America's Cup - Oracle come close to a nosedive at 42kts in Bermuda

by Sail-World.com on 2 Nov 2016 Just over four years to the day after Oracle Team USA pitchpoled their AC72 in San Francisco, the America's Cup Defender have once again demonstrated how counter-intuitive foiling multihull sailing can be for sailors bought up on monohulls.

In this video clip taken in winds of around 22kts on the Great Sound in Bermuda, with the team's AC45S sailing at speeds in excess of 40kts, they come close to a pitchpole after the wingsailed foiler powers up a few seconds after a bear-away.

The theory, always hard to put into practice is that when caught in a gust the trimmer has to trim-on the wingsail rather than ease the sheet to spill pressure as would be done in a monohull.

When the wingsail is sheeted on, the load on the leeward foil is increased, its response is to generate lift and raise the leeward hull vertically - meaning the AC45S will lift up on her foils and sail even faster.

In the first video Oracle Team USA are actually able to save the boat by trimming on, despite being well into the nosedive, getting the sailing physics back into balance, and then sail away.

As Tom Slingsby notes on the video, trimming-on is completely counter intuitive, and requires quick thinking on the part of the wingsail trimmer.



In the 2013 Louis Vuitton Cup Emirates Team New Zealand nosedived spectacularly, being saved only by the buoyancy of her hulls which were designed to sail in winds of 33kts. Although the camera angle is not always the best, the occasional shot shows the wingsail well eased.



Of course the ultimate nosedive occurred, just over four years to the day, early in the 34th America's Cup on October 17, 2012 when Oracle Team USA nosedived in their AC72. Again the wingsail appears to be well eased (see 39secs into the video clip below).

Of course there, can be and usually are other factors which contribute to the nosedive in these situations, but the point remains - trim on, not out.

Encouragingly, Oracle Team USA recovered well from the AC45S nosedive and sailed away after a lesson was once again learned.