First there was the winged keel, then came 'plastic fantastic', the 'hula' and now a swinging keel is being touted as a potential America's Cup trump card in Valencia.

The Challenger Elimination Series gets underway late tonight with Team New Zealand racing Mascalzone Latino on day one.

It has emerged one of the teams, possibly defender Alinghi, has engineered a breakthrough that could give them a huge advantage.

Yachting commentator Peter Lester says a swinging keel would be significant and it is the equivalent of putting the All Black front row on the deck of the boat and giving it more stability and power.

Team New Zealand believes the hype surrounding a supposed revolutionary keel is being overplayed.

Team New Zealand Director of Sailing Kevin Shoebridge, says he had an inkling some time back that something was in the wind, but a lot of it has been blown out of proportion.