Left: two-time America’s Cup winner and longtime catamaran enthusiast Ernesto Bertarelli working up his new TF35 semi automatic foiling cat on Lake Geneva and (above) racing his D35 cat in the Bol d’Or. Note the way in which the vertical spar of the T-foil is radiused outwards so that as the working foil is lowered the horizontal foil is canted inward to increase sideways lift component and help to reduce leeway
figuration. This work was done using real historical wind data during known races, then evaluating how the new configuration would have done against the D35 fleet as a baseline or control. This highlighted the potential weaknesses and strengths for rac- ing a foiler against a conventional catama- ran with drastically different performance profiles. In the end the decision was made to go with the outward canted T-foil con- figuration as the right answer for the lake.
of the boat consists of Gonzalo Redondo (D3 Applied), Dirk Kramers (SDK Struc- tures), Luc Dubois, Adam May, Marc Menec and Jean-Marie Fragnière. The design group started as the team that put together a bid for a similarly sized boat for the Volvo Ocean Race inshore events. All of us have been passionate about multihull and foil sailing for a long time, and we have all been through the battles as the America’s Cup itself evolved from mono- hulls to DoG Match giant multihulls onto AC72s and AC50s and now the AC75… although often on opposing teams.
Brief Lake Geneva with its very light winds is affectionately known as the vacuum capital of the world. So why make a foiling boat for these super-light conditions, you ask? Good question! But a foiler it should be and the resultant brief for the project was a bit daunting: come up with a high- performing foiling boat with the exciting features that foils bring, while maintaining
the capability to win the Bol d’Or in light – often non-flying – winds. Who says you can’t have your cake and eat it too?
Concepts Given the owner-driver aspect of the fleet, we first proposed a four-pointer configura- tion. Much like an A-Class cat or the TF10 tri. This configuration is self-adjusting in terms of ride height and does not require active control. We thought this would be appropriate for the intended client base. By contrast, three-pointers with L-foils,
like the AC72/45/50 and GP50, need very intense ride height control by the crew – although they are potentially faster. After a few meetings with the owners
and their teams, it became clear that they wanted something more aggressive than the four-pointer! We next undertook a lot of VPP work
and (weather) routeing simulations to evaluate how much of a potential perfor- mance advantage the three-pointer has over the more conservative four-point con-
Control But what about the lack of ride height control with this configuration? All foilers, three-pointers in particular, require ex - treme concentration and lots of practice to keep the boats on their foils. Lapses of con- centration result in spectacular crashes – which is great for stadium sailing events. Well… since the owners and drivers of
these boats do not go to the gym every day, nor do they race simulators when not out sailing on the water as today’s professional America’s Cup or SailGP sailors do, we had to come up with another solution. The log- ical avenue is therefore a control system. As it happened, at the time we (at SDK
Structures) had been working on a full-fly- by-wire electric foiling motor boat for a year or so and we had a pretty good under- standing of what it would take to imple- ment such a system on a sailboat. Automated control systems are generally
not allowed in the sailing world, not even in the Cup; even the wands used on Moths are only allowed by special dispensation. So much credit goes here to the owners’ vision to see that a control system can benefit a class such as the TF35 just as it does the Moth class. The actuators we use are all electric, and the system battery pack is large enough for one-design sprint racing events,
SEAHORSE 53
LORIS VON SIEBENTHAL
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