Design
Simple and elegant, the Rafale C-Class is a bold undertaking for a group of students with a budget less than what some of the biggest Little America’s Cup teams will spend on a new foil set. The hulls (below) are even lower in volume than some of the super-small designs in Falmouth in 2013. The J-foil (right) is the default for most teams, even those with more resources – the tighter the ‘V’ the more stable the platform, though at a price of less lift and increased drag. The simple alloy mandrel (far right) used for the main structural spar
Oak trees and acorns
A new C-Class challenger is quietly emerging from a Montreal university campus
The Rafale C-Class project was born in autumn 2013 in Montreal, the creation of students from the École de Technologie Supérieure (ETS). It is a colossal two-year project that aims to design and build a catamaran to take part in the C-Class world championship in Geneva this Sept - ember. Supported by Julien Chaussée, a former member of the British Invictus team, and Simon Joncas, a professor at ETS and specialist in composite materials, 20 undergraduate students are working with a budget of just $130,000, mostly in-kind, with the aim of being on the startline alongside some of the best-known – and best-funded – sailing teams in the world.
Foils
When we started designing our C-Class in early 2014 we had to ask ourselves a lot of questions because we had so little experi- ence in the field. Our first task was to design trial hydrofoils for the 20ft Espadon cat built by Mystère Composites; to estab- lish the forces acting on these boats we then set about developing our own numeric model. After trialling a variety of foil configurations for the Espadon we settled upon J-foils because this shape offers the
40 SEAHORSE
best balance between speed and stability. The same configuration was also the start point for our C-Class, with our first full carbon foils, with no metal reinforcement, weighing in at 13kg each. We benefited notably here from the assistance of Altair, who provided us with their powerful Hyper- works software which is ideal for composite design (as a university project, there was a further motivation for us to succeed in better understanding lift-foils since there are poten- tial knock-on benefits for reducing the fuel consumption of powercraft).
Hulls
Taking full advantage of the plentiful liter- ature available on designs from both the America’s Cup and previous Little Amer- ica’s Cups in C-Class boats, we created our own hull design incorporating many of the best elements of previous designs. We chose a shape just a little smaller (lower displacement) than a generic C-Class because we wanted to reduce drag, work- ing on the basis of maximising flight time. For our first hull the main difficulty was finding the right compromise between strength and light weight; in fact, our initial ‘gentle’ target (without centreboard case) was around 35kg per hull… which is still quite aggressive. If we get the chance to build a second pair of hulls we are confident of reducing this figure further. That said, we are very mindful that we are students and must stay grounded in terms of available resources.
Beams
The crossbeams were also designed using Altair Hyperworks. Thanks to the optimi- sation tools available, we were able to analyse and optimise the laminate but were constrained financially and so had to employ an aluminium cylinder mandrel because we didn’t have the money to create a custom mandrel… let alone a female mould. We also lacked the specialist experi- ence to deal with very complex laminates. In the end, the final beam designs are the best compromise we could find taking account of these factors. Of course, a circular cross-section isn’t the best aero - dynamically, but we will try to improve the situation by adding some light fairings in due course. We have also experienced definite challenges extracting the mandrels from the cured beams; but even so using good pre-pregs we got our beam weights down to 7kg (front) and 3.5kg (rear).
Wing
Detailed wing design began in summer 2014. The wing spans 45ft and is very close to the 300ft2
area limit. We have also
opted for the highest practical aspect ratio to maximise efficiency.
The design of the wing is fairly classic for a current C-Class. It is a two-element design with a tab at the trailing edge of the front element. The main difference compared to other wings is the use of a ‘morphing’ trailing edge, instead of a rigid (aileron-like) tab. This is an evolution of an
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