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Thread: Foam core boat project.

  1. #1
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    Default Foam core boat project.

    Started a foam core boat build. 1248 boat will fiberglass inside and out. Then float test it before continuing with project. Still learning how to upload pics. Ill probably finish this one and then not build another one, im not a quitter so i have no choice but to finish it, unless float test fails. Mainly looking to see if boat floats good and is balanced. Also will need to re-enforce the transom. Will upload pics if i can figure it out. Any thoughts on doing boats this way ? Should be a light boat. Im hoping itll atleast handle a 20hp tiller handle , but then again its a project and im no engineer.
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  2. #2
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    Not sure what kinda foam that is but you better make sure your resin of choice is compatible with it.

  3. #3
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    Yeah i thought about that. Some resins melt foam so will need to get compatible resin for sure !

  4. #4
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    You will need epoxy resin, I have glassed over this foam for projects before. With the right lamination schedule it can be very strong.

    You will want to core your transom with a different material if you want to put a motor on it.

    Interested to follow this one along.

  5. #5
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    Will definitely follow along on this. Got the itch to build a boat but never thought about foam board. How are the pieces of foam held together?


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  6. #6
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    Foam is glued with non foaming gorilla glue then screwed into another piece with 3” screws every 3”. Then i taped seems. Yeah im going to put treated plywood on the transom for sure, wanted to do coosa board but at $600 for a 4x8 sheet ill pass

  7. #7
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    The bottom is 2” thick. Took 3 pieces of 4x8x1” thick foam to make the bottom 12’ x 48” wide. I found the exact center on a 8’ piece ( they arent exactly 8’) then glued another 8’ piece’s end on the centerline. Then cut my 3rd piece exaclty down the middle and glued each half to the 2 pieces i done first . Not very good at explaining haha. Then just bent the nose up 9” or so on a tire using a weight and then glued/screwed my sides on. Sides are angled outwards at roughly 12-15 degrees. I used a skillsaw to cut all the sides of the bottom at an angle and then put the sides on

  8. #8
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    Also, once i fiberglass the inside ill flip the boat over and add keel strips before fiber glassing over them. Ill do 2-3 layers of glass on the bottom then do a gel coat paint on the bottom to make the bottom smooth. Then flip it back over and do seats and maybe some gun racks on the inside and also a front storage compartment

  9. #9
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    You are going to want to add some support for the transom. You are going to want to add a stringer system that ties the front of the boat to the rear of the boat and adds some rigidity and will help carry the load of the outboard. Plywood along will not hold the weight of a 20Hp.

  10. #10
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    Quote Originally Posted by birdman1992 View Post
    Also, once i fiberglass the inside ill flip the boat over and add keel strips before fiber glassing over them. Ill do 2-3 layers of glass on the bottom then do a gel coat paint on the bottom to make the bottom smooth. Then flip it back over and do seats and maybe some gun racks on the inside and also a front storage compartment
    What glass are you planning on?

    To make life easier (and less expensive) instead of gelcoat I would just mix up some fairing compound using your already purchased epoxy resin and some micro balloons or equivalent. Give it a skim coat and sand smooth. After that I would paint.
    Main use for the gelcoat is to cure poly resin which you will not be using.

  11. #11
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    If you cover foam with latex paint regular fiberglass resin won't eat it.

    I'd put longitudinal ribs in a build like this in order to tie into the transom. There is a LOT of force exerted just trailering a boat with an outboard hanging on the back let alone running WOT. I'm looking forward to seeing how this build comes together!
    Listen to your elders. Not because they are always right but because they have more experiences of being wrong.

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  12. #12
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    Thanks for the tips guys. Ill definantly add longitudinal ribs along the inside. And also triangular braces on the transom. Going to focus on the transom for now. Thats needs to be strong for sure. Ill keep posting pics as i make progress

  13. #13
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    Im digging the total boat fairing compound. From what im reading its good for above and below water and just paint it after applying a barrier coat. Might go that route for sure

  14. #14
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    Will fairing the joints work on foam board? Just curious. I've done it on a little stitch and glue plywood boat I built years ago using epoxy resin. Makes for a light strong boat if done right.
    Last edited by cajunwannabe; 01-18-2021 at 09:23 PM.
    Listen to your elders. Not because they are always right but because they have more experiences of being wrong.

    "We make a living by what we get, we make a life by what we give" Sir Winston Churchill

  15. #15
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    This is cool. I want to do this now.
    Quote Originally Posted by ecu1984 View Post
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  16. #16
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    I’m in the process of building a pirogue from 1/4” plywood. Never occurred to me to use foam instead. Cool idea. Good luck.

  17. #17
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    Quote Originally Posted by cajunwannabe View Post
    Will fairing the joints work on foam board? Just curious. I've done it on a little stitch and glue plywood boat I built years ago using epoxy resin. Makes for a light strong boat if done right.
    I have always done small scale trials before I put it to use. That fairing compound is much stronger than the foam board it is adhering to. I would feel more comfortable glassing first and then fairing. The corners are going to be tough though. I am not sure the foam board will be able to handle much stress.

    To the OP. I would definitely do a bunch of trials to see what kind of results you get. I would hate to see a failure at the end.

  18. #18
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    Im planning on glassing over the board first, then fairing. Then do a camo paint job if possible on the fairing. Was going to do a gel coat at first but then Southern Wake mentioned fairing and i like that route better.

  19. #19
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    Where are you located? I may have some glass and odds and ends that may help you.

  20. #20
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    Quote Originally Posted by birdman1992 View Post
    Im digging the total boat fairing compound. From what im reading its good for above and below water and just paint it after applying a barrier coat. Might go that route for sure
    I have used it and it works great. That being said for the cost learn to mix up your own with the epoxy you are already using for your glass.
    The glass won’t want to do tight bends so you will need to make fillets on your joints, thickening the epoxy will be needed here as well.

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