Opposite/above: through the World Series racing and early practice Team NZ stuck with their concept of small, straight foils with a forward-extended bulb at the foil/arm intersection. They have also tried moving this intersection fore and aft on the arm for reasons explained in Dave Hollom’s article in the previous issue. Note too how refined the ends of the arms are on the New Zealand design, tapering down sharply approaching the bulb – the Kiwis aim to fly so that this fine section sits where air and water meet and drag can be very high. In the World Series the Ineos team carried their Stuka wings (left) with a kink at mid-plane. These foils are also believed to have been flexing badly, probably not helped by the complex hinge mechanism needed with a dual plane flap
a boat without any documents from the naval architect’s office. Yet it seems that now the design teams are increasingly composed of hydrodynamic and aerody- namic engineers, and that the share remaining for the architects is getting smaller and smaller. For my part I’ve never spent so much time trying to understand the shapes of these yachts. And I cannot, as usual, refer to the per-
sonality of the naval architect. It is impos- sible to confuse a William Fife plan with a Nat Herreshoff plan. But here ideas fly as much as boats do, and each one exploits a strong idea so as not to slow down and when you do then to quickly regain speed.
Britannia 2 The first Britannia was an extraordinary craft, looking rather like the aerodynamic roof box on your motor car. Their other idea had consisted of digging a tunnel along the centreline to increase the surface
area of the lower part of the mainsail. As a result the mast support was raised on a console. Indeed, the rule provides that the foot of the mast should be at least 1.5m above the measured waterline. By lowering the central part of the deck it is possible to gain more than 2m2
of sail. However, this solution had some draw-
backs – the sailboat won the prize for the largest hull shell, and in general this is not a desirable goal. From an aerodynamic point of view the ‘roof box’ solution is not a panacea. The hull, very wide at the back with a fairly round hull but quite flat lower sections, stuck to the sea before take-off and hit the water very hard when it landed. Very quickly it appeared obvious to add a central ‘hull’ or large skeg to reduce the effects of these situations. For the second yacht, Britannia 2, the
design team completely revised its philosophy, more so than the other teams. On top the wind corridor is gone, at the
bottom is a large, flat-bottomed keel which starts under the bowsprit, widens quickly as it deepens before reducing and turning into a rather old-fashioned bustle in front of the rudder. The hull itself is matched beneath it with a second, nar- rower hull, which starts in front of the foils and dies away aft. In fact, the sailboat is composed of three hulls superimposed. As all the competitors can see, the AC75
does not require width at the waterline at rest. The arms and foils act as stabilisers. This is a concept that was taken into account very little in the first generation, but which everyone has since integrated. A great deal more aerodynamic work
has also been undertaken, for good pene- tration through the air, and for the end- plate effect between the sails and the deck to be as efficient as possible. To make this concept fly, large foils have been retained, to start with using a pair of ‘kinked’ Stuka wings out at the side. Theoretically for maximum dynamic stability… After a poor performance before Christmas Stuka wings do not reappear for the Prada Cup.
SEAHORSE 61
GILLES MARTIN-RAGET
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