Multihull manuverability

Discussion in 'Multihulls' started by rapscallion, Dec 28, 2011.

  1. rayaldridge
    Joined: Jun 2006
    Posts: 581
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    Location: USA

    rayaldridge Senior Member

    I agree, though honesty compels me to mention that with Slider, the boat's behavior at high speed is really not an issue. I'm a fairly cowardly sailor, and the fastest I've ever pushed the little cat is 10 knots. That's not terrible for the average 16 foot open boat but pretty slow for a 16 foot beach cat.

    That said, I'm using similar sections on the new boat, which has a lot more sail area and should be faster. I like NACA 0009 for the board and 0012 for the rudders.

    I have to say that even though I'm no great shakes as a boatbuilder, I think that good foils are extremely important, so I expend the effort needed to get them pretty close to perfect.

  2. oldsailor7
    Joined: May 2008
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    Location: Sydney Australia

    oldsailor7 Senior Member

    IDKFA said:- I'm suggesting that a LAR board will make more drag at 20deg than a HAR board at 20deg? (the sim thickness & profile) by virtue of it being square.

    That is not so. A foil with a given section and a rectangular plan form will stall at the same angle regardless of it's aspect ratio.
    The lower aspect ratio square foil will have a much greater tip vortex, resulting in greater drag. It also induces "Tip Stall".
    Winglets help airplanes prevent this.
    Water weighs 800 times more than air. Therefore moving it around (as in a water vortex) robs the force required (F*MA) from the sails.
    That means DRAG.
    Well designed multi's with LAR keels are designed to have as small a tip vortex as possible. Lock Crowthers International 23 was a good example.
    It won races.
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