Best “One_Off” building method using foamcore

Discussion in 'Materials' started by jedkins, Jan 5, 2007.

  1. jedkins
    Joined: Jul 2006
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    jedkins Junior Member

    What is the Best “One_Off” building method using PVC Closed Cell Foam

    I want to build a “one-off” 20’ catamaran hull in PVC Closed Cell Foam. I have built a solid male mold. The shape of the hull is similar to any typical beach cat hull – round bilges and fairly flat sided.

    I want the hull to be as light as possible but I do not want to vacuum bag. I want to hand lay up.

    There seems to be 2 options:
    1. Strip plank over the male mold, hand lay up the outside , take out the mold then hand lay up the inside. For this I would use 12mm thick foam core but I am uncertain of the lay up fabric to use both inside and out. Also I am confused abt the right brand of foam to use – I want the most “bendable” type. What type bends bests in 12mm thickness?

    2. I am also considering grid scored (kerfed) foam sheet that I should be able to drape and attach to the mold then fill the kerfs. Then lay up. I realize this might be a bit heavier than 1. but can anyone recommend a light filling material and most importantly the correct lay up fabric. Again I don’t want to vac bag.
    Thanks for any help.
  2. yokebutt
    Joined: Aug 2004
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    yokebutt Boatbuilder

    Fasten on sheets of foam onto the mold by screwing through the mold from the inside, use heat to bend the foam if neccessary. Laminate the outside skin, pull the part off, and laminate the inside skin.
  3. henrikb
    Joined: Jul 2002
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    henrikb Senior Member

    I built my boat on a male plug. For the deck I built a plug, made a female mould.
    Take a look at my project on:

    If/when I build my next boat I would probably build using method like this:

    Another interesting idea is to build a hull using flat panels (like Bruce roberts etc). Then you could make the panels on a flat surface and put the hull together using the finnished panels. Or, you could easily build a female mould for the complete hull using plywood.
  4. jonsailor
    Joined: Sep 2005
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    jonsailor Boat designer/builder

    If/when I build my next boat I would probably build using method like this:

    I built the yacht in question and it was a pretty good way of doing a one off.
    What I liked about it was that we locked the whole shape in very accurately by building the complete inside and then glassing the outside last.

    Quite frankly, we vacuum everything now days and if you have a male mould, then you are mad not to use it as a vacuum mould.

    If you want it light and strong, then you are kidding yourself without it.
    we have a few methods to see at
  5. henrikb
    Joined: Jul 2002
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    henrikb Senior Member

    That was exactly what I was thinking about also!
    Impressive build by the way, and a very nice yacht!

    I was loooking at your homepage, on the construction of the Wasabi a couple of weeks ago. I was wondering about how to get accuracy on the female mould when building it like that? It must be almost impossible to use battens to check for bumps and hollows?
  6. John ilett
    Joined: Nov 2003
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    John ilett Senior Member

    The solid mould would be good for a vacuum job or screw the foam on as mentioned above.

    For foam without vacuum bagging a stringer only jig is all that is needed. You can screw or copper wire the foam to the stringers. Layup the outside, remove hull and layup the inside.

    PVC will be softer than acrylic foams. You should find some offcuts to test the bend on your mould. If it is too stiff to bend without breaking then maybe try 1 ft wide strips with some heat and bending the foam across the bilge. A thinner foam of higher density may bend easier/safer if the 12mm-80kg seems a problem.

  7. War Whoop
    Joined: Jun 2003
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    War Whoop Senior Member

    Plastic foam only one system to use that being the bead and cove method.
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