AC75 roll stability?

Discussion in 'Stability' started by Gordon Kirkwood, May 11, 2021.

  1. Gordon Kirkwood
    Joined: Feb 2019
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    Location: 94025

    Gordon Kirkwood New Member

    I'm getting stuck trying to understand how the AC75s achieve such excellent roll axis stability when flying with one foil raised. With the windward foil lifted, can flap deflections on the leeward foil be helpful in balancing the boat in roll, or is roll stability entirely achieved with agile mainsheet manipulation? It does not seem like moveable mass (via motions of the raised foil, or crew movement) would be fast enough to balance changing and huge forces on the sails.
  2. tlouth7
    Joined: Jun 2013
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    Location: Cambridge, UK

    tlouth7 Senior Member

    Heel is adjusted through sail trim exclusively on these boats. This can be sail shape or more often twist adjustment as well as mainsheet adjustment. You will have heard the near-continuous groaning from the Kiwi mainsheet track as they trimmed their mainsail. Also note how all teams would sometimes bring the mainsail considerably above the centreline following a manoeuvre in order to keep the boat from tipping to windward.
  3. jehardiman
    Joined: Aug 2004
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    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    I'm not sure about the AC75's, but since the 2010 defense, I understand that the helmsman had a "quickened" display of roll to weather that they used to steer the boat back under the buoyancy (i.e. todays foil). Augmented Reality is a drop in the bucket today.
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