AC 36 Foiling Monohulls

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

  1. Doug Lord
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    Doug Lord Flight Ready

  2. Earl Boebert
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    Earl Boebert Senior Member

    So, for those of you who understand this stuff, here's my detailed question: the takeoff on a beat starts with both arms down in takeoff position and the hull in the water, at which point I am assuming that the righting moment is the combination of RM[form stability] and RM[pendulum] and that combined RM is sufficient to prevent capsize. The takeoff is complete when the hull is out of the water and the windward arm is full raised. At this point I assume RM[form stability] is zero and RM[pendulum] is sufficient to prevent capsize. Presumably their simulations show that the RM during "handoff" from hull+arm to arm-only is always adequate to prevent capsize but it sure looks dicey to me, especially when hull is part out of the water and the windward arm is only partly raised. Or are we assuming that they will stay in displacement mode until the windward arm is fully raised and only then attempt to take off?

    Cheers,

    Earl
     
  3. Doug Lord
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    Doug Lord Flight Ready

    I don't think the windward arm would be raised in displacement mode since the effectiveness of the leeward foil is not what it should be until lift off. Max rm is not possible until the lee foil carries about 80% of the total load.(assuming that differential lift requiring windward foil downforce is not legal.)
    I think there is some video of Ineos tacking that could shed some light on this.......
    PS It's possible in the takeoff sequence, that the flaps on the windward foil would be moved toward zero as speed builds and that they would raise the windward arm shortly after setting the windward flaps to zero.
     
    Last edited: Feb 2, 2019
  4. Earl Boebert
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    Earl Boebert Senior Member

    Still seems like a complex and risky evolution. But the simulation must be saying its OK, so I guess it is. :)

    Cheers,

    Earl
     
  5. Doug Lord
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    Doug Lord Flight Ready

    Seems fairly simple to think about it with steady wind and flat water. But add in strong, gusty winds and big waves and I'd guess it will get really dicey. I would think that those conditions would be just the sort of thing that would prompt "the powers that be" to allow windward downforce*.....

    * assuming it's even technically feasible?
     
  6. OzFred
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    OzFred Senior Member

    I think the answer is "no one knows", at least not outside the AC design and sailing teams. There are no videos that I know of showing the transition to foiling. They may use different techniques in different wind strengths.

    I expect they will only use the windward foil for lift in light conditions (whatever that might be, maybe less than 12kn as a guess). The foil gives a lot more RM lifted out of the water, if it's in the water and lifting it's taking away from already reduced RM. Its assistance is only required if the leeward foil can't generate enough lift, which I don't think will be a problem in reasonable breeze.

    There is speculation that the head of the mainsail may be twisted to leeward to generate RM once the boat is foiling, which I think, overall, would be much more efficient than using the windward foil for downforce. The rule leaves a lot of room for sophisticated solid–wing like controls in the upper 4m of the sail. But we'll have to wait and see on that.
     
  7. Earl Boebert
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    Earl Boebert Senior Member

    Some of the chatter on Sailing Anarchy suggests that touchdown may be equally tricky.

    Cheers,

    Earl
     
  8. OzFred
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    OzFred Senior Member

    Only if uncontrolled, e.g. the lifting foil ventilates or stalls (or the battery pack dies). But otherwise, I can't see any issues. As long as they have boat speed, the foils can do the work. The test boats have been struggling for sure, but they're really nothing like the real thing, nor were they built as scale models, they're just built from something reasonably cheap and handy that is under the 40' limit for test boats probably to provide some real world data for CAD systems.

    All this stuff is guess work until we see the real boats sailing, I think many perceived issues will be resolved. 31 March can't come quickly enough… :)
     
  9. Doug Lord
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  10. John Perry
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    John Perry Senior Member

  11. OzFred
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    OzFred Senior Member

    Doug Lord likes this.
  12. Doug Lord
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    Doug Lord Flight Ready

  13. Doug Lord
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    Doug Lord Flight Ready

    AC 36 arm testing-again from Jack Griffin-click on vimeo to watch:


     
  14. Doug Lord
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  15. Doug Lord
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    Doug Lord Flight Ready

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