Interesting stuff from that article above Philip, thanks. Obviously that's reason why ETNZ is so much faster/better at foiling. Why LE didn't hire M+M is beyond me, but I'm sure he had a reason...?

One of the team's early hires was designer and foiling expert Pete Melvin, who had worked on Oracle's successful 2010 campaign and was commissioned by Ellison to create the guidelines for the cutting-edge, double-hulled AC 72 yachts used in the 2013 Cup. "That was the target for us," said Grant Dalton, the team's managing director. "What's this thing supposed to look like? The best way to find that out is to go to one of the guys who wrote the rule in the first place."

A former U.S. Olympic sailor, Melvin said he was unsure whether the boats, which were speedy but unwieldy, would be able to achieve stable foiling. But Melvin said his team found a way to do it six to eight months ahead of the competition. The Kiwis tried to hide the breakthrough from their competitor's spy boats, so they foiled only when they thought the scouts were out of sight.

The other three teams in the Cup eventually replicated the discovery, but the Kiwis do it better, especially upwind, said Chris Draper, the helmsman of the Italian team Luna Rossa, which New Zealand eliminated in a preliminary round.

To sail upwind, a boat zigzags, making a series of turns called tacks. When New Zealand tacks, it keeps one hull above the water and stays at 10 knots or above, Draper said. But when Oracle tacks, both hulls remain in the sea and the yacht slows to around nine knots, Draper said, because Oracle's foiling system is more rudimentary. The Kiwis "are able to achieve a tack that will be very hard for Oracle to replicate," Draper said. "Oracle's going to have to sail exceptionally well to win this."