Defending Swiss champions Alinghi are hell bent on retaining their America's Cup crown next year in Valencia, but forecast the toughest of challenges for next month's preliminary regattas.

"I am always optimistic, but they are going to be new boats, especially with the big challenges like Luna Rossa, Emirates team New Zealand or Oracle", the squad's New Zealand skipper Brad Butterworth said. "So I think it's going to be more difficult to beat them than has proved in the past two years", a period thoroughly dominated by Alinghi.

"We have to optimise our SUI 75 and 64 boats to match them, but I think there will be hard races to win," said three-time America Cup winner Butterworth.

Alinghi, in contrast to its main rivals, is not using this season its brand new Class America SUI-91 vessel fresh from the shipyard at Vevey to keep its hand under wraps as competitors, sponsors and clients come along hoping for a peek.

"The smaller teams are all working hard. The Spanish, I think, will be a tough team to beat. Team New Zealand, they are good sailors, they seem to be doing well. Luna Rossa will be a hard team to beat. The other teams are just as strong as Alinghi," said Butterworth.

"There is a lot of effort going in. If we could win (in 2007) it would be huge for this team because we have gone through good times and bad times", he added in reference to the controversial departure last year of 2003 winning skipper Russell Coutts.

"They are very relaxed and will be tough to beat in the forthcoming Acts with their Sui-75 boat, almost unbeateable last year," on observer of the squad said. But he added that "the only really important rendezvous is the final in June 2007".