Australia have won the SailGP Championship for a second successive year, beating Japan and the United States in the Grand Final on a crazy, incident-filled day in San Francisco.

The Aussies and Driver Tom Slingsby, who won the inaugural Championship in 2019, defeated incredibly tough conditions to win the entire Mubadala Sail Grand Prix event, before overcoming Nathan Outteridge's Japan and Jimmy Spithill's USA in the winner-takes-all final race.

A crazy day on the Bay saw collisions between France and New Zealand and Spain and the USA, while two races were abandoned and restarted - including the Grand Final itself due to a whale entering the racecourse.

But, once the race was restarted, the Aussies overcame all this adversity to prove their talent once again, and wild cheers greeted their lifting of the Championship trophy in the San Francisco race village.

"We’ve never really seen this calibre of fleet anywhere in the world," said Slingsby. "You always talk about, 'Who is the best sailor around the world?', but to be here with all even boats makes it huge for me that Australia came out on top.

"We can call ourselves the best sailors in the world. That is more important than money. Glory lasts forever, and it really feels like that."

Despite losing in the final, it was incredible that the United States even managed to race at all, having suffered serious hull damage when the Spanish crashed into their boat during the opening race of the day.

But, despite rapid repair work ensuring they could race, and a huge number of fans cheering them on from the shore, Spithill's team only managed a third place finish in the final, continuing his record of never having actually won a SailGP event.

As Australia celebrate their back-to-back successes, they must also start preparing for their title defence with Season 3 starting in just over a month, with the Bermuda Sail Grand Prix taking place on 14-15 May.