A 72-foot-long, high-tech catamaran sailboat capsized Thursday in San Francisco Bay while practicing for the America's Cup races this summer, killing an Olympic gold medalist from England and injuring another sailor, authorities said.

Artemis Racing said Andrew "Bart" Simpson died after the capsized boat's platform trapped him underwater for about 10 minutes shortly after 1 p.m. Artemis and two other yacht teams each outfitted with multimillion-dollar racing boats that can achieve speeds of 45 mph are challenging defending champions Oracle Racing for the America's Cup, sailing's most prestigious trophy.