Call it a second-skin, a prosthetic underbody extension or even an outer shell but the latest design innovation sported by Team New Zealand, and now replicated by the Swiss Alinghi and Larry Ellison's Oracle BMW team, is one of the most creative circumventions of the design rules in 151 years of America's Cup racing.
"We don't really want to talk about our boats. We've got to keep pretty tight on this," says Tom Schnackenberg, boss and design leader for the America's Cup defenders, who had fervently hoped to keep the ruse secret until the official unveiling ceremony on 7 January.
Russell Coutts, TNZ's skipper last time and now in the opposing camp with Alinghi, says: "There is not a designer in Auckland who wouldn't say 'that's got to be faster' when they see this development." Team New Zealand incorporated the ruse on NZL 82, the last of the current crop of Cup boats to be launched, but Alinghi are thought to have retro-fitted one on SUI 75, as have Oracle BMW on USA 71.
What the teams have been able to do is have a completely separate piece of the hull counted as an appendage under the America's Cup Class rule. The purpose is two-fold. Firstly, where the normal hull is constrained by the measurement rule with data obtained at pre-determined points, the extra false skin means the boat is actually a different shape from that 'seen' by the rule. Secondly, the volume in the hull is re-distributed so that the boat is faster.
Even if an extra piece of false hull adds drag through additional wetted surface, this is more than offset by the hull having more effective sailing length, one of the most powerful generators of speed in yacht design.
The America's Cup Class yachts have unusually fair shapes because the ACC rule expressly prohibits any discontinuities of shape such as hollows, bumps and creases which are the normal ways of tricking a measurement rule in other classes of yacht. The 'no hollows' clauses in the ACC rules is very influential.
The only exception is that hollows are permitted some 250mm either side of an appendage, which are the normal rudders and keel fins located on the yacht's centreline. The class rules imposes a limit of two moveable surfaces which means that, in all 82 yachts built to the ACC rules since its inception 10 years ago, one of these vertical foils has been used to steer the boat and the other to be set at an angle of attack to generate lift.
But in a breathtaking piece of lateral thinking, TNZ's designers realised there was no limit on appendages that didn't move. Since changes of shape were allowed 250mm on either side, they reasoned 'why not actually suspend an entire false section off the bottom of the hull and call it an appendage?'
This could be done under the entire length of the hull between front and back measurement points, or at the bow and at the stern - it's thought that the three teams are concentrating only on the after underbody at present.
Radical it maybe, but the ruse is legal. The Kiwi Cup holders asked ACC technical director Ken McAlpine for a confidential interpretation, No 5, which he issued on 8 October 2001. Such interpretations remain confidential or until racing starts, so TNZ's cat was let out of the bag two months ago.
Alinghi skipper Russell Coutts confirms that the Swiss team had already drawn similar prosthetic pieces of hull over a year ago, but anticipated that McAlpine would not agree to them.
"When the interpretation was published, we thought 'Hell, we should have pursued this a bit further. Rolf's (Vrolijk) really keen on it," explains Coutts. "We're fortunate in that we'd considered it really thoroughly in the early days."
Crucial to making these falsies work is the engineering required to fit them around the proper hull as closely as possible so that the water flowing past bridges the gap with minimal disturbance. McAlpine's interpretation expressly prohibits such devices from actually touching the hull other than at their centreline attachments.
Schnackenberg was a senior member of Alan Bond's history-making Australia II campaign in 1983, when the Aussies had an upside-down winged-keel. They managed to keep this largely secret, going on to end the New York Yacht Club's 132-year tenure of the Cup. Then, a yacht only had to be presented to a class measurer and approved.
"There is a lot more awareness now that the game has ramped up so much," concedes Schnackenberg of the failure to keep the device secret for longer. "And in 1983, there were no confidential interpretations that were then later published while racing was going on. But the America's Cup is the America's Cup: there is always development going on."
Tim Jeffery, 16 December 2002
