Core compression insert material question

Discussion in 'Fiberglass and Composite Boat Building' started by Skip Johnson, Nov 15, 2022.

  1. Skip Johnson
    Joined: Feb 2021
    Posts: 28
    Likes: 16, Points: 3
    Location: Lake Tenkiller, Ok, usa

    Skip Johnson Junior Member

    I'm getting ready to build a small proa schooner primarily with 12 mm gpet foam with corecell for bottom planks in large flat panels similar to a stitch and glue plywood craft. There are a few places where I know I'll need inserts at the rudders and bushings for telescoping alum tube beams.
    Plan to vacuum bag inside skins on table and then glass exterior after assembly.
    I'd like to go ahead and mold in the known inserts while vacuum bagging. The question is what to use.

    Higher density foam is one option but I just need a little bit which seems hard to come by. I'm leaning towards using some cellular pvc trim lumber, it's easy to get and one 1/2" thick board would do all that I need. Inserts for all the rigging and such would be done after the fact wallowed out foam and poured in place the conventional way.
     
  2. kapnD
    Joined: Jan 2003
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    Location: hawaii, usa

    kapnD Senior Member

    That’s some weak ****, why not just taper your core out and thicken the laminate in those areas.
    You can use G 10 for backing if it needs more support.
     
    fallguy likes this.
  3. wet feet
    Joined: Nov 2004
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    Location: East Anglia,England

    wet feet Senior Member

    What does the designer specify?That has to be the obvious solution.I'm detecting a bit of a lack of experience here as glassing the outside of the hulls last will lead to a huge amount of fairing,when laminating the outer skin on a well finished table would leave the rougher surface on the inside.
     
  4. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    Cellular PVC is garbage for structural use, but OK for house trim. Is this your design? If so, how did you calculate the laminate schedule and type of foam core?
     
    fallguy likes this.
  5. Skip Johnson
    Joined: Feb 2021
    Posts: 28
    Likes: 16, Points: 3
    Location: Lake Tenkiller, Ok, usa

    Skip Johnson Junior Member

    Thanks, a better solution I think.
     
  6. Skip Johnson
    Joined: Feb 2021
    Posts: 28
    Likes: 16, Points: 3
    Location: Lake Tenkiller, Ok, usa

    Skip Johnson Junior Member

    Self designed I'm afraid. I've built a number of foam core, wood strip and plywood boats over the years. There will be some fairing involved but proper technique and peel ply go a long way towards easing the pain, along with being ok with a workboat style finish.
     
  7. Skip Johnson
    Joined: Feb 2021
    Posts: 28
    Likes: 16, Points: 3
    Location: Lake Tenkiller, Ok, usa

    Skip Johnson Junior Member

    Laminate schedule and type of foam core based on previous experience and in the case of the foam core cost is a major factor.
     
  8. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    No! Glad two others said so first. That stuff is crap.

    I would recommend Roseburg plywood. It is actually a plus if it is dimensionally different (within reason) because you can locate them easier. As the builder, you have tobe disciplined and overbore and fill the holes with thickened epoxy to make it less likely to rot if a seal ever fails. This is done with tape on one side and empty caulk tube. And sometimes, you can use a piece of raw core to temp fill an inside hole. So, say you want to make a 1" hole, you 1.5" overbore 12mm thick. This is at great risk of cracking diring exotherm, so you make a 3/4" corecell plug and bond it all in over tape on the convenient side filling 3/8" all the way around the plug. After it cures, you cut the hole at 1" and there is 1/4" margin to protect the plywood from seeing water if the caulk seam ever leaks. You can also block and use hot glue for a stiffer backing vs tape.

    The harder part is being disciplined about it. It is damned easy to say, that is marine plywood and will be fine....
     

  9. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    If you want to buy some corecell M200 from me, I might have some here I could sell you as your cutouts, but I prefer the plywood or coosa as inserts.

    Just private message or post the sizes you need and I'll see what I have. Pretty sure I have one decent offcut.
     
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