Outboard transom core area

Discussion in 'Fiberglass and Composite Boat Building' started by Toepfer Marine, Apr 27, 2021.

  1. Toepfer Marine
    Joined: Apr 2021
    Posts: 3
    Likes: 0, Points: 1
    Location: east coast USA

    Toepfer Marine New Member

    Hello friends, Some how my old log in Creds got lost or removed, any how, I am taking over a project of building a simple 18' outboard powered skiff. powered by a 115 HP Mercury Outboard, the stringers are to be 24 " on center and approx 6" tall and 2.5 wide with two laminates of 1708 continuously tabbed to the hull bottom, first tab to cover 4 " of ground hull bottom second to cover 3" of primary laminate, speeds projection is max 35 knots, I do not know the hull lamination schedule, but I will bore a hole for a raw water wash down and burn the plug to see what she might be made of. My question is what area of the transom needs to be cored I have noticed over time many builders are getting away from coring the complete transom and keeping the core material fairly local to the foot print of the Motor mounting area, this transom measure 73.25 at the Sheer and 62."at the Chine and has a vertical measurement of 20" at the cut out for the Motor. in the big picture its no big deal to core the complete area but I have a nice piece of high density corecel foam that I can do the local area,, Thanks Bo
     
    Last edited: Apr 27, 2021
  2. kapnD
    Joined: Jan 2003
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    Location: hawaii, usa

    kapnD Senior Member

    Your question begs for details, engineering data does not emerge from a crystal ball!
    Will it be 3 hp or 300?
    What will the boat weigh?
    How fast do you expect it to go, and what’s the bottom and stringer configuration?
    What’s the laminate schedule?
    Localizing the cored transom area means that the uncored part must be as strong as the cored part, or the load must be transferred to the stringers.
    Pictures?
     
    fallguy likes this.
  3. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    Typically, corecell density is not high enough for a transom.
     
  4. Toepfer Marine
    Joined: Apr 2021
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    Location: east coast USA

    Toepfer Marine New Member

    Thank you Kapn D I have edited my post with all the info I currently have
     
  5. comfisherman
    Joined: Apr 2009
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    Location: Alaska

    comfisherman Senior Member

    Ours up here are a bit thicker. But our boats are used a bit heavier and usually rougher weather. Seems like most are coosa 26 spanning at least the stringers and outboard area.
     
  6. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    Minimum transom density is about 24#/cuft. Corecell M HD is only 12# density. It won't work. fyi

    Also, a transom like yours wouldn't get a local insert as that would present a weakness to the balance.

    These transoms are not repaired like an aluminum skiff where you put a piece of plywood as a clamping board, and I have never seen any repairs done with discontinuity.

    Before you do a burn test, take a caliper and measure the plug and try to count the layers.

    The post is still a bit confusing. Is this a plywood build?
     
  7. Toepfer Marine
    Joined: Apr 2021
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    Location: east coast USA

    Toepfer Marine New Member

    No its solid FRP, Thanks for the info on the core cell
     

  8. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    so, why would you want to install a light core in a solid frp boat? Assuming you realize this is now wrong...

    is the transom done and needs repair or not done and adding at the end or some such?

    if you are planning a cored transom for an unfinished solid frp boat, you need a laminate schedule for an appropriate core
     
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