Leeboard lead

Discussion in 'Sailboats' started by leonabcy, Jul 25, 2008.

  1. leonabcy
    Joined: Jul 2008
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    leonabcy New Member

    Hi my first post here I have a question about how much lead would you use
    for a leeboard design. I can find the answer for centerboards and fixed keels
    in Dave Gerr's and Howard Chapelle's books. But I haven't seen any thing on leeboards. Most of the drawings I've seen have the leeboards pretty far forward.
    Thanks
     
  2. lewisboats
    Joined: Oct 2002
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    lewisboats Obsessed Member

    If I read this correct you are looking for the lead of the sail center of effort and the leeboard. that is easy...it is approximately the same as a daggerboard but the leeboard must go parallel to the centerline of the boat so it must be at the position of max beam. this means that you will have to create your lead by moving the center of effort of the sail...either by selecting a type and size of sail that will give you the lead that you want or by the position of the mast or both. Using a head sail will move the CE of the total sail area forward, a gaff rigged sail will have a CE further back than a bermuda rig. If you rig the mast far forward and use a gaff sail you will get similar CE to a bermuda rig with the mast further aft. Jim Michalak likes to have the CE of his lug sails fall right around the aft edge of a vertical leeboard if this gives you any sort of a starting point.

    Steve

    Edited to add: If this is a small boat (most leeboarders are) then boat shape and load placement will affect balance about as much as the precise placement of the lead. Moving forward in a boat with rocker will shift the clr forward affecting the overall balance as much as raking a mast would or setting a headsail or changing sail types.
     
  3. leonabcy
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    leonabcy New Member

    Steve
    Thanks for the reply that is what I'm asking about. I don't have Gerr's book with me now but he says something like 11-15% lead CE in front of CLR just wanted to know if that would work with leeboards also
     
  4. alan white
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    alan white Senior Member

    I just went out for a quick sail, whereupon my head became clear and I realized a bit too late that I'd pronounced the word 'lead' wrong.
    Wonderful thing about leeboards is the way you can very easily position and test them using clamps before drilling any holes or setting up the final mechanism.

    Alan
     
  5. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Steve had most of it correct. Your leeboard is balanced much like a centerboard. Ketches about 7 - 8 %, schooners around 10% and sloops requiring more so to balance them up, depending on aspect ratio and type.

    A leeboard that doesn't "fully deploy" requires less lead, where as a leeboard of reasonable aspect, requires more.

    Much depends on the hull shape, appendages, rig selection and general arrangement, before general discussion about what you need can be seriously contemplated.
     

  6. leonabcy
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    leonabcy New Member

    Thanks so much for the responses
    Leon
     
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