Oracle Racing chief executive Russell Coutts sent one of the nimble AC45 into a cartwheel during an informal race against skipper James Spithill as they began practicing in San Francisco Bay, where they will be during June.
"We'll be duking it out and trying to beat the hell out of each other to get these guys ready to go and race the cup," Coutts told reporters before the capsize left a damaged sail and sent one crew member to hospital for x-rays.
"Everyone's wearing helmets for a reason, there's a significant amount of risk," said Spithill.
"They're the fastest boats out there at the moment, and to get the most out of them you have to push."
Oracle Racing, backed by billionaire Larry Ellison, designed the 45-foot boats - with hard sails shaped like an airplane wing - as part of broader efforts to attract more viewers to the America's Cup.
Built in New Zealand, this is their first US appearance.
Standardizing the boats used in sailing's most prestigious event is meant to put the focus squarely on sailors' talent instead of the technological advantages of their designs.
The competition has been reorganized to attract sponsors put off by bitter legal wrangling that clouded the 2010 Cup won in Valencia by Oracle.
Competitors will use the new 45-foot carbon-fibre catamarans in the 2011-2012 Americas Cup World Series starting in Cascais, Portugal in August, with larger AC72 72-foot catamarans, which have yet to be built, raced the following year at the America's Cup in San Francisco.
Changes also include shorter races, independent race management with an international jury and cost-cutting measures such as limits on the number of boats, sails, equipment and support vessels.
The winner of the Louis Vuitton Cup, held in San Francisco Bay and starting in July 2013, will race Oracle, the Golden Gate Yacht Club's defending team, in the America's Cup in September.
BMW Oracle won the last America's Cup racing a giant trimaran featuring a 20-storey wing sail.
But that Cup was overshadowed by more than two years of legal battles between Ellison and biotechnology tycoon Ernesto Bertarelli, owner of Swiss team Alinghi.
Wranglings over the hosting rights and race rules resulted in a rare two-boat match without the usual challengers series that had helped increase interest in previous editions, costing millions in potential sponsorship and broadcasting rights.
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