Kevlar boat plug/mold help

Discussion in 'Boat Design' started by jka251, Feb 15, 2021.

  1. jka251
    Joined: Feb 2021
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    jka251 Junior Member

    So it sounds like I can build the shape I want out of foam and glass inside and out and have a very simple, lightweight boat- which is what I'm looking for. Nothing fancy and I'm not concerned about cosmetics.

    As far as fiberglassing goes, how many layers on the outside and what type? 6oz?
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    I think you need to supply a rough drawing of what this boat entails, so we can comment further, my idea was using foam blocks shaped to what you want, with a hollow to accommodate you ,and glass over the whole thing, no moulds, frames or jigs required, but that may be impractical without knowing the configuration of it.
     
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  3. wet feet
    Joined: Nov 2004
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    wet feet Senior Member

    It seems that not everybody is familiar with the technique of building over a male mould.There is quite a good procedural explanation here Building in Foam Sandwich [UK-Cherub Class] http://www.uk-cherub.org/doku.php/tech/foam_sandwich .for those who don't know the Cherub it is a 12 foot high performance racing dinghy with a hull weight of a little over 100 lbs.The outer skin is normally finished to at least the primer stage while still inverted and then a glass skin is applied internally after turning over as I described in an earlier post.

    [​IMG]

    I would re-emphasise avoiding Kevlar as it really is a nightmare to work with.
     
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  4. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    That depends on what you call lightweight. It will be heavier than a plywood boat.
     
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  5. jka251
    Joined: Feb 2021
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    jka251 Junior Member

    Let me know if you can see the pic or not. This would be about 14'-15' long, 42" wide at the beam and about 16" tall at the stern. I don't have any drawings but this is something that I would model it after. The bottom (at least the rear portion) would be somewhat rounded with a keel and maybe flatten out going forward. The inside, under the deck would be open. Let me know if this gives you a better idea.
     

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  6. Mr Efficiency
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    Mr Efficiency Senior Member

    OK, the hollow under the deck complicates things a bit, but I think the idea of treating it as a surfboard glassing exercise could still be accomplished easily enough, you can roof over the open part last.
     
  7. jka251
    Joined: Feb 2021
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    jka251 Junior Member

    I was thinking I'd have to build it in two sections- top and bottom. So, Kevlar is out of the equation now. What glass should I use and how many layers? Also, how thick would you recommend the foam? 1/2", 3/4"? I plan to use epoxy resin.
     
  8. wet feet
    Joined: Nov 2004
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    wet feet Senior Member

    I don't know how rocky your proposed area of operations may be and puncturing the outer skin can be a possibility if you are standing in the boat with a sharp rock under the bilge and no other support.I do know that for more than 15 years I have been racing a trapezing dinghy with no structural problems whatever.The construction is a polyester layup of 600 g/sq m either side of 8mm foam of 85 Kg/cu m density.I think you would be right in making the modest sized deck as a separate component and to have a flange of maybe 1 1/4 inches wide to sit it on.A good splodge of bonding paste should be enough.If you might ever consider standing on the deck, a support post beneath it would be a good idea.I suspect the hull will be sufficiently skinny that taking a swim is quite likely if you ever try a stroll on the deck..........
     
    Last edited: Feb 17, 2021
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  9. gonzo
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    gonzo Senior Member

    A surfboard is not a good comparison to a kayak. They are lightweight, but have minimal puncture resistance and crack in half if someone steps on them and are not completely supported. The fiberglass delaminates from the deck by getting hit by the knees of inexperienced surfers.
     
  10. jka251
    Joined: Feb 2021
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    Location: AL

    jka251 Junior Member

    Where I'll be on the water at there are no rocks. Mainly used in a few freshwater lakes and some small bays on the Gulf Coast. I'll also have my 17' aluminum boat as a tender boat. The main thing I'll have to watch out for is underwater logs but I won't be going fast at all in this boat since it's used as a sneak boat for hunting. I also don't plan to sit or stand on the deck. And thanks for the glass and deck info. I was thinking that would be ok to join the two pieces.
     

  11. Milehog
    Joined: Aug 2006
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    Milehog Clever Quip

    Newbies reinventing the wheel scare the hell out of me.
    For a first build I recommend you consider plans from a living designer.
    You can thank me later.
     
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