New Zealand unveiled a radically different keel on the yacht it is to use on Saturday in its defence of the Americas Cup when it meets Italy's Prada Challenge in the best of nine races.

Team New Zealand's NZL60 has its keel winglets in the middle of the bulb at the bottom, rather than winglets at the stern of the bulb.

It also revealed rivalry between the designers, New Zealand's Mike Drummond and Prada counterpart Doug Peterson, also a New Zealander.

Peterson and his former co-designer Laurie Davidson, who stills works for Team New Zealand, exchanged barbs during the unveiling.

Peterson questioned Team New Zealand's shift of the keel winglets. He said the position had been trialed, and had failed, in the 1992 and 1995 cups.

Davidson chipped in by suggesting while Luna Rossa was a "typical" Peterson boat, others in Prada's design team had clearly improved it.

Luna Rossa's keel unveiling showed some minor changes to the configuration used in the finals and semi-finals of the challenger series. The boat's winglets have been altered, although Peterson and his fellow designers would not reveal how.

"There's something different there, in the various components, from the finals. Like everything else we've done, it works," Peterson said.

Luna Rossa also has a slightly wider rudder. Peterson said the changes would boost upwind speed, while not compromising downwind speed.

Team New Zealand's design team unveiled a keel very similar to one displayed on NZL60 last month.

Design team co-ordinator Tom Schnackenberg said the keel was "pretty close" to the one unveiled in January.