If Ineos UK were trying to underplay their performance during the World Series they succeeded… not likely given the frantic few weeks’ work the whole team then had to put in before the start of the Prada Cup. Also shown at the bottom of the drawing below are the double-cranked foils used on Britannia during the early races. If as we understand foil flexing was a big issue then it seems certain that Ineos partners Mercedes Petronas F1 (in which Ineos now own a one-third stake) would have been called in to help resolve a problem in an area in which they are world leaders – controlling local and global rigidity in highly loaded composite foil structures
ition unstable. Ever since I watched my first America’s Cup Class boats crossing under spinnaker in Auckland I’ve known that nothing is predictable on the water. For their second yacht the Americans
chose to refine the forward shapes enor- mously while keeping the wide deck, just within the maximum allowed beam. There isn’t a single place where the hull or the hull shape would be flat. All the surfaces are rounded to perfection. The keel starts under the bowsprit and is thin, plunges almost straight down to the location of the arms of the foils and then rises up on the hull before disappearing three-quarters of the way to a shallow transom. The keel with its sharp blade will be extended further aft before the start of the Prada Cup. The deck of the yacht is slightly hollowed out to gain sail area and lower the centre of gravity. At rest the AC75s all sit level. But, in
flight, pitch develops and the boats gener- ally tilt forward by at least 1.5°. Some- times pitch reaches 5°, but rarely for very long. Luna Rossa tilts a little less and Patriot tilts forward the most, more still after the changes made for the Prada Cup. In our line drawing one can clearly see
the narrow waterlines, with a pinched entry. The foils are wide, V-shaped and thin, with a bulb in the centre and two small winglets folding up at each end.
Luna Rossa 2 The Italians had opted from the outset for a long keel and a rather symmetrical silhouette fore and aft, with the freeboard at its maximum at the foot of the mast. The cockpits are divided up as we see on the big multihulls, allowing a very tight seal between the mainsail and the convex deck in between. Like the profile the hull shape of the first Italian boat is almost symmetrical under the waterline. Version 2 does not show radical change,
Patriot The first version of the AC75 in the New York Yacht Club challenge focused on the aerodynamic problem. A big bar of soap shaved away to exploit the limits of the rule in a shape with the least resistance. The first reaction of Bruno Troublé
62 SEAHORSE
when he learned that the next monohulls would fly had surprised me, he was con- vinced that only the foils would count, a farewell to the naval architects! However, it is not so simple to remain stable and in the air – the sea and the wind are by defin-
but the keel, still V-shaped, is deeper, and the hollow below the bow is more marked making the forward waterlines more pinched. The foils remain with an inverted V-shape with a generous surface area, and with no bulb the ballast is integrated into the arm and the foils, which are again equipped with small winglets at the end.
Te Rehutai The shape of the Defender’s first boat, Te Aihe, had surprised us: an inverted multihull bow, a big canoe hull beneath a
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