Asymetric foils - are they worth it?

Discussion in 'Multihulls' started by JackIron, Apr 17, 2007.

  1. JackIron
    Joined: Apr 2007
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    JackIron New Member


    I am currently working with Dazcat in the UK on the build of a 10m cat, I was going to put asymetric dagger boards in, however I have heard some reports of difficulty in lifting the windward one if you are moving, and if it stays down it feels like you are "dragging a bucket". The boards are 3.3m long, but only 1.6m will be in the water when fully down. This is a large casing to drag it up through - (even through there will be an up haul on the board)

    Does anyone have experience of same? Is there real benefit to the asymetry, or would ease of symetric boards outweigh these benefits?

    Many thank in advance
  2. waikikin
    Joined: Jan 2006
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    waikikin Senior Member

    Jackiron, I reckon it could be worth it if the Dazcat? is a performance machine(I'm not familiar with the design). A freind of mine has a hot 9.5M tri that has the rudders & boards in the floats & he drives it around on 1 hull, he has symetrical boards but the rectangular section case has replacable guides so he could tune the angle of attack so thats kinda/sorta assimetrical by 2 degrees or so to the float centreline, he's looked into actual assymetrcal boards but hasn't gone for them yet, the cat I'm doing is having double symetrical boards, side to side & top to bottom- cos I only need one half mold(so save tooling cost) to make 'em & can end for end in case of light damage, I'm also gunna have the rectangular case- in case I wanna tune the angle or try another foil section. Regards from Jeff:)
  3. JackIron
    Joined: Apr 2007
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    JackIron New Member

    Thanks for that Jeff
    My main concern is the lift the asymetry will generate meaning the board will wedge itself in the box at anything over zero speed. If leaving the w/w board down feels like dragging a bucket, then surely it should benefit if I can get them to work. The design can be seen at D10R.htm and the first hull is about to pop out of the mould.

  4. tspeer
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    tspeer Senior Member

    It doesn't have to wedge itself in if the boards are toed out so the zero lift lines are parallel. Then they will behave the same as symmetrical boards when unloaded.

    The leeway angles will be the same as with symmetrical boards, too. The difference is if you operate with the windward board retracted, the minimum profile drag can be centered on the operating condition, which effectively reduces the wetted area of the board somewhat.
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