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America's Cup: American Magic release video of Test Boat nosedive

by Sail-World.com/nz 11 Feb 2020 19:00 PST 12 February 2020
American Magic's The Mule sailing in regular low-flight mode off Newport, RI © Amory Ross

New York Yacht Club's America's Cup team, American Magic have released a video of their test boat doing a spectacular nosedive while sailing off the team's base in Newport.

The team is now in Pensacola, Florida their training base during the northern hemisphere winter.

They have taken their AC75 Defiant to Pensacola.

The video is shot from one of the team's drones flying above and astern, whether the nosedive was intentional (to get test/simulator data) or accidental is not clear.

While splashdowns (where the bow enters the water with a spectacular splash) are commonplace on the larger AC75's, only one boat (and maybe two) have capsized, most of the foiling mishaps have occurred on the test boats. American Magic's test boat, named "The Mule" is designed (apart from the 38ft production M38 hull) to be as close to an AC75 as possible.

The reason for this nosedive is two-fold. First, the boat is flying very high on her foils, and second, the rudder wing breaks free of the water about midway through the low-resolution clip, and at that point the nosedive becomes inevitable. The "phenomenon" is common to all boats that have similar foiling physics such as the AC50, F50, AC72 and AC75. In the AC50 it was reckoned that a rudder wing contributed 500kg of downforce when immersed in the water, and if it breaks clear of the water then that 500kg of downforce is suddenly released triggering the nosedive.

It is not known if The Mule was flying under manual or automatic flight height control at the time.

Within the leadup to the nosedive The Mule is flying high and level, rather than going through a rear up, followed by a crash/splash which is the common routine on an AC75.

At the end of the video an on-board sequence shows the top of the rudder post being moved fore and aft - this controls the angle of attack of the wing rudder - and it is this movement coupled with the high flight height that triggered the incident causing The Mule to trip over her foils, nosedive and then capsize.

Newport Mule ops... always valuable, never boring! ??

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