America's Cup: Emirates Team NZ's has high speed dive

by Richard Gladwell/Sail-World.com/nz 7 Nov 2019 21:49 AEDT 7 November 2019

Emirates Team New Zealand's Te Aihe, Waitemata Harbour, November 7, 2019 © Richard Gladwell / Sail-World.com

Emirates Team New Zealand's AC75 had another high-speed smash while training in moderate to fresh winds on the Hauraki Gulf today.

The sequence was caught on camera, at long distance, by Sail-World NZ, and revealed some interesting characteristics of the AC75. Please excuse the graininess of the images which were shot at a range of 2.5nm.

The incident happened in a steady sea breeze (NE) of around 18kts, with some chop/wind waves with no accompanying swell.

The nosedive happened very quickly while the AC75 was sailing at very impressive speed to windward and suddenly nosedived.

The skiff hull threw a lot of white water, and the upward force generated by the leeward wing was sufficient to force the AC75 to roll sharply before the wing lifted clear of the water during the roll.

The mainsail appeared not to be tensioned in some shots of the AC75 sailing on her centre bustle and windward side. The soft mainsail (and suddenly release of pressure onto the downward foil) could account for the foil driving upwards and rolling the AC75 onto her centre bustle and windward side. The windward foil arm was still extended pulling the AC75 over to windward, aiding, and not countering the rolling motion induced by the leeward wing.

The AC75 slithered along the surface, still heeled before rolling upright, and coming to a complete stop.

After a pausing sailing for a few minutes, presumably to check and mark the data stream, and converse with design engineers on the chase boat, the AC75 took off again sailing very quickly to windward, before turning downwind and sailing at high speed without further nosediving. The incident was later dismissed as "learning".

The rest of the seven-hour training session was conducted in flatter water in "The Paddock" - the area to the east of Browns Island and sheltered by Waiheke Island to the north, used by ETNZ in their build-up to the America's Cup in Bermuda.