Feature 1 | Yacht Design anD construction
cruncher had done it in 12 seconds.
The kspline would eliminate much of
the tedium usually involved and allow
Raymond to spend a great deal more
time investigating the performance of his
hulls, which was, after all, the main object
of the project.
The project presented a unique set of
requirements and this was reflected in
Raymond’s framework of sections and
longitudinal lines. He wanted to study
the dynamic performance of his hulls, so
the position of the static waterline was far
less important than dynamic lift and trim.
The hulls were based on the latest (2007)
Groupe Finot Open 60 hulls, which feature
a pronounced knuckle or chine in the
topsides. So, whereas the section curves
in the author’s demonstration model
were referenced to the design waterline,
Raymond referenced his kspline sections tank testing the groupe Finot open 60 (as used on Generali) the parent hull for
to the chine. raymond’s systematic series (credit: Jérémie raymond).
In other respects, Raymond’s framework
resembled the demonstration model. The
values of various kspline parameters are under various conditions. The parent that small, limited-budget projects can
defined by smooth longitudinal curves hull was an Open 60 designed in 2007 benefit from the results of a detailed
or straight lines, which define the value by Groupe Finot, and used in four programme of CFD and tank-testing, via
of a parameter as a function of the 2008/2009 Vendée Globe competitors: the VPP system.
position along the length of the hull. The Generali, Hugo Boss, DCNS, and BritAir Raymond’s VPP remains a work in
longitudinal centreplane curve is a pair (which eventually finished second). Its progress. The project confirmed that
of ksplines (one forward, one aft). Other performance had been characterised by RANS-VOF CFD codes are capable of
longitudinal lines, such as the chine and an extensive tank-testing programme, predicting the performance of planing
sheer, are fsplines. and the tank-testing model was available hulls. Relative to tank test data, ISIS-CFD
The complete model was defined by for further testing. produced realistic results up to a Froude
40 numbers, or ‘parameters’. Changing Rather than build a series of new number of 1.2, equivalent to about 31kts
the value of any parameter will change tank-testing models, Raymond chose to on an Open 60. But the hulls were analysed
the hull shape. Raymond created a series analyse the hulls using a CFD code. The only at one value of displacement, and the
of 15 hulls by varying the values of key results could be validated by comparing analysis did not investigate their heeled
parameters, such as the curvature of the the CFD analysis of the parent hull with performance.
aft centreplane curve. measurements from the tank testing Even so, Groupe Finot has already
Creating a series of hulls was only the programme. After evaluating several CFD pressed the new VPP into service. Its first
first step of a complex project. The next systems, he selected ISIS-CFD. serious application was a 3.6m dinghy, the
step was to measure their performance Data from the CFD analysis was prototype of which was built in October
used to develop a VPP system based on 2009. According to Raymond, the ability
regression formulae. Whereas the CFD to rapidly develop a systematic series of
analysis takes many hours to calculate hull shapes was critical to the success of
the performance of one hull under one the project. Asked how he would have
set of operating conditions, the VPP can done it, without the kspline and the
provide more or less real-time estimates Friendship Framework, he said: “I can’t
of a hull’s potential behaviour. This means imagine.” SBI
A hull framework with one side of the skin omitted. Area coefficient curve and bilge factor
curve specify the values of section shape parameters as a function of longitudinal position.
Overall section dimensions are defined by longitudinal curves such as Deck edge curve,
Datum, and Centreplane curve. Raymond’s hull series was based on a similar, but more
complex, framework.
28 Ship & Boat International March/April 2010
SBI_MarApr10_p26-27-28.indd 28 26/02/2010 12:22:24
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