Initially considering the Lightship: - LIGHTSHIP = Steel Weight (Ws) + Outfit Weight (Wo) + Machinery Weight (Wm) + Margin The Margin is an essential part of the weight make up as it allows for errors andomissions in the remainder of the calculations. For a vessel whose Lightship is a relativelysmall part of the full load displacement a value of about 2% of Lightship is likely to beappropriate. Where the Lightship is a much greater proportion of the full load displacementand a weight over-run would be seriously embarrassing then a greater percentage may bechosen. Let us look at each Weight Group in turn.6.2 Steel Weight Representing principally the hull structure: - Plates and sections forming Shell, Outer Bottom, Inner Bottom, Girders, Upper Deck, Tween Decks, Bulkheads, Superstructure(s), Seats for equipment & Appendages together with Forgings/Castings for Stem, Sternframe, Rudder Stock(s) and Shaft Brackets.___________________________________________________________________________ September 2005
  • 43. Marine Design 43__________________________________________________________________________________________We will consider two ways to calculate the Steel Weight just now: - a) Cubic Number Method The principle of this method is that Ws = Cubic Number Coefficient x LBD x Correction Factors where LBD/100 is the Cubic NumberThis is applied as follows Ws* = Ws x L*B*D* x Correction Factors LBD where * denotes a dimension or property of the new design. The use of this method implies accurate knowledge of past similar ships as no accountis taken of changes to major items of steelwork such as number of bulkheads or number ofdecks. For a good level of accuracy changes in L, B or D from the basis ship should be nomore than 10% but often the method is applied outwith such limits.Correction Factors :- Form Correction = 1 + ½CB* 1 + ½CB ½ L/D Correction = (L*/D*) ½ (L/D) b) Rate per Metre Difference Method This is a slightly more refined system than the Cubic Number Method being able totake account of the different effects of changes in the principal dimensions. Once again,dimensional changes of up to 10% can be allowed for. The basis of the method is that the effect on the Steel Weight of change in each of thethree principal dimensions can be weighted by different amounts. An increase in Length will lead to an increase in the weight of all elements of the hull- Bottom, Side Shell, Decks, Bulkheads etc. In addition the Hull Girder Bending Moment willtend to increase at a faster rate than Length. Bending Moment ∝ ∆L = ρLBTCBL 2 ∝ L Therefore there may be an increase in the thickness of the plating used in the Bottomand the Upper Deck in order to increase the Hull Girder Section Modulus to resist theincreasing Bending Moment. Overall an increase in Length will produce a greater than___________________________________________________________________________ September 2005
  • 44. Marine Design 44__________________________________________________________________________________________proportionate increase in Ws. An increase in Breadth will increase the weight of Bottom, Decks and Bulkheads butwill have little effect on the weight of the Side Shell. Overall an increase in Breadth willproduce a roughly proportionate increase in Ws. An increase in Depth will increase the weight of Side Shell and Bulkheads but willcause little or no change to the Bottom or Decks except that plating thickness may be reducedwhile still providing the same Hull Girder Section Modulus. Overall this should lead to theincrease in Ws being less than proportional to the increase in Depth. Typical values of the weighting factors are 1.45 for Length, 0.95 for Breadth and 0.65for Depth. i.e. the rate of change of steel weight per one metre change in length is 1.45Ws/L, per one metre change in breadth is 0.95 Ws/B and per one metre change in Depth is0.65 Ws/D A Form Correction is applied for change in Block Coefficient as for the CubicNumber Method If a ship of dimensions L, B, D has a steel weight of Ws tonnes then the rates per metrefor each of the dimensions are: - a Ws/L, b Ws/B, c Ws/D where a = 1.45, b = 0.95, c = 0.65 For a new ship of dimensions L*, B*, D* the change in each dimension is given by: - δL = L* - L δB = B* - B δD = D* - DThen Ws* = {a(Ws/L)δL + b(Ws/B)δB + c(Ws/D)δD + Ws} x Form Correction = Ws {a((L*/L) - 1) + b((B*/B) - 1) + c((D*/D) - 1) + 1} x Form CorrectionExampleA basis ship has the following characteristics: -L = 104.0 m, B = 15.71 m, D = 9.26 m, CB = 0.725 and Ws = 1521 tonnes.A new ship has the following characteristics: -L* = 114.5 m, B* = 16.86 m, D* = 10.08 m and CB = 0.735___________________________________________________________________________ September 2005
  • 45. Marine Design 45__________________________________________________________________________________________Find Ws* using both estimation methodsCubic Number Method Ws* = Ws x L*B*D* x CB Correction x L/D Correction LBD ½ = 1521 x 114.5 x 16.86 x 10.08 x (1 + ½ x 0.735) x (114.5/10.08) ½ 104 x 15.71 x 9.26 (1 + ½ x 0.725) (104/9.26) = 1521 x 1.2862 x 1.0037 x 1.0057 = 1975 tonnesRate Per Metre Difference Method L B D CBBasis Ship 104.0 15.71 9.26 0.725New Ship 114.5 16.86 10.08 0.735Ratio of Dimensions 1.101 1.073 1.088(Ratio) - 1 0.101 0.073 0.088Weighting Factors 1.45 0.95 0.65Products 0.146 + 0.069 + 0.057 = 0.272Form Correction = 1 + ½ x CB* = 1 + ½ x 0.735 = 1.0037 1 + ½ x CB 1 + ½ x 0.725 Ws* = 1521 x ( 1 + 0.272) x 1.0037 = 1942 tonnes More refined methods may be used if a better breakdown of the steel weight of thebasis ship is available, e.g.: - Upper Deck Tween Deck Inner Bottom Outer Bottom Side Shell Bulkheads Superstructure___________________________________________________________________________ September 2005
  • 46. Marine Design 46__________________________________________________________________________________________ A square number approach is probably appropriate for each of the above elements ofthe structure, except Superstructure. For the Upper Deck WUD ∝ L x B with a form correction ideally dependent on thewaterplane area coefficient but practically varying with the block coefficient and a scantlingcorrection depending on L/D ratio. The Outer Bottom could be treated in a similar way. Tween Deck(s) and Inner Bottom will tend to vary only with L x B and blockcoefficient, while Side Shell will follow L x D and block coefficient. Bulkhead weight will tend to vary with B x D, block coefficient and number ofbulkheads. Superstructure(s) can be treated using their own mini cubic number lsbshs, where ls,bsand hs are the mean values of length, breadth and height of the superstructure. Schneekluth quotes a number of methods for scaling steel weight and also formulaefor calculating steel weight from the principal dimensions. Two of the latter, applicable toCargo Ships are:- -5.73 x 10-7Wehkamp/Kerlen Ws = 0.0832 X e 2 3 where X = ( LPP B/12) √CB 2/3 0.72 2and Carryette Ws = CB (L B /6) D [0.002(L/D) + 1] Taking the SD14 as an example where L = 137.5 m, B = 20.42 m,D = 11.75 m and CB = 0.7438, the steel weight is 2382 tonnes by Wehkamp/Kerlen or 2884tonnes by Carryette. Shipyard data provided for use in a Ship Design Project based on the SD14 gave the‘real’ steelweight as 2505 tonnes.6.3 Outfit Weight Outfit can be considered to include: - Hatch covers, Cargo handling equipment, Equipment and facilities in the living quarters (such as furniture, galley equipment, heating, ventilation & air conditioning, doors, windows & sidelights, sanitary installations, deck, bulkhead & deckhead coverings & insulation and non-steel compartment boundaries) and Miscellaneous items (such as anchoring & mooring equipment, steering gear, bridge consoles, Refrigerating plant, paint, lifesaving equipment, firefighting equipment, hold ventilation and radio & radar equipment)___________________________________________________________________________ September 2005
  • 47. Marine Design 47__________________________________________________________________________________________ The majority of outfit weight items can be considered to be proportioned betweensimilar ships on the basis of Deck Area i.e. using a square number approach where Wo ∝ L xB. The diagram, again taken from ‘Practical Ship Design’ by D. G. M Watson (based on aFigure in the 1977 RINA Paper by Watson & Gilfillan), shows how outfit weight varies withsquare number for various types of ship. Note the way that the outfit weight of the passengerships increases very sharply with length. This is probably due to the increase in the number ofdecks found in large passenger carrying ships. The square number method is applied as follows Wo* = Wo L*B* LB An alternative approach holds half of the outfit weight constant and proportions theremainder by the square number. This variation is applied as follows Wo* = Wo( 1 + L*B* ) 2 LB This approach can be further refined if a known weight item such as a heavy liftderrick is either common to both ships or is present in the basis ship but not in the new design.The known item should be deducted from the basis Wo, the revised value scaled suitably andthe known item added back on if necessary. Once again if a more detailed breakdown of the outfit weight of the basis ship isavailable then more refined methods can be applied to each part.___________________________________________________________________________ September 2005
  • 48. Marine Design 48__________________________________________________________________________________________(Both Diagrams from Watson, Practical Ship Design, 1998)6.4 Machinery Weight Representing: - Main Engine(s), Gearbox (if fitted), Bearings, Shafting, Propeller(s),Generators, Switchboards, Cabling, Pumps, Valves, Piping etc. The fundamental parameter by which machinery weight can be proportioned is theinstalled power of the main machinery, conventionally taken as Shaft Power, Ps. An introduction to some methods of estimating Ps will follow in a later lecture andwill subsequently be further developed in the class Resistance and Propulsion. For the purpose of making the very first estimate of Ps for small changes indimensions and speed from a basis ship we can take 2/3 3 Ps ∝∆ V Given that a value of Ps has been obtained for the new design it is possible to take 2/3 Wm ∝ Ps___________________________________________________________________________ September 2005
  • 49. Marine Design 49__________________________________________________________________________________________ D. G. M. Watson has presented a very simple two-group breakdown of machineryweight in a range of vessels. Their two groups are made up as follows (1) The main engine itself (2) The remainder of the machinery installation By studying engine manufacturers data he found that over a wide range of engine typehe could express the bare weight of an engine in the form 0.84 Weight = 12 ( MCR ) (tonnes) RPM where MCR = Maximum Continuous Rating (kW) RPM = Engine crankshaft revs per minute at MCR For a given MCR the higher the RPM then the lower the torque the engine mustproduce. The lower the torque, the smaller are the forces produced inside the engine andhence the smaller are the components and the lower is its weight. The weight of the remainder of the machinery was given by 0.7 Weight = k ( MCR ) (tonnes) where k = 0.56 for Bulk Carriers and General Cargo Ships 0.59 for Tankers (due to additional weight for cargo pumping) 0.65 for Passenger Ships and Ferries (additional weight devoted to power for hotel services, lighting and heating, ventilation & air conditioning (HVAC))6.5 Weights of Consumables Fuel Oil & Diesel Oil The requirement for fuel is based on Engine Power, Fuel Consumption (SFC) and theduration of the voyage - i.e. Endurance / Speed. Fuel Required = Power x SFC x Endurance / Service Speed Fuel Carried = Fuel Required / 0.975 * Tank Volume Required = Fuel Carried / 0.95 x Density *** Allows for 2.5% of the fuel carried being unpumpable at the bottom of the tanks** Allows for tanks not being filled to more than 95% of their capacity to allow for expansion in hot climates. Take care with the units! A similar calculation should be carried out for the fuel required for electrical powergeneration based on a suitable number of generators running for the duration of the voyageplus a margin for the time spent in port.___________________________________________________________________________ September 2005
  • 50. Marine Design 50__________________________________________________________________________________________(Both Diagrams from Watson, Practical Ship Design, 1998)___________________________________________________________________________ September 2005
  • 51. Marine Design 51__________________________________________________________________________________________ Lubricating Oil The requirement for Lubricating Oil is based on Engine Power, Lubricating OilConsumption and the duration of the voyage. For similar engines it is therefore proportionalto the product of the power of the main engine(s) and the duration of the voyage. Fresh Water The requirement for Fresh Water can be satisfied in one of two ways. Many ships arefitted with equipment to produce Fresh Water from Sea Water on a continuous basis either bydistillation or by reverse osmosis. In this case it is only necessary to store a few days supplyof water in two tanks each capable of holding say two or three days consumption at a rate ofabout 100 litres per person per day. Ships which do not have such equipment need to carryenough water to last the duration of the voyage at the same daily rate. This would normally besplit between two tanks to guard against the whole supply becoming contaminated. The tankswould then be filled in each port of call. Approximately 133 tonnes of fresh water would be required by a crew of 32 on avoyage of 16000 nautical miles at 16 knots with a consumption of 100 litres per day.Distillation plant will typically produce 10 tonnes of water from the heat input of one tonne offuel oil so the fresh water for the above voyage could be provided from two storage tanks of10 tonnes each plus distillation plant plus the carriage of an extra 13 tonnes of fuel oil. Stores Stores. in the sense of food, drink etc, are normally assessed on the basis of so muchper person per day. The weight carried is therefore proportional to the product of the numberof crew (+ passengers if appropriate) times the voyage duration in days. Spare Gear Spare gear is notoriously difficult to estimate. It is very much dependent on the advicefrom the manufacturers of all the various pieces of equipment on board the ship and soaccurate information is unlikely until the ship is ready for sea. A fixed weight based on asimilar ship is probably sufficiently accurate for preliminary design. Crew & Passengers The present allowance for an average crew member is 75 kg and if effects (personalbelongings, luggage, baggage etc.) are included then the value should double. You shouldallow 75 kg for each passenger on a daytime commuter or excursion trip and up to 150 kg (i.e.with baggage) on a longer-term holiday or cruise.6.6 Centre of Gravity Estimation Weight estimates alone are not sufficient to allow ship design to progress - theposition of the centre of gravity (C of G) - Vertically, Longitudinally and Transversely - ofeach item of weight must also be determined in order to find the overall Centre of Gravity ofthe ship.___________________________________________________________________________ September 2005
  • 52. Marine Design 52__________________________________________________________________________________________ This must be assessed to give reasonable assurance that the ship will be stable, float atthe intended fore and aft trim and float upright. In the early stages of Design Port/Starboardsymmetry is often assumed and the Transverse Centre of Gravity is thus sometimes ignored. NOTE:- In some ship types it may be important that the ship floats exactly upright.This is almost certainly the occasion when you cannot ignore TCG. Sods Law says that if twoheavy items are to be positioned on a ship, both will be placed where they have the greatestimpact on TCG and both will be on the side of the ship nearest to the designer when (s)he waslaying out the General Arrangement. Two methods of determining C of G can be applied to all weight groups depending onthe stage of the design process and the amount of information you have on the ship. a) Scaled C of G (early design stages) The position of the LCG of the weight item relative to a suitable datum position(usually amidships or the A.P.) is proportional to the length of the vessel. LCG* = LCG x L*/L The position of the VCG above the baseline is proportional to the depth of the vessel VCG* = VCG x D*/D b) Real C of G (later design stages) The position of the LCG, VCG or TCG of an item is measured from a suitable datumon a scale drawing of the vessel or is known by definition, e.g. if the height of a tween deckabove base is 7.6 m then the VCG of the plating will be 7.6 m plus one half of its thicknessabove base. As the VCG of the stiffening will be slightly below 7.6 m a reasonable estimateof the VCG of the deck will be 7.6 m. If the C of G of an engine is given by the manufacturer as x metres above a datumlevel then position the engine in the machinery space, find the height of the datum above baseand the VCG can be found. The weight of an item may have a recognisable geometric distribution - rectangular,triangular, parabolic etc. The formulae for finding the centroids of such shapes may then beuseful in determining the C of G of the item with respect to one or more of the usual axes. As you progress through successive iterations of weight calculations or successivestages of the design process as a whole you should always consider the use of more refinedand more detailed weight/centre estimation techniques appropriate to your increasingknowledge of the design - subdivide weight groups, use “real” engine data etc. In the later stages of the ship design project you are likely to have real centres for themajority of the deadweight items although the Lightship centres will probably still be scaled.___________________________________________________________________________ September 2005
  • 53. Marine Design 53__________________________________________________________________________________________ Variations or combinations of these basic procedures may be appropriate in particularcases. You may be asked to move the engine room or superstructure from one location on thevessel to another. From the given data find the C of G of the machinery relative to one of theEngine Room boundary bulkheads. If you then move the entire engine room along the vesselthe C of G will move by approximately the same distance as the datum bulkhead. If you movea superstructure you may have to estimate its weight and C of G, deduct it from the totalsteelweight to find a “Hull” steelweight and C of G and then add it back on, scaled fordimensional change if necessary, at a C of G corresponding to its new position.6.7 Principal Items of Machinery WeightPROPULSION Main Engine(s) Gearbox(es) Propeller(s) and Shafting Pumps, Compressors & Separators Engine Room Pipework Air Intakes Exhaust uptakesSERVICES Fresh Water Plant Sewage Plant Cargo pumps Gratings, Ladders, Walkways, Insulation in Engine Room.ELECTRICAL Electrical Generators Switchboards Cabling Lighting Systems___________________________________________________________________________ September 2005
  • 54. Marine Design 54__________________________________________________________________________________________6.8 Principal Items of Outfit WeightGROUP 1 - Hatch Covers & Drive MechanismsGROUP 2 - Cargo Handling Equipment Derricks, Winches & Cranes Hold Ceilings Container Lashing GearGROUP 3 - Accommodation Divisional/Non-structural Bulkheads Deck/Bulkhead/Deckhead Coverings Doors, Windows & Sidelights (Portholes) Sanitary Installations &Piping Heating, Ventilation & Air Conditioning (HVAC) Galley and Dining Equipment Furniture & BeddingGROUP 4 - Miscellaneous Anchors, Chain, Hawsers Anchor/Chain/Hawser Handling Equipment Steering Gear & Control Equipment Navigation & Communication Equipment Firefighting Equipment Life Saving Appliances (LSA) Guardrails, Ladders etc General Pipework Hold Ventilation Cargo Refrigeration Paint Deck Coverings excluding Accommodation AreasA Weight Breakdown system with more detailed subdivision is shown below. It is based onUK Naval Practice and is taken from Watson, Practical Ship Design, 1998.___________________________________________________________________________ September 2005
  • 55. Marine Design 55_____________________________________________________________________________________________________________________________________________________________________ September 2005
  • 56. Marine Design 56__________________________________________________________________________________________7 Power Estimation and Service Margins7.1 General An estimate of the power requirement forms one of the most important and criticalsteps in preliminary design. It is also one of the most complex processes in ship design, beinginfluenced by a large number of design parameters. The power derived has a significant anddirect effect on the deadweight which can be carried by a given ship. In days gone by (whenfuel was cheap) it was important to keep both engine weight & volume and fuel weight &volume to the minimum to maximise deadweight and cargo capacity. Nowadays theshipowner seeks optimum fuel economy primarily on cost grounds and secondarily ondeadweight. The choice of propelling machinery for a tanker, a bulk carrier or a general cargovessel is now invariably restricted to the direct drive diesel which is by far the mosteconomical prime mover. The installed power has a direct influence on another of the owners requirements -speed. Since severe penalties can be incurred for not achieving the design trial speed, thedesigner has to allow for a margin of uncertainty in his power requirements to give the ship ahigh probability of success. There is a wide selection of diesel engines available to thedesigner but it is rare for there to be an engine which exactly suits the power requirement of aparticular ship. The designer then has to choose the best engine which develops sufficientpower over a useful range.7.2 Definitions of Power The power needed for propulsion is the aggregate effect of a number of componentswhich can be considered in three groups as follows: - a) Those affecting Hull Resistance, that is the force which must be applied to push or pull the hull through the water at the required speed. The product of Hull Resistance (R) and speed through the water (V) is called the Effective Power (PE). b) Those affecting the conversion of torque into useful thrust which determine the power to be delivered to the propeller. The product of 2π times Shaft Torque (Q) and Revs per second is known as the Delivered Power (PD). PD is related to PE by the Quasi- Propulsive Coefficient (Q.P.C.) c) The loss of power during its transmission from the engine to the propeller. The Shaft Power (PS) of the installation is related to PD by the transmission efficiency ηt. As Shaft Power is usually measured aft of the thrust block there may be a smallcorrection for this and for any power lost in gearing in order to arrive at the Installed BrakePower required from the engine. A further correction may be required to adjust the engine manufacturers figure ofBrake Power (Test Bed) for differences in air and water temperatures and losses in the airintake and exhaust gas systems between Test Bed and Service conditions.___________________________________________________________________________ September 2005
  • 57. Marine Design 57__________________________________________________________________________________________ Thus PS = PE /( QPC × ηt ) where PD = PE / QPC and PS = PD / ηt The following empirical relationship, known as Emerson’s formula, is often used toestimate the value of the Quasi-Propulsive Coefficient of a single screw ship: QPC = 0.85 - ( √ L × N ) / 10000 Where L is the length of the ship in metres and N is Revs per minute of the propeller. ηt takes typical values of 0.99 for aft end machinery and 0.98 for amidships machinery The losses in a the thrust block should be less than 1% of the power transmitted.7.3 Standard Series As an aid to design, a number of organisations have performed resistance (andpropulsion tests) on methodically varied series of ship forms. By varying the main parametersof ship proportion and form which affect ship resistance, a series of resistance result areobtained which can be presented in graphical form. The designer can then interpolate withinor between the graphs to establish the resistance of any form which has a valid combination ofparameters. Among the best known of these series are Taylor (and the Re-Analysis by Gertler),Series 60 and the BSRA Series. Further details of these series and their uses will be providedin the class on Resistance and Propulsion.7.4 Components of Resistance William Froude established the fundamental principles of predicting Ship Resistancefrom Model Tests more than a century ago. When a ship model is towed at a steady speed insmooth, deep water, we observe: - a) Resistance to motion b) A pattern of surface waves is produced (and if the model is run at a series of steady speeds then there is a unique wave pattern for each speed). c) Depending on the speed, the model experiences a change in both draught and trim by comparison with the draught and trim at rest. It is reasonable to suppose that there is friction between the hull surface and the waterthrough which it passes. It can be inferred that the motion causes pressure between parts ofthe hull and the water and that it is these pressures which cause the waves to form. Movingthe hull against these frictional and wavemaking forces will absorb energy and so thecombined effect must be responsible for the resistance to motion.___________________________________________________________________________ September 2005
  • 58. Marine Design 58_____________________________________________________________________________________________________________________________________________________________________ September 2005
  • 59. Marine Design 59__________________________________________________________________________________________ Froude tested "geometrically similar" models and argued that the total resistance ofany hull, either model or ship, must be the sum of two components which he called FrictionalResistance and Residuary Resistance RT = RF + RR He measured the resistance of a series of thin planks and, assuming that theirmeasured resistances were due to friction alone, he derived a formula for the frictionalresistance of a plank of arbitrary length and surface area moving at a specified speed. By further assuming that the frictional resistance of a model equalled that of the flatplate of the same length, area and surface finish he calculated the frictional resistance RF ofeach model at various speeds. By subtracting the calculated values of RF from the measuredvalues of RT he deduced the corresponding values of the residuary resistance RR. He then discovered that plotting values of residuary resistance per ton of displacement,RR, to a base of V/ √L or speed in knots divided by the square root of length in feet, gave aunique curve for all the "geometrically similar" models. Hence from the measured resistanceof a model over a range of speeds he was able to predict the resistance of a geometricallysimilar model or ship. Froudes basic principle still holds today although some changes in the fine detail havetaken place.7.5 Frictional Resistance The International Towing Tank Conference (ITTC) is a body which co-ordinatesresearch into ship hydrodynamics. By studying a wide range of experiments in which theresistance of ships, ship models, planks and other objects was measured and by looking at theunderlying scientific principles a consensus was reached as to the most reliable way ofpredicting the variation of frictional resistance of a smooth surface with Length and Speed.This is normally referred to as the 1957 ITTC Line. The modern method for calculating thefrictional resistance of a ship is to use the 1957 ITTC Line with a roughness allowance(typically taken as 0.0004) added to take account of the distinctly unsmooth surface of a realship: - 2 Cf = 0.0004 + 0.075 / (log10Rn - 2 ) where Cf is the coefficient of frictional resistance 0.0004 is a roughness allowance and Rn is Reynolds Number given by Rn = vL / ν where v is the ships speed in m/s L is the ships length in m___________________________________________________________________________ September 2005
  • 60. Marine Design 60__________________________________________________________________________________________ ν is the kinematic viscosity which takes the following typical values: - -6 2 In Fresh Water at 15 deg C 1.139×10 m /s -6 2 In Salt Water at 15 deg C 1.188×10 m /s The frictional resistance is then given by 2 RF = 0.5ρSv Cf where 3 ρ is the density of water in kg/m 2 S is the wetted surface area in m and may be given by S = 1.7LT + LBCB (The Denny - Mumford formula)7.6 Residuary Resistance The residuary resistance of a new design is not quite so easy to calculate as itsfrictional resistance. The coefficient of residuary resistance (CR) of a merchant ship havingthe optimum position of the LCB can be approximated using the following formula developedby Schneekluth. The formula tends to smooth out the effect of the humps and hollows of theresistance curves. It is based on the published residuary resistance curves of Taylor - Gertlerand Harvald - Guldhammer. 3 4 2 3 10 CR = (10Fn - 0.8) (10CP - 3.3) (10 C + 4)0.0012 3 + (10 C 0.05) + 0.2 + (B/T - 2.5)0.17 where CR is the coefficient of residuary resistance 3 C = /L and the other terms have their usual meanings. The residuary resistance is then given by 2 RR = 0.5ρSv CR The limits of validity of the formula are 0.17 < Fn < 0.30 3 2.0 < 10 C < 11.0 0.50 < CP < 0.80 CB ≤ CB (Ayre) + 0.06 (CB (Ayre) = 1.08 - 1.68Fn ) 5.0 < L/B < 10.0 2.0 < B/T < 4.5 The formula should not be used outside the specified limits.___________________________________________________________________________ September 2005
  • 61. Marine Design 61__________________________________________________________________________________________7.7 Rapid Power Estimates for New Ship Designs It is useful at times for the designer to be able to find quickly the total resistance of aship in some everyday terms such as pounds of total resistance per ton of displacement,expressed as RT/∆, at say the design speed, when only the type of ship and the approximateSpeed-Length ratio or Froude Number are known. For example, the value of RT/∆ for a large,modern Great Lakes freighter at its designed speed is about 2 lb/ton and that of a fastmotorboat is of the order of 600 lb/ton. Such data for a large variety of waterborne craft, both large and small, have beenplotted in Fig 56.I. The Admiralty Coefficient approach can give a useful first approximation to therequired power for small changes in speed, dimensions or displacement from a basis ship. Itcan also provide a guide to the likely power requirement of a ship at an early stage of design.The original form of the Admiralty Coefficient is given below: - 2/3 3 A.C. = (Displacement) × (Speed) / I.H.P. where Displacement is in tons, Speed is in knots and I.H.P. is Indicated Horse Power. I.H.P. was a measure of the power developed in the cylinders of a steam engine. Formodern ships I.H.P. is replaced by Shaft Horse Power and Fig 2.3.1, a BSRA diagram,derives the relationship by Dimensional Analysis and gives typical values of A.C. in respectof the trial performance of a number of ship types.7.8 Trial and Service Margins The shipowners normal requirement is in terms of service speed, although the contractterms will be agreed on the basis of a trial speed i.e. speed obtained under good weatherconditions, in deep water, with the hull in a clean condition. The difference between Trial andService conditions is caused by wind and wave action, fouling and increasing hull roughness.It is normal to provide an allowance of between 15% and 25% on power to cope with thedifference, with the final choice being dependent on such factors as the paint system, cathodicprotection, voyage patterns and hull maintenance policy. If the allowance (service margin) on power is taken as 25 % this corresponds to a TrialSpeed which is approximately 6% greater than the required Service Speed since in this regionof the Speed/Power curve Power varies as V4 for a well designed hull form. The graph below illustrates the application of a service margin to the speed/powercurve of a new ship design. The trial speed is derived from the speed/power curve for trialconditions at 90% of the Maximum Continuous Rating (MCR) of the machinery. The servicespeed is taken from the same curve after allowing for the service margin (here taken as anincrease of 25% over the power requirement under trial conditions). That is, Service Speed isachieved under trial conditions at 80% of the Power used to achieve the Trial Speed.___________________________________________________________________________ September 2005
  • 62. Marine Design 62__________________________________________________________________________________________ A similar result would be obtained by creating a speed/power curve for serviceconditions 25% above that for trial conditions. Its intersection with the maximum power levelfor the engine would then give the same value of service speed. That is the power the enginewould be expected to produce to achieve the service speed, at sea, battling against wind andwaves, with the bottom covered with rough paint, weed and barnacles The practice of setting a maximum usable power of 90% of MCR is considered by theshipowner to have two beneficial effects. Firstly it gives a slight improvement in specific fuelconsumption. Secondly it gives a reduction in wear and tear on the engine which has theeffect of reducing maintenance costs and improving reliability.7.9 Speed Margins An alternative method of establishing the required margin on installed power is moresubtle and involves designing in a speed margin, which implies a power margin, rather thanusing an explicit power margin. The effect of this approach is that the ships hull is designed to be driven efficiently ata speed greater than the service speed when the machinery is developing its maximum power. A ship design starts with the designed sea speed or service speed, determined from theschedule which the ship must maintain, or from a study of economic or other reasons. Tocompensate for having to slow down in heavy weather a reserve of speed above the designedsea speed, sufficient to bring the ship back onto its schedule, is necessary. This can beachieved by either of the following approaches or a combination of both: - i) Specify an increment of speed say 1.0 or 1.5 knots above the designed sea speed. ii) Specify a percentage increase of between, typically, 8 and 15 per cent on the designed sea speed.___________________________________________________________________________ September 2005
  • 63. Marine Design 63_____________________________________________________________________________________________________________________________________________________________________ September 2005
  • 64. Marine Design 64__________________________________________________________________________________________Note:- 1 lb = 0.453592 kg ; 1 ft = 0.3048 m Tq = V/√L where V is in knots and L is in ft___________________________________________________________________________ September 2005
  • 65. Marine Design 65__________________________________________________________________________________________(Taken from a BSRA Publication)___________________________________________________________________________ September 2005
  • 66. Marine Design 66__________________________________________________________________________________________8 Selection of Main Machinery8.1 Factors in the choice of Main Machinery 1) Burn Heavy Fuel Oil 2) Requires Low Maintenance 3) Suitable for Unattended Operation 4) Low Shaft Speed 5) Size and Weight 6) Purchase and Installation Costs 7) Reputation for Reliability8.2 Types of Diesel Engine 1) Slow Speed 80 - 250 RPM 2) Medium Speed 400 - 1000 RPM 3) High Speed 1200 - 1800 RPMThe following attributes of the above types of engine vary as shown below (1) --> (2) --> (3) (i) Decreasing Size (ii) Decreasing Weight (iii) Increasing Fuel Consumption (iv) Increasing Maintenance (v) Increasing Systems Complexity8.3 Auxiliary Machinery 1) Electric Power Generation 2) Systems for Main Engine(s) 3) Ship & Crew Safety___________________________________________________________________________ September 2005
  • 67. Marine Design 67__________________________________________________________________________________________ 4) Hotel Services 5) Cargo/Ballast Systems (1) is carried to provide power for (2) to (5)8.4 Principal Main Engine Systems 1) Fuel 2) Lubrication 3) Cooling 4) Exhaust 5) Compressed Air 6) Monitoring and Control Similar systems will be required to support the Auxiliary Machinery. These may beStand-Alone systems or integrated with those for the main engine(s).8.5 Electric Power GenerationAn Ocean-going cargo merchant ship will normally have three service generator sets plus one(small) emergency set.Of the three service sets:- One will be providing the Normal Sea Load One will be available as back up (It will be running in circumstances when loss of power could be dangerous). One may be under maintenance.When a ship habitually undertakes long sea voyages at constant speed then it may be practicalto derive some of the electric power from a generator driven by the Main Engine via thepropeller shaft or a Power Take Off (PTO) Advantages:- (i) Main Engine S.F.C. is better than an Auxiliary Engines (ii) Main Engine Fuel (Heavy Fuel) is cheaper. Disadvantages:- (i) More complex system (ii) Still needs three conventional generators plus emergency set.___________________________________________________________________________ September 2005
  • 68. Marine Design 68__________________________________________________________________________________________8.6 Fuel System Functions 1) Distribution/Transfer to & from Tanks 2) Settling Tanks 3) Centrifugal Separators 4) Service Tanks 5) Heating for Viscosity Control 6) Filtration8.7 Preliminary Estimation of Propeller DiameterThere are two formulae which may be helpful in making an initial assessment of PropellerDiameter. This may be needed to confirm that the draught of a ship is sufficient to ensure thatits propeller(s) is(are) adequately immersed at all times. D = 16.2 * Ps 0.2 / N 0.6 metres (1) Where D is the Propeller Diameter Ps is the Shaft Power (per shaft) in kW and N is the shaft revolutions per minuteAlternatively, D = 0.2 * √ (Ps / V) metres (2) Where V is the ship’s design speed in knots. (1) above is generally quite accurate for Cargo Ships, Bulk Carriers and Container Ships. (2) tends to underestimate the diameter for merchant ships by about 10% but may be more reliable in its own field of high-powered Naval vessels fitted with Controllable Pitch Propellers.___________________________________________________________________________ September 2005
  • 69. Marine Design 69_____________________________________________________________________________________________________________________________________________________________________ September 2005
  • 70. Marine Design 70_____________________________________________________________________________________________________________________________________________________________________ September 2005
  • 71. Marine Design 71__________________________________________________________________________________________9 Estimating Hydrostatic Properties and Initial Stability___________________________________________________________________________ September 2005
  • 72. Marine Design 72_____________________________________________________________________________________________________________________________________________________________________ September 2005
  • 73. Marine Design 73_____________________________________________________________________________________________________________________________________________________________________ September 2005
  • 74. Marine Design 74_____________________________________________________________________________________________________________________________________________________________________ September 2005
  • 75. Marine Design 75_____________________________________________________________________________________________________________________________________________________________________ September 2005
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  • 77. Marine Design 77__________________________________________________________________________________________9.x Undamped Roll Motion in Still WaterLet φ be the inclination of the ship to the vertical at any instant of time. The moment acting ona stable ship will be in a sense to decrease φ. For small values of φ, Restoring Moment = - ∆ * GMT * φApplying Newton’s Laws of Motion, Moment = (moment of inertia about OX) * (angular acceleration)i.e. - ∆ * GMT * φ = +(∆/g) *kxx2 * d2φ/dt2i.e. d2φ/dt2 + (g * GMT / kxx2 ) φ = 0This is a form of the differential equation denoting simple harmonic motion with frequency ω. Let φ = φo sin ωt where φ o is the maximum amplitude of the motion. then dφ/dt = ω φ o cos ωt and d2φ/dt2 = - ω2φ o sin ωt = - ω2φi.e. d2φ/dt2 + ω2φ = 0then for a ship rolling, ω2 = g * GMT / kxx2 ∴ ω = √ (g * GMT / kxx2 ) and Period, Tφ = 2π/ω = 2 π √ (kxx2 / ( g * GMT )) = 2 π kxx / √ ( g * GMT )___________________________________________________________________________ September 2005
  • 78. Marine Design 78__________________________________________________________________________________________9.y Worked Example - Capacity CarrierA design study has been made for a ferry and the following basic dimensions have beenchosen:- L = 106 m; B = 17 m; D = 19 m; T = 6 m; CB = 0.62This achieves both the design capacity and the design displacement. A suitable hull form hasbeen chosen from a standard series and at a draught of 6 m the following hydrostatic data isfound:- KB = 3.5 m; CIT = 0.71(where CIT is the Coefficient of Transverse Inertia; IT = CIT * L * B3 /12)From a study of the loading and operating pattern of a similar ship it is estimated thatKG = 0.6D in the worst operating condition.Check the initial stability of the design and modify it if necessary, keeping both capacity anddisplacement constant, to ensure that GMT > 0.6 m for safety while also ensuring that therolling period Tφ is greater than 11 seconds for comfort.IT = CIT * L * B3 /12 = 0.71 * 106 * 173 / 12 = 30813 m4 = LBTCB = 106 * 17 * 6 * 0.62 = 6703 m3 BMT = IT / = 30813 / 6703 = 4.60 mGMT = KB + BMT - KG = 3.5 + 4.6 - 0.6 * 19 = 8.1 - 11.4 = -3.3 m Clearly unsatisfactory.Speed depends on L & CB , so it is preferable that they are left unchanged. If B is increasedthen BMT will be increased; if T & D are reduced in the same proportion as B is increasedthen displacement and capacity will remain unchanged.Try B’ = 20 mReduce Draught, T to maintain constant displacement∴ T’ = 6 * 17 / 20 = 5.1 mReduce Depth, D to maintain capacity ( ∝ L * B * D)∴ D’ = 19 * 17 / 20 = 16.15 mHence KB’ = 3.5 * 5.1 / 6.0 = 2.975 mand KG’ = 0.6 * 16.15 = 9.69 m___________________________________________________________________________ September 2005
  • 79. Marine Design 79__________________________________________________________________________________________IT’ = CIT * L * B3 /12 = 0.71 * 106 * 203 / 12 = 50173 m4 BMT’ = IT’ / = 50173 / 6703 = 7.485 mGMT’ = KB’ + BMT’ - KG’ = 2.975 + 7.485 - 9.69 = 0.77 mThis satisfies the first criterion.To check the Rolling Period,Tφ = 2 *π * k / √ (g * GMT) where k = 0.32 √ (B * D) = 2 * π * 5.751/ √ (9.81 * 0.77) = 0.32 √ (20 * 16.15) = 36.135 / 2.748 = 5.751 m = 13.15 secsThis satisfies the second criterion.It is also possible to determine the maximum value of GMT which will give a Rolling Periodof 11 secsTφ = 2 *π * k / √ (g * GMT) and by squaring both sides and transposing,GMT = 4 * π2 *k2 / (g * Tφ2) = 4 * 9.8696 * 5.7512 / (9.81 * 112) = 1.100 m(Can you determine the maximum value of GMT which will give the desired Rolling Periodbefore changing the dimensions? What was the value of k for the initial design?)It would be preferable to have a method of calculating the required change in dimensionsdirectly and to be able to investigate the sensitivity of GMT to changes in L, B, T or D.Let ∆ = constant * L * B * TThen, taking logarithms of both sides,log ∆ = log (constant) + log L + log B + log Tand differentiatingd∆ / ∆ = dL / L + dB / B + dT / T that is, if the fractional changes in dimensions are small then their sum gives the fractional change in displacement.___________________________________________________________________________ September 2005
  • 80. Marine Design 80__________________________________________________________________________________________BMT = IT / = constant * B2 / TAnd by following the same approach, d BMT / BMT = 2 * dB / B + dT / TAlso, d BMT / BMT = ( d BG + d GM ) / (BG + GM )Now for constant ∆ & L, dT / T = - dB / BTaking Capacity = constant * L * B * D and following the above processFor constant Capacity & L ( as well as constant ∆ and L)dD / D = - dB / B = dT / TWe have KG = constant * D and KB = constant * T = constant * ( D / T ) * T = constant’ * T∴ BG = KG - KB = constant’’ * T∴ d BG / BG = dT / T = - dB / BBut we have( d BG + d GM ) / (BG + GM ) = 2 * dB / B + dT / T = 3 * dB /B∴ d BG + d GM = 3 * ( BG + GM ) * d B/ B∴ - BG * dB / B + d GM = 3 * ( BG + GM ) * dB / B∴ d GM = ( 4 BG + 3 GM ) * dB / B∴ dB / B = d GM / ( 4 BG + 3 GM )Applying this relationship to the example,for GMT’ = 0.6 m, d GM = 3.3 + 0.6 = 3.9 mand BG = KG - KB = 11.4 - 3.5 = 7.9 m∴ dB / B = 3.9 / ( 4 * 7.9 + 3 * ( -3.3) ) = 3.9 / ( 31.6 - 9.9 ) = 0.1797∴ dB = 0.1797 * 17.0 = 3.055∴ B’ = 20.055 m___________________________________________________________________________ September 2005
  • 81. Marine Design 81__________________________________________________________________________________________Noting the requirement for small changes in dimensions then this is a fair result.for GMT’’ = 1.1 m, d GM = 3.3 + 1.1 = 4.4 m∴ dB / B = 4.4 / ( 31.6 - 9.9 ) = 0.2028∴ dB = 0.2028 * 17.0 = 3.055 and B’’ = 20.45 mReturning to the example,Try B’’ = 20.45 m, then for constant ∆ T’’ = 6 * 17 / 20.45 = 4.988 mand for constant Capacity D’’ = 19 * 17 / 20.45 = 15.795 mHence KB’’ = 3.5 * 4.988 / 6.0 = 2.910 mand KG’’ = 0.6 * 15.795 = 9.477 mIT’’ = CIT * L * B’’3 /12 = 0.71 * 106 * 20.453 / 12 = 53637 m4 BMT’’ = IT’’ / = 53637 / 6703 = 8.002 mGMT’’ = KB’’ + BMT’’ - KG’’ = 2.910 + 8.002 - 9.477 = 1.435 mThis is rather higher than was expected but the method is specifically for small changes indimensions. The change in Beam is of the order of 20% which is not a small change.If we now apply the method a second time to reduce GMT’’ from 1.435 m to 1.100 m weshould find an answer that is very close. d GM = -0.335 m BG = KG - KB = 9.477 - 2.910 = 6.567 m∴ dB / B = d GM / ( 4 BG + 3 GM ) = -0.335 / ( 4 * 6.567 + 3 * 1.435 ) = -0.335 / (26.268 + 4.305 ) = -0.011∴ dB = -0.011 * 20.45 = -0.225 and B’’’ = 20.225 mThen for constant ∆___________________________________________________________________________ September 2005
  • 82. Marine Design 82__________________________________________________________________________________________ T’’’ = 6 * 17 / 20.225 = 5.043 mand for constant Capacity D’’’ = 19 * 17 / 20.225 = 15.970 mHence KB’’’ = 3.5 * 5.043 / 6.0 = 2.942 mand KG’’’ = 0.6 * 15.970 = 9.582 mIT’’’ = CIT * L * B’’’3 /12 = 0.71 * 106 * 20.2253 / 12 = 51886 m4BMT’’’ = IT’’’ / = 51886 / 6703 = 7.741 mGMT’’’ = KB’’’ + BMT’’’ - KG’’’ = 2.942 + 7.741 - 9.582 = 1.101 m___________________________________________________________________________ September 2005
  • 83. Marine Design 83__________________________________________________________________________________________10 General Arrangement10.1 Introduction Once the Main Dimensions and Hull Form have been fixed consideration can be givento the General Arrangement. Normally this will be done by means of the drawing of a smallscale General Arrangement plan. A scale of 1 to 200 is quite suitable although a larger scalemay be more appropriate for small ships. The only boundaries which have been fixed so farare the hull surface and any deck lines which affect freeboard. The remaining spaceboundaries in the ship remain to be fixed. A major decision is to determine the position of themachinery space. In a light condition the density of the machinery space and theaccommodation, taken together, is greater that the rest of the ships length. In a loadedcondition the reverse is truer. This is important when considering trim.10.2 Trim A level keel trim is usually specified for the full load condition with homogeneouscargo. This is mainly to make the best use of the available depth of water in port - usually arestrictive item. Of course the cargo distribution may never quite produce such a trim but itmust be possible without ridiculous cargo stowage and the homogeneous condition usually isquoted t‹ ensure this. Some designs either specify a design trim or must accept one. There areships in which the weight distribution is so extreme that balance between the LCG and LCBcan only be achieved by using trim to make a radical adjustment to the sectional area curve.Tugs and fishing vessels are common examples where the need for propeller immersion alsoplays its part and warships often have this feature. As ships tend to trim by the bow relative to their static trim when running at normalspeeds, no bow trim at all can be permitted at rest. Usually cargo is disposed to ensure somestern trim in most sea-going conditions. Steering and directional stability can be upset by bowtrim. In the initial design stages trim is mainly controlled by the location of the machineryspace relative to the cargo holds. Provision of ballast spaces including the peak tanks givessome control over trim but carrying ballast is a waste of deadweight and may imposeundesirable stresses. Reasonable trim must also be maintained during cargo working atintermediate ports. In the case of the traditional general cargo vessel this was no easy thing todo unless the machinery space was amidships.10.3 Location of the Machinery Space The most common position for the machinery space in modern cargo ships iscompletely aft. Trim problems are severe in general cargo vessels and cannot be solvedwithout ballast tanks forward to use in the light condition. Sometimes it is difficult to avoidbow trim when loaded. This location is suitable for, and typical of, ships which carryhomogeneous cargoes such as tankers and bulk carriers, especially when the cargo is denserthan seawater since their weight distribution can be controlled to solve trim problems. Whilethe best part of the ship is given to the cargo holds the machinery space may require morelength than expected in order to accommodate the auxiliary machinery. The use of segregatedballast tanks in tankers or a floodable hold in bulk carriers provides control of draught, trimand bending moment if carefully sized and located.___________________________________________________________________________ September 2005
  • 84. Marine Design 84__________________________________________________________________________________________ In large high-speed and high-powered container ships the machinery space is oftensituated in the three-quarters aft position. Although this splits the container stowage area intotwo parts it allows the machinery to be installed in a fairly full part of the ship. Trim can bekept under control with only a modest requirement for water ballast and bending of the hullgirder between loaded and light condition may be minimised.10.4 Length of Machinery Space Assuming that diesel propulsion is to be adopted (and it usually is) then the length ofthe machinery space is governed either by 1) The Main Engine, Gearbox (if fitted) and Thrust Blockor 2) The Generators An end clearance of one or two frame spaces should be added to the neat length. Caremust be taken to ensure that there is sufficient space for the auxiliary machinery. Ideally theseshould be sited on the tank top, particularly those requiring a solid foundation to minimisevibration e.g. Generators and Compressors. Flats can be fitted to provide additional area butoften cannot be made stiff enough to support major auxiliaries. Technological change tends to make the machinery grow in complexity but to shrinkin size and so machinery spaces tend to become smaller over time. However enginemaintenance is an important consideration for the effective operation of the ship. Toocompact an engine room may make maintenance more difficult and even more expensive.Access to the equipment and removal routes for parts from them should be adequate.10.5 Storage of Liquids Once the Position and size of the machinery space has been decided then attention canbe turned to tank spaces. Normally these are confined to double bottoms but deep tanks maybe arranged for additional water ballast in the Fore and After Peaks for trim or near amidshipsto control hull girder bending. Engine Room double bottoms will first be allocated to Lubricating Oil storage, drainand sump tanks together with cofferdams to ensure there is no Lub. Oil/Salt Water interfacewhich could leak and cause contamination. While main propulsion engines will be happy running on fairly heavy fuel oil, dieselgenerators normally require the lighter Diesel Oil. This should be stowed reasonably close tothe generators. Ideally, the tanks for fuel oil can then be allocated with a view to ensuring thatthe LCG of the fuel is forward of the LCG of the loaded ship so that as fuel is consumed theship will not tend to trim by the bow. Modern practice, driven by pollution control requirements, discourages the use ofdouble bottom tanks for fuel storage. Thus the only way to have control over fuel LCG is tofit deep tanks forward and aft of the cargo holds and accept long filling and supply linesto/from the forward tanks. The alternative of only having fuel tanks aft has the consequencethat a significant stern trim in the Departure condition will be followed by a significant bowtrim in the arrival condition.___________________________________________________________________________ September 2005
  • 85. Marine Design 85__________________________________________________________________________________________ In addition to the storage tanks, space also needs to be found for settling tanks anddaily service tanks to satisfy the needs of the main and auxiliary machinery. These are usuallylocated within the boundaries of the machinery space. Actually finding the space for themmay not be a task for the Naval Architect but the Weight & centre of gravity of their contentsis a legitimate concern. Water ballast is required to give adequate propeller immersion in the lightest seagoingcondition and to ensure that the minimum draught forward is sufficient to avoid excessiveslamming. While many ships now distil their own Fresh Water from sea water a limited storagecapacity is necessary for use when the ship is in polluted or coastal waters where distillation isnot possible. Holding tanks for sewage and waste water are necessary to avoid marine pollution.They are small in a cargo ship but of significant size in passenger ships.10.6 Cargo Holds The number of holds is dictated largely by the size of the ship and the type of cargo.Requirements, which came into force in February 1994 for the damage stability andsurvivability of cargo ships, have brought flooding into consideration. Holds in containerships will have lengths which are multiples of the container length (plus an allowance for thecell guides). A hold around 40 ft long can take either one 40 ft container or two 20 ftcontainers; a hold 60 feet long can take 3 at 20 ft or two at 30 ft or one at 40 ft and one at 20 ftdepending on how the cell guides are set up. In dry bulk carriers the usual of number of holds is a choice from 5, 7 or 9. Five holdsare common in Handy Size vessels of around 25,000 tonnes deadweight; seven holds are theusual choice for a 75,000 tonnes deadweight Panamax vesssel; while nine holds are oftenfound in the largest Capesize vessels of 150,000 tonnes and over. The height from the double bottom to the upper deck will be divided by tween decksin accordance with the requirements of the trade. Thus none will be found in Bulk Carrierswhile Fruit Carriers and Banana Carriers will have the total depth of the hold divided intotween decks. The height of the tween deck may vary between 2.4m and 3.0m. The clearheight in the hold varies immensely but it should be noted that some cargoes will crush ifloaded too deeply.10.7 Hatchways Large hatchways assist easy cargo working but hatch widths are restricted by the needto maintain not only the cross sectional area of deck material for structural reasons but alsothe shelf space at the tween deck levels. The ingenious use of twin hatches, side by side, canfacilitate both good cargo working and the containment of grain cargoes in a general cargoship. The length of hatches is constrained by the length of deck taken up by cargo gear andhatch cover stowage. General cargo ships usually have the capability of carrying some___________________________________________________________________________ September 2005
  • 86. Marine Design 86__________________________________________________________________________________________containers within the line of hatches and this will lead to hatch dimensions tending to be amultiple of container lengths and widths with an allowance for clearance between them. Flush hatches are clearly desirable for ease of cargo working but in general load linerequirements will prohibit or severely penalise the ship for their use on a weather deck.10.8 Accommodation Arrangement Usually the accommodation is sited above the machinery space and around the enginecasing to minimise interference with cargo operations. The result is a short, highsuperstructure giving good forward visibility but possibly compromising stability. A goodarrangement is largely a matter of common sense, experience and foresight. Any difficultieswhich arise in service should be noted and avoided in the next design. Minimum manning scales and minimum standards for accommodation are laid downin regulations. Virtually every crew member nowadays will have a single cabin and officersmay well have suites with dayroom, sleeping cabin, bathroom etc. Automation has acontinuing influence, gradually reducing crew numbers and further significant changes maytake place in the coming decades. Remember that the accommodation is where the seafarer lives out his/her life. It ishis/her home for long periods as well as his/her place of work. There must be public space tosocialise in and private space as a retreat from work.10.9 Minimum Requirements for Crew Accommodation Segregation into Officers, Petty Officers and Ratings is still common in the MerchantNavy although it becomes harder to sustain as crews become smaller. A ship which had 30 ofa crew thirty years ago would be designed to run with half that number now. Justifyingseparate facilities for each grade becomes very difficult. a) Deck and Engineer Officers. In single or double cabins (Master and Chief Engineer should each have an individual cabin). Bathroom with one bath or shower and one wash basin for every six persons. Separate dining saloon and smoke room. b) Petty Officers. Cabins and washing facilities as for officers. Separate messroom (1m2 per person) c) Engine Room Hands. Separate sleeping and dining accommodation (but numbers sharing cabins not specified). Bathrooms as for Officers. The International Labour Organisation (ILO) recommends minimum floor areas per person in sleeping rooms as: - 3.75 m2 in ships of 1000-3000 tons, 4.25 m2 in ships of 3000-10000 tons and 4.75 m2 in ships over 10000 tons. (Tons are gross tons; a volumetric measure.) Where two ratings share a cabin the above figures are reduced by 1 m2 per person___________________________________________________________________________ September 2005
  • 87. Marine Design 87__________________________________________________________________________________________ d) Deck Hands. Cabins, dining accommodation and bathrooms as for Engine Room Hands. Crew’s smoke room shared with Engine Room Hands. Many ships offer higher standards than these such that all crew have single cabinswith ensuite bathrooms and perhaps double beds so that wives can travel on some voyages.An officer’s single cabin could reach 21 m2 with bathroom and a crew’s single cabin 16 m2,also with bathroom. The combination of tall superstructures and double beds can be a problem though. TheMaster and the Chief Officer of a ship so fitted both fell asleep on watch because they couldnot sleep comfortably alone in their double beds near the top of a tall superstructure on arolling ship.10.9 More Complex General Arrangement Problems The preceding notes relate specifically to cargo carrying ships where a comparativelysmall number of compartment and functions have to be considered in preparing anarrangement. In Passenger Ships and Warships the problems are more complex and muchmore specialised. There are more compartments of many different types which can bearranged in a multitude of different ways. Consideration must be given to passenger flow atmeal times; potentially noisy areas such as cinemas or discos must be separated from sleepingareas and a host of other problems must be solved. In warships the arrangement of accommodation has all the problems of the passengership together with the additional difficulties of ensuring protection for weapon magazines,separating radar and radio antennae, providing clear arcs of fire for guns and missiles andavoiding noise paths to sensitive sonar equipment to name but a few. Finding the solutions to these problems is something which must be left to yourongoing professional development should you choose to work in these fields.The FINNCLIPPER is designed as a Ro-Ro Freight Ferry with a significant passengercapacity. She can carry 454 passengers in 192 two- and four- berth cabins. For vehicles shehas 2450 lanes-metres arranged over three decks. Fixed and hinged ramps allow access fromthe main vehicle deck to the upper and to the lower vehicle decks. Four diesel engines eachrated at 5760 kW @ 510 rpm drive twin controllable pitch propellers through doubleinput/single output gearboxes to give a speed of 22 knots. There are three diesel alternatorseach rated at 1088 kW and two shaft driven alternators each rated at 1648 kW.LBP 170.00 m; B mld 26.70 m; Design Draught 6.00 mThe VOYAGER OF THE SEAS at a gross tonnage of 137,300 was, at the time she was built,the largest cruise liner in the world. She can accommodate 3840 passengers in 1557 cabinsand in addition carries a crew of 1180 in 667 cabins. Six diesel alternator sets each produce17,600 kVA (electrical) from 12,600 kW @ 514 rpm (mechanical) and drive three electricmotors in Azipods each of which can absorb 14,000 kW @ 140 rpm. This gives her a servicespeed of 22 knots.LBP 274.70 m; B mld 38.60 m (Bmax 47.40 m); Design Draught 8.60 m___________________________________________________________________________ September 2005
  • 88. Marine Design 88__________________________________________________________________________________________From Chapman, The Optimum Machinery Position in Dry Cargo Vessels, NECIES___________________________________________________________________________ September 2005
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  • 93. Marine Design 93__________________________________________________________________________________________11 Capacity and Centre of Volume Estimates___________________________________________________________________________ September 2005
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  • 98. Marine Design 98__________________________________________________________________________________________12 The Regulation of Shipping The history of regulation of shipping starts with taxation. Rules were devised tomeasure the amount of cargo a ship could carry - its "Tonnage" so that Kings and port ownerscould charge tax or dues on that cargo. The next development was "Registration" - thedetermination of ownership which was necessary to enforce the collection of dues or taxesand to decide in time of war whether a ship belonged to friend or foe. The last area to developwas setting up rules for the construction of ships to ensure their strength and safety at sea. Therules were required to classify in terms of quality of the ships which were carryingcommercial cargoes for private owners who wished to insure the ship, the cargo or bothagainst the risk of being lost at sea. These three activities are representative of the three main subdivisions of regulation -International, National/Governmental i.e. Statutory and Private/ Commercial i.e.Classification. While, historically, they have developed in the above order, the NavalArchitects interest in these areas increases in the reverse order and so that is how they will beapproached in this section.12.1 The Role of the Classification Society There can be little doubt that the classification societies have a profound influence onshipping, ship design and ship safety. The fundamental purpose of classification is to ensurethat all classed ships are seaworthy when admitted to class and remain so throughout theirworking lives. The principal maritime nations have the undernoted classification societies: - United Kingdom - Lloyds Register of Shipping U.S.A. - American Bureau of Shipping France - Bureau Veritas Germany - Germanischer Lloyd Norway - Det Norske Veritas Italy - Registro Italiano Russia - Register of Shipping of the USSR Japan - Nippon Kaiji Kyokai Poland - Polish Register of Shipping Lloyds Register of Shipping is the worlds oldest classification society and its originsgo back more than two hundred years. In the latter part of the eighteenth century, cargoowners, ship owners and ship builders met in Mr Lloyds Coffee House in London to discussand arrange their business. The cargo owners knew that many ships were lost at sea takingtheir cargoes down with them. An insurance market developed in the Coffee House wherebythe owners paid so much a voyage as premium and if their cargo was lost they were repaid itsvalue. Neither the cargo owners nor the insurers entirely trusted the ship owners who mightbe inclined to lie about how seaworthy their ship might be. The people who supported theinsurance schemes, called underwriters, decided to keep a register with details of all the ships___________________________________________________________________________ September 2005
  • 99. Marine Design 99__________________________________________________________________________________________they knew about and how good they were. Eventually they were able to classify just howgood any ship would be by looking at it and knowing who built it. When the underwriters began to say how ships should be built both the ship ownersand the ship builders became very worried. After much argument and unpleasantness it wasdecided to form a new society with representatives from all three groups to supervise shipconstruction and maintenance and to put ships into classes depending on their quality.Because of its place of origin it was called Lloyds Register of Shipping and it was theforerunner of similar societies set up in many of the major shipbuilding nations. The insurancemarket developed separately into the Corporation of Lloyds and set about insuring all sorts ofthings as well as ships. The classification societies operate on a world-wide basis and publish rules andregulations governing the structural strength of the ship and the reliability of its propellingmachinery. Classification implies that the ship and its machinery conform to the standardspublished in the rules of the Society. Classification is voluntary on the part of the ship ownerand the only penalty that can be imposed for non-compliance with the rules is suspension ofclass. In general, a ship will have difficulty in gaining insurance unless it is classed by arecognised classification society. Classification of a new ship with, for example, Lloyds Register, entails approval ofconstructional drawings, testing of materials, special survey while the vessel is underconstruction and a recommendation for class from the surveyor by report to the committee.Following acceptance of the report by the committee, the certificate of class is issued and theappropriate entry made in the Register book. The highest class given by Lloyds Register is +100A1. New ships built under SpecialSurvey are given the Maltese Cross (+) before the character figure in the register book. Thecharacter figure 100 indicates that the vessel is suitable for sea-going service, while thecharacter letter A indicates that the vessel accords with the Societys Rules and Regulationsand is maintained in good and efficient condition. The figure 1 following the character letterindicates that the mooring equipment comprising anchors, cables and hawsers, is in goodcondition. When the class +100A1 is assigned it may be followed by a descriptive notation suchas Oil Tanker, Bulk Carrier etc. plus a service restriction notation such as Ice Class 2 orStrengthened for Heavy Cargoes. Additional Class notations may be added for the condition of Propulsion Machineryand/or Refrigerating Machinery. +LMC indicates that the Propulsion Machinery and essentialAuxiliary Machinery has been constructed, installed and tested under Special Survey and inaccordance with the Rules and Regulations. UMS indicates that the control arrangements ofthe ship allow the machinery spaces to be unmanned during normal operations. Maintenance of standards is an important function of any classification society.Periodical surveys are required and failure to conform may result in removal of the ship fromclass and a reduction in its value as well as an increase in its insurance premium, assumingcover can be obtained.___________________________________________________________________________ September 2005
  • 100. Marine Design 100__________________________________________________________________________________________ Some aspects of Classification work are: - a) Annual Surveys All steel ships should be surveyed at intervals of approximately one year inaccordance with the rules. These annual surveys should, where practicable, be heldconcurrently with Load Line or other statutory annual surveys. b) Docking Surveys A ship should be examined in dry dock at intervals of about 12 months. The maximuminterval is 24 months. c) Special Surveys All steel vessels are subjected to special surveys in accordance with the rules. Thesesurveys become due at five-yearly intervals, the first being five years from the date of build ordate of special survey for classification and thereafter five years from the date of the lastspecial survey. The date of build of a ship built under a societys inspection is normally taken as thedate of completion of the special survey during construction. For Lloyds Register of Shipping, the standards to which the ship must be built andmaintained are laid down in the publication "Rules and Regulations for the Construction andClassification of Ships". This is regularly revised and updated to meet new demands. TheRegister Book itself is published annually and now extends to three volumes. It is a splendidwork of reference containing as complete a list as possible of all sea-going merchant ships inthe world of 100 gross tons or more whether classed by Lloyds or not. The number of shipsincluded exceeds 80,000. Many societies are empowered to assign Load Lines to ships and issue the Load Linecertificates on behalf of many Governments provided they are satisfied that all the necessaryconditions have been met. They may also be empowered to perform the same function inrespect of Tonnage Measurement. In addition to ships, most Societies are also active in the fields of High Speed andLight Craft, Yachts and Small Craft, Mobile Offshore Units, Floating Docks, andSubmersibles. Therefore they publish Registers of such craft and Rules and Regulations fortheir construction. They are even involved in the design of warship structures. It is apparent that the classification societies are not only able to assist to an enormousextent in making ships safe to travel the seas, but also are able to accumulate a vast amount ofinformation on the behaviour of ship-structures under sea-going conditions. This informationleads to improvements to the Rules and improvements in the structural design of ships. Individually and collectively through IACS (the International Association ofClassification Societies) the societies carry out extensive research to investigate failures inparticular types of ship and to recommend areas of structure where improvement is needed.___________________________________________________________________________ September 2005
  • 101. Marine Design 101__________________________________________________________________________________________ Having started out as organisations promoting Quality long before the term wasrecognised by shipbuilders, many of the societies now offer a wide range of services far fromthe sea to industries which recognise their expertise in Quality Control, Quality Assuranceand all other aspects of Quality Management. They are also heavily involved in the implementation of the International SafetyManagement Code (the ISM Code) both in advising companies how to set up SafetyManagement Systems and in auditing their success in doing so. Once again this is a logicaldevelopment from their origins in promoting Safety.12.2 Statutory Regulations Historically, Registration preceded Safety as a concern of Government and the subjectof statutory regulation. However, Naval Architects are professionally concerned with safetyand only have a passing interest in registration. This section therefore starts with Safety.a) Safety Almost all merchant ships are built in accordance with the rules of a classificationsociety. In addition, all must comply with statutory regulations enacted by the government ofthe state whose flag they fly and in which they are registered. In Britain, Parliament passesActs which affect merchant shipping and, under the Acts, Regulations are prepared by theDepartment of the Environment, Transport and the Regions (DETR) which is the governmentdepartment responsible for the standards of safety of British merchant ships. In 1994,executive authority for marine safety in the UK was vested in the Marine Safety Agency(MSA), - now called the Maritime and Coastguard Agency (MCA) - an agency of the DETR.The investigation of accidents and disasters at sea is organised by the Marine AccidentsInvestigation Branch (MAIB). The regulations are published as Statutory Instruments approved by Parliament andrelate to such matters as damage, subdivision, life-saving equipment, loading & stability, crew& accommodation, fishing vessels, hovercraft, fire protection, navigation & collision, carriageof dangerous cargoes, tonnage measurement and other allied subjects. Many of theseregulations derive from international agreements and the MCA represents Britain at theconferences and on the committees which discuss these matters. The MCA also publishes a series of Merchant Shipping Notices (M Notices) whichprovide advice, information and guidance on many matters related to the construction andoperation of ships. The primary objectives of statutory regulations are to promote safety of life andproperty at sea and to minimise environmental damage. The rules and regulationsadministered by the MCA are compulsory and are enforced by the MCA with penalties fornon-compliance set out in the relevant Acts of Parliament. The international scope of shipoperations means there is a considerable need for conformity between the regulations imposedby different states. Uniformity is sought by means of international conferences at whichconventions are formulated. Typical examples of these are the International Load LineConvention (ILLC), the International Convention for the Safety of Life at Sea (SOLAS) andthe International Convention on Tonnage Measurement of Ships.___________________________________________________________________________ September 2005
  • 102. Marine Design 102__________________________________________________________________________________________ An indication of the work of the MCA may be obtained from the following list of theirmain activities.i) Load Line Rules The MCA administer the British interpretation of the International Load LineConvention and assigns freeboards according to the geometric properties of the ship and itsstructural strength, in conjunction with the strength and security of covers to deck andsuperstructure openings among other considerations.ii) Survey of Passenger Ships A ship intended to carry more than 12 passengers must conform to the regulations forpassenger ships and be issued with a Passenger Certificate appropriate to the number ofpassengers and the place of operation. Every passenger ship and every cargo ship must be inclined in the presence of a MCAsurveyor, on completion, to determine its Lightship Weight and C.G. position for theassessment of stability. Based on these results the ships master must be supplied withinformation for guidance on the safe loading and ballasting of the ship.iii) Life Saving Appliances (LSA) In general, passenger ships are required to carry lifeboats under davits for all personson aboard and life rafts for an additional percentage of the number on aboard. Passenger shipsoperating in river and coastal waters may be permitted to reduce the number of lifeboats andrely on life rafts for the safe evacuation in emergency of all on board. Cargo ships, generally,are required to be provided with, on each side of the ship, life boats under davits which willaccommodate all persons on board and life rafts which will similarly accommodate allpersons on board. All lifeboats must be built to conform to the requirements of the LSA rules and areinspected during construction. All persons on board must be provided with an approved life jacket.iv) Masters and Seamen (Crew Accommodation) The Merchant Shipping Acts lay down minimum standards for crew spaces in terms offloor area, construction, lighting, heating, ventilation etc. Plans and details of accommodationareas must be submitted to the MCA at an early stage of design for approval. The actualaccommodation is subsequently inspected and measured at the ship.v) Tonnage Measurement Ships must be measured for tonnage to establish the Gross and Net tonnages on whichport, canal and navigation dues are levied.___________________________________________________________________________ September 2005
  • 103. Marine Design 103__________________________________________________________________________________________vi) Grain Cargoes Regulations are laid down for the stowage of grain cargoes in order to limit the risk ofa transverse shift of the cargo which could cause a serious loss of stability. Additionalinformation must be supplied to the ships master on the effect of these cargoes.vii) Light and Sound Signals International regulations for preventing collisions at sea require than all ships displayproper navigation and other lights to indicate their size and course. They should also have themeans for producing certain sound signals such as bells or sirens. The lights are screened sothan they are only visible from particular directions.viii) Fire Appliances The provision of arrangements for the prevention, detection and extinguishing of fireon board ship are most extensive. The means adopted to achieve these aims can be dividedinto three parts, namely a) Fire-proofing the ships structure as far as possible b) Providing equipment for detecting a fire whenever and wherever it starts. c) Providing equipment for extinguishing fires. In passenger ships, fire patrols must be maintained and an alarm and detecting systemfitted. Extinguishing is performed by jets of water or foam from fixed hoses and portable fireextinguishers. Fires in cargo spaces are extinguished by smothering with gas or steam distributed bypermanently installed piping systems. Special arrangements such as inert gas systems or foam discharged through a systemof fixed nozzles are required in propelling machinery spaces.b) Registration The other main area covered by statutory regulation is that concerned with proof ofownership - Registration. The compulsory registration of British ships was brought aboutinitially under the Navigation Acts from 1660 onwards. The Registry Act of 1786 made itcompulsory for every ship to display its name and the port to which it belonged (port ofregistry) on the astern. In addition the certificate of registry had to contain details of the shipsdimensions. The Merchant Shipping Act of 1854 reinforced the requirements of previous Acts andput in place a system of Registry documents, Registrars in Ports around both the British Islesand British Possessions overseas. The organisation which maintained these records was basedin Cardiff and headed by the Registrar General of Shipping and Seamen.___________________________________________________________________________ September 2005
  • 104. Marine Design 104__________________________________________________________________________________________ The provisions of a number of amending Acts were consolidated in the MerchantShipping Act of 1894 which required that every British ship, with certain minor exceptions,must be registered. A vessel coming within the terms of the Act and not so registered is notconsidered to be a British ship. The ships master must always have the certificate of registryin his possession on board - in default of this the ship is liable to be detained in port. Beforesuch a vessel proceeds to sea the draughts must be recorded in the official log-book andreported to the Customs Authority. Prior to Registration the ship must be surveyed, measured for tonnage, and the draughtmarks cut in, or welded on, each side of the stem and of the sternpost. For metric ships, thedraught marks are numerals 1 dm high placed at every 2 dm interval. At 10 dm intervals thefull 10, 20 or 30 dm etc. appears while at the other intervals only the last digit of the draughtappears. . On completion of the registration survey, a Certificate of Registry is prepared bythe surveyor and forwarded to the Registrar of Shipping and Seamen at the intended port ofregistry. This Certificate sets out particulars of the build of the ship and its dimensions bywhich the ship may be identified, also particulars of tonnage, and details of the propellingmachinery. Application for registration must be made by the owner of the ship and beaccompanied by a formal declaration of ownership. If a new ship is being registered then aBuilders Certificate must also be submitted to the registrar. He enters the particulars in theofficial Register Book, allocates the next available Official Number to the ship and enters iton the Certificate of Registry. Prior to the delivery of the Certificate the registrar issues a carving note giving detailsof the markings required on the ship, these being: - i) The ships name to be marked each side of the bow, and the name and port of registry to be marked on the stern. ii) The Official Number and Net Tonnage to be marked on the main beam. When these items are satisfactorily marked the surveyor certifies the carving note andreturns it to the registrar who can now sign the Certificate of Registry and hand it over to theowner on receipt of the appropriate fee. A ship may change its name or port of registry under certain regulated circumstances(and the choice of name is subject to official approval) but the Official Number allocates onits first registry is never changed. If a ship ceases to be a British ship by reason of sale orother circumstance then the Certificate of Registry must be returned to the Registrar at its portof registry and its registration is cancelled. If the vessel later returns to British ownership thenit may be re-registered after survey and will be known by its original Official Number. The Merchant Shipping (Registration etc.) Act 1993 introduced changes to the detailof the process of registration during 1994 so that all the recording of data is centralised underthe Registrar General of Shipping and Seamen. There are no longer Registrars in the portshandling registration. Thus there are no longer "Ports of Registry"; instead the port named onthe stern of a ship will be a "Port of Choice".___________________________________________________________________________ September 2005
  • 105. Marine Design 105__________________________________________________________________________________________12.3 International Maritime Organisation (IMO) In 1948 the United Nations Maritime Conference at Geneva drew up the conventionwhich created the Intergovernmental Maritime Consultative Organisation (IMCO) as anAgency of the United Nations. The purpose of the organisation was to provide for co-operation between governments on the whole field of sea transport with particular reference totechnical matters affecting international merchant shipping, especially the Safety of Life atSea and the efficiency of navigation. The IMCO Convention required the formal approval of21 states before the organisation could begin to function This was achieved in March 1958and on 6th January 1959 the IMCO Assembly met in London where the headquarters were setup. The first permanent international maritime body had come into being. In 1982 the namewas changed to International Maritime Organisation (IMO). Before detailing the activities of IMO over the past decade or so, it may be of interestto examine the background to sea transport - one of mankinds oldest callings. Due to itsessentially international character, sea transport has for ages demanded a high standard of co-operation between the maritime countries of the world, but lacked a central organisation to co-ordinate activities. In spite of the extensive practical co-operation of governments where thesaving of life was concerned, it was not until 1881 that the first international conference onmaritime affairs took place. This conference, held in Washington discussed such matters as: - - Regulations for Preventing Collisions a Sea - Saving of Life and Property from Shipwreck - Qualifications for Officers and Seamen - Lanes for Vessels on Frequented Routes - Establishment of a Permanent International Maritime Commission In 1897 the International Maritime Committee was formed to cope with the legalaspects of Merchant Shipping. This body also assisted in the work of several Internationalconferences, including that called in 1914 as a direct result of the loss of the Titanic in 1912.A draft document was prepared - The 1914 Convention for the Safety of Life at Sea - butnever came into effect because of the outbreak of the First World War. After that war the British Government saw the need to prepare up-to-daterequirements and as a result a conference was held in London in 1929 leading to the 1929Convention for the Safety of Life at Sea. In 1930 a further International Conference drew upregulations for determining the freeboard of merchant ships engaged in international trade -the 1930 International Load Line Convention. Following the Second World War, the founding of the United Nations in 1945 markeda significant advance in Inter-governmental co-operation and led to the formation of IMCO. The principal role of IMO is the preparation and maintenance of internationalconventions related to maritime affairs. Naval Architects are normally most interested in thoseconventions with an impact on the technical aspects of ship design but much valuable work isalso done in the area of legal liability. IMO is the international forum in which problems areaired and solutions thrashed out. Once a new convention has been agreed by IMO it must beratified by the member states and then embodied in national law. Only then can the newrequirements be enforced.___________________________________________________________________________ September 2005
  • 106. Marine Design 106__________________________________________________________________________________________ Originally, the same procedure had to be followed for amendments to Conventions butthis was later modified to allow amendments approved by IMO to be implemented a fixedperiod of time after their approval. Given that it took 25 years for the full implementation ofthe 1969 Convention on Tonnage Measurement the change of approach for amendments wasclearly much needed! The governing body of IMO is the Assembly, which meets once every two years andcomprises all the member states. In the period between sessions of the Assembly a Councilruns the affairs of the Organisation. The Council consists of 32 member states elected by theAssembly for two-year terms. The organisation’s technical work is carried out by a number of committees, the mostsenior of which is the Maritime Safety Committee (MSC). This has ten sub-committeeswhose titles reflect their areas of interest (See figure). The other committees are the MarineEnvironment Protection Committee (MEPC) which has two sub-committees (one is sharedwith MSC), the Legal Committee, the Facilitation Committee and the Committee onTechnical Co-operation.International Conventions The IMO has been responsible for instigating and introducing the followingInternational Conventions: - - For the Safety of Life at Sea 1960 (SOLAS 1960) - For the Safety of Life at Sea 1974 (SOLAS 1974) - SOLAS Protocol 1978 - SOLAS Protocol 1988 - For the Safety of Life at Sea 1990 (SOLAS 1990) - For the Safety of Life at Sea 1995 (SOLAS 1995) - For the Prevention of Pollution of the Sea by Oil 1973 (MARPOL 1973) - MARPOL Protocol 1978 - On Facilitation of International Maritime Traffic 1965 - International Load Line Convention 1966 (LL 1966) - Load Line Protocol 1988 - On Tonnage Measurement of Ships 1969 - On Intervention on the High Seas in cases of Oil Pollution Casualties 1969 - On Civil Liability for Oil Pollution Damage 1969 - On Civil Liability in the Field of Maritime Carriage of Nuclear Material 1971 - Establishment of an International Fund for compensation for Oil Pollution Damage 1971 - Special Trade Passenger Ships Agreement 1971 - Safe Containers 1972 - On Regulations for Preventing Collisions at Sea (COLREG 1972) - International Maritime Satellite Organisation 1976 (INMARSAT 1976) - Safety of Fishing Vessels 1977 - Standards of Training, Certification and Watchkeeping for Seafarers 1978 (STCW78) - Standards of Training, Certification and Watchkeeping for Seafarers 1995 (STCW95)___________________________________________________________________________ September 2005
  • 107. Marine Design 107__________________________________________________________________________________________ - Maritime Search and Rescue 1979 - Salvage 1989(Note: - A Convention on the Carriage of Passengers and Their Luggage by Sea was agreed in1974 but has not yet come into force - again demonstrating one of the weaknesses of IMO -the length of time it can take for a sufficient number of governments to ratify a convention.) While the Conventions are negotiated and approved at specially convenedConferences, the Assembly approves Codes and Resolutions which provide guidance andtechnical criteria on a wide range of topics, some of which are mentioned briefly below.Safety of Navigation IMO has put in a great deal of effort into introducing measures and policies designedto improve the safety of navigation. Among the most important are those which concern thecompulsory carriage of navigational equipment and the principle of ship routing andseparation of traffic at sea. Navigational equipment such as: - - Radar - Echo Sounder - Gyro Compass - Radio Direction Finder - Satellite Navigationwhich until recently were carried at the discretion of the owner are now mandatory in shipsabove a certain size. Considerable effort has been concentrated on two further aspects of safety ofnavigation: - - Measures for regulating traffic in confined waters - Revised International Regulations for the Prevention of Collisions at SeaRadio Communications A wide range of operational initiatives designed to improve or reshape the existingMaritime Distress System was studied. By making use of the INMARSAT network oforbiting satellites in space to give global surveillance of the maritime broadcast bands aGlobal Maritime Distress and Safety System (GMDSS) was introduced in 1992 and takes fulleffect from February 1999 for ships of over 300 tons.Life Saving Appliances IMCO & IMO in turn have developed standards for the testing and approval of life-jackets and requirements concerning the life-saving appliances to be carried on air cushionvehicles and on mobile offshore units engaged in exploration for hydrocarbons, as well asthose traditionally associated with ships.___________________________________________________________________________ September 2005
  • 108. Marine Design 108__________________________________________________________________________________________Search and Rescue Manual As a guide for masters and others involved in incidents of distress at sea, IMO hasprepared the Merchant Ship Search and Rescue Manual (MERSAR). This contains specificinstructions on the actions to be taken by the vessel in distress, by those participating in thesearch and general guidelines on the organisation and conduct of such search and rescueoperations.Guidance on Training The training of masters, officers and seamen is an integral part of assuring safety atsea. In 1983 the IMO Committee on Training issued a "Document for Guidance", proposingsyllabi on various topics which should be included in maritime training programmes.Subdivision and Stability of Ships This is an area of constant interest to both the maritime community and the generalpublic in the light of the loss of vessels such as Herald of Free Enterprise and Estonia. Proposals for new subdivision regulations for Passenger Ships based on the probabilityof the ship surviving a variety of damage conditions were developed many years ago but hadto await the development of computer power before the calculations involved could be tackledon a regular basis. These proposals took into account the longitudinal subdivision commonlyfound in passenger ships and were alternatives to the existing requirements in SOLAS 1960. From 1992 these proposals apply to cargo ships of over 100 m in length which are notrequired to comply with any other subdivision and damage stability requirements. Considerably enhanced requirements for the stability and subdivision of passengerships were introduced by SOLAS 1995 following the loss of the Estonia.Safety of Fishing Vessels IMO has developed simplified Stability Criteria for fishing vessels from 12 mregistered length upwards. It has also co-operated with two other UN Agencies - the Food andAgriculture Organisation (FAO) and the International Labour Organisation (ILO) - to developa Code covering the Health and Safety of Fishermen.Tanker Construction and Equipment Studies into the construction and equipment of oil tankers from the point of view ofpreventing or minimising pollution by oil in the event of stranding or collision were begun in1968 following the catastrophic effects of the grounding and break-up of the Torrey Canyon.These studies not only considered the problem of oil outflow in the event of damage but alsoembraced comprehensive investigations into the economic implications of tank sizelimitation. The technical factors involved in outflow limitation include the use of doublebottom or double skin construction, the arrangement of tanks and the use of segregated ballasttanks.___________________________________________________________________________ September 2005
  • 109. Marine Design 109__________________________________________________________________________________________ The IMO Maritime Safety Committee has recommended that the maximum¡ size oftank in the largest tankers should be limited to 50000 m3 for centre tanks and 30000 m3 forwing tanks. This would limit the hypothetical oil outflow in the event of collision or strandingto 30000 m3. In the case of normal tankers with two longitudinal bulkheads, the capacity of acentre tank and of a wing tank will be limited to 30000 m3 and 15000 m3 respectively. Further international debate on tanker safety followed the grounding of the ExxonValdez on the coast of Alaska in 1989 and the resulting oil spill. The United States ofAmerica unilaterally imposed its Oil Pollution Act 1990, demanding double skin constructionfor all tankers trading to U.S. ports. IMO has conducted a wide-ranging enquiry intoalternative means but has not settled on one ideal arrangement.The Carriage of Chemicals in Bulk In view of the increase in the sea transportation of hazardous or noxious chemicals inbulk it became apparent that there was a need for international measures to ensure their safecarriage. The Maritime Safety Committee approved an interim recommendation for existingships of the tanker type carrying dangerous chemicals in bulk liquid form.Fire Safety in Ships Fire is one of the most serious hazards facing ships at sea, especially passenger ships.IMO has recommended a series of amendments to the 1960 SOLAS convention for existingpassenger ships and a further series which would apply to new ships only.Marine PollutionThe British government convened an International Conference which resulted in theInternational Convention for the Prevention of Pollution of the Sea by Oil 1954. Responsibility for this convention was transferred to IMCO when it came into being.The 1954 convention dealt only with the deliberate or operational discharge of oil from shipsand did not relate to pollution arising from maritime accidents. The 1954 convention was extensively amended in 1969 to cover the following topics:- - Prohibition of deliberate discharge - Prevention of accidental discharge - Powers given to states for dealing with pollution - Provisions for redress for damage caused - Methods for dealing with spillages At the 1973 IMO Conference on Marine Pollution the main objective was thecomplete elimination of wilful and intentional marine pollution by oil and other noxiouspollutants coupled with the minimisation of accidental spills.___________________________________________________________________________ September 2005
  • 110. Marine Design 110__________________________________________________________________________________________Administration and Enforcement While it is clear that IMO does a tremendous amount of good work it is also clear thatobtaining agreement to all its decisions from all its member governments is a major problem.In addition, even when agreement is reached, implementation of the decisions is a matter forlegislation by the individual governments and may be delayed in many ways. IMO has no executive authority to police the operation of its conventions. Again it isin the hands of the individual governments and their maritime administrators to provide thedetermination and the financial and human resources to inspect ships and detain theunsatisfactory ones until they are made seaworthy. The most effective means of enforcing theconventions is for ships to be systematically inspected before they leave port by arepresentative of the national authority - Port State Control. This has, however, been madeless effective because of the lack of a mechanism for the ready international exchange of theoutcomes of Port State Inspections. Thus if defects are noted at one port it is not easy foranother port to find out (a) that they exist and (b) if they have been remedied. The shipownercan easily deny that any faults existed in his ship and it is difficult to prove that a defect mayhave been present for a long period of time.International action to enforce standards of ship safety is presently heading in two differentdirections: - i) Increasing survey activity by individual cargo owners and ship charterers to allow them to select the ships they are prepared to employ. ii) The formation of regional or continental groupings of maritime administrations to make a concerted effort to find and detain sub-standard ships through efficient Port State Inspections coupled with an internationally organised database detailing when and where a ship was last inspected, what defects were found (if any) and what action (if any) the shipowner promised. Such groupings now exist over a wide area of Western Europe and around the Pacific Rim.___________________________________________________________________________ September 2005
  • 111. Marine Design 111__________________________________________________________________________________________13 Tonnage13.1 Introduction Tonnage is a measure of the internal volume of a ship and was originally introduced torepresent its size or its earning capacity in assessing port or harbour dues and the charges forcertain services rendered to the ship. It then became convenient to use a scale of tonnage toset requirements for manning levels, provision of safety and lifesaving equipment, etc.Shipowners usually consider it an advantage to obtain the minimum tonnage for a given ship. The word ton originally came from tun which was a wine cask and, in some cases, thecargo capacity of a ship was measured by the number of wine casks it could carry. In the 13thCentury when tonnage measurement first arose the most valuable cargo and the mostprofitable trade for England was wine shipment across the Channel from France. The system of tonnage measurement used in the UK until 1982 derived from thatenacted in the Merchant Shipping Act of 1854 and is associated with the name of GeorgeMoorsom. The rest of the world then based their schemes for tonnage measurement to agreater or lesser extent on the Moorsom system. Initially the Moorsom system was quite simple. Gross tonnage based on the totalenclosed volume of the ship represented its size and Net or Register tonnage based on thevolume of the cargo and/or passenger spaces represented its earning capacity. The unit oftonnage was a volume of 100 cubic feet and although called a ton bore no direct relationshipto the weight of cargo which would occupy that volume. However, through time, it lost itssimplicity. Complex rules developed to determine whether particular spaces were included inthe gross tonnage or exempt (not included) or deductable (in the gross but not in the net).Some of these rules encouraged the building of inherently unsafe ships – the “Open” ShelterDecker – which had no permanent means of making watertight the transverse bulkheadsabove the tonnage deck. The spaces bounded by these bulkheads were “open” and thus“exempt” and not included in the gross tonnage. Unfortunately they were unlikely tocontribute to keeping the ship afloat after it was damaged.13.2 Present Tonnage Regulations The Moorsom system was superseded by the Universal Measurement System agreedat the 1969 Conference organised by IMCO. This system came into force for new or rebuiltships (and for existing ships by request of the owner) in July 1982. It was not until July 1994,twenty-five years after the conference that the new system applied to all existing ships. In theUK the system is described and enforced by The Merchant Shipping (Tonnage) Regulations1997, S.I. 1997 No 1510. We will first consider these regulations and study them in detail.The previous system will then be discussed in outline because an appreciation of its workingis helpful in understanding design decisions made in many existing ship types.1969 Tonnage Convention (Universal Measurement System) The conference aimed to find simple ways of providing the two measurements whichtonnage was supposed to provide - Gross Tonnage, representing by its size the demand a shipmade on Port or Harbour Resources, and Net Tonnage, representing by its cargo or passenger___________________________________________________________________________ September 2005
  • 112. Marine Design 112__________________________________________________________________________________________capacity its ability to pay for services rendered. The resulting measures were not to result intoo great a change to existing ships and were not to act to distort the criteria of the ship designprocess. When the new rules were established it was intended that in general the existingtonnages should be unchanged. However two types of ship, small open shelter deck cargoships and Ro-Ro ships did suffer a significant increase in both gross tonnage and net tonnage.Passenger ships (without Ro-Ro capability), Bulk Carriers and Ore Carriers were awarded asignificant reduction in net tonnage. The provisions of the Convention came into force on 18th July 1982 for new ships,converted ships and ships changing registry and on 18th July 1994 for all ships. The two parameters used for the measurement of tonnage are still called GrossTonnage and Net Tonnage but are dimensionless numbers and so bear no units. Gross Tonnage is based on the Volume of all enclosed spaces in the ship. Net Tonnage is generally based on the Volume of the cargo spaces. In passenger shipsaccount is also taken of the Number of passengers carried in two categories – those in cabinswith up to 8 berths and those carried in larger cabins or without cabins. All volumes included in the calculation of Gross and Net Tonnages are measured tothe inner side of the shell plating, i.e. moulded dimensions are used. Volumes of appendagesare included in the total volume; volumes of spaces open to the sea are excluded from the totalvolume. The Gross Tonnage (GT) of a ship is determined by the formula: - GT = K1*V where V is the total volume of all enclosed spaces in the ship in cubic metres and K1 = 0.2 + 0.02*log10(V) The Net Tonnage (NT) of a ship is determined by the formula: - NT = K2Vc(4T/3D)2 + K3(N1 + N2/10) where Vc is the total volume of cargo spaces in the ship in cubic metres K2 = 0.2 + 0.02*log10(Vc) K3 = 1.25((GT + 10000)/10000) D = Moulded Depth amidships in metres T = Moulded Draught amidships in metres N1 = Number of Passengers in cabins with not more than 8 berths N2 = Number of other Passengers Now the factor (4T/3D)2 must not be taken greater than 1.0000 the term K2Vc(4T/3D)2 shall not be taken less than 0.25*GT N1 and N2 shall be taken as zero when N1 + N2 < 13 NT shall not be taken less than 0.30*GT These rules now apply to virtually all ships.___________________________________________________________________________ September 2005
  • 113. Marine Design 113__________________________________________________________________________________________ (However you should be aware that different Regulations may apply to FishingVessels and to vessels under 24 m in length.) Excluded spaces are defined as those open to the sea and not suitable for the carriage of cargo. Cargo spaces are defined as compartments for the carriage of cargo which is to be discharged from the ship and are to be permanently marked with the letters CC. Alteration to the parameters of the net tonnage formula that would result in a reductionof net tonnage is restricted to once a year.Segregated Ballast Oil Tankers Tankers with segregated ballast tanks complying with MARPOL 1973 may have thetonnage of these tanks entered in the tonnage certificate. The tonnage of these tanks is to becalculated according to the formula: - TSB = K1*Vb where TSB = Tonnage of Segregated Ballast Tanks Vb = Total volume of segregated ballast tanks in cubic metres K1 = 0.2 + 0.02*log10(V) and V is the total volume of all enclosed spaces in the ship in cubic metresDeck Cargoes Where cargo is carried in any uncovered space on deck the tonnage of the spaceoccupied to be taken into account for the payment of dues where goods are carried in spacesnot forming part of the gross or net tonnages shall be determined by the formula: TDK =0.535(mean length*mean breadth*mean height) where TDK is deck cargo tonnage and the mean length, mean breadth and mean height are measured in metresDefinitions In the context of the Tonnage Regulations, the following definitions apply: -Length is the greater of (a) the distance between the fore side of the stem and the axis of therudder stock or (b) the distance measured from the fore side of the stem being 96% of thedistance between that point and the aft side of the stern, both measurements being taken at awaterline corresponding to 85% of the least moulded depth of the ship. In the case of a shiphaving rake of keel the waterline shall be parallel to the designed waterline.Moulded Depth is the vertical distance from the top of the keel to the underside of the upperdeck at side. In a ship with a rounded gunwale the moulded depth shall be measured to thepoint of intersection of the moulded lines of the deck and side shell, the lines extending asthough the gunwale was angular. Where the upper deck is stepped and the raised part of thedeck extends over the point where the depth is to be determined then the moulded depth shall___________________________________________________________________________ September 2005
  • 114. Marine Design 114__________________________________________________________________________________________be measured to a reference line extending from the lower part of the deck parallel to the raisedpart.Moulded Draught is the draught corresponding to the Summer Load Line, or the deepestsubdivision load line assigned to a passenger ship. These notes provide an extract from the Regulations sufficient for the work of thisclass. For professional work you should be in possession of a copy of the full Regulations andany amendments.13.3 The Moorsom Tonnage Measurement System The old tonnage measurement system required the calculation of the gross tonnagedefined as the tonnage of spaces below the tonnage deck (the second deck or deck below theupper deck) plus the tonnage of spaces between the tonnage deck and the upper deck plus thetonnage of closed in spaces above the upper deck plus the tonnage of hatchways. As theunderdeck tonnage (that of spaces below the tonnage deck) was measured above the innerbottom (if fitted) then double bottom spaces were excluded from tonnage. The net or register tonnage was then derived from the gross tonnage by makingcertain deductions. An allowance was made for the propelling machinery space, master’s andcrew accommodation and working spaces such as wheelhouse, chartroom, chain lockers,anchor stowage, steering gear, donkey engine, pump room, boiler room, etc. The deductionfor the machinery space was intended to include space occupied by coal bunkers (nowsuperseded by fuel oil) and was the subject of a sliding scale calculated as follows: - 1) If the tonnage of the machinery space was greater than 13% of the gross tonnage but less than 20% then the allowance was 32% of the gross tonnage. 2) If the tonnage of the machinery space was less than 13% of the gross tonnage then the allowance was the actual tonnage of the machinery space multiplied by 32/13. It was possible to have certain spaces below the upper deck exempt from tonnagemeasurement, such as the space between the upper deck and the second deck. This exemptionfollowed from a court case in 1875 involving the S.S. Bear. The ship’s owner claimed that byhaving a small opening in the uppermost or weather deck, the space below the weather deckwas not closed in and should therefore not be included in the gross tonnage. Ships whichsatisfied this requirement were known as open shelter deck ships. The resulting internal arrangements were not conducive to safety in a damagedcondition. Although the upper deck or shelter deck above the tonnage deck was regarded asthe strength deck of the ship, the space it enclosed was regarded as being open if a tonnagehatch or opening which was not capable of being made watertight was provided in the shelterdeck. Bulkheads were stopped at the second deck or if they continued to the upper deck theyalso had openings not capable of being made watertight. These shelter deck ships had a very small freeboard measured to the tonnage deck andin the event of damage they had very little reserve of buoyancy, risking sinking with only onecompartment damaged. Should an owner decide to carry the bulkheads watertight to the upper___________________________________________________________________________ September 2005
  • 115. Marine Design 115__________________________________________________________________________________________deck then the exemption in the tonnage rules did not apply. Thus the tonnage rulesencouraged a design of ship which was not as safe as it might be. Many ships with non-watertight bulkheads in the tween decks were in existence in 1939 and during the SecondWorld War their increased vulnerability was recognised. As a temporary measure thebulkheads were made watertight to improve their subdivision. In the years following 1945 steps were taken to amend the existing regulations inorder to eliminate open shelter deck ships without removing from them the benefit of reducedtonnage. Eventually ships were measured for tonnage in both the open and the closedcondition and the decision as to which applied depended on the draught of the ship. A tonnagemark was set on either side of the ship at amidships to correspond to the draught which wouldbe obtained if the second deck were the freeboard deck. If the mark was immersed then theclosed (higher) tonnage applied and if the mark was not immersed then the open (lower)tonnage applied. Paragraph ships were designed to gain an advantage from certain paragraphs in thetonnage regulations and their impact on other statutory requirements. For example a shipexceeding 500 gross tons was required to carry a fully qualified radio officer.To avoid such requirements, many ships were designed to be 499 gross tons. Over a period oftime designers became very adept at interpreting the regulations so that a ship of increasingcargo deadweight still remained under 500 gross tons. These observations principally apply to the British tonnage regulations but similaranomalies were found in the rules of most other nations. All of these rules (except for thespecial rules used by the authorities of the Suez and Panama Canals) were superseded by the1969 International Convention on Tonnage Measurement.BibliographyThe Merchant Shipping (Tonnage) Regulations 1997, S.I. 1997 No 1510The 1969 International Conference on Tonnage Measurement of Ships by E. Wilson,Transactions RINA Volume 112, 1970 pp357-390___________________________________________________________________________ September 2005
  • 116. Marine Design 116__________________________________________________________________________________________14 The Assignment of Freeboard14.1 What is Freeboard? Freeboard locates the load line on a ship. It is the vertical distance below the freeboarddeck at side to the load line mark. It represents the minimum amount of the ship which mustproject above the water in its deepest operating draught in order for the ship to remain safe.14.2 What is the Purpose of Freeboard? National and International control of the loading of ships by the assignment of a loadline guaranteeing a minimum freeboard is intended to “provide overall protection against thesea.” When the last (and current) International Convention on Load Lines assembled in1966, the following criteria for satisfactory freeboard were in the minds of the delegates: - 1) Prevent entry of water into the hull 2) Possess adequate reserve of buoyancy 3) Provide protection to the crew 4) Have adequate hull strength & stability 5) Limit deck wetness These can be placed into three categories as far as regulation is concerned: - 1 & 3 can be satisfied by go/no go decisions under the heading of conditions of assignment. 4 is normally achieved by ensuring that the structure complies with the rules of a recognised classification society plus some simple stability criteria. 2 & 5 are left to be dependent on the geometry of the ship. The purpose of the freeboard calculations to be discussed later is to assess the geometry of the ship’s hull so that the minimum freeboard can be determined.14.3 The Development of Freeboard Rules Freeboard was first considered rationally about 1830 when Lloyds Register evolved a ruleof thumb relating freeboard to depth which gave a reasonable measure of safety. At this time,of course, it was the safety of the cargo which was the matter of concern rather than the crewor passengers. However overloading remained commonplace and continued to be viewed as an increasedrisk to the cargo. Eventually concern over the safety of the crew led to the British Governmentpassing the Merchant Shipping Act of 1876 which required that all ships be marked with aLoad Line but did not specify how to determine its position. This was the Act that we nowassociate with Samuel Plimsoll.___________________________________________________________________________ September 2005
  • 117. Marine Design 117__________________________________________________________________________________________ In the mean time Lloyds had evolved a calculation for freeboard based on the tonnagecoefficient (Underdeck Tonnage in cubic feet divided by the product of Length, Breadth andDepth). In 1886 the Board of Trade stated that ships marked in accordance with thiscalculation would not be detained for overloading. The calculation was brought into the law in1890. The rules were revised in 1906 when freeboards were reduced. A committee investigatedLoad Lines in 1913-15 following the loss of the Titanic and considered that the reduction of1906 was justified. The first international conference on Load Lines was held in 1930 and theviews of the 1913-15 committee and two others, which had met in 1925 and 1929, were thebasis for its consideration. Hitherto the purpose of freeboard was simply to ensure a reserve ofbuoyancy and that was all that the rules sought to impose. Under the International Conventionagreed in 1930 the assignment of freeboard was to be dependent on the ship having adequatestrength and being well constructed and maintained. In addition passenger ships had to satisfyrequirements on subdivision and intact stability.14.4 Current requirements for freeboard The rules were once again thoroughly revised at an International Conference in 1966when subdivision and stability requirements for cargo ships were introduced. The rulesembody basic freeboards which depend on the length and type of vessel. There are two typesof ship - Type A and Type B. Type A ships are designed only for the carriage of bulk liquidcargoes in tanks with small access openings closed by watertight gasketed covers of steel oran equivalent material. These ships are entitled to the minimum assignable freeboard. Allother ships which do not meet the definition of a Type A ship are considered as Type B ships.(Passenger carrying ships are assessed separately with the minimum freeboard alwaysdependent on the final waterline after damage – a so called “subdivision load line”. Thedetermination of the subdivision load line of a passenger ship is governed by regulationsmade under the SOLAS (Safety Of Life At Sea) Conventions.) Clearly a wide variety of ship types come within the category of Type B. The freeboardsassigned to Type B ships are based on a tabular freeboard which is greater than that assignedto Type A ships and there are corrections applied to increase or reduce these freeboardsdepending on the watertight integrity and subdivision standards appropriate to individualships. Ships whose watertightness and subdivision are particularly good may qualify for areduction of the basic freeboard set out for a Type B ship which effectively grants the ship aType A freeboard. This is referred to as a Type B-100 ship (The basic freeboard of a Type Bminus 100% of the difference between the basic freeboards of Type A and Type B). Other Type B ships which cannot comply with the most severe subdivision requirementscan be assigned a basic freeboard reduced by up to 60% of the difference between the basic Aand B values (Type B–60). Having decided on the type of ship, the computation of the freeboard is relativelystraightforward with a number of corrections being applied to the basic rule freeboard for thelength of the ship. For the full details it is necessary to refer to the official version of the rulesIn the UK these are presented in a Statutory Instrument (S.I.) supported by a MerchantShipping Notice (MSN). Only the Principles of the corrections are discussed here.___________________________________________________________________________ September 2005
  • 118. Marine Design 118__________________________________________________________________________________________ a) Flush Deck Correction The freeboard of a Type B ship of less than 100 metres in length and havingsuperstructure of less than 35% of that length will have its freeboard increased. This isbecause small ships without superstructures are thought to be more vulnerable than similarships with superstructures and so should have a greater freeboard. b) Block Coefficient Correction Where the block coefficient CB exceeds 0.68 the basic freeboard (as modified by a) above,if appropriate) is increased. CB is calculated at a draught which is 85% of the least mouldeddepth of the ship. The reserve buoyancy above the load line should increase if the displacedvolume below the load line increases. c) Depth Correction The depth (D) for freeboard is defined in the rules. Where D exceeds L/15 the freeboard isincreased. Where D is less than L/15 a reduction in freeboard may be granted if the ship hasan enclosed superstructure covering at least 0.6L amidships. This is also concerned withmaintaining adequate reserve buoyancy above the load line. d) Superstructure Correction A reduction may be made in the freeboard if the effective length of the superstructure is1.0L. A percentage of this reduction is available when the total effective length is less than1.0L. These are set out in the rules, together with corrections for the length of forecastles forType B ships. If the superstructure can be considered strong enough and large enough tocontribute some reserve buoyancy then the contribution demanded from the hull above theload line may be reduced. e) Sheer Correction The area under the actual sheer curve is compared with that under a standard parabolicsheer curve whose forward ordinate is twice the height of its aft ordinate given by a standardformula. Where the height of a poop or forecastle is greater than the standard height then anaddition to the sheer of the freeboard deck may be made. Where the sheer so calculated is lessthan the standard then an addition is made to the freeboard. Once again this is to maintainadequate reserve buoyancy. Where the sheer is greater than the standard a reduction in freeboard may be permitted ifthe ship has a superstructure covering 0.1L abaft and 0.1L forward of amidships. Apercentage of this reduction is available if the superstructure covers less than 0.1L abaft andforward of amidships. f) Minimum Bow Height The bow height is the vertical distance at the forward perpendicular between the waterlinecorresponding to the assigned summer freeboard and the top of the exposed deck at side. Aminimum bow height is quoted in the rules.___________________________________________________________________________ September 2005
  • 119. Marine Design 119__________________________________________________________________________________________14.5 Determination of Minimum Freeboard When all the above corrections have been made to the basic tabular freeboard, thecalculated freeboard will set the maximum summer draught for the vessel. However if theresulting bow height is insufficient, or if the owners request a draught less than the maximumpossible then the freeboard will be increased again. The requirement for a minimum bowheight is meant to help keep water off the deck and improve the working conditions of thecrew.14.6 General Conditions of Assignment of Freeboard Having established the geometry of the freeboard the following aspects of the shipsconstruction must be in accordance with the rules in order that the calculated freeboard can beassigned to the ship: - 1) Structural Strength and Stability 2) Construction of and Openings in Superstructure End Bulkheads 3) Hatchways closed by Portable Covers with Tarpaulins 4) Hatchways closed by Weathertight Steel Covers 5) Machinery Space Openings 6) Other Openings in Freeboard and Superstructure Decks 7) Ventilators 8) Air Pipes 9) Cargo Ports and similar Side Openings 10) Scuppers, Inlets and Discharges 11) Side Scuttles 12) Freeing Ports 13) Protection of Crew Type A ships require that special attention be given to further aspects of theirconstruction:- 1) Machinery Casings - To ensure their watertightness. 2) Gangway and Access - To ensure the crew can safely get to all parts of the ship. 3) Hatchways - To ensure their watertightness. 4) Freeing Arrangements - To ensure that water does not build up on deck.A Summary of the Subdivision Requirements for the Assigning of Type A, Type B,Type B – 60 & Type B – 100 FreeboardsType Length Subdivision requirementsA Less than 150 m NoneA Greater than 150 m To withstand the flooding of any compartment within but Less than 225 m the cargo tank length which is designed to be empty when the ship is loaded to the summer water line at an assumed permeability of 0 95A Greater than 225 m As above, but the machinery space is also to be treated as a floodable compartment at an assumed permeability of 0 85___________________________________________________________________________ September 2005
  • 120. Marine Design 120__________________________________________________________________________________________B+ — NoneB — NoneB-60 100 m to 225 m To withstand the flooding of any single damaged compartment within the cargo hold length at an assumed permeability of 0 95B-60 Greater than 225 m As above, but the machinery space also to be treated as a floodable compartment at an assumed permeability of 0 85B-100 100 m to 225 m To withstand the flooding of any two adjacent fore and aft compartments within the cargo hold length at an assumed permeability of 0 95B-100 Greater than 225 m As above, but the machinery space, taken alone, also to be treated as a floodable compartment at an assumed permeability of 0 85 Damage is assumed as being for the full depth of the ship, with a penetration of 1/5 thebeam clear of main transverse bulkheads. After flooding the final water-line is to be below thelower edge of any opening through which progressive flooding may take place. Themaximum angle of heel is to be 15°, and the metacentric height in the flooded conditionshould be positive.BibliographyThe Merchant Shipping (Load Line) Regulations 1998, S.I. 1998 No 2241as amended by,The Merchant Shipping (Load Line)(Amendment) Regulations 2000, S.I. 2000 No 1335Merchant Shipping Notice MSN 1752 (M)The 1966 International Conference on Load Lines by D. R. Murray Smith, TransactionsRINA Volume 111, 1969 pp 1-20___________________________________________________________________________ September 2005
  • 121. Marine Design 121__________________________________________________________________________________________15 Further Reading15.1 Books Practical Ship Design, by D. G. M. Watson, Elsevier Science Ltd, Oxford 1998 Elements of Ship Design, by R Munro-Smith, Institute of Marine Engineers, London 1975 reprinted Ship Design for Efficiency and Economy, by H Schneekluth, Butterworth, London 1987 (First Edition) (There is now a Second Edition - 1998 - but it is rather less useful than the First Edition) Ship Design and Construction, by T. Lamb (Ed.), SNAME, Jersey City, NJ 2003 Basic Ship Theory (Volume 2), by K J Rawson & E C Tupper, 5th Edition, Butterworth-Heinemann, Oxford 200115.2 Technical Papers Some Ship Design Methods, by D G M Watson & A W Gilfillan Trans. R.I.N.A. Volume 119, 1977 pp 279-324 (Also The Naval Architect, July 1977) Economic Optimisation Procedures in Preliminary Ship Design (Applied to the Australian Ore Trade), by K W Fisher Trans R.I.N.A. Volume 114, 1972 pp 293-317 (Also The Naval Architect, April 1972) Engineering Economics Applied to Ship Design, by I L Buxton Trans R.I.N.A. Volume 114, 1972 pp 409-428 (Also The Naval Architect, October 1972) Computer Representation of Numerical Expertise for Preliminary Ship Design, by A H B Duffy & K J MacCallum Marine Technology, Volume 26 No 4 October 1989 pp 289-302 Ethics and Fashion in Design, by K J Rawson Trans R.I.N.A. Volume 132, 1990 pp1-27 The Evolution of the Modern Cruise Liner,by S M Payne Trans R.I.N.A.Volume 132, 1990 pp 163-188 A Comparative Study of US and UK Frigate Design, by L D Ferreiro & M H Stonehouse Trans SNAME Volume 99, 1991 pp 147-175___________________________________________________________________________ September 2005
  • 122. Marine Design 122__________________________________________________________________________________________ The Application of an Expert System to Ship Concept Design Investigations, by M Welsh, I L Buxton & W Hills Trans R.I.N.A. Volume 133, 1991 pp 99-122 Optimisation Techniques in Ship Concept Design, by A J Keane, W G Price & R D Schachter Trans R.I.N.A. Volume 133, 1991 pp 123-143 FRV Corystes: A Purpose built Fisheries Research Vessel by B. J. Kay, D. K. Jones & R. B. Mitson Transactions RINA Volume 134, 1992 pp 33-52 A New Danish Fishery Inspection Ship Type, by D. G. M. Watson & A. M. Friis Transactions RINA Volume 134, 1992 pp 53-72 Marine Design: The Multiple Criteria Approach, by P. Sen Transactions RINA Volume 134, 1992 pp 261-276 On the Variety of Monohull Warship Geometry, by W. J. van Griethuysen Transactions RINA Volume 134, 1992 pp 277-298 The Management of Warship Design – The MoD Warship Project Manager’s Perspective, by D. J. Andrews Transactions RINA Volume 135, 1993 pp 1-24 History as a Design Tool, by David K. Brown, RCNC Transactions RINA Volume 135, 1993 pp 41-60 Preliminary Warship Design, by D. J. Andrews Transactions RINA Volume 136, 1994 pp 37-56 On the Choice of Monohull Warship Geometry, by W. J. van Griethuysen Transactions RINA Volume 136, 1997 pp 57-78 Advanced Warship Design, Limited Resources - A Personal Perspective by David K. Brown, RCNC Transactions RINA Volume 137, 1995 pp 163-188 From Tropicale to Fantasy: A Decade of Cruiseship Development, by S. M. Payne Transactions RINA Volume 135, 1993 pp 25-40 An Engineering Approach to Predicting the Hydrodynamic Performance of Planing Craft using Computer Techniques, by D. Radojcic Transactions RINA Volume 133, 1991 pp 251-268 An Investigation into the Resistance Components of High Speed Displacement Catamarans, by M. Insel & A. F. Molland Transactions RINA Volume 134, 1992 pp 1-20___________________________________________________________________________ September 2005
  • 123. Marine Design 123__________________________________________________________________________________________ Resistance Experiments on a Systematic Series of High Speed Displacement Catamaran Forms: Variation of Length/Displacement Ratio and Breadth/Draught Ratio, by A. F. Molland, J. F. Wellicome & P. Couser Transactions RINA Volume 138, 1996 pp 55-72 An Investigation into the Effect of Prismatic Coefficient on Catamaran Resistance by A. F. Molland & A. R. Lee Transactions RINA Volume 139, 1997 pp 157-165___________________________________________________________________________ September 2005

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