2. i
ACKNOWLEDGMENTS
The author would sincerely like to thank all of the individuals that contributed time and
expertise to the successful completion of this project. Professor George Petrie, the project’s
principal advisor, was invaluable for his guidance, suggestions and support throughout the
project. He would also like to thank Professors Matthew Werner, Richard Royce, Neil
Gallagher, Richard Harris, John Lutz and Dean Roger Compton for their support and effort to
promote the technical validity and quality of this project. The project would have suffered
immensely were it not for these individuals.
The author would also like to thank Professor Paul Miller at the United States Naval
Academy for his continued interest and assistance with the project, as well as for the impact he
had on the project with his insight. Mr. James Moran of Sparkman & Stephens provided the
project with valuable parametric data that greatly improved the validity of the design and the
author extends his gratitude to him. Mr. Timothy Graul proved an excellent SNAME mentor.
His input and the materials he provided are very much appreciated and a great help.
The author would like to thank the incredible group of friends that is the Webb Institute
Class of 2009 for their unending support, humor, and good-nature. He would also like to thank
his family for their support.
Finally, Mr. William H. Webb deserves great thanks for his generosity that provided the
education necessary to complete this project successfully.
3. ii
ABSTRACT
The principal objective of this thesis was to produce a design for a freight-carrying
cruising sailing yacht for entrance into the 2009 SNAME Student Workboat/Small Craft/Yacht
Design Competition (ISWSCYDC). The goal of this project was to perform a preliminary
business analysis and to execute a preliminary design that supports the assumptions made in the
business model. The design focused on the implementation of proven traditional design
characteristics drawn from the lumber scow concept that was popular at the end of the 19th
century and the beginning of the 20th
, updated with modern design attributes drawn from
contemporary racing and cruising sailing designs in all areas of design. The design combines the
positive aspects of both old and new designs in order to be effective at the mission of bluewater
cruising while generating a positive cash flow for the owner-operator of the design.
Keywords: Sail; Merchant; Bluewater; Cruising; Wood
7. vi
LIST OF FIGURES
Figure 1: Timothy Graul sailing vessel design with cargo hold..................................................... 3
Figure 2: Balance of sailing forces ................................................................................................. 7
Figure 3: Present value of lifetime cash flow with LWL & design points ................................... 13
Figure 4: The design spiral ........................................................................................................... 15
Figure 5: Scow midship section and stern sections ...................................................................... 16
Figure 6: Scow bow shape............................................................................................................ 17
Figure 7: Half-hull shape: perspective view................................................................................. 17
Figure 8: Wolczko 30 sail plan..................................................................................................... 19
Figure 9: Rudders: perspective view from starboard quarter........................................................ 21
Figure 10: Keel configuration, centerboard down, with rudders.................................................. 22
Figure 11: Perspective inboard profile showing interior layout ................................................... 24
Figure 12: Accommodation spaces plan view .............................................................................. 25
Figure 13: Propeller shaft “vee” configuration............................................................................. 27
Figure 14: Required EkW with vessel speed by several methods ................................................ 28
Figure 15: Centerboard lifting system .......................................................................................... 33
Figure 16: Burton and fall cargo handling method plan view ...................................................... 35
LIST OF TABLES
Table 1: Yearly fuel consumption comparison............................................................................. 31
8. vii
NOMENCLATURE
ACRONYMS
ABS American Bureau of Shipping (classification society)
AC Alternating Current Electrical Power
B Beam
BkW Brake Power, in kW
BV Bureau Veritas (classification society)
CB Block Coefficient
CD Drag Coefficient
CE Center of Effort
CFD Computational Fluid Dynamics
CG Center of Gravity
CLR Center of Lateral Resistance
CPP Controllable-Pitch Propeller
DC Direct Current Electrical Power
EkW Effective Power, in kW
EMS Electrical Management System
F Denotes a force quantity
Fn Froude Number
ft Feet
Genset Generator unit, e.g. a Generator and Engine as a Set
GZ Righting Moment Arm
HVAC Heating, Ventilation, and Air Conditioning
in Inches
ISWSCYDC International Student Workboat / Small Craft / Yacht Design Competition
kgf Kilo-gram Force
kN Kilo-Newton (Unit of Force)
kW Kilo-Watts (Unit of Power)
LED Light Emitting Diode
L Length
L Liters
lbf Pounds-Force (BG Unit of Force)
LPG Liquefied Propane Gas
LWL Length on the Waterline
m Meter
NM Nautical Miles
NSMBREG Netherlands Ship Model Basin Regression Resistance Method
RIB Rigid Bottom Inflatable boat
RPM Revolutions per Minute
SA Sail Area
sec Seconds
SNAME Society of Naval Architects and Marine Engineers
SSB Single-Side Band Radio
T Draft
t Tonne—metric tonne: 1,000 kg or approx. 2,200 lbs
TVC Total Vessel Cost
9. viii
US United States
V Denotes a velocity quantity
V Volts
VBA Visual Basic for Applications (programming language)
VHF Very High Frequency (Short-Range) Marine Radio
W Watt (Unit of Power)
PHYSICAL CONSTANTS
g Acceleration due to gravity: 9.807
ρsw Density of seawater: 1025.9
νsw Kinematic viscosity (seawater) 1.17 · 10
SYMBOLS
Displaced volume (in units of m3
for this project)
10. 1
INTRODUCTION
OBJECTIVES
1. To develop a set of design requirements and to produce a design for a sailing
vessel equipped to carry a cargo payload that can be operated by non-professional
cruising sailors in a bluewater cruising setting.
2. To enter this design in the 2009 Society of Naval Architects and Marine
Engineers’ (SNAME) Student Workboat/Small Craft/Yacht Design Competition
(ISWSCYDC).
SCOPE
This project consisted of two parts: the business analysis, and the preliminary design.
The business model developed in this project served to analyze the finances of a business that
would operate a vessel such as that described above in the Objectives section. This in turn led to
an initial design point for the design phase of the project based on profitability of the business
model and the design requirements produced for the ISWSCYDC. The design was then
produced to the requirements of the competition as set forth in the SNAME guidelines, which
can be found in Appendix A.
BACKGROUND
HISTORY
The idea of transporting goods with sailing craft is obviously not a new one. Sailing
merchant ships were once the grandest sight on the world’s oceans and were also quite lucrative,
but during the 19th
century the advent of steam ships ended their dominance of the shipping
market. The shipping industry was evolving, first with the “China Trade” and the great “clipper”
ships, and then by taking advantage of new technology in the form of steam power, to be a
business founded upon schedule, speed, and tonnage. As a result, it has become virtually
postulate that sailing vessels, because of their reliance upon the ever-changing and unpredictable
meteorology of the oceans, are an impractical solution to the issue of shipping goods.
This may seem a valid point. Time has indeed become an essential factor in the shipping
industry; many types of cargo have an extremely high time value and must be delivered from
port to port within a strict timeline. The days when the vast majority of shipping was performed
by sailing ships may indeed be over, but this study sees a niche for small-scale shipping to be
performed by sailing vessels.
The fact that the shipping industry is dependent upon reliable speed and meeting
schedules forces shipping companies to utilize petroleum-based fuels for propulsion. These fuels
constitute a significant portion of a ship’s operating expenses, and history has shown that the
price of petroleum can increase substantially in a short period of time, which interferes with a
shipping company’s ability to make a profit.
The desire to eliminate this factor from the business model, along with environmental
concerns, leads to the conclusion that a possibility exists that the carriage of cargoes (that have a
relatively low time value) could be performed by a sail-powered vessel. The use of low time-
value cargo allows for a business venture less dependent on scheduling than a conventional
11. 2
shipping operation. Conveniently, the framework necessary for such a niche industry to
establish itself already exists—cruising sailing yachts are ideal for this sort of operation.
CRUISING SAILING YACHTS
Sailing yachtsmen aboard a wide variety of vessel types and hailing from all over the
developed world ply our planet’s oceans by the hundreds every year. Their goals vary: some are
sailing for world circumnavigation time records, others simply want to sail one great family
adventure through the South Pacific islands, and others still try to find ways to make cruising
their permanent way of life.
Many people who decide to cruise long-term are required to stop for extended periods of
time to work temporary jobs in order to support their lifestyle. There are also those who do not
have even this option, due to restrictions on some foreign nationals’ employment in different
regions, which may be force them to abandon the sailing lifestyle and return to their home
country.
Situations such as this could be averted with some entrepreneurial spirit. These cruiser
sailors comprise a plentiful stream of people sailing the oceans on yachts that serve to transport
only the operators and their belongings. If yachtsmen wishing to cruise indefinitely were
equipped to carry a payload along with them, there could potentially be a profitable business
venture inherent in the cruising lifestyle. There are many poorly accessible cruising destinations,
such as the many remote island groups of the Pacific, which could allow for sailing vessels to
occupy the inter-island merchant niche. In addition to this, there is also potential for long-
distance trade to be facilitated by such sailing vessels along routes that are already traveled by
yachtsmen at their own expense. This is especially true if cargo with a low time value can be
carried, as this could level the playing field between small sailing merchant operations and
relatively large, well established shipping companies. All of these possibilities indicate potential
for a profitable business venture stemming from sailing merchant craft.
This idea is not new. Since the decline of mainstream sailing merchant vessels—even
quite recently—several notable designs along these lines have been produced. A yacht designer
named Mr. Dudley Dix has produced a design called the Hout 70, which is a 70-foot, hard-chine
steel gaff-rigged schooner that is marketed as a charter or excursion boat as well as a cargo
carrier (Dix). There is also a 100-foot traditional trading schooner design that has operated
principally as a passenger/charter boat (but was built in wood as an island trader in 1990) for sale
in Dominica at the time of writing (Escape Artist).
Mr. Timothy Graul, an esteemed naval architect who has worked for many years on the
Great Lakes, has designed a wooden-hulled, 50-foot ketch-rigged sailboat with a 21-foot cargo
hold for inter-island or coastal trade (Graul, Profile and Midship Section). The design, which
can be seen below in Figure 1, was never built due to difficulties with the builder, but demand
for such a vessel was demonstrated by this and the aforementioned vessels. Although this
demand is important, however, the possibility of generating a profit with the operation must be
considered in the proposed project, and thus possible markets should be explored.
12. 3
Figure 1: Timothy Graul sailing vessel design with cargo hold
Source: Timothy Graul
MOTIVATION AND BUSINESS BACKGROUND
Webb Institute has an excellent and well-rounded academic program, which is tailored to
an industry that is predominantly composed of work with ships and large commercial craft with a
brief emphasis on small craft design. Naturally, the Webb education is oriented in this way and
not toward yacht design, which is a small niche in the field. This thesis project was largely
motivated by an inclination toward more education in the field of yacht design. Familiarity with
the tools of yacht designers and the concepts involved with the design of sailboats were
significant factors in choosing this topic. Additionally, this project was an opportunity to explore
the idea of a sailing yacht that is more than an instrument of recreation; the idea of working with
sailing yachts that also fulfill a productive function was very appealing.
The original motivation for this project, however, began when the author sailed offshore
with his family for sixteen months during 2001 and 2002. During the journey through the South
Pacific, some unexpected rig maintenance alerted the family to the presence of exotic hardwood
products that were priced at retail values roughly one-twentieth the price of the same product in
the United States at the time (Wolczko). The discovery of such a large difference in cost
between regions led to the obvious conclusion that this type of cargo represented a business
possibility that merited investigation.
After conducting preliminary research into the concept, it became clear that the potential
for business niches of the nature described in the Cruising Sailing Yachts section is real and
pronounced in underdeveloped areas (such as the island groups of the South Pacific) more than it
13. 4
is in urban regions. This is largely attributable to the fact that competition with large, well
established shipping companies would be greater in urban areas than in those that are less
developed, namely because of the inherent smaller demand for the transportation of goods in the
less developed areas. This fact is highly beneficial for this type of project, both because it limits
competition, and because it supports the small cargo carrying capacity available on a typical
cruising-size yacht.
The appeal of underdeveloped areas coupled with the desire to have a multi-functional
cruising/merchant vessel makes the island groups of the Pacific Ocean a logical choice of
exemplary regions to consider for the project—though many other areas worldwide are equally
valid for consideration. A consultation regarding trade statistics from the United States (US)
Department of Commerce has indicated that trade with an interesting candidate island group,
French Polynesia (an overseas collective of France relatively near Hawaii and North America),
operates in both directions. There is a heavy deficit sustained by French Polynesia in the current
trade arrangement, as is the case with most other similar island groups and nations, which
indicates that many products are already transported to these regions and hence it would be wise
to consider the importation of goods to somewhere like French Polynesia from the US or another
industrialized state, such as New Zealand, which is one of the collective’s other main trade
partners aside from France (United States Department of Commerce).
It is natural and reasonable to operate a transport venture that strives to supply a group of
islands with products that it is not be able to produce on its own, such as in one of the long-
distance trade arrangements described above. However, there may be import regulations that
could hinder such action. A dialogue with a customs official at the French Embassy in
Washington, DC, raised the issue that importation of foreign goods into French Polynesia may be
difficult for a small operation due to regulations against non-French imports (Sanford). This
could present problems with the ability to carry a payload on all legs of a cruise. This fact,
coupled with the goal of maximizing the vessel’s potential income, leads to the conclusion that
consideration of multiple locations in the Pacific (namely those with less stringent import
regulations) would be prudent, and also that exportation of goods from regions like French
Polynesia would be a logical course of action.
Although the resources available to the island groups obviously include many perishable
items such as fish, aquaculture and agricultural foodstuffs, these items would be inappropriate
for this venture, because a sailing transport operation would stand little chance competing with
the containerized sector for such products, because of their high time value. There are non-
perishable items such as precious stones and metals, as well as processed food products which
are imported to the US in quantities on the order of US$55 million per year (United States
Department of Commerce). This is the major part of French Polynesia’s exports to the US.
Included in this number are also wood products, including exotic hardwoods, which are imported
to the US in quantities up to the order of $100,000 per year, according to the Department of
Commerce. Assuming that the large working capital required to transport these goods would not
be a prohibitive issue, these high-value products are an ideal cargo for use in this project, as they
are farmed in some relatively inaccessible island groups, such as the Marquesas (Îles Marquises)
in French Polynesia—the location of the author’s discovery mentioned above. In 2001, this
particular archipelago had one inter-island merchant ship, based in Tahiti, which operated on a
monthly schedule and transported goods to and from the islands. A conversation with a former
importer of exotic hardwoods in Seattle, Washington, indicated that importation of wood
products into the United States would be quite feasible, providing the operation did not attempt
14. 5
to import any species listed as endangered or otherwise restricted by United States or
international regulations (Roberts).
The issue of payload on a southbound route from the United States (or equivalent
“outbound” route) can be investigated further and probably with more success if the area of
consideration includes more island groups. The Cook Islands are in free association with New
Zealand, from whom they import extensively, and they have several remote outlying islands with
small populations. The Samoan islands, slightly farther west, include both American and
independent territories, and are also potential markets to investigate, as are nations like the
Marshall Islands, which is heavily dependent on its ties to the United States. Some research,
including email correspondence with an associate that sells wood in Fiji, indicates that there is
currently a premature forestry industry in the island nation that is beginning to produce
mahogany and other potentially profitable wood products (Baldwin). Including island groups
such as these could minimize the time when the vessel is not carrying a payload, and it could
also provide opportunities for the expansion of markets served and greater income.
SNAME INTERNATIONAL STUDENT WORKBOAT / SMALL CRAFT / YACHT DESIGN COMPETITION
(ISWSCYDC)
The International Student Workboat / Small Craft / Yacht Design Competition
(ISWSCYDC) is a competition sponsored by SNAME. The competition encourages students
who are members of SNAME and enrolled in naval architecture, marine engineering, or ocean
engineering (or an accredited yacht design program) to submit designs of virtually any kind of
vessel smaller than 500 tonnes of displacement.
The competition begins with each competitor or group of competitors submitting a set of
design requirements for their design. Upon return of these requirements with comments from the
judges, the design can commence. At the end of the design, the submissions are narrowed down
to the top five contenders based on stated criteria. Once these designs have been selected, the
winning designs will be selected based on the following:
• Technical Content (40%)
• Documentation (15%)
• Originality (10%)
• Practicality (10%)
• Compliance with Design Requirements (25%)
The full rules, list of required deliverables, and judging criteria can be found in the Rules
Publication for the competition to be judged in 2009 in Appendix A.
SCOPE OF BUSINESS ANALYSIS AND DESIGN WORK
In order to keep this project at a manageable level of detail, a specific business plan that
serves as an example case to study has been selected for further analysis. This case involves a
round trip that begins in Seattle, Washington, traveling next to the Îles Marquises and then on to
the Fijian Islands before traveling back to Seattle. The two cargoes considered are teak and
mahogany, because the dimensional lumber nature of these cargoes would be ideal for this
project and because research has indicated the existence of at least small or developing markets
for both types of wood on the South Pacific route described.
While more cargoes and ports of call would be considered in reality, the case described
above is considered to be adequate for this project. It has been assumed that the maximum
amount of cargo can be carried by the vessel on the maximum number of trips possible as
determined in the Viability and Business Analysis section.
15. 6
The Viability and Business Analysis section describes work completed to determine that
there is a possibility of a profitable business venture inherent in the idea of a merchant cruising
sailing yacht. It then goes on to present an optimum design based on profitability. The work
completed in this project is intended to be a preliminary design as is outlined in the list of
submittals provided in the Rules Publication (Appendix A).
PRINCIPLES AND THEORY OF YACHT DESIGN
Introduction
The issue of using wind power to propel a boat through the water is rather complex, but
like many engineering problems of this nature, it can be broken down and simplified to be better
understood. The problem of harnessing the power of the wind is a very dynamic one in which
the forces involved and their reactions to each other are constantly changing due to the variation
in their magnitude and direction and the motions of the vessel being acted upon by these forces.
The use of forces broken down into components and the assumption that static analysis
can be used are helpful to produce a problem simple enough to be solved without complex
computation to determine the forces and reactions involved in the problem.
Discussion
Ideally, the problem of sailing can be described as the interaction between the
aerodynamic forces on the vessel and the hydrodynamic forces on the vessel. These forces are
simplified to be a single aerodynamic force, acting at the “center of effort” (CE) on the sails, and
a single hydrodynamic force, acting at the “center of lateral resistance” (CLR) on the submerged
portion of the hull. These forces and their components can be seen below in Figure 2.
16. 7
Figure 2: Balance of sailing forces
Source: Larsson & Eliasson
As can be seen above in Figure 2, the forces acting on the vessel make more sense once
they are broken up. The aerodynamic force is broken up into a driving force, acting in the
direction of the vessel’s travel, and a heeling force, which acts to heel the vessel over on its side.
Similarly, the hydrodynamic force is broken up into a resistance force, acting in the opposite
direction to the vessels travel, and a hydrodynamic side force, which acts in a direction to oppose
the vessel’s leeway, which is defined as the travel in the same general direction as the wind
perpendicular to the forward travel of the vessel.
The aerodynamic forces most significantly act upon the sails. The density of the medium
in which these airfoils act, air, is relatively low, and thus the sails are much larger than their
hydrofoil counterparts, which operate in water, a much denser fluid. In the conditions in which
the vessel is traveling with the wind, the sails work to produce drag in order to drive the vessel;
this is a condition often referred to as “barn door sailing,” and the defining characteristic of these
conditions is that the sails are simply being pushed upon by the wind rather than generating lift
as foils.
CE
CLR
17. 8
The conditions in which the vessel is traveling against the wind (as well as perpendicular
to the wind direction, in general terms), are different in that the sails are used as airfoils to
produce lift in a direction roughly normal to the axis of the boom.
The underwater portion of the hull, along with the appendages, serves to resist the
component of the aerodynamic force normal to the direction of travel. This reaction is quantified
by the side component of the hydrodynamic force. The other component is the resistance force,
which is quantified by the frictional resistance and the residuary resistance, which is primarily
dependent on the shape of the hull. Additionally, the rudder is a moveable control surface that
usually serves to vary the amount of side force produced near the stern. This effectively changes
the longitudinal location of the CLR and produces a turning moment.
The primary goal in the design of a sailing vessel is to produce a vessel that can balance
all of the components of these aerodynamic and hydrodynamic forces with a minimal amount of
user adjustment of controls (such as sail control lines or the rudder) at any given point of sail. A
vessel capable of sailing as such would be an efficient sailing craft and is the goal of the sailing
craft design process.
DESIGN METHODOLOGY
The preparatory and design work completed in this project is detailed in the succeeding
sections. The preliminary work sections describe the development of the design requirements,
the parametric analysis, the viability and business analysis, and the determination of the vessel’s
design point. The design work sections describe the design work completed to satisfy the
requirements for submission to the ISWSCYDC.
PRELIMINARY WORK
Design Requirements
In order to compete in the ISWSCYDC, a set of design requirements was developed and
submitted to the competition’s judges. This served as the entry into the competition and was
returned by the head judge with positive remarks about the nature of the project and the
development of the requirements. The full document submitted to the judges is available in
Appendix B.
The requirements developed strove to produce a preliminary design for a bluewater
sailing cruiser that has a capability to carry a cargo of hardwood. Emphasis is placed on the
design’s safety, seaworthiness and efficiency in terms of ergonomics, cost and energy. Another
important factor in the design requirements is that the design should avoid classification as a
commercial vessel wherever possible, which is to say that the design will be classified as a
“functional yacht”—not as a merchant vessel—with regard to regulation and operation.
The requirements state that the operation of this functional yacht must be possible by a
small crew of non-professional but experienced sailors (the requirements specify three). As
such, the requirements stipulate that the design be made comfortable for three people while
maximizing the design’s ability to carry payload. As in any design, the vessel’s attractiveness to
the target owners (bluewater cruising sailors, in this case) is also a primary concern.
The requirements also mention ascertaining that the vessel can operate in the United
States and abroad with regard to regulations. This leads to the requirement that the design be
suitable for classification by a major classification society, such as the American Bureau of
Shipping (ABS) Aluminum Vessel Rules. The concern with regulation also leads to the
18. 9
requirement that the vessel be able to manage the cargo in such a way that importation into the
US will be possible, should any special treatment be required. Additionally, it is required to
make accommodations in the design to maintain the quality of the product during transit.
Provisions for the design to be able to load and unload its cargo are also made in the design
requirements.
Finally, the design requirements state that the design should work to rely on renewable
energy sources as much as possible, within reason. The idea behind this is that the operation can
save on costs, as it does with fuel by the use of sails, by utilizing renewable energy with items
like solar panels, wind generators and others perhaps coupled with a hybrid auxiliary drive
system. Emphasis is placed, of course, on making the design profitable, and therefore,
prohibitively high capital costs for any of these items (such as for highly customized systems not
commercially widely available) would preclude their use.
Parametric Analysis
At the beginning of the project, design data for different vessels exhibiting desirable traits
were collected to create a parametric database. The usefulness of this database is somewhat
limited in the context of this project, as few boats, if any, have the characteristics of a cargo-
capable sailboat with a modern hull form. Efforts were made to include vessels of various sizes
and types over an initial range of lengths from 13 m to approximately 60 m even though it was
anticipated that the vessel would be in the 30 m length range, based on the design requirements
and as such the majority of the designs collected were in this size range.
The design database includes a number of vessels generously provided by Mr. James
Moran of the yacht design office of Sparkman & Stephens in New York as well as some large-
yacht data from the website of Dutch mega yacht builder Royal Huisman. The database also
includes more classical designs, largely drawn from Chappelle’s work with American fishing
schooners (Chappelle). The initial assessment of the “scow” type schooners used in the United
States lumber trade on the West Coast (among other applications) found that the designs of these
vessels were too outdated and too heavily oriented toward cargo volume to be considered for this
project.
The parametric database of designs developed for this project was used to determine non-
dimensional coefficients by regression to dictate the characteristics of the family of vessels
considered in the Viability and Business Analysis as a function of waterline length and
displacement.
These coefficients were developed using linear regressions and, in some cases, margins
on the slope and intercepts of the regression lines. This was done as a means of compensation
for the shortcomings of the parametric database regarding the matching of the database
constituents to the mission of the design. While some characteristics were determined to
correlate well between the goal design and the vessels in the database, others did not, and thus,
regressions corresponding to such characteristics were given a margin to compensate and cause
the regressions to make more intuitive sense.
One example of characteristics that were thought to correlate fairly well in the parametric
analysis phase was the ratio of sail area to displaced volume. It is logical that these
characteristics should correlate well, as the sail area correlates directly to the amount of driving
force required to drive a hull through the water, which is largely dependent on displaced volume.
This is also related to the wetted surface area (frictional drag) and the underwater profile (form
drag) of a vessel. As such, no margin was applied to this regression.
19. 10
An example of a characteristic that was determined to correlate poorly was the length-to-
beam ratio, which was assumed too large due to the fact that both the design’s beam and draft
(draft was determined by the beam to draft ratio) were going to be greater for a given length than
the vessels in the database given the assumption that the target vessel would have a larger
displacement-to-length ratio than the database constituents. The regression value for beam was
thus inflated by adding a negative value to the intercept of the length to beam line, which
increased the regression value for beam and in turn also increased the value found for draft. This
alteration effectively gave the design a greater displacement and thus cargo carrying capacity
than the “average” vessel in the database, which was partly based upon a number of Sparkman &
Stephens’ yachts. The designs in the business model were thus better suited to their stated
mission.
The use of these regressions can be seen in the business model. They are shown as
unitless fractions and there is an example section of the model shown in Appendix C.
VIABILITY AND BUSINESS ANALYSIS
Vessel Family Development
This project included a study of the viability of the design and its associated business
venture. The analysis was conducted in a spreadsheet and strove to determine the optimum
vessel size and characteristics for maximized profits for the business venture. The analysis
began with the implementation of the non-dimensional coefficients described in the Parametric
Analysis section to create a table containing the principal characteristics of each individual entity
in the family of vessels considered in the analysis. The family under consideration consisted of
vessels ranging in length from 10 m to 35 m at increments of 1 m, and each vessel was related to
the other members of the family in that they were developed from the same regressions, but
differed in that they varied over a range of vessel length and displacement.
Within the family of vessels, there was a variation in block coefficient (CB) for each
vessel along the range of lengths between CB = 0.50 to 0.80 in increments of 0.05 to account for
displacement. Block coefficient is defined as follows:
· ·
Eq. 1
where is displaced volume, L is length, B is beam, and T is draft. Thus, the entire range of
lengths along the entire range of block coefficients stated above was considered in the analysis to
determine the optimum. This translated to an optimal displacement, since the other elements of
the equation (beam and draft) remained constant for a given length across the range of block
coefficients. The case of the 0.60 block coefficient section of the vessel family has been
followed through the length of the model to the cost curve and can be found in Appendix C.
Revenue Prediction
With these data, each vessel in the family had the necessary characteristics defined to
perform a comparative study of the vessels’ cargo capacities. It was initially attempted to
determine a vessel’s cargo capacity by volume, on the assumption that the relatively low density
wood or similar cargo would be “volume limited” by the vessel size. This is to say that the
required space for accommodations, mechanical compartments, tanks, and other volume
elements of the design would infringe upon the cargo capacity more than any other factor. While
this may be a valid assumption for smaller vessels, a check with the larger vessels in the family
showed that, in fact, the cargo capacity was limited by the cargo weight in order to keep the
vessel floating at the design waterline. It was thus decided to assume a cargo weight in exotic
20. 11
hardwood equivalent to the difference between the values for full-load displacement and
lightship displacement determined in the model. Thus each vessel would possess a cargo space
large enough to accommodate a relatively full load of lighter cargo than the hardwood in
situations where that was the going fare (after accounting for the other components of
deadweight, such as fuel, water ballast, and others).
Using the data determined for the family of vessels in the model, it was also possible to
make a comparison of the vessels in the model based on operating speed. In order to achieve this
end, sail area was determined by regression with displacement. With this information and the
assumption that a single trip is equivalent to a straight line course on a broad reach in a breeze of
15 knots, we can estimate the average thrust to be expected from the sails using an
experimentally derived equation for the force on a sail, which is shown below:
0.00119 · · · Eq. 2
where F is the aerodynamic force on the sail (in lbf), VA is the velocity of the apparent wind (in
ft/sec), SA is the sail area (in ft2
), and CD is the aerodynamic drag coefficient for the sails, which
is unitless (Marchaj).
Once thrust had been determined, the analysis utilized some original and borrowed code
in Visual Basic for Applications (VBA) embedded in the model spreadsheet to approximate the
Froude number (Fn) at which each vessel’s thrust is equal to the resistance it encounters by
moving through the water. Froude number is defined as follows:
·
Eq. 3
where V is defined as the vessel’s speed through the water, g is the acceleration due to the
Earth’s gravitational pull, and L is the length of the vessel. The program developed utilized the
Netherlands Ship Model Basin Regression (NSMBREG) prediction program originally
developed by Professor Jacques Hadler and adapted to VBA by Peter Bryn (Webb Class of
2006). The original code written for this project input the characteristics for each vessel into the
Hadler code, ran the Hadler code for a predetermined range of boat speeds, determined the
closest resistance to the thrust value, and returned the resistance value and Froude number to the
main analysis spreadsheet. With this Froude number, operating speed for each vessel was
determined. This estimate returned a value for operating speed based solely on resistance in the
upright position and the assumption of relatively constant favorable conditions—which is not
wholly unreasonable for most tropical regions on the intended generic trade route, but it is an
approximation for the entire scope of the intended operation.
Using this estimation of speed and an estimate of distance along the journey (including a
“distance margin” of 15% to account for the unlikelihood of absolute great circle routes in the
vessel’s transit of the route), the number of trips possible per year could be estimated. This
information, coupled with the cargo capacity for each vessel determined in the model and
assumptions for the purchase and sale price of mahogany and teak, yielded estimations for
revenue per trip and then yearly revenue. These values were determined assuming that the
business venture would purchase the product, own it while in transit, and then possess the
capability to store and sell it once the product was in the United States. The costs associated
with these assumptions were accounted for with rough estimates in the model in the form of
management, storage, insurance, and customs (federal importation) costs, but these amounts
must be further researched to be fully reliable.
21. 12
Capital and Recurring Costs
Capital costs were estimated primarily as a function of weight and material cost, as in the
case of hull and structural material, or power required, as in the case of auxiliary power, or as
percentages of a related cost such as material or auxiliary power. An example of this would be
the electrical system cost, which was assumed a percentage of auxiliary power cost. Recurring
costs, such as those seen in Appendix C, were determined as percentages of total vessel cost
(TVC) in many cases, as recommended by Cyrus Hamlin (Hamlin), while others, such as sail and
rigging maintenance, were instead based on sail cost (a function of sail area).
Costs were also determined based on the size of the crew. The capital cost of the
accommodations was based on the required crew size, which varies with length, and
provisioning cost was an example of recurring cost based on crew size. It was determined for the
design requirements that a crew of three—which is the maximum expected volunteer crew size
on a relevant cruising vessel—would be adequately able to manage a vessel of up to
approximately 30 m in length. Any length greater than 30 m, which would involve at least one
crew member above three, would thus incur the costs necessary to employ that crewmember as a
professional mariner aboard the vessel. This could have an impact far greater than that mariner’s
salary on the operation if one considers the possibility that hiring professional mariners could
invalidate the non-commercial nature of the venture, and therefore hiring crew and bearing the
associated costs was not considered as an option in this analysis.
The profitability of a design was determined after the analysis was complete by
calculating the present value of the total cash flow each for vessel’s associated business over a
twenty-year period, assuming an interest rate of 10%. This cash flow included the TVC as well
as the yearly revenues and yearly expenditures for each of the twenty years.
Model Sensitivity
It should be noted that the financial model sensitivity to alterations in the founding
assumptions was tested with interesting results. The most notable parameter changed was the
difference between the purchase and sale costs for the cargo, which obviously changed the
profitability of the operation, while the optimum design point remained relatively constant.
When the price differential is greatly inflated, such as to the order of $20 (cost units) per board
foot, the optimum point changes to favor the highest displacement vessel of the greatest length.
This effect makes logical sense, because it corroborates the theory of economies of scale. At
lower price differentials, the model showed that the higher speed of a lighter displacement vessel
at a given length proved significantly beneficial over payload capacity by allowing a vessel to
make a greater number of trips per year. The model thus indicates that greater overall payload
capacity for a given year’s operations can be achieved by optimizing speed and displacement and
further leads to the conclusion that the profit optimization in the business analysis and the
determination of the design point was successful.
Design Point
At the end of the Viability and Business Analysis, one set of characteristics from the
family of vessels under consideration was chosen to be the most profitable design based on the
analysis. This set of characteristics helped to determine the starting point for the design work
and can be seen below in Figure 3.
22. A
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23. 14
and to avoid dangerous situations is imperative in an offshore sailing vessel; therefore,
performance must not be overlooked.
The amount of sail area required to drive a vessel of the magnitude of displacement
defined by the model (roughly 310 t at CB = 0.70 versus 260 t at CB = 0.60) is greatly increased,
and this would likely be coupled with a potentially negligible increase in righting potential and
resistance to heel because the operating region of the Pacific Islands restricts the design’s draft to
the minimum possible since potential ports-of-call could lie within lagoons with shallow passes.
While constituting a negative impact on safety for a shorthanded crew, this also results in an
increased resistance component due to heel and loss of driving force not accounted for in the
model. Additionally, there exists a possibility that the stability of the vessel would be negatively
impacted by including the volume of the hull form for a CB = 0.70. This is attributable to the fact
that the difference between these two values for CB would be accounted for almost entirely in the
ends—or prismatic coefficient—for this type of hull form, because the midship section has
nearly maximum area regardless of condition (as illustrated by the midship coefficient of roughly
0.95). This increased submerged volume fore and aft would lower the vertical center of
buoyancy, which creates a potential for lowered transverse stability depending on the placement
of weight (namely payload), and could therefore potentially increase the need for water or fixed
ballast.
The larger volume of the 0.70 block vessel and the associated higher resistance and larger
required sail area, coupled with potentially negligible increase in resistance to heel, would
severely limit the vessel’s ability to perform at any point of sail other than a limited range of off-
wind courses. While the winds along the course are assumed to be generally astern for this
model, in reality there will be times when the desired course will lie closer to the wind, be it for
the next port or to escape an encroaching cyclone or typhoon. At those times, the vessel with
upwind capability will be on its way while the vessel without waits for more favorable
conditions.
The differences in sailing capability and safety—due to differences in wetted surface
area (frictional resistance), displaced volume (wave resistance), fineness of entry and exit (wave
–making and –breaking resistance), and stability (resistance due to heel, diminished driving force
due to heel, vulnerability to sudden loss of vessel manageability and knockdown)—have led to
the decision to design for a smaller CB.
DESIGN WORK
The design work performed in this project, along with the associated decision making
processes, is outlined in the following sections. The general outline of the design process is
shown below. Supplementary calculations, drawings, and renderings can be found in the
Appendices under related headings.
DESIGN SPIRAL
The design process is an iterative exercise in which the design of a vessel is repeatedly
performed over an ongoing cycle, with each phase in the process building upon the last. A
diagram of the process can be seen below in Figure 4. This diagram shows the spiral and the
different aspects of design that occur over the course of a single iteration of the design.
24. 15
Figure 4: The design spiral
As can be seen above, the design process has a clear set of issues to be dealt with, and
there is also a clear order to follow in the design process. The design spiral is different for
different types of vessels, but the version shown in Figure 4 represents the process used for the
vessel designed herein. The following sections detail the approach taken for each of the design
categories shown in the spiral.
VESSEL MISSION
The mission and desired function of the vessel designed in this project were defined in
the design requirements and have already been described in the Design Requirements section of
this paper. Any issues raised in the process of the design completed in this project were solved
by consulting the requirements (shown in Appendix B) by using direct mandates set forth in the
document, or by otherwise trying to adhere to the character of the document when explicit
requirements were not present. The general themes set by the design requirements were safety,
functionality, simplicity of design, shorthanded manageability, and versatility in function and
route capability.
HULL FORM DEVELOPMENT
Influences
The hull form was developed with many considerations in mind. Quite important among
these were the proven concepts that have been used in designs of the past. It was intended for
this design to draw upon influences from multiple sources, including the load-bearing hulls of
traditional sailing work boats as well as the efficient, fast boats of more modern design.
It was initially intended to model the vessel after the traditional fishing schooners
described in some of Howard Chapelle’s work, because they were relatively slender boats that
still managed to carry a significant load. It was believed that this concept best represented what
25. 16
should happen with the design of the subject vessel, largely because in some ways—such as the
long, slender nature of these boats in particular—these seemed to have the characteristics of
traditional load-bearing hull forms that could be most easily and effectively adapted to the
modern concept desired for this design.
Interestingly, it was determined that, in fact, the fish cargoes carried by the fishing
schooners were denser than the wood and other cargo intended to be carried by this design. It
thus followed that the design would require more internal volume than the fishing schooners
analyzed in the research for this project. This realization led to an expansion of the range of
traditional sailing working craft types considered for the project’s influences.
The initial assessment of the scow schooners involved in the lumber trade (notably on the
West Coast of the United States) for the design database and parametric study found that these
vessels had too many undesirable and outdated design traits for inclusion in the database, but,
after discussions about these vessels with Professor Paul Miller at the United States Naval
Academy (who has been involved with design projects involving the scow hull form), it was
determined that, in fact, there was much to be learned from the scow concept and that it is quite
applicable for this project. This is attributable to the large internal volume afforded by the flat
bottom, hard chine turn of the bilge, vertical side shell, and full ends, shown in Figure 5. There
are other favorable features of the scow design, such as its shallow draft, which is desirable given
the need for an ability to enter potentially shallow lagoons in the Pacific Islands. Ultimately, the
scow hull form was the foundation of the concept for the hull form in the subject design.
Figure 5: Scow midship section and stern sections
Source: Olmsted
While the traditional design influence was quite specific once it had been narrowed down
to the lumber scow, the modern influences on the design were less tangible. This fact was
primarily due to the expectation—largely inspired by Professor Miller—that the more “modern”
design attributes were going to be less significant than the traditional features. The design
ultimately included some significant alterations to the traditional scow concept that will be
discussed below, including modification of the traditional scow bow shape shown below in
Figure 6.
26. 17
Figure 6: Scow bow shape
Source: Latitude 38
Hull Form Design Work
One of the primary concerns in the design of the hull form was to meet the size and shape
requirements set forth by the actual design point selection in the business analysis. It was
determined that the preferred methodology was to design to the correct length (on the design
waterline) within 1 m while designing to the correct displacement as closely as possible. This
constraint helped to ensure that the design would have a high operating speed because speed is
significantly dependent on Froude number—thus placing a high value on maximizing waterline
length. Additionally, it also ensured that the projected cargo capacity determined in the business
model for the selected vessel would be met, assuming the lightship displacement was not grossly
underestimated.
The hull form produced in this design can be seen in perspective view below in Figure 7.
A lines drawing showing the hull form and major appendages can also be found in Appendix D.
The hull form was based upon the shape of a traditional lumber scow with several significant
alterations to better fit the mission of the vessel, to better reflect the state of the art of hull design,
and to better suit the hull for offshore operation.
Figure 7: Half-hull shape: perspective view
One of the most notable of these alterations is the tapering of the ends, which is a severe
departure from the traditional scow hull form. This taper is quite pronounced at the bow and was
included primarily to improve the vessel’s seakindliness and upwind sailing capability. There
was some deliberation about the inclusion of flair and rake in the bow, and this was weighed
against maximized waterline length within the overall length of the hull. Ultimately, it was
27. 18
decided to include roughly 20° of rake in the bow, and the waterlines were faired between the
base of the stem and the point of the bow to include the appropriate amount of flair. This
decision was justified by the benefits afforded the vessel in heeled waterline length (which is
improved by including overhangs) and in the ability of the crew to perform work on deck while
in a seaway. This aspect of hull design translates to the amount of water expected to be on deck
while sailing in rough conditions, because this is directly related to the overhang and flair of the
bow—the more of each within reason, the drier the deck. These features are all visible in the
Lines Drawing in Appendix D.
While the hull taper is much more pronounced for the bow than the stern, it does occur
aft in the form of a rounding of the hull sections aft of the hard-chined midship sections to a
transom defined by a series of arcs varying in radius from the sheer to the centerline. The goal of
this feature is to promote smooth flow around the hull, reduce the possibility of flow separation
from hard corners in the hull shape, and prevent the transom from becoming submerged at any
angle of heel (which could cause significant base drag if allowed to occur at any operating
condition). In the heeled condition, this configuration allows the vessel to take advantage of the
hard corner of the bilge chine for directional stability and resistance to leeway while avoiding the
potential of transom immersion, which would be more likely with a hard corner in the transom
that would occur if the hard chine of the bilge were continued all the way aft.
The hull shape was developed using the latest version of Orca3D (developed by DRS
Technologies), which is an add-on to Robert McNeel and Associates’ Rhinoceros. Orca3D uses
the intuitive and efficient three-dimensional design environment inherent in the Rhino software
and adds functionality that greatly expedites the creation of the desired hull surface by the
designer. This software allowed for the successful completion of the hull form design for this
project and integrated well with the other software used subsequently for the other elements of
the vessel’s design, which included a significant amount of design in Rhino subsequent to the
hull design.
SAIL AND RIG DESIGN
The sail and rig plan for this design was developed with the constraint on sail area
developed in the business model. This figure was based upon the regression relating displaced
volume to sail area, and as described above, sail area is directly related to the amount of driving
force required to move a vessel of a given displacement through the water. Consequently, it was
decided that the sail area determined by this regression should be matched in the design if
possible.
It was expected that this large requirement would produce a sail plan that appeared to be
too large for the vessel’s length when viewed in profile, and this expectation was founded in the
fact that the vessel designed in this project has a significantly higher displacement than the norm
for a vessel of similar length. High sail area was viewed as a necessity, and it was determined
that high beam in the design inherited from the scow hull form, coupled with the use of seawater
ballast in the design, would compensate for the added heeling moment in normal conditions.
The addition of easily reefing with roller furling on all sails (including in-boom furling for the
sails on booms) for more rough conditions justified the use of such a large sail plan within the
restrictions from the design requirements.
To achieve the goal of so much sail area, it was decided early in the design process that a
double-masted rig type would be utilized, making the vessel either a ketch or a schooner. While
accommodating this vessel’s large requirement for sail area, this mast configuration also allows
for a great deal of versatility in bluewater cruising that is preferred by many offshore sailors. An
28. 19
initial attempt to use a ketch rig design with the mizzen luff length roughly 75% of the main luff
length resulted in a requirement for the height of the main mast to exceed 40 m, which is
approaching the air draft maximum for many large ships. In response to this, the mizzen mast
was increased in height so that the two luff lengths were equal to each other, and, effectively,
each mast carried the same sail on the boom.
This arrangement remained with the vessel labeled as a ketch until interference between
the mizzen boom and the wheelhouse top forced the height of the aft mast upward to retain the
original luff length on the aft mast. This change effectively made the vessel a schooner, though a
much more modern version of the rig than the gaff-rigs carried by the scows of a century ago.
The design sports a full roach on the fore sail, which could not be mimicked by the main sail
because of restrictions on the available space in the sail triangle imposed by the back stays on the
main mast. The sail plan in profile can be seen below in Figure 8.
Figure 8: Wolczko 30 sail plan
29. 20
The target sail area from the business analysis was approximately 965 m2
, which was
effectively met in the initial drawing of the sail plan. This version of the sail plan had overly
inflated the amount of roach in the main sail (with each sail at an aspect ratio of 3 and an area of
267 m2
), and also had an unmanageably large genoa (432 m2
). The aspect ratio of 3.0 was
selected as an effective sail on all points of sail but slightly more optimized as an off-wind sail
than as an upwind sail, as recommended by Larsson and Eliasson (Larsson and Eliasson). The
use of a bowsprit was determined to be necessary to allow for the aspect ratio of 3.0 in the sails
while retaining the necessary longitudinal configuration of the sail plan for proper operation of
the sailing equipment.
The sizing of the sails was revisited with the design of the rig, and ultimately the sail area
was decreased to allow for a more reasonable jib size (155% of the foretriangle area at 350 m2
),
and virtually no roach in the main sail to ensure no interference between the main sail and the
backstays. The main boom was also slightly shortened to permit its passage outboard of the
backstays. Ultimately, the main sail area was designed to be 200 m2
while the fore main sail was
designed with extra roach to have an area of 300 m2
. The calculations of areas, along with the
determination of upwind sailing performance according to the sail force coefficient method
developed by Professor Jerome Milgram at MIT (Milgram) and diagrams of the sail plan and
rigging and spreader arrangements, can be found in Appendix F.
The rig was specified to be built of aluminum with stainless wire rigging for cost reasons.
Calculations detailing the sections required for the vessel, as well as various other sizing and
strength calculations for other aspects related to the vessel’s rigging, can also be found in
Appendix F. Calculations were conducted in accordance with rule-of-thumb methods, such as
those developed by Skene (Skene), as well as by guidelines from Bureau Veritas (BV) in their
Yacht Rules (Bureau Veritas).
APPENDAGE DESIGN
The appendage design for this vessel was strongly driven by the requirement for shallow
draft inferred from the design requirements, because the vessel needs to be operable in remote
island settings. These likely would include lagoons of various tropical islands which are
relatively shallow, and thus deep draft severely limits the vessel’s capability to enter these
locations and engage in business activity, severely limiting the design’s viability. The business
model of the vessel’s operation is partly based upon the ability of the vessel to exploit the
relatively unmet need in remote regions for water-borne transport; therefore, the design cannot
afford to have a deep draft.
Rudder Design
As a result, the appendages used in the design of the subject vessel are somewhat peculiar
for a cruising sailing yacht. The most readily noticeable aspect of this is the vessel’s steering
surfaces, which are manifested in the form of two low-aspect-ratio rudders, shown in Figure 9.
In the conceptual or preliminary design phase of a sailing yacht, it is difficult to quantify the
amount of turning capability necessary for the vessel to be safely operable in an offshore sailing
situation. This is because the relationship between turning moment and the actual rate of turn is
difficult to accurately determine without some form of model test. As a result, the amount of
planform area required for the turning control surface(s) on a sailing yacht is generally
determined as a percentage of sail area. In the case of this vessel, rudder area was determined to
be approximately 1.5% of the vessel’s sail area, which is considered an average value in
Principles of Yacht Design (Larsson and Eliasson). This value of rudder planform area was
30. 21
assumed to be a minimum value due to the fact that this vessel’s rudders do not have the added
benefit of increased lift force for high aspect ratio foils. Constrained by this value, the maximum
average geometric aspect ratio of the rudder foils is 1.0 assuming that the rudders can extend a 1
m distance below the full-load canoebody baseline. This increases the draft of the fully laden
yacht from approximately 1.8 m unappended to a minimum value of 2.8 m—a depth which
restricts the vessel’s safe entry into some islands’ lagoon passes and limits business potential, but
which reflects the outcome of the compromise between shallow draft and safe vessel
management at sea.
Figure 9: Rudders: perspective view from starboard quarter
It was decided that a draft of 2.8 m was allowable in order to permit the placement of the
rudders seen in the appended lines drawing in Appendix D and in Figure 9. These rudders have
been determined by initial check with the empirical method shown in Principles of Yacht Design
to provide the necessary turning moment to allow for the safe operation of the vessel in an
offshore sailing situation.
The rudders were also angled slightly outward in the design, as can best be seen in the
Lines Drawing (Appendix D. The angle of rudder flair was determined with the use of a
Dellenbaugh Angle calculation, a preliminary method for the determination of vessel stiffness
(Larsson and Eliasson). This calculation can be found in Appendix F. The benefit served in this
context was that the equation uses a limited amount of information about the vessel to make a
reasonable estimate of the approximate angle of heel in 15 knots of breeze. At this phase of
design, this could be considered the effective optimum heel angle, and, as a result, it was used
here to determine the angle to flair the rudders away from the vessel centerline. The
Dellenbaugh calculation yielded a heel angle of approximately 5° in this breeze, and since that is
the expected average wind speed for the vessel, the rudders were designed with the same angle
of flair in order to ensure that one rudder remains vertical (the angle at which it is most effective)
for as much time as possible.
31. 22
Keel Design
The vessel’s keel was sized vertically based on what was deemed the necessary draft and
is described above. This allowed for a keel that extended roughly as far below the lowest extent
of the canoebody as the rudders or to a maximum draft of roughly 2.8 m below the fully laden
waterline. This value was mandated by a need for ability to travel to islands with shallow
navigational passages. This restriction, in effect only for the time when the vessel is transiting
shallow water, led to the idea of a moving keel, or, more specifically, one that could be retracted
to meet the draft restriction when necessary. The selected configuration of the keel for this
design is shown below in Figure 10. This was ultimately done in order to generate enough side
force in the upwind sailing condition for the vessel to be operable.
Figure 10: Keel configuration, centerboard down, with rudders
Using the values for side force on the sails calculated for the upwind sailing condition by
the Milgram method, a design point for the necessary hydrodynamic side force could be
established. Once this was done, a method needed to be found to predict the hydrodynamic side
force produced by the vessel at a given speed and leeway angle, or angle of attack. Ultimately, it
was determined that the slender body theory developed by J. M. Newman, as presented in
Professor Richard Royce’s Sailing Yacht Design class, would provide a good basis for the
estimation of lift.
This method operates on the principle that lift is generated both from the hull and from
the keel and strives to quantify the lift coefficient of the system including both of the lift
generating bodies and their interactions. The method is simple enough to implement for a design
with a conventional keel type, but, when the system of lift-producing elements has a third
element, the method breaks down to some extent. The solution to this problem was determined
to revolve around approximating the system in different ways to simplify it enough to allow the
slender body method to be used. The methodology involved determining the lift coefficient for
the hull and the fixed keel as a system by the conventional method and then finding a different
lift coefficient for the system. This combined system was represented by the centerboard
planform extended to the hull profile as the keel and the hull profile area, corrected to include the
area of the fixed keel with the actual profile area and with a corresponding effective canoebody
draft as the hull, and then using the slender body method with this approximated system. Once
this was done, the two different lift coefficients were used to determine the lift generated by the
entire system—the first of these with the use of low-aspect-ratio theory, and the other with high-
aspect-ratio theory.
32. 23
The calculations for the lift generated by the keel system at various speeds and angles of
attack (leeway angles) can be found in Appendix E. The fixed draft of the vessel remains at 2.8
m while the draft with the centerboard lowered is 7.8 m.
Balance
The balance of the vessel is essentially its ability to sail at any point of sail with minimal
operator adjustment of either the sail controls or steering controls. In other words, a well-
balanced vessel can be sailed on any given point of sail with the sails’ sheets and tiller or wheel
lashed at a constant angle (which should be 0° rudder angle). A slight variation in the trim of the
sails or in the rudder angle should be adequate to steer such a vessel.
The determination of a vessel’s balance is very complex. To accurately determine
whether or not a vessel is balanced, a calculation must be made of the locations of the CE and the
CLR at each potential point of sail and the turning moments caused by the longitudinal
separation of these two points (which is effectively the turning couple moment arm that causes
either weather or lee helm in an unbalanced design), also known as lead, at each of these points
of sail. Obviously, a well-balanced vessel will have small values of lead, but the actual
determination of the effect of the aerodynamic and hydrodynamic forces cannot be done
accurately without some form of model test. As a result, the use of simplified methods has been
employed in this project.
Larsson and Eliasson’s Principles of Yacht Design suggests a method utilizing the
geometric centers of area for the planform shapes of the sails to determine the location of the CE.
This was employed for this project. This method also determines the CLR by placing an
intersection at the 0.4 design draft along the quarter-chord of the keel fin, which is an
approximation of the center of load on the keel foil. While this method may be adequate for
vessels with fin keels providing the vast majority of lift force for round-bilge hull forms with
elliptical or circular hull sections, this method was determined to be inadequate for this project
because of the wall-sidedness of the design, hard chines, and the depth of the canoebody relative
to the vessel’s overall draft. As a result, the location of the CLR was determined while
remaining mindful of the planform area of the canoebody hull, which is both more logical in the
context of this design and more in line with the methods used to determine the vessel’s resistance
to lateral motion described in the Appendage Design section. This was done by assuming that
the CLR is located at the average point between the 40% span of the centerboard foil and the
center of the planform area of the combined canoebody and the fixed keel and by assuming that
each element delivers roughly half of the lifting force. The locations of the CE and the CLR can
be seen in the Sail Plan in Appendix F.
This vessel was initially designed to have a value of lead within 10% of the vessel’s
design load waterline length, as recommended by Larsson and Eliasson. At the outset of the rig
design, the keel and centerboard were placed to allow for a slight margin of about 2.50 m of lead
to account for alterations in the sail plan. Ultimately, at the end of the preliminary design
iterations, the design settled at 3.07 m of lead, which is effectively the target of 10% of the DWL
length. This value for lead essentially accounts for the increase in weather helm of a heeled
vessel, and helps keep the CE forward in off-wind sailing conditions, thus having a positive
effect on directional stability.
33. 24
GENERAL ARRANGEMENT
The arrangement of this design was carried out mindful of the design requirements,
synergy of design, and efficient operation. The manifestations of these design themes can be
seen in Appendix G.
The primary issue to be reckoned with in the arrangement of this vessel was the
maximization of cargo and working interior volume while maintaining a reasonable amount of
accommodation space to make the design comfortable and workable as a cruising sailboat. The
spaces were grouped as much as possible by related function, which is common practice in the
arrangement of a vessel for the reason that it both increases the ease and efficiency of the
vessel’s operation and prevents spillover from one space to another. In other words, it would
prevent something like the management or stowage of cargo from infringing upon the
accommodation space.
On the whole, this arrangement was quite successful. The spaces used for each function
of the yacht are reasonably subdivided so that each function can be carried out, yet the spaces
also overlap one another in such a way that the vessel has a minimum amount of wasted space
and can be effectively operated in all of its intended capacities. The cargo stowage and
management systems and their associated areas of operation were grouped quite easily, since
these comprise the inside of the midship region of the vessel for the stowage of cargo along with
the deck area immediately above this area of the interior space. This part of the deck includes
the cargo hoist and the hatches through which cargo is loaded and unloaded. Cargo spaces and
systems are thus concentrated at the midship and are relatively subdivided from the rest of the
vessel by way of watertight bulkheads and deck divisions. In addition to the drawings available
in Appendix G, the interior layout can be better understood from Figure 11.
Figure 11: Perspective inboard profile showing interior layout
The spaces required to operate the vessel in the underway condition were grouped
effectively together. These primarily include the cockpit (also referred to as the wheelhouse),
from which most of the underway functionality of the vessel is controlled, and the deck, which is
where the sails and most of the sailing gear is actually located (along with the ground tackle and
mooring gear for the anchoring and berthing of the vessel). These spaces also include the
forecastle, which contains the spare and unused sails along with a workshop for sails and
miscellaneous maintenance work for deck and sailing equipment.
The engine room should also be mentioned with these spaces. While intended to be fully
unmanned, this space will be used to perform engine maintenance on the auxiliary propulsion
engine and the generator engines. Any other dirty mechanical work could also be performed in
this space, because it will be better equipped to handle such work and the associated cleanup
than the forward work space in the forecastle. Because of the intentional inconsistent predicted
Cargo
Fore
Castle
Accom. Spaces
Eng. Rm.
34. 25
use of this space, its separation from the other underway working spaces, while perhaps
unavoidable, was deemed to be of no real concern. Small equipment may be brought in or out of
the space by way of the stairwells, while soft patches can accommodate large equipment where
necessary.
The design also includes a compartment for the stowage of a Rigid Bottom Inflatable
(RIB) tender as well as any associated gear and deck gear, such as mooring fenders, which is not
intended to be accessed at any time other than when the gear inside is needed (such as prior to
berthing). This compartment can be reached by way of a hatch in the transom, from which the
RIB is launched, or by way of a watertight hatch located in the sole of the wheelhouse. This
space also contains the vessel’s propane tanks, and is ventilated by two dorade-type vents aft of
the wheelhouse.
The accommodation spaces, shown in Figure 12, were very successfully arranged in this
design. The accommodations make efficient use of the transverse and vertical space afforded by
this vessel’s hull form and size, and, as a result, the accommodation spaces comparable to that of
a spacious boat half as long as this design or more, are fit into roughly one-third of the subject
design’s length. The accommodation space includes two staterooms aft abutting the aft
watertight bulkhead toward the steering gear compartment. Each stateroom can sleep up to two
people; one is a master stateroom with a longitudinally oriented queen-size bunk, and the other is
a crew stateroom opposite the master with two longitudinal twin-size bunks in case there are no
two among the crew that would share a bunk. All bunks are equipped with lee-cloths for
underway use while the vessel is heeled so that the bunks can be safely used.
Figure 12: Accommodation spaces plan view
In the vicinity of these staterooms is a common passageway area, which leads aft to
access the steering gear room, and athwartships to the common head/shower and companionway
to the pilothouse to starboard or to the engine room stair and a pantry space to port. This space,
which makes up the central part of the accommodation block, also contains a diesel heater at the
35. 26
forward end of the passageway on the centerline, which is intended to provide heat for the entire
accommodation space while the vessel is operating in cooler climates. While this system may
not be sufficient for polar operation, it will be adequate at the moderate climates at which the
business plan operates.
Forward of the accommodation spaces and down a stairwell lies the engine room, which
contains the bulk of the design’s mechanical components. Above this is the pilothouse, which
houses the galley and mess space along with the compartments used for refrigeration and
freezing. This space also contains a significant amount of pantry-style food provision stowage to
ensure the vessel’s capability to support the crew for prolonged periods away from bulk sources
of food. This is estimated to provide food for time on the order of double the anticipated trip
time of three-and-a-half months for the crew. To port and aft in the pilothouse is the
companionway to the wheelhouse, which is considered a living space since it is intended to be
occupied at all times during the underway operation of the vessel.
As such, the wheelhouse has been equipped with a set of seats forward, which double as
an athwartships pilot berth, a comfortable captain’s chair. A series of large Lexan windows
provide ventilation. The space also houses the navigation equipment, with the computerized
equipment mounted on the wheel pedestal, and the paper charts and plotting tools stored in and
used on the chart table in the aft section of the space. Opposite the chart table is the
communication station, which contains the VHF, Single Side Band (SSB) and Ham radio
equipment along with the weatherfax equipment and any other communications equipment
deemed necessary by the operator. Email communications will be managed with a Pactor-type
SSB/Ham modem. While more reliable satellite communications and email would be desirable
for the business operations, the added cost for satellite subscriptions and equipment was deemed
not worth whatever financial gain they could facilitate.
The inclination to optimize the design for the sailing condition led to an interesting
configuration of the auxiliary propulsion engine and propeller shafting. A common problem
exists in many sailing yacht designs in which a propeller must be placed somewhere on the
submerged portion of the hull for the conditions that require its use, while it will cause
significant drag in the sailing condition, whether locked or freewheeling.
The subject design attempted to deal with this issue by a somewhat unconventional
method. In order to avoid the added cost or added complication of a large folding or
controllable-pitch propeller (CPP), the propeller was placed as close to the trailing edge of the
keel as possible in order to mask the profile of the propeller, shaft and struts in the keel wake
disturbance. This placement effectively reduces the propeller’s negative effect on the yacht’s
sailing performance. To achieve this end, the engine was oriented such that the flywheel faced
forward and led to a marine gear of the “vee” type configuration. This configuration can be seen
in the profile view of the General Arrangement and below in Figure 13. The propeller was then
placed as far forward as possible within the constraints of a 14° angle between the two shafts (ZF
Gears), the propeller diameter, and a separation between the propeller blade tips and the hull of
10% of the propeller diameter.
36. 27
Figure 13: Propeller shaft “vee” configuration
Ultimately, because of the propeller speed and gear problems described in the next
section, this design placed the propeller farther aft than was desired. Because of this, further
design iterations would select a smaller diameter propeller over a propeller of a less aggressive
pitch angle, both because it would alleviate these problems and because it would be more likely
to be an optimal design rather than a re-pitched propeller of otherwise similar character. With a
smaller diameter propeller, the goal of masking the profile in the keel’s wake would be better
achieved.
The arrangement consists of five watertight subdivisions, and the largest compartments—
the cargo hold, accommodation block, and forecastle—are at least partially protected from
puncture by integral double-bottom tanks. The engine space, which lies within the
accommodation block, is the only space among these compartments not protected from below by
a double-bottom, but it is protected by the fixed keel. In all, this arrangement, which includes a
collision bulkhead 3 m aft of the forward perpendicular, enhances the vessel’s safety should a
collision or grounding occur.
PROPELLER AND ENGINE
The propeller and engine were selected by the determination of a desired speed under
power and a calculation of the necessary equipment to drive the yacht in the fully loaded
condition. This speed was determined to be 9.0 knots, because at this speed, the vessel can
operate reasonably on schedule when the engine is needed in times of too little wind to power the
boat by sail. The calculations performed to the select these components can be found in
Appendix H.
The process of selecting a propulsor and power plant began with a resistance analysis of
the hull in the under-power configuration, which stipulated the centerboard be in the retracted
position. This was performed in Hullspeed, which is a component of the Maxsurf suite. The
results from this program, which can also be found in Appendix H, yielded the effective power
(EkW) required to drive the vessel at a given speed. The effective power curves for each
different regression method used by Hullspeed can be seen below in Figure 14.
