Alinghi unveil their AC Cup boat

The months of conjecture are over. Yesterday in Villeneuve, Switzerland, the World got the long awaited first glimpse of Alinghi’s radical new AC33 defender.

In very general terms the boat is what may have been  expected - a scaled-up D35. But while the D35 tries to be effectively a trimaran without a centre hull, the new Alinghi goes substantially further down this concept route with a catamaran that is 90ft long and somewhere between 70-90ft wide (many think she is more or less square but this is so far uncertain having only had to opportunity to get a perspective from the bow, and no measurements being given)

So why an ultra wide catamaran? How much sail a monohull can carry in a particular wind strength is determined by bulb weight, draft and to some extent by beam. For multihulls without keels, righting moment is achieved principally by the extent of the beam and this is one reason why in the past trimarans have typically been faster than catamarans - very simply, they are wider. With trimarans the main hull is structurally useful for supporting the cross beams, handling fore and aft rig loads and stepping the mast and being a convenient place to mount a daggerboard, however, when sailing, the hull itself represents unnecessary hydrodynamic drag and weight; two items fundamental in making a multihull go quick. So in theory if you could remove that centre hull, but keep the rest the same…

The D35s are a half way house towards this goal, having a centre hull, more of a fore and aft strut, out of the water, but strong enough to enable the forestay to be cranked up.

With a beam of 6.9m or 65% of LOA (excluding the racks taking it out to 8.74m), the D35s still had some way to go towards reaching a typical racing trimaran’s beam and righting moment potential. And this is why the new Alinghi cat will be such an engineering masterpiece if she works. She has an unprecedented beam for a catamaran of her size, but her success will depend upon how well her structural engineers have succeeded in riding the possibly very fine line between making her crossbeams too strong and thus too heavy, thereby killing her performance, or, worse, too light and susceptible to breakage.

When pitted against BMW Oracles trimaran next February it will make for an interesting contest – if only of technology.

Watch this space!