Whats the strongest bulkhead joint

Discussion in 'Boat Design' started by leegrace, Jan 24, 2006.

  1. leegrace
    Joined: Oct 2005
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    leegrace Junior Member

    Hi,

    Just wondering what the strongest way to bond a plywood bulkhead onto a GRP hull is?

    Use fillets, L brackets bonded to hull and bolted through bulkhead, etc?

    Thanks

    Lee
     
  2. BillyDoc
    Joined: May 2005
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    Location: Pensacola, Florida

    BillyDoc Senior Member

    Hi Lee,

    I should leave this to the experts, but I suspect you are asking the wrong question. If you make your bulkhead/hull joint stronger than anything else in your structure, you are going to shift stresses elsewhere and probably cause a stress concentration fracture nearby. Perhaps a better question would be: "How can I balance the strength of my bulkhead/hull joint with the strength of the bulkhead and the strength of the hull." Ideally, the whole structure will have essentially the same strength throughout its various parts. That way, weight and materials are minimized and overall strength is maximized.

    Bill
     
  3. lewisboats
    Joined: Oct 2002
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    lewisboats Obsessed Member

    I would say filleted (Epoxy), then 3 layers of cloth, each wider than the last, on each mating surface (both sides, top and bottom) of the bulkhead.

    Steve
     
  4. jegsmith
    Joined: Jan 2006
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    jegsmith New Member

    The best way to join a bulkhead to a grp hull is by using high density foam blocks between the bulkhead and the hull to spread the load of the bulkhead around the area it is being bonded to the hull. Fiberglass tabbing must be applied over this assembly. There needs to be a lot of contact for the fiberglass tabbing and dont forget to wet out the plywood before tabbing it on because the plywood tends to absorb whatever glue used and cause a dry and weak joint.
     
  5. leegrace
    Joined: Oct 2005
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    leegrace Junior Member

    Thanks for your replies. Its not for a real life situation but for a university project so it is a case of making it as strong as possible but also get the balance with weight as the assessment marks will be awarded for the load taken before failure divided by the overall weight of the test panel.

    http://boatdesign.net/forums/showthread.php?p=73830#post73830

    Thanks for all you input. Keep it coming!!!
     
  6. Darren
    Joined: Aug 2004
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    Darren Junior Member

    Hi
    We use 1152 PA (Filleting Paste) with a 50mm rad & then bond the bulkheads to the hull/deck using chop strand/biaxial/chop strand
    We use this method on boats up to 30 mts
     
  7. LP
    Joined: Jul 2005
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    LP Flying Boatman

    +/-45 deg. bi-axe will give greater strength across the joint since all strands will be crossing the joint whereas, 0/90 will have half of the strands running parallel to the joint with no contribution to the strenght of the joint. The chopped strand mat should not be needed if working with epoxy.
     
  8. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Isn't the object of the lesson problem, to insure you understand the concepts and can work toward the solutions with the necessary engineering?
     
  9. glassman
    Joined: Nov 2004
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    glassman Junior Member

    it seems the kids today dont want to get dirty , Par ,I like the way you think
     
  10. BOATMIK
    Joined: Nov 2004
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    BOATMIK Deeply flawed human being

    The strongest joint is the one that you have added the most materials to and that affects the largest amount of material in the panels being joined.

    The limitation comes with expense, weight, complication.

    MIK :)
     

  11. Robjl
    Joined: Nov 2005
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    Robjl Senior Member

    What thickness hull and bulkhead are we dealing with?
    And how will it be supported for testing?
    Need this to advise on layup/connection.
    Cheers
    Rob
     
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