Dennis Conner is worried the cost of the radical new America's Cup yachts could prevent some syndicates from entering.

The Cup legend believes a syndicate could require more than $200 million for a competitive challenge with the radical new foiling monohulls planned for the 2021 event in Auckland.

The new AC75 will be complicated, expensive and likely to capsize. But he said on his sailing podcast the new boat ''would be really something''.

"It's a radical new boat. We knew it had to be something special and, boy, they didn't let us down.

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"We've got a boat with no keel, it looks to me like a preying mantis or a big daddy long-legs spider," Conner said.

"Talk about an engineering nightmare ... or an opportunity. It will be incredibly complex, the operating of this (foils) system. Breakdowns are part of racing ... not only does it have to be complex it has to be totally reliable, which is saying a lot. And these boats will capsize.

"But it's fantastic sailing on the Hauraki Gulf in Auckland and this is going to be really something."

Small teams would struggle to be part of the regatta.

"The costs involved are going to be horrific for a low-budget syndicate. Maybe between US$100-150 million, that's a tremendous amount of money to the folks in sailing. But the best sailor in the world can't win without a good boat and a good team.

"I don't think they want a whole lot of competitors in this event. They are going to limit it to extremely high calibre teams, teams that are going to be extremely well financed."

Emirates Team New Zealand had an advantage in setting the parameters for the new boat.

"This is going to give the defending team the little edge they need to try to keep this cup there. Don't forget they are still making the rules – he who has the gold, makes the rules. We haven't seen the end of this."

Entries open on January 1 and the final class rule isn't due until March 31 which placed challenging teams in an awkward position.

"How do you enter a race when you don't know the design? How wide, how deep, how many appendages, how do they move?

"The logistics of working on this boat are tricky."