About ship structures

1. MARINE STRUCTURES - I
INTRODUCTION TO SHIP STRUCTURE
DESIGN

2. Intro to Ship Structures
• There are many types of structures. The
definition of the word structure (Webster’s) is;
a. manner of building, constructing, or organizing
b. something built or constructed, as a building or dam
c. the arrangement or interrelation of all the parts of a
whole; manner of organization or construction: the
structure of the atom, the structure of society
d. something composed of interrelated parts forming
an organism or an organization

3. Intro to Ship Structures
• Here is an example of some parts of a ship
structure:

4. Intro to Ship Structures
• An example of civil structures;

5. Intro to Ship Structures
• A ship structure is quite a distinct type of
structure, especially in the arrangement of
components
• But also in the many unique constraints and
regulatory context that influence ship structural
design
• This course will focus on the technical elements
of structural design and analysis of ships

6. Guesstimation
• One of the aims of the course is for the students to develop the
ability to make an educated guess
• Such guesses are not wild or random. Educated guesses are based
on sound reasoning, careful approximation and simplification of the
problem
• Basic laws of mechanics are considered to determine what
fundamental principle might govern the outcome
• The ability to make quick assessments is the mark of an expert and
is a crucial skill to avoid costly and dangerous mistakes
• Such guesses never remove the need for detailed calculations, but
they do improve the quality and efficiency of the engineering

7. Background
• Humans have been constructing structures for a
long time. A structure is a tool for carrying and
protecting
• Ship structures have evolved like all other types
of structures (buildings, aircraft, bridges)
• Design was once purely a craft. Design is evolving
as we understand more about the structure itself
and the environment that we subject it to

8. Background

9. The Aim Of Structural Design
• The purpose of structural design of ships is to
design the most efficient structure for
purpose. Here efficiency is taken to mean a
wide array of factors.
• The structural designer must be aware of the
effects of their decision on the cost and
maintenance of the ship

10. Purpose of Ship Structures
• The structure of a ship or ocean platform has 3
principal functions:
a. Strength (resist weight, environmental forces – waves + )
b. Stiffness (resist deflections – allow ship/equipment to
function)
c. Water tight integrity (stay floating)
• There are two other important functions
a. provide subdivision (tolerance to damage of 1,3 above)
b. support payloads

11. Ship Examples

12. Ship Examples

13. Ship Examples

14. Structural Design Requirements
• The particular arrangement of the structure is done to suit
a variety of demands:
a. Hull is shaped (reduce resistance, reduce motions, reduce ice
forces, increase ice forces, reduce noise)
b. Holds are arranged for holding/loading cargo
c. Holds are arranged for holding/installing engines
d. Superstructure is arranged for accommodation/navigation
e. All structure is arranged for build-ability/maintainability
f. All structure is arranged for safety
g. All structure is arranged for low cost

15. Structural Design Requirements
• Ships are a class of structures called "semi-
monocoque“
• In a pure monocoque, all the strength comes from the
outer shell ("coque" in french)
• To contrast, in "skin-onframe” construction, the loads
are all borne by a structure of framing under the skin
• In ships, the skin is structurally integral with the
framing which supports it, with the skin providing a
substantial portion of the overall strength

17. Role of the Designer
• The role of the structural designer changes in each stage of
ship design.
• Designer must not go into more detail than in required at
current stage.
• At all stages the designer must satisfied with the overall
architecture of the ship such that a solution can be
achieved within the required levels of cost, weight, space
and levels of reliability
• Margins must also be specifies taking into account
uncertainties at each design stage

18. Evolution of the Design
• The structure design moves through a series of
evolutionary phases e.g. in initial design several
different design options will be considered in
sufficient detail to allow for identifying feasible
design options
• These options are refined and in later phases,
they are considered in greater depth until the
most efficient structure can be indentified

19. Types of Structural Work
• Ship structural specialists are involved in a variety
of work:
– Design
– Analysis
– Construction
– Maintenance
– Repair
– Regulation

20. Synthesis Analysis & Optimization
• Synthesis: Development of a system from its
components while ensuring compatibility between
components, loads and in-service functions
• Analysis: Is the proof that synthesised system will
provide functions that will satisfy reliability
requirements
• Optimisation: Is the process of ensuring that analysed
system is most efficient and economic

21. Historical Perspective
• A knowledge about the history of ship design is
important for understanding the design process
• Until 1970s wave loading was assessed using a static
wave balance with wave height taken as L/20. Although
this resulted in conservative estimations this
assumption was severe but not extreme. This was used
together with classical methods to check for buckling in
stiffeners and buckling.

22. Historical Perspective
• In the 1950s and 60s, methods involving elasto-plastic
techniques were formalised. A large margin of 5.0 was
applied for this case, while a margin of 2.0 was required for
column buckling case against L/20 wave loading.
• In this period there was no explicit method for assessing
fatigue in design. For the first all welded ships, all ships
designed achieved over 20 years of service life and were
limited by fatigue at around 23-25 years.

23. Historical Perspective
• In the 1950s and 1960s brittle fracture was seen as a
problem due to poor steel quality, this was solved by the
introduction of notch tough steels
• In the 1970s two major beak through took place, one was
the use of stochastic techniques and rigid body dynamics to
calculate wave bending. The other was a method for
assessing the ultimate strength of the hull girder as a
complete entity rather than in parts
• Additionally FEA became more readily available for detailed
analysis.

24. Current Design
• Following changes in the design process in the
1970s examples of recent successful structures
have come about. Examples Include the UK Tribal
and Type 22 classes
• Reason for successful designs include the greater
analysis that was carried out along with larger
margins used in areas of uncertainty

25. Current Design
Type – 22 Class Frigate

26. Current Design
• Hulls should be designed according to realistic life
expectations. Circumstances are likely to change
through the ships life, regardless of what is hopes
in initial requirements
• From experience it is shown that 25 years is a
practical life span for a ship and hulls should be
designed to last that long without imposing too
much on the maintainers.

27. Practical Designs
• All aspects of the design process from loadings to
the environment are non-linear and thus difficult
to model. The skill of the designer lies in their
ability to chose the simplest models on the parts
of the design experience tells them to be most
important. They should also be able to use past
experience to validate approximate models

28. Practical Designs
• Over the last 30 years, the rational approach
has gained prominence. This approach uses
techniques from probability and statistics
coupled with advancements in structural
analysis software's to pursue objectives with a
larger degree of sophistication.

29. Engineering Design
• Design, analysis, construction and regulation are separate
specialties
• In the 1950 tabulated requirements were found in Class Rules.
By the 70s all codes had changed to include prescriptive algebra
• New trends are towards "LRFD - load and resistance factored
design", "risk based design" and "goal based design“
• Current practice in large (novel) projects make extensive use of
"scenario based" design, with HAZIDs (hazard identification and
mitigation).

30. Practical Designs
• While embracing new technology it is important
to be fully aware of their pitfalls and to use them
within the range of their limitations.
• The results from modern analytical techniques
should be compared with past successful practice
and any deviations be clearly explained.

31. Ship Structural Photos

32. Ship Structural Photos

33. Ship Structural Photos

34. Ship Structural Photos