The 12-metre class yacht "Australia II" (KA6) was the winner of the 25th America's Cup in September 1983, the first successful challenger in the Cup's 132 history, beating the defender Liberty of the New York Yacht Club (NYYC) and ending the longest defence of a sporting trophy in history.
When Australia II arrived at Newport shrouded with much secrecy, under yachting rules, the New York Yacht Club were allowed to inspect the yacht once. The Australian syndicate scheduled the inspection for 2 a.m. in the morning, without telling the NYYC until too late, which subsequently they were unable to see the keel before the race. Rumours then circulated in the press that the Australian challenge was using a new radical type of 'winged keel', that was not legitimate. During the contest, the American syndicate led by captain Dennis Conner, sailing the 12-metre Liberty, took the Australian team captained by John Bertrand, and financed by Alan Bond to court, over the design origin and legality of the use of the yacht's keel. Under the NYYC sailing rules, '... a yacht should be designed by residents or citizens of the nation it represents', otherwise it would be disqualified. The courts were unable to prove conclusively the foreign origin of the keel, and the case by the NYYC was subsequently dismissed, before the finals race. In the final, the Australians recovered from a bad start to win the America's Cup 4-3 in a best-of-seven format. The Australian media subsequently branded the NYYC as 'sore losers'.
In October 2009, a Dutch marine architect Peter van Oossanen, claimed that the winged keel was not designed by chief Australian architect Ben Lexcen, as previously believed, but rather a group of contracted Dutch designers based in The Netherlands. This keel was also tested in tanks in secret in The Netherlands. Oossanen has also stated that Bond had paid him AU$25,000 not to say anything to the public at the time.
- McDonald, Timothy. Dutchman claims Australia II keel design, ABC News, Australian Broadcasting Corporation, 14 October 2009. Retrieved on 4 October 2013.
- O'Loughlin, Toni. Australian 'did not invent winged keel on yacht that won America's Cup', The Guardian, Guardian News and Media Limited, 15 October 2009. Retrieved on 4 October 2013.