Need your expertise for bonding the top of a boat to the bottom half

Discussion in 'Fiberglass and Composite Boat Building' started by aaronhl, Dec 27, 2020.

  1. aaronhl
    Joined: Aug 2012
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    Location: Central Connecticut

    aaronhl Senior Member

    I am working on a 18 foot closed bow outboard speedboat and after replacing the floor inside, this Spring I will be working on bonding the top to the bottom of the boat. It uses a "shoe box" design with about 1-1/2" face for the rub rail to go over it. Originally, the boat had rivets, screws, nuts and some fiberglass joining the top to the bottom (a previous owner did some repairs). I am planning on having a 1-1/4" wood strip along the inside of the boat which will allow me to secure the rub rail. Ideally, I would like to epoxy (and fiberglass) the top to the bottom, my concern is filling the gap between the top and the bottom since that would be an area of movement and potential flex. Normally, the joint is caulked after it is screwed or riveted, but I want this build to be one solid piece without screws because I will be fiberglassing the transom and knees in the rear to connect the top to the bottom. Hope you guys can picture what I am talking about. I'll try to upload some pictures.
     
  2. aaronhl
    Joined: Aug 2012
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    Location: Central Connecticut

    aaronhl Senior Member

    uploaded pics
     

    Attached Files:

  3. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    If you epoxy and screw through it, there shouldn't be any need to also fiberglass it. The screws from the rubrail will also help.
     
  4. aaronhl
    Joined: Aug 2012
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    Location: Central Connecticut

    aaronhl Senior Member

    Do you see any issues with having to squeeze the epoxy into the joint given that there may be a 1/4" gap at some areas? Because of the gaps, I feel I would have to squeeze thicken epoxy from the inside and the outside. The only reason why I say I would fiberglass the top to the bottom is because I want to put a light layer of glass over the wood trim pieces on the inside and figured it would be covering the top and the bottom at the same time.
     
  5. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    You need to make a thickened resin fairly thick is all.

    Mix fumed silica into epoxy by volume at 2.1-2.1 to one. Mix in a bucket and homogenize on a board to keep ot from kicking too fast.

    As long as it isn't too runny; it'll stay in at 1/4", but you need to stimp test it and make sure it doesn't collapse in a pile on a board. Pretty messy. Not sure I wouldn't just use 3m 4200.

    Any real deep areas you can jist use some tape to hold in and remove the tape after cure. Might be a bit of sandi g to remove tape bits.
     
  6. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    If you precoat the wood cleats with epoxy; there is little need for glass. You could also use 3/4" coosa same way to avoid rot concerns.
     

  7. mudsailor
    Joined: Mar 2013
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    Location: United States

    mudsailor Junior Member

    3M 5200.....a boat that size does not need to be glassed
    5200 will fill the gap fine, then screw the rubrail on through deck and hull
     
    fallguy likes this.
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