America's Cup holders Team New Zealand are causing a stir in the Hauraki Gulf with a radical piece of new technology that threatens to turn the competition on its head.

Although still shrouded in mystery, Team NZ's boat - which will race against the winner of the Louis Vuitton Cup in February - is thought to have a false hull to enhance performance.

And concerned challengers Alinghi, OneWorld and Oracle are known to be researching the breakthrough design to try to keep pace.

I'd like to think they found out by legitimate means Tom Schnackenberg Team NZ syndicate head

New Zealand syndicate head Tom Schnackenberg had hoped to keep the "Kiwi clip-on" secret until the America's Cup proper.

But although Team NZ have reportedly threatened Swiss bid Alinghi with formal action for breaches of Cup surveillance rules, Schnakenberg accepted that rivals could have discovered the design by "legitimate" means.

"I'd like to think (they found out) just by legitimate means, by looking at us from outside 200 metres when we're sailing and using logic," he said.

"We would've hoped that nobody would figure out our boats until after the Cup. But the reality is that people may well have learned or deduced what we were doing a lot earlier."

Kiwi Coutts now skippers Swiss bis Alinghi

Louis Vuitton Cup finalists Alinghi have already admitted to testing and finding potential in the innovative design - a partial false hull that alters the distribution of a boat's buoyancy.

Oracle owner Larry Ellison, meanwhile, said in a statement on Tuesday that reports that his team had the same technology were "speculative and inaccurate".

The San Francisco-based outfit face Seattle's OneWorld in a best-of-seven semi-final repecharge which starts on Friday.

The winner will take on Alinghi in January for the right to challenge Team NZ.

Whoever that challenger turns out to be, there is a fair chance that their boat will now sport a version of the "Kiwi clip-on".

However, OneWorld have played down their interest in the design, saying they were "not convinced of its effectiveness".