Two sailors from America's Cup holders Alinghi were injured when the multihull the team were training on capsized off the French port of Lorient on Saturday.
Piet van Niekerk and Francesco Rapetti were airlifted to hospital but escaped serious injuries when the 60ft Foncia rolled in 20-knot winds and lumpy seas.
The remaining crew clung to the netting of the trimaran before being rescued.
Alinghi are set to race BMW Oracle in a controversial catamaran series for the next America's Cup.
Swiss syndicate Alinghi, who have little experience on multihulls, were training under the guidance of French expert Alain Gautier.
"As we were bearing away, always the highest risk situation on a multihull, both the leeward and the central hull dug into the water and the rudders came out," said Alinghi's Ed Baird.
"From then it was out of our hands and we capsized forwards. As the mast hit the water, it broke, followed by the rear beam.
"The crew reacted very quickly in getting everyone back on board, doing a head count and checking injuries before calling for help and beginning to secure the boat.
"We have all been through crashes and capsizes before, this is all part of the sport."
Alinghi and BMW Oracle are embroiled in a legal battle to decide the format for the next staging of the America's Cup.
Alinghi beat Team New Zealand to win the Cup in its normal multi-team format in monohulls in 2007.
But since then the proposed 33rd staging of the famous event has been postponed after American syndicate BMW Oracle contested the protocol in court, becoming the official challenger in the process.
Because of the complex rules of the event, BMW Oracle and Alinghi are now set to race off in catamarans sometime this year or next before the traditional competition - with a challengers' series followed by a head-to-head final - resumes some time after 2010.
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