The build
idea first tried on the Airbus-backed Invic- tus project in 2010 (designed by Julien Chaussée). At the heart of the wing is a 32ft carbon spar, 120mm in diameter and weighing 16kg. The rest of the structure resembles a jigsaw puzzle which is built around this primary structural element. In terms of controls, the systems used are fairly conventional C-Class, but with simplifications. What drove the design of the wing throughout was weight reduction and we tipped the compromise slightly towards this rather than pure aero efficiency. Every control system must earn its place on the boat.
Systems
As on most modern C-Class designs, the mainsheet controls not only the angle of attack of the wing but also camber. Wind pressure forces the wing to essentially fold and create the angle between the front and rear elements, which also makes the system self-tacking and so reduces the crew work- load. A camber control is added to limit and adjust this angle between the two elements; I guess this is the hard-sail equivalent of the downhaul or Cunningham.
In addition, the flap (rear element) can be twisted using a similar system to the camber, to alter lift distribution along the wing. This is the equivalent of changing the leech tension on a soft sail.
One of the beauties of a C-Class wing is that this last control is independent of other variables like camber or mainsheet tension, making it much easier to fine-tune. One control that we dispensed with early on was front-element twist. In the past this has proved indispensable, as so cleverly demonstrated by Steve Clarke’s Cogito when it first appeared 20 years ago. But for us it was defined more by increased complexity and added weight.
Our choice was also guided by studying current C-Class performance; with speeds drastically increased thanks to hydrofoils, today’s boats are easily hitting ratios of boatspeed to true wind of 2.5 to 3. This means that the apparent wind downwind is continually moving further forward
(almost equivalent to upwind), which in turn drastically reduces the wind shear effect. So instead of twisting the front element we played with the planform shape of the wing (with a cutback in the leading edge) to get a bit of ‘natural’ or geometric twist into the shape.
Looking back at Falmouth two years ago, another interesting concept intro- duced by the Groupama team was their wing-canting system. This almost went unnoticed because of the big interest generated by the hydrofoils but it does offer a significant increase in power. In fact, the Invictus team considered adding this system to their boat in 2010 – Paul Larsen even tested it on his A-class. How- ever, in the end it was not implemented because of lack of time. For Rafale this is something we definitely want to add, but at this stage this is not a priority. The immediate objective is to get on the water with a reliable boat and work from there. A lot of work has also gone into our hydrofoil control system. First, we needed to design a centreboard case to allow us to control both the angle of attack and cant- ing angle of the foils – and because this was our first hull we didn’t want too complex a system. The control of our hydrofoils is simple, but with J-foils we still require three variables: angle of attack, cant and depth. We use an elastic system to ensure our foils default to a neutral angle of attack and neutral angle of cant, with a simple pulley system inputting different angles. (At the moment it is too early to say whether our main foil control will end up fully active or whether we will continue to use it in a more passive way, as a tuning tool rather than full-on ride height control as on the AC72s).
In terms of lifting the windward foil we implemented a similar system to the Hydros and Groupama teams back in 2013, in other words the lifting is done by the weight of the crew on the trapeze line. Again we chose to control the angle of attack of our rudders with a pulley system, but this will not be fully active – it will stay fixed once sailing.
First we should clarify our situation. Our university (ETS) gave us space in the main workshop, plus access to specialist areas including a paint shop, sanding shop, welding area (all of which we of course share with other students). So we enjoy good conditions to complete our project… but, don’t forget, we are still building a lightweight 25’x14’x45’ racing catamaran on university premises. In terms of the rest of the faculty, we are still rather prominent when we move around our hull (27ft, 850kg) and spar moulds (33ft, 100kg). We need to carefully plan every task to avoid problems, making sure we have enough people on hand to manage all the elements. To summarise, we started the manufac- turing process in July 2014 with the plug for the starboard test foil. We delivered this to Mystère Composites, who made the mould and laminated the first foil (trialled on Espadon in November). We had lami- nated our two beams in carbon pre-preg by mid-January this year. In the same time we also machined the aluminium moulds for the rudders.
For most of us this was all a new experi- ence. We didn’t have any background in composites manufacturing so there was a lot of trial and error (lots of error). Also, finding an autoclave big enough for the beams and mast has not been easy. Since January we have been preparing the hull moulds… long and precise work. The surface finish must be perfect so we spend many hours applying filler before repeatedly sanding it back by hand. The thermoforming of the core-cell has just been completed. Now we are doing our first experiments as we learn about resin infusion. For our first ‘trial’ hull we will manufacture in fibreglass. In parallel, we recently finished the plugs for the second generation of foil. We will shortly infuse them, with supervision from Mystère Composites.
Recently the manufacturing of the mast has started. We received our spar ‘mould’, a 33ft aluminium conical pipe, and the first carbon pre-preg plies have been cut. Once again we had to adapt to what we could fit in the shop (some plies exceed 40ft). The mast was laminated last week in less than 36 hours, running three continu- ous shifts. Here again we have to give a big thank you to Bombardier Aerospace for allowing us to piggyback one of their auto- clave cycles to cure our mast.
So far we have overcome many big chal- lenges. Many more lie ahead. But our team is really starting to come together and we are making good progress, learning every day. Our goal is slowly becoming real… which is both exciting and scary. But at every step of the way somehow we have so far managed to react quickly to problems and find solutions. We are excited and proud about what has already been achieved by our enthusiastic little team. Tristan Vanderhaeghe, Xavier Grossman, Simon Joncas and Sylvain Viallon
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