Split Paddleboard for Amas

Discussion in 'Multihulls' started by lane, Sep 30, 2022.

  1. lane
    Joined: Dec 2005
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    Location: Austin TX

    lane Junior Member

    I am trying to build a small 10 foot long Trimaran using materials I have readily available. I wanted to use a fiberglass paddleboard /surfboard as amas. The board would be split down the center and the cut edge fiberglassed over to seal the board. Each half of the board will be mounted lengthwise, flat edge up, as an ama. Each half of the board would be mounted vertically to serve as a waive piercing ama.
    Does this sound possible or do you see problems inherent with this design?
    Thomas in Texas
     
  2. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    Hello Tom,
    I am sure it is possible, but it is also possible that it might not work very well.
    However the cost of this trimaran will hopefully be not-very-much (re the materials you have available), so even if it does not work out well, it will still be an interesting design / build experience.

    You have not mentioned anything though about the main hull - what are you going to use for this?
    And what type of rig are you proposing to install?
    I presume that this will be a sailing trimaran, not a power tri?
     
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  3. lane
    Joined: Dec 2005
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    lane Junior Member


    Banjansailor,
    This is to be a sailing trimaran, center hull is to be either a 10 ft kayak or 11 ft Escape Captiva. While I will sail it with a Escape 67 sqft sail rig, I want to eventually use two 50 sqft windsurf rigs in a biplane configuration. Adequate flotation from each amas will be needed to support their individual wind surf rig. I am looking at boards that support 200 to 250 lb. When the board is split, each resulting ama will have a flotation of 100+ lb each. Is that enough?
    Thomas
     
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  4. kapnD
    Joined: Jan 2003
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    kapnD Senior Member

    Most paddle board/surfboards have too much rocker to use on edge as an ama. The downwind ama will try to pull the boat to leeward, the deeper it buries, the harder it will pull, as the rocker becomes more extreme at the pointy end.
    I’m assuming that your trimaran is probably very small, so Perhaps cutting the board in less than half (thirds or quarters) would eliminate a good deal of the curvature.
    Best to keep the sails on the center hull, they will bury your amas rapidly in a stiff breeze, an cause more weird handling quirks.
     
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  5. waynemarlow
    Joined: Nov 2006
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    waynemarlow Senior Member

    Been there and done that but with the 1/2 board acting like a Hobie asymmetric hull. Took forever to repair the halved boards and forever to work out a way to mount them. So much time was wasted that I can only recommend to simply get 110mm PVC drain pipe and make a nose and stopper or look how old fashioned surf boards were made, splitting an existing board in my view was a waste of time.

    Your big problem with a solid foam core is when you capsize. You can’t submerge the AMA low enough in the water to be able to right the trimaran, look up Weta and see how they flood the AMA’s so that the main hull then becomes the pivot point to roll the boat back upright.

    Incidentally my main hull was an F16 hull and A Class mast and rig with F16 Spinny, fast fun boat but totally useless as I could never right it once capsized.
     
  6. Manfred.pech
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    Manfred.pech Senior Member

    lane, may be you like this for a better lift to drag ratio.
    [​IMG]
     
    Last edited: Oct 9, 2022
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  7. Manfred.pech
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    Manfred.pech Senior Member

  8. Manfred.pech
    Joined: Apr 2010
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    Location: EU

    Manfred.pech Senior Member

  9. Manfred.pech
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    Manfred.pech Senior Member

    "While I will sail it with a Escape 67 sqft sail rig, I want to eventually use two 50 sqft windsurf rigs in a biplane configuration. Adequate flotation from each amas will be needed to support their individual wind surf rig. I am looking at boards that support 200 to 250 lb. When the board is split, each resulting ama will have a flotation of 100+ lb each. Is that enough?"

    Hi Thomas, as you can see on the picture of the last posting, you can tilt the floats to - say - 45 degrees. When sailing, you will have more hydrodynamic stability and you will
    get a certain amount of lateral resistance. When the little trimaran will heel there will be less lateral resistance and more stability and so on, til the boat will drift to leeward. This is a safety margin you get. The old ngalawa found out this benefit for theire fishing outriggers. A hundred years ago they used to have flat outriggers like an inverted T which did not give enough lateral resistance but enough stability for them if not heeling too much. That is evolution.
    When you build your trimaran with adjustable floats from the half surfboard you can do some development work. You can test some toe out or toe in. You can lift the bows and lower the sterns. Old boards are longer and have more flotation and .. less rocker .. may be. If you like experiments there is a lot room for them.
    Helpful might be a small stub mast from which you can place and lower the whole surfmast and sail. I´ve found nice drawing from the great Gary Dierking.
    Regards, Manfred

    upload_2022-10-5_16-33-23.png
     
    Last edited: Oct 11, 2022
  10. Manfred.pech
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    Manfred.pech Senior Member

  11. Manfred.pech
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    Manfred.pech Senior Member

    You do not need to split the board and build a trimaran. A simple outrigger with a smaller surfboard will also be able
    to take you out for sailing. And you can experiment with an angled daggerboard in the outrigger to give you lift or suction by changing
    the angle of attack. PROJECT WINDRIGGER http://fionamsinclair.co.uk/yachts/smith/page25.ht

    [​IMG]


    [​IMG]
     
    Last edited: Oct 10, 2022
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  12. Manfred.pech
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    Manfred.pech Senior Member

    Last edited: Oct 15, 2022
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