Build up core for transom.

Discussion in 'Fiberglass and Composite Boat Building' started by fallguy, Oct 26, 2017.

  1. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    I want to build up a core to 1 3/4" for a transom. I will use two pieces of 1/2" and one 3/4" high density M200.

    The lamination schedule for the transom is 4 layers each side of 22 ounce triaxial. The triax is 0 +45, -45. I rebated the bottom and the sides of the hull to accept all 4 layers if needed.

    Part of me thinks I could probably put one of the laminations onto the core under vac...

    So, my questions.

    Would you cut the transom to fit inside the hull panels all the way or would you cut two panels for the inside of the hull and sort of cap the other panel over the hull sides with a nice 1/2" radius to the rebates?

    And would you hot coat the two outside panels and vac bag the three panels together, or would you mix up some say 1 to 1 epoxy and cabosil and vac that? It might be rather tricky to vac bag with the step in the part...if I do the step method as I might get some excess epoxy there

    My high density stuff (I think) does not have perforations, well, the 1/2" is here and doesn't. I don't know for sure on the 3/4". Would you perf it? And if so, would the perfs need to be all aligned or preferred not.

    Thanks for any replies. I doubt I can purchase 1 3/4" high density foam. And it would probably cost like 100 bucks a square foot, so....yeah. And I can't really afford to screw it up, so the hot coating idea is a little nerve wracking..
     
  2. gonzo
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    gonzo Senior Member

    Is this a repair?
     
  3. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    NO. New build. Powerboat, 70hp 4 stroke on each, 10M catamaran
     
    Last edited: Oct 27, 2017
  4. fallguy
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    fallguy Senior Member

    File Sep 29, 11 42 57 PM.jpeg


    Here is a picture of the transom location in the frames/hull setup. 19" high plus the 1/2" core under for a total of 19 1/2" high for 20" motor spec. Just under 36" wide. If you look close, there is a little black line struck at 19". There are a couple of shims to keep the rebates from getting misshapen or flaring out at the join to the frame. The hull is in a female frame; disregard the long pine boards in the picture, those are just to keep the spans dimensionally accurate on assembly of the top panels and because we had to split the female frame to make room for the hull lift out of the frames so we don't need to remove the entire frame as there is another hull to build after this one.

    There is a motor well for the transom that'll sit above DWL, and I'll probably run a drain about 1" above DWL. The transom is the last thing going into the hull on the transverse before we deck it.

    We are further along in the build; this is just a picture I grabbed for a visual.

    Just want to know if you'd put two pieces of core on the inside of the panels and run the other one over the edge and put a nice radius on it, etc. If you did it that way, the 3/4" might be the nicer on the outside, etc.

    Please just looking for build advice; thank you. By the way, a number of you contributed to this project already when recommending female frame; here is it.
     
  5. ondarvr
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    ondarvr Senior Member

    12# foam wouldn't typically be used in a transom for an outboard, you'd normally start at maybe double that. Although with the correct methods it could be used, you either need to increase the density where the motor is bolted in place, or make a solid area around the bolts.
     
  6. missinginaction
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    missinginaction Senior Member


  7. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    Thanks! Coosa is on the way. I will use my high density in other areas where I want hardware.
     
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