A 72-foot catamaran being sailed by America's Cup champion Oracle Racing has capsized on San Francisco Bay.
While some of the crew were thrown into the water, all are accounted for and there are no serious injuries, according to a statement released by the syndicate.
The boat was being skippered by Jimmy Spithill, who led Oracle to a two-race sweep of Alinghi of Switzerland in 2010 to bring the America's Cup to San Francisco.
The syndicate said the boat was carrying 11 crew and possibly some extra sailors and designers.
Tactician Tom Slingsby says the wing sail was badly damaged. The boat pitch-poled, or tumbled end-over-end.
"Luckily everyone is accounted for, no one hurt. Wing is pretty badly damaged. Working to get #AC72 back to Pier 80" Slingsby said in a press release.
"We called for a bear-away as we were out training. The winds were blowing about 25 knots, and there was strong ebb current at the time. We started the bear-away, and as the boat accelerated it pitch-poled.
"We didn't know what was going to happen with the new boat. When the nose went down, the wing hit and a few guys went in the water. We were unsure if the wing would snap, so we all climbed off the boat."
Oracle is testing its 72-footer for the 34th America's Cup next year. The America's Cup World Series is being contested in 45-foot cats, and there have been a number of capsizes.
Some reports say the catamaran is worth an estimated $US8-$10 million.