text on yacht design, in it they have this to say about the nature of yacht design:
“Yacht design is by its very nature a quantitative process. A designer, professional or amateur, is not much helped by qualitative reasoning. It is not enough to know that the hull can withstand a greater load if the skin is made thicker, or that stability is increased by more lead in the keel. What he needs to know is the minimum skin thickness and the least amount of lead needed in the keel for the yacht to be safe under all possible conditions. If he is not able to compute these quantities the yacht may be slower and more expensive than necessary, and worst of all, it may be unsafe”.
Contradictory though it may seem, the author agrees with this statement, a substantial part of the nature of yacht design is quantitative, however it is considered that the designer is continually making qualitative evaluations and judgements of their proposals as a design develops. Especially in the initial conceptual stages, where the overall configuration and layout is conceived. As the programme moves forward the
design requires
progressively more focus on precise engineering analysis, to refine and optimise the technical design of hull and all aspects and the hydrodynamics of the keel and rudder, rig or the structural design of the vessel.
In minimum condition design, that is design which when operating produces the minimum number of unwanted outputs or responses, there must be a very precisely defined set
of miniscule gains).
However it must also be remembered that any minimum condition is a chosen condition,
physical performance requirements, to be and “optimum
performance” at least in pleasure and leisure craft, must include the human psychological, emotional, symbolic, and
an
effective design. For example some clients are very demanding regarding the symbolic aspects of a design, as expressed by the visual style of the vessel, responses in this case are not physical they are emotional, so one can argue they are subjective and cannot be evaluated.
Consider the issue of ambiguity in selecting a coefficient, say for example the Prismatic Coefficient. This compares the volume of a prism projected fore and aft the length of LWL, from the midship (or largest) section against the volume of a rectangular prism corresponding to LWL & BWL & Canoe body draught.
Cp = AML
AM = the area of the midship or largest section of the immersed hull. L = the Design Waterline. = the Volume of displacement
B-26 Figure 11. Traditional option values achieving what in against normal which the actual
performance of any design can be measured, (As in the case of an America’s cup boat, where millions may be spent
terms would be
The Cp relates to the distribution of the immersed volume of the vessel. But it says nothing at all about the shape of this, which may vary substantially from design to design. The designer will manipulate this shape in developing a design and may work through a substantial number of iterations before being satisfied. The exploration in a high performance craft would involve numerical analysis and comparative analysis offered by such techniques as VPP.
4. A SIMPLE EXAMPLE 18FT CENTREBOARD DESIGN
Figures 11 and 12 show rough sketches of a simple conceptual
coefficients (only Cp and D/L are shown) and nearly identical geometric dimensions, any deliberate.
design, both examples with the same variations
Traditional Design: 1. D/L = 150 2. Cp = 0.58
3. = 1770lbs (approx 800kg) 4. LOA = 18ft 0” (5.5m) 5. DWL = 17ft 5” (5.3m) 6. BOA = 7ft 10” = 7.8ft (2.4m) 7. BWLmax @ DWL = 6.0ft (2.24m) 8.
Stem height 1.0m Lowest point on sheer 0.82 Transom height 0.85
are
© 2008: Royal Institution of Naval Architects
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