Oracle Team USA has denied an American journalist's claims they took out the 2013 America's Cup by breaking the rules.

Team New Zealand had been winning the competition but Oracle made an incredible comeback, winning 8 races in a row to steal the cup.

Bruce Knecht has written a new electronic book called The Comeback and says the team came up with a novel way to go about pulling off the ultimate come-from-behind victory.

The crew used a method called 'pumping', which flapped the yacht's wing providing extra propulsion.

Mr Knecht says it was key to Oracle's comeback, but there were also other contributing factors.

"It was one of the crucial factors that gave Oracle the edge and enabled them to pull off this incredible comeback."

But he says it was breaking the rules.

"They were moving it back and forth almost like a bird flapping its wing, and what that essentially did was convert human power into propulsion, something that is not permitted."

Mr Knecht interviewed crucial members of Oracle Team USA and says that they didn't necessarily know what they were doing was against the rules. He says because of that, the crew told him exactly what they did.

The practice wasn't picked up on cameras because the wing was being turned by the yacht's grinders.

"The so-called grinders are always turning those handles, constantly, and it's never clear exactly what they're grinding," says Mr Knecht.

He says the wings wouldn't have been visibly flapping because the crowds, cameras and journalists were too far away to tell.

"To move the wing against the wind was a big challenge. They were only able to do it because six members of the crew were working as hard as they could to turn the winches. Bringing in the wing, releasing it, bringing it in again, it essentially converted the power, the human power, of what those six guys were doing -- the strongest guys on the boat in fact -- into added propulsion" says Mr Knecht.

Oracle Team USA is currently sailing in Bermuda, and to say they're slightly bemused by Mr Knecht's claims is an understatement.

Spokesman Peter Rusch says Mr Knecht is referring to the wrong racing rules -- there was a specific edition written for the America's Cup, and pumping isn't in there.

Team NZ CEO Grant Dalton wouldn't be drawn on whether his team questioned the pumping, but commentators in New Zealand say course umpires certainly didn't.

"Within the sport everyone pretty much knows how the boats work," says commentator Peter Lester. "I don't think anything was missed, I just think a book's come out and he's looking for a bit of a rating game to sell a few."

So Oracle may have pumped, and pushed the limits, but it doesn't change the result.

Knecht is a former foreign correspondent and senior writer for The Wall Street Journal.

His new electronic book The Comeback: How Larry Ellison's Team Won the America's Cup has just been released.

Newshub.