Bulkhead relocation

Discussion in 'Boat Design' started by Liamrye, Jul 23, 2023.

  1. Liamrye
    Joined: Jul 2023
    Posts: 4
    Likes: 1, Points: 3
    Location: Sandwich

    Liamrye New Member

    Hi all

    Recently acquired my first boat, to be used primarily as a liveaboard. I have little information on the boat, but it's a 30ft grp cabin cruiser from the 80s or so, twin engines, fore cabin, nice large saloon/galley and a large head

    The existing bulkhead had been butchered. Their construction consists of two up 12mm ply rights forming a doorway, tabbed into the hull and joining underneath the floor. They had been pretty badly butchered. One had been cut half way up, the top half removed and replaced with PU foam in plastic sheets. Which just met the side and ceiling and wasn't tabbed in.
    The other side had a large section where it joins the side of the hull to run services (I assume)

    As they'd been butchered I removed them with the intent to replace them, but I'm wonder if they can be replaced properly (leaving the existing stringer in the floor) but installed 7 inches or so aft of their original position without causing issues.
    If they were originally structural then I think their integrity had been compromised so should I tab the nee bulkheads in as the originals were?

    Many thanks
  2. Liamrye
    Joined: Jul 2023
    Posts: 4
    Likes: 1, Points: 3
    Location: Sandwich

    Liamrye New Member

    I realise photos will be helpful, so just tell me what you'd need photos of and I'll add some.
    Thanks again
  3. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    Yes please re some photos Liam - and welcome to the Forum.

    Re how you are not sure what make of boat you have, please do post some general photos of the boat on here, and the odds are good that somebody will recognise her.

    Some photos of the interior showing the butchered bulkhead and surroundings would be useful as well.
  4. Liamrye
    Joined: Jul 2023
    Posts: 4
    Likes: 1, Points: 3
    Location: Sandwich

    Liamrye New Member

    Thanks for having me! I've uploaded the pictures now, the bulkheads are removed now, as I just wasn't happy with how one of them had been (poorly) replaced with foam

    So first photo shows the removed bulkhead

    Second the old bulkhead on the left this one had been butchered for services and on the right that's with the foam section removed.

    Last photo is exterior. Thanks again!

    I can get some more detailed photos tomorrow

    Attached Files:

  5. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    Most people come to this website with queries like yours and all they really want is affirmation that their desired goals are permissable. It looks like you wish to extend the berth dimensions.

    It is impossible here on the forum to foresee all the issues you make encounter moving the bulkhead or even if it is much of a bulkhead. A first obvious question is do the windows intersect the bulkhead at a mullion? Or how then? Or is the bulkhead only up to the windows? The ideal way to fix this would be to maintain the original bulkhead to below the berth and then add the other bulkhead to support the new deck. This way; the hull design is enhanced and not changed. The 7" in between could become a small cabinet as boat storage is always a coveted bonus.

    If the bulkhead is not tabbed into the hull; then it is only an interior wall. No concern for prior errors ought to be given.

    There are too many unknowns for holy water.

    For example, are the stringers continuous or do one or any end at the original bulkhead..etc.
    bajansailor likes this.
  6. Liamrye
    Joined: Jul 2023
    Posts: 4
    Likes: 1, Points: 3
    Location: Sandwich

    Liamrye New Member

    Yes, want to extend the fore birth.

    No the bulk head just bridged the windows and looked awful, both from inside and outside. This can be seen in the photos.

    Now the bulkhead has been removed, below the floor level is a stringer that formed part of the bulk head. That will remain, and I plan to build the new bulk head 7 inches aft of its original position either to the floor level or below into the bilge forming another stringer aft of the existing one. There is some more stringers in the V berth these will remain unchanged.

    In my mind atleast, the bulkhead supported the deck above and the stringer (which will remain) supported the hull.

    Many thanks

    Attached Files:

    bajansailor likes this.
  7. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    The bulkhead and stringers are structural members that work together. Shifting the bulkhead 7 inches is not a significant change. However, if you have a problem with the bulkhead against the window, that is a completely different issue. It supports the cabin top, which otherwise would be supported by glass.
    bajansailor likes this.
  8. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    Most of these old boats were not engineered to any spec, they built them to whatever design they worked out on the back of a napkin after too many beers.

    So moving it 7" means nothing. Now making the rest of it work to your liking is a bit more involved only because you have other limitations or concerns to work with.
    bajansailor, fallguy and gonzo like this.

  9. kapnD
    Joined: Jan 2003
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    Location: hawaii, usa

    kapnD Senior Member

    Have a friend walk on the deck while you observe from below. That should tell you something about the need for the bulkheads and their location.
    Typically they’d be located at the bottom of the windshields.
    Partial bulkheads may suffice, or a post and beam type of support, impossible to assess from online conversation.
    fallguy likes this.
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