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.
Simpson, 36, served as the Swedish team's strategist.
"The entire Artemis team is devastated by what happened," CEO Paul Cayard said in a statement on the team's website. "Our heartfelt condolences are with Andrew's wife and family."
Cayard didn't take questions during a brief news conference Thursday evening and didn't return telephone calls.
British newspapers reported that Simpson is survived by a wife and an infant.
Artemis Racing said doctors "afloat" with the team and on shore were unable to revive Simpson after he was freed from the wreckage. The other sailor suffered minor injuries, and the rest of the crew of about a dozen people was accounted for and taken back to their dock in Alameda.
Officials said winds were blowing between 15 and 20 knots (17 to 23 mph) when the boat capsized. The National Weather Service later issued a small-craft advisory, warning inexperienced mariners to stay off the bay and indicating winds of between 21 knots and 33 knots (up to 28 mph).
The Artemis boat flipped in winds of about 20 knots near Treasure Island, which is bisected by the Oakland-San Francisco Bay Bridge. The armada of rescue boats and helicopters were visible from the roadway.
Simpson and the unidentified injured sailor were brought to shore as the St. Francis Yacht Club in San Francisco, where paramedics performed CPR on Simpson. He was pronounced dead a short time later.
This is the second time a sailor has died during training for the America's Cup. In 1999, Martin Wizner of the Spanish Challenge died almost instantly when he was hit in the head by a broken piece of equipment.
No deaths have been recorded during the actual racing since its inception in 1851.
Simpson and his partner Iain Percy won an Olympic gold medal for England in 2008 in the Star class of sailing. The duo was expected to repeat in London in 2012 but was upset by a Swedish team and settled for silver.
Percy is Artemis' director and the boat's tactician. The team announced Feb. 23 that Simpson was joining Artemis to "provide weather and tactics support" to the crew.
A month later, Simpson tweeted: "Moving the family to San Fran for 6 months is pretty hectic!!! The cup should be fun though!!"
Artemis Racing has had its share of upheaval in the buildup to the 34th America's Cup. Late last year, skipper Terry Huthinson of Annapolis, Md., was released. He was replaced by Nathan Outteridge of Australia, who won a gold medal at the London Olympics.
The team has had technical problems, as well. Last fall, Artemis said the front beam of its AC72 catamaran was damaged during structural tests, delaying the boat's christening. A year ago, Artemis' AC72 wing sail sustained serious damage while it was being tested on a modified trimaran in Valencia, Spain.
This also wasn't the first America's Cup boat to capsize on the hard-blowing San Francisco Bay. Oracle's $10 million boat capsized in 25-knot winds in October, and strong tides swept it four miles past the Golden Gate Bridge. No one was injured, but the rough waters destroyed the 131-foot wing sail, and the boat was sidelined until a new sail shipped from New Zealand was installed in February.
Stephen Barclay, CEO of the America's Cup Event Authority, said officials were investigating Thursday's accident. He said it was unclear what effect the death will have on the America' Cup races, which are scheduled to run from July to September.
It was too soon to answer questions about the safety of the high-tech boats on the San Francisco Bay, Barclay said.
"Obviously a catamaran is more prone to capsizing than a mono-hull," he said. "Whether boats are safe or unsafe, we're not going to speculate on those things."
In addition to sailors wearing crash helmets and life vests, chase boats carry doctors and divers, Barclay said.
"There are lots of precautions that are taken, and some of those are as a result of Oracle's mishap last year," he said.
The boats participating in the latest America's Cup more resemble a space craft than the traditional sloops that historically competed for the trophy.
Financed by billionaire Larry Ellison, Oracle Team USA won the 2010 cup and made several changes to the races this year in an attempt to make the staid competition more fan- and TV-friendly.
While much faster and more exciting than the sloops, the catamarans have proved hard to handle. The wing sail looks and acts like an airplane wing, improving the yacht's speed and manoeuvrability. The 7-ton boat's hulls are lifted out of the water and it skims along the waves on "foils," reducing the drag on the boat and increasing speed dramatically.
Coast Guard Lt. Jeannie Crump said the agency did not know the extent of the damage to the Artemis boat. A commercial salvage boat would tow the vessel to Clipper Cove, between Yerba Buena Island and Treasure Island, Crump said.
She added that Coast Guard officials weren't sure what caused the boat to capsize. The Swedish team has two boats, she said.
Associated Press writers Terry Collins, Sudhin Thanawala and Garance Burke contributed to this report.