A statement from Swedish team Artemis Racing, which owns the 72-foot-long AC72 class yacht Simpson used Thursday, said the 36-year-old British sailor was trapped under the vessel when it capsized in strong winds, the team said on its website.
"Despite attempts to revive him, by doctors afloat and subsequently ashore, his life was lost," the statement said.
"The entire Artemis Racing team is devastated by what happened," said Paul Cayard, a veteran U.S. sailor and chief executive of Artemis. "Our heartfelt condolences are with Andrew's wife and family."
Simpson had been on a training run Thursday for the America's Cup, a race scheduled for this year in San Francisco.
Simpson won the gold medal in sailing in at the 2008 Olympics and took the silver in 2012. He also was the gold medalist at the 2010 World Championships in Brazil.