He heard a crack, and the next thing Nathan Outteridge knew, the catamaran he was piloting was airborne.

As it rose and fell back into the San Francisco Bay, the 72-foot catamaran cracked into pieces, folding in on itself  ‘‘like a taco shell’’.

Then the Olympic hero from the NSW Hunter was in the water, along with 10 other crew members including his gold medal winning teammate Iain Jensen, their America’s Cup boat – Artemis Racing’s AC72 – in ruins and floundering.

A quick head count revealed one member of the crew was missing – Andrew Simpson – triggering a desperate search.

The British two-time Olympic gold medallist was trapped underwater, wedged underneath ‘‘a few tonnes’’ of carbon fibre, frantically trying to free himself.

His crew members could see him, fighting for his life and dived beneath the water to try to set him free.

They  handed the man they called ‘‘Bart’’ emergency oxygen bottles – which hold about 10 breaths each – in a bid to keep him alive in the hope rescue crews would arrive in time.

They didn’t.

The 36-year-old Briton, who was a strategist for Artemis Racing, was pronounced dead at the Saint Francis Yacht Club, after spending between 10 and 15 minutes underwater. Less than a year ago, Outteridge and Jensen were celebrating Olympic glory.

Now the Wangi Wangi duo were facing the tragedy of losing a teammate, and a friend.

Outteridge’s father, Tony, told the Newcastle Herald his son had called home early yesterday morning to explain what had happened and let his family know he was shaken by the incident but uninjured. ‘‘Nathan called this morning about 7am to let us know he was OK before we found out about what had happened another way,’’ Mr Outteridge said.

‘‘He was shattered, he said it was the worst day of his life.’’

Outteridge, Jensen – on board as a sail trimmer, fellow Australian Rodney Daniel, Simpson and several New Zealanders were on board the Swedish racing team’s America’s Cup catamaran about 800metres north of Treasure Island at 1.15pm. 

With the wind picking up, the decision was made to come in and Outteridge, who was at the helm, attempted to ‘‘bear away’’ – a nautical term for turning around with the wind, Mr Outteridge said. 

The catamaran, capable of speeds in excess of 70km/h, was executing the turn in a 20-knot breeze when it pitched under the water, tossing the vessel into the air and causing it to break into pieces. 

There is no suggestion Outteridge was at any fault.

‘‘Nathan told me [the turn] didn’t seem any different to any other occasion,’’ Mr Outteridge said.

‘‘The bow dug in a little bit but he said that’s not unusual.

‘‘The next thing he heard a cracking noise and the boat went on its side.

‘‘Before it capsized it snapped in half, Nathan described it as folding like a taco shell.’’

Artemis Racing CEO Paul Cayard said the team was devastated by what had happened. 

‘‘Simpson was trapped underneath the boat and despite attempts to revive him, by doctors afloat and subsequently ashore, his life was lost,’’ Mr Cayard said.

‘‘Our heartfelt condolences are with Andrew’s wife and family.’’

A second Artemis crew member, New Zealander Craig Monk, suffered minor injuries.

Mr Outteridge said his son was good friends with  Simpson, who along with bowman and best mate Iain Percy claimed silver in the star class at the London Olympics last year. 

He said Nathan was unsure if he was going to compete in the 34th America’s Cup, which begins in July in San Francisco.

‘‘I hope that he will, I think Bart would want them to continue doing what they’re doing,’’ he said.

‘‘Nathan’s so passionate about sailing but he’s not in good shape mentally at the moment.’’

The incident is likely to raise safety concerns surrounding the super-fast America’s Cup catamarans, which reach speeds of more than 70km/h.

Mr Outteridge said the new revolutionary design of the AC72s meant they could break into pieces during capsize.

‘‘Normally when a boat is capsized everyone falls into the water and then they climb back on but when these flip over they break up,’’ he said. 

‘‘If the boat was structurally held together it wouldn’t have happened.’’

Yachting Australia vice-president Matt Allen described the AC72s as ‘‘experimental’’.

‘‘Clearly this is a very different end to the sport from what we see on Sydney Harbour,’’ added Allen, a 22-time Sydney-Hobart veteran.

‘‘These boats are going very fast and it’s the pointy end of the sport so the risk is a lot greater.’’

Australian Olympic gold medallist Tom Slingsby and compatriot yachtsman James Spithill were involved in a dramatic capsize in their Team Oracle catamaran on San Francisco Bay in October.

The incident threw most of the Oracle sailors into the water and virtually destroyed their $8million boat.

Mr Outteridge said his youngest son, Beau, was in San Francisco working for Artemis and had witnessed the aftermath of the crash. 

He and his wife Jasmine were considering flying to San Francisco today to be with their sons.