Graphic: Team New Zealand's secret weapons

America's Cup defenders Team New Zealand stole the show during today's unveiling ceremonies at Viaduct Basin.

While the two remaining challengers, Alinghi and Oracle BMW, showed conventional hull configurations, the New Zealanders unveiled a design breakthrough many believe may be the secret weapon to help keep the Cup.

Dubbed the "Kiwi clip-on", the radical appendage hangs just millimetres off the Team New Zealand hull. About 6 metres long, and 2.5 metres wide, the appendage is attached to the centre of the hull but cannot touch it elsewhere.

Its aim is to increase the waterline length of the boat, and therefore speed.

While both Team New Zealand boats were unveiled with the appendage, Team New Zealand would not say whether the clip-ons were identical.

The innovative "false hull" appendage was not the only design surprise unveiled at the Viaduct Harbour.

The keel bulbs on both Team New Zealand boats were very long, with the longest one also very narrow. The two boats also sported different rudders, suggesting the boats had been configured for different wind strengths.

Either way, Team New Zealand can still make alterations to their boats after the challenger series ends and before the America's Cup begins next month.

Alinghi race Oracle for the Louis Vuitton Cup from Saturday, with the first team to win five races sailing Team New Zealand for the America's Cup from February 15.

America's Cup Class rule

(51 pages)

nzherald.co.nz/americascup

Racing schedule, results and standings