The America's Cup will stage single-yacht 'ghost races' as US entrant American Magic scrambles to repair damage sustained when it spectacularly capsized in Auckland Harbour, regatta organisers said Wednesday.

The New York Yacht Club's boat, estimated to be worth US$80 million, was upended by a freak wind gust on Sunday, leaving a gaping hole in the hull that almost sank it.

The accident has forced major changes to the Prada Cup, the challenger series that will determine who races defending champion Team New Zealand for the America's Cup proper in March.

Organisers said the final set of round-robin races would take place over two days this weekend rather than three because there were only two challengers - Ineos Team UK and Italy's Luna Rossa.

But a quirk of the rules means both teams must still start the races they would have contested against American Magic, even though there is no rival boat on the water.

"In order to comply with the formality of the regulations... both competitors will have to take the start of a 'ghost race' vs New York Yacht Club American Magic," a Prada Cup statement said.

"(This will) allow the regatta director to award the point to the relevant team."

It said the ghost races would last only a few minutes before being suspended.

In the meantime, American Magic is racing to get back on the water for the Prada Cup semi-finals, which are due to begin on 29 January.

The Americans need to repair their damaged hull and reinstall the intricate electronic equipment that helps the 23-metre (75-foot) yachts "fly" above the water on foiling arms.

Ineos Team UK, led by four-time Olympic champion Ben Ainslie, have a 4-0 record in the round robins and need to win only one of their two races against Luna Rossa this weekend to reach the Prada Cup final.

The winner of the challenger series races Team New Zealand from 6-21 March for the America's Cup.

Source: News24