Fiberglass over plywood vs all fiberglass hull

Discussion in 'Boat Design' started by thundermountain, Sep 17, 2022.

  1. thundermountain
    Joined: Sep 2022
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    thundermountain Junior Member

    Can I get you guys opinion on the pros and cons for DIY boat hull construction ? I'm building a light weight flat skiff style boat with minimal power intended to use in small rivers here in Arkansas. I have been tossing around the idea of creating flat sheets of fiberglass to use in place of the plywood which would be glassed anyway on both sides to incapsulate the plywood. Would love to get some thoughts from anyone who has built stich frame plywood or plywood over rigid frame boats . Thanks in advance... Robert
     
  2. fallguy
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    fallguy Senior Member

    Building in glass sheets would not really be wise.

    stiffness is not as good

    sheets constructed with unknown resins

    tabbing would be significant and be proud on the exterior

    not sure the station jigs could be far apart or that it could be done without battens

    Not saying it can't be done, but it really doesn't make sense to me.
     
  3. thundermountain
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    thundermountain Junior Member

    Thanks for the reply fallguy, Perhaps I should have noted the fiberglass sheets would be a replacement for the plywood and would be glassed over using the same methods as if it were plywood. Sheets proposed would be around 1/8 thick. Rocks abound in the Arkansas rivers such as the White and hull penetration would be a concern but not as much as delamination of stressed (bent) 1/4 thick plywood. Sheets would be produced from same glass/resins as boat and bulkheads and flooring jigs would be cut from similar panels with built in stiffeners and glassed in after hull is flipped.
     
  4. Rumars
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    Rumars Senior Member

    In short, fiberglass is much more flexible then ply, and it's heavier. Overall you can't match the weight of a ply boat. But yes, it can be done successfully, here an example in G10.

     
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  5. Milehog
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    Milehog Clever Quip

    Fiberglass is floppy stuff unless it is thick and heavy, cored, laid up in a compound curve or supported at close intervals.
    Cored is easiest for beginners. All it takes is laying glass on plywood.
     
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  6. thundermountain
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    thundermountain Junior Member

    You guys are great ! the video is much as I had expected but it reveals one thing I didn't count on , cost and it surprisingly shows the glass boat to be heavier than a plywood/epoxyglass sandwich

    the pic is for reference to the kind of boat I am building... flats boat.png
     
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  7. Milehog
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    Milehog Clever Quip

    Do you have plans picked out yet?
     
  8. fallguy
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    fallguy Senior Member

    build that boat stitch and glue plywood, no looking back; it'll be awesome
     
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  9. thundermountain
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    thundermountain Junior Member

    Drawing them myself , it will be a similar boat to the one pictured, fun thing is building a frame to begin with. So much of the how to is readably available on the internet so drawing the plans is no big deal. I'm really surprised there aren't more people drawing their own plans so they can adjust the width and length to their needs. attached are some notes... Untitled.png
     
  10. thundermountain
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    thundermountain Junior Member

    Curious to your thoughts of stitch and glue vs ply on frame...
     
  11. Milehog
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    Milehog Clever Quip

    Suggest you start a new thread and ask some of the experts here about that idea.
     
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  12. fallguy
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    fallguy Senior Member

    I am biased to the monocoque, stitch n glue design. The reason is simple. I just really like full encapsulation in epoxy and hard to do in ply on frame.

    EDIT: I cannot determine from the drawing you made if that is possible and was offering a generic response based on the picture of the boat you provided..
     
    Last edited: Sep 18, 2022
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  13. fallguy
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    fallguy Senior Member

    Why would you draw it yourself? Boat designers have been making these drawings for like 35 years, tweaking errors, correcting issues like chine walk, adjusting the tunnels to avoid problems like drag. I just really think it is unwise when you can pay someone $150 and then modify the inside to suit your wishes for fishing.

    These boat types have a big following on boat builder central.

    You show a 6" tall keel. Is that a keelson or stringer or a true keel? No flats boat would be built like that because the boat will bottom out too easy. Perhaps it is your wordchoice and just a longitudinal stringer.
     
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  14. Milehog
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    Milehog Clever Quip

    I'm usually blunt on this topic but am trying to be diplomatic.
     
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  15. philSweet
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    philSweet Senior Member

    Given its a flats boat with at most a small foot well, ply on frame is probably the best bet for a first time build. Use full chine logs and sheer logs to control curvature. The side frames won't lay flat. Bend on the sides, spile the side frames to the curve, reset the chines and sheer, and then hang the sides to the flush frames. Or if you enjoy math and drafting, you can develop the curves in advance using Rabl's method. 16' hull should weigh about 600 pounds when finished.

    There's a wonderful old book by Glen L. Witt called Boat building with plywood. I was thinking you could probably find it for $2 on Amazon, but apparently it is still in demand, and they are getting $25-$30 for it! That's more than I paid for my Principals of Yacht Design

    I used to lead canoe trips down those rivers when I was at Kia Kima Scout Camp near Hardy.

    This is what it should look like when it's done right - Willy Roberts. Bob Hewes was doing something similar around the same time. Then Mako came along.
    upload_2022-9-18_22-54-12.jpeg
    [​IMG]
     
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