Brad Butterworth, the skipper of America's Cup holder Alinghi, has yet to decide whether he will continue in the event after defending the title next year but he wants it to be held every two years rather than every four.

"It's too long between them. It should be changed. Every two years would be great," the 46-year-old told Reuters at an event for one of the team's main sponsors in the City of London.

But he is looking over his shoulder at the current New Zealand team, along with US syndicate BMW Oracle and Italy's Luna Rossa as the likely challengers to his crew when Alinghi defends the cup in June 2007 in Valencia, Spain.

Eleven syndicates -- including teams from China, South Africa, Sweden, Spain, Germany and Italy -- are vying for a chance to wrest the trophy from Alinghi, which has been bankrolled by Swiss billionaire Ernesto Bertarelli.

"The final spot is going to be a tough one. I reckon its going to be too close to call. The boats (Team New Zealand, BMW Oracle and Luna Rossa) seem to be the same speed. It's between the three of them," Butterworth said.

He has not yet made up his mind whether to carry on beyond the Valencia cup next year, a decision he says will depend on who else remains with the Alinghi team. But at 46 it's getting tougher to compete at the top.

"It's getting near the end. It's harder, much harder, both physically and mentally," he added.

Butterworth thinks that British helmsman Ben Ainslie, a double Olympic gold medallist, is a possible future America's Cup winner but says he should be competing in 2007 rather than sailing as the back-up helmsman for Team New Zealand.

"I think he's under-utilised. It's a pity he's not having a shot at it with a team that's using him." "Ben's obviously special. I don't know how many Olympic medals he's got, but the fact is he'll learn a lot in that group," he said.