Team New Zealand have made significant gains in testing their 72-foot (22-metre) America's Cup catamaran, reaching speeds close to 40 knots (74kmh) and apparently sailing foil-borne.

The achievements came in just their fourth day out on the giant boat on Auckland's Waitemata Harbour and created a buzz around the team and the international sailing community.

The speeds were achieved in winds of about 20 knots.

“It's been a big step,” Team New Zealand boss Grant Dalton said.

“We were in the high 30s; we didn't touch 40 but we were close at one stage. But it was fair flying.”

Dalton said only the team's largest chase boat could stay with the cat at top speed and he was encouraged at the way it not only performed but came through damage-free under the stresses involved.

Team New Zealand veteran Tony Rae admitted it was a new experience.

“You've got no idea of how fast you are going. You've got no real sensation of pace . . . until you look down and see the speedo or the water going underneath the boat,” Rae said.

“The more you sail the boat, the better you get at it . . . changing direction, gibing, tacking and that sort of thing.

“It makes it feel like a better day's sailing every time. I think it's going to come along in leaps and bounds really.”

In the hush-hush world that envelops America's Cup development, Team New Zealand are coy on any details of using the foils, which are essentially L-shaped dagger boards that have a hydrofoil effect of lifting the hulls out of the water, reducing drag and increasing speed.

Team New Zealand have experimented with them in their 33-foot catamarans and America's Cup holders Oracle have also done extensive trialling in their 45-foot cats. Oracle are also using them on their AC72 that was launched last week but reportedly damaged a foil in trials.

Photographs published on Sail-World.com show Team New Zealand's AC72 hurtling along with both hulls out of the water. Their research on a series of 25 photographs suggested the AC72 was fully foil-borne for a distance of more than 1.5 nautical miles (2.8km).

“The achievement would appear to give Team New Zealand a significant jump on the other teams, only one of which [Oracle] is currently sailing,” the website reported.

Team New Zealand are in a race to squeeze data out of their new AC72 before building starts on their second cat, which will be used in next year's America's Cup in San Francisco.

- © Fairfax NZ News