Fabric on frame to save on foam in a plug

Discussion in 'Fiberglass and Composite Boat Building' started by fairing guy, Aug 2, 2022.

  1. fairing guy
    Joined: Feb 2020
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    fairing guy Junior Member

    The problem in plug making is a lot of foam is needed to fill the volume of a plug. Maybe to solution is to replace this foam with air.

    Stretch fabric tight using heat over the wooden template, coat with epoxy and/or fiberglass the harden this base. Now fill the low points with pour foam. Carve, sand, fill, paint... and the plug is finished with less materials used.

    Is that a crazy idea?

    Foam and template method. I would want to make a similar shape as in this video.
  2. Rumars
    Joined: Mar 2013
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    Rumars Senior Member

    The crazy idea is to fill the whole volume with foam in the first place.
    Don't use fabric, just strip plank the mold. Glue isn't necessary, screw or nail the battens to the frames and sand them fair.
    fallguy likes this.
  3. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    If the plug is stronger...no need for much

    like @Rumars said
  4. jehardiman
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    jehardiman Senior Member

    I think it depends on what the "plug" is for. Is it a plug to be used as a male mould or a plug to be used to make a female mould? And how many finished pieces are you going to make? What I would do for a one-off is very different than what I would do for high production, long life runs.
    Rumars and fallguy like this.
  5. wet feet
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    wet feet Senior Member

    I wouldn't want to be using fabric and a light skim of filler if there is the slightest chance of two or three hefty laminators walking around on the plug.Similarly,strip planking is best reserved for those surfaces which are not developable as sheets of plywood or MDF will cover an area faster if the shape permits.If foam is used,it saves time and foam to build "shelves" at a convenient height and then add the foam.fine quality carpentry isn't essential even though accuracy is a big help.
  6. Kayakmarathon
    Joined: Sep 2014
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    Kayakmarathon Senior Member

    I built a plug using wood strips on sections for a sea kayak. I used sheet-rock joint compound to fill gaps between strips. It was the best boat I ever made.
  7. fairing guy
    Joined: Feb 2020
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    fairing guy Junior Member

    The plug would be similar in shape to the one in the video. Size about 0.6m x 0.3m x 2.2m.

    It would be used to create a minimum of 4 female molds. After that it can be discarded if I have nowhere to put it.

    I considered strip planking but the cost of the wood and labour is high similar to solid foam.

    Thank you for your replies.
  8. Rumars
    Joined: Mar 2013
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    Rumars Senior Member

    Expensive we can solve, go dumpster diving at a construction site. Or get creative, old newspaper and cardboard, rocks, sand and clay, or whatever other resources are available locally for free.

    Labor is a different game, plug making is work intensive however you approach it.
  9. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    The fabric will shrink greatly between the frames. It will take a whole bunch of filler then fairing.
    Better to use lots of battons as Rumors said.
  10. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    Going cheap on the plug or mold is foolish. Any imperfection will be repeated in all the hulls taken out of it. Plugs should be as close to perfect as possible. Also, fabric and filler will deform when something get laminated over it. The heat and the force of laying down the laminate will be too much for it. Wood is cheap. It needs to be dry but not necessarily of the best quality. Any pine will work fine.
  11. trip the light fandango
    Joined: Apr 2018
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    trip the light fandango Senior Member

    Old Venetian/slat horizontal blinds .
  12. comfisherman
    Joined: Apr 2009
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    comfisherman Senior Member

    One of our more eccentric boat Builders up here in the early 80s built a tunnel mold for a complex Atkins tunnel shape out of Spruce covered in aircraft cloth. I've only seen one of the tunnels but I can't imagine making that complex a shape without carving out of a solid Billet. Granite he was not spanning large gaps with cloth.

  13. rwatson
    Joined: Aug 2007
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    rwatson Senior Member

    I've built FG structures on stretched fabric. You have to be aware that the curing glass will deform the fabric, even if stretched tightly.
    Theoretically, if you can inflate the fabric with air, you could use it.
    You may have more success turning the fabric upside down, and filling with sand or similar, to get a uniform, fair shape.
    Glassing from underneath is tricky, but you could establish the shape with a few light coats of FG, just enough to hold the shape. Then you can empty the form, and apply the heavier layers without fear of deformation.
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