A Dutch naval architect say his team designed the winged keel behind Australia's win in the 1983 America's Cup, not the Australian credited for it.

Australian boat designer Ben Lexcen was famous for inventing the winged keel on the winning yacht Australia II.

But now marine architect Peter van Oossanen, who worked with Lexcen, says it was his team of Dutch designers who invented the upside down keel, and Lexcen played only a minor role.

The Dutchman says he would have taken this information to the grave, but was compelled to speak out after more than two decades when letters and articles started appearing, claiming he had nothing to do with the famous design.

"For me, that was enough reason to say 'well all right, let the facts come out, let the truth come out'," he said.

He says Lexcen originally abandoned a radical redesign of the previous America's Cup entry instead opting for a more cautious approach and then changed his tune when the Dutch team began having some success.

"Ben said to me 'well you go ahead and do the difficult approach. I will look at the small refinements in the hope of finding a better boat for 1983'," he said.

"And after a few weeks he really, really wasn't very interested in what we were doing and he went back to Australia.

"He came back to us later on when we reported very good things but he had, in other words, very little to do with the winged keel at all."

But in an interview with the ABC in 1983, Mr van Oossanen played down his involvement in the design.

"We evaluated Ben's designs, we did calculations for him, and we didn't do anything out of the ordinary for him."

'Skulduggery'

At the time of Australia II's win, rules required that each yacht be designed by citizens of the country it represented.

Mr van Oossanen says everyone in the team, from financial backer Alan Bond to the crew, knew that the involvement of Dutch designers was possibly in breach of the rules.

But he says their enthusiasm and his own was enough to keep the extent of their involvement secret for all this time.

He says the America's Cup has always been rife with skulduggery and the victory should stand.

"The America's Cup has always been a devious affair with a lot of political problems, with the feeling in the Australian camp that we were giving the New York Yacht Club and the Yanks something of their own, of their own behaviour," he said.

John Bertrand was the skipper of Australia II 26 years ago. He has told AM he is confident Ben Lexcen was the yacht's principal designer.

"I regard Ben as the Leonardo da Vinci of this country in so many ways," he said.

"Ben used many consultants in many areas which he had - a very complex project designing the America's Cup boat.

"Ben was the man who pulled all the elements together that was required to finally pull that package together, which included the winged keel."

Mr Bertrand says the Dutch team played a consultant role and that was par for the course in those days.

He says the Americans were doing it too as was every other team.

"So were the British and so were the French and so were the Italians. It just went on and on and on. All part of the overall requirements," he said.

He says Australia II's victory has long been mired in controversy, but every investigation has always vindicated the victory.

"Administrators have gone back a million times, I can assure you that over, particularly during the hiatus of the America's Cup and I am totally confident on that," he said.

Evidence

A yachting expert says the evidence proving that Ben Lexcen designed the winning yacht is stored at the West Australian Maritime Museum.

Yachting journalist and author, Rob Mundle, says all evidence points to the Lexcen taking the credit.

He says it is not the first time the Dutch naval architect has made the claims.

"There's no grounds whatsoever for any investigation. The New York Yacht Club did their level best in 1983 to have the yacht disqualified and couldn't find any evidence," he said.

"And beyond that, if they want to take it further, all the documentation exists to prove otherwise. Communications with the Netherlands ship basin. Everything else - it all exists in the West Australian Maritime Museum."

Australian sailor Sir James Hardy, who was part of the Australia II team, says while the Dutch team worked on the keel's wings, Lexcen turned the keel upside down.

He says the yacht featured technology other than the keel which contributed to its success.

"The upside down keel, the stability it gave Ben's little 12-metre was the main thing rather than the wings," he said.

"I mean Peter's no doubt saying what he believes happened, but I can tell you that Benny's hull shape and everything and his ability to make sails - You wouldn't know which piece of coal made the whistle blow."