AC 36 Foiling Monohulls

Discussion in 'Sailboats' started by OzFred, Sep 13, 2017.

  1. OzFred
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    OzFred Senior Member

    For those who missed it, here is American Magic's capsize:



    There were a number of things going on:
    1. Significant increase in wind just before they tacked
    2. After the tack they went straight into a bearaway, a very tough manoeuvre at the best of times in a foiler
    3. A mainsail batten got hooked on a backstay (that should have been loosened after the tack) during the bearaway so the main didn't ease as it should
    Forces during the capsize caused a large hole forward of the port foil into the required sealed buoyancy area, almost causing the boat to sink (I'll put credits on the images if I can find them).

    amTroubles.jpeg

    AM will not compete further in the round robins and hopes to have the boat ready for the finals starting on 29 January.

    INEOS and Luna Rossa will sail against against each other on Saturday and Sunday (two races total) to decide who goes directly into the final. If INEOS wins either race, they go directly to the final. If LR wins both, they go into the final. The other boat sails a semi final against AM to determine the second finalist (first to 4 wins).

    The final starts on 13 Feb, first to 7 wins wins the Prada Cup and becomes the challenger.
     
    Doug Lord likes this.
  2. Tiny Turnip
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    Tiny Turnip Senior Member

    Likely not connected, but you never know: a couple of the AC videos use footage which shows a relatively large piece of debris in the water shortly after the capsize:

    AM cap.png
     
  3. wet feet
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    wet feet Senior Member

    Might that have been the bit that was retrieved by a rescue boat? Its been posted online that the hull now has no hole in it,presumably the other repairs and replacements are proceeding equally rapidly.
     
  4. AlexanderSahlin
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    AlexanderSahlin Junior Member

    The capsize was certainly caused by a strong gust while they were bearing away after the tack and were not able to release the main-sheet, yes. But when the heeling angle increases fast during the capsize, the boat rotates around an axis from the leeward-foil to the rudder-foil, which results in the high nose-up attitude, because this axis is at some 30° to 40° to the hull's centre-line. I estimate that the bow is some 10 m above the water before it starts falling down. When you drop the boat from that height you can get very high slamming loads, and as I understand from Terry Hutchinson's press-conference, they built the boat to stand hitting the water in an up-right position, not during a capsize.
    A hydrofoil-configuration based on a multihull, like e.g. William Sunnuck's Vampire, with the rudder-foils more straight behind the main-foils would behave better during this kind of capsize. Narrow catamaran hulls are also easier to build strong enough for slamming loads at a low weight than the wide AC-75 hull.
     
  5. Konstanty
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    Konstanty Junior Member

    I would like to note that two lightweight carbon foils on the broadside with increasing angle of attack would give better stability. The ballast should provide a classic keel canting. Earlier in this post, I included drawing of this solution.
     
    Last edited: Jan 24, 2021
  6. Doug Lord
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    Doug Lord Flight Ready

    Wow!
     
  7. OzFred
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    OzFred Senior Member

    Was that you on the camera Doug?
     
  8. AlexanderSahlin
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    AlexanderSahlin Junior Member

    Konstanty, on what page in this thread is your drawing? This thread is very long, so it would help if we get the page-nr.
     
  9. Konstanty
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    Konstanty Junior Member

    Welcome.
    AC 36 Foiling Monohulls https://www.boatdesign.net/threads/ac-36-foiling-monohulls.59160/page-31
    and too: Induced drag https://www.boatdesign.net/threads/induced-drag.60862/page-3#post-852024
    I am going to draw a version with one mast and a sail on the backstay. Besides, a normal gaff main sail with additional power from induced air flow and front staysails on the balestron.
     
    Last edited: Jan 28, 2021
  10. Konstanty
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    Konstanty Junior Member

    I see that in all races the bowsprit serves as a support for the camera.
     
  11. Doug Lord
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    Doug Lord Flight Ready

    =============
    At least(thank the Lord) there was a camera!
     
  12. peter radclyffe
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    peter radclyffe Senior Member

  13. AlexanderSahlin
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    AlexanderSahlin Junior Member

    Yes, your position for the rudder-foil is certainly less sensitive for changes in heeling angle. Much better than the AC-75. But why have two main-foils in tandem when you have a stabilising foil on the rudder? One single main-foil on each side can be made more efficient. Here is a link to a project, where they have developed a very practical and efficient hydrofoil system: The Vampire Project https://vampire-project.com
     
  14. AlexanderSahlin
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    AlexanderSahlin Junior Member

    In race 4 in the challenger's semifinal American Magic suffered from what appears to be a failure in the foil-control system (FCS), which resulted in that they lost the race by some 3 min. Does anyone here know any details about that FCS-failure?
    If the failure depends on a malfunction in the FCS, the organiser must be responsible, since they made this as a one-design component, and all competitors have to use that FCS. And the race shall be re-sailed after the organisers have provided American Magic with the necessary components for their FCS to work properly.
     

  15. Konstanty
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    Konstanty Junior Member

    The two foils on the broadside and the rudder foil should give better longitudinal stability. They pass each other in a trace on the water.
     
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