Hat Section Bulkheads? These I DO plan to install.

Discussion in 'Boat Design' started by CatBuilder, Dec 25, 2011.

  1. iceboater
    Joined: Jan 2011
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    iceboater Junior Member

    I make 6 metre long male mold of different sizes I use. Then I lay one 900gr strand mat on the mold and use that to build up the stiffener on the hull.
    These stiffeners are always empty on my boats, so they can be used for for wires or pluming if you are careful about where you put the hole in them.
    The file is for calculating sizes according to NBS and you might be able to use it for reference.


    Attached Files:

    Last edited: Dec 27, 2011
  2. upchurchmr
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    upchurchmr Senior Member


    I find it hard to give "enough" but not cause confusion and I know I err on the side of too much.

    In my case its easy to know a little more but not actually help because I don't know enough about boats. Even in my own business you have to know all the details of a particular airplane to provide something actually correct.

    We do not disagree and I respect you making the effort.


    I should have known you would already have tried. I'm a little shocked.

    I've never made a hat in anything but aluminum or graphite composite, can't help you with the scantlings.

    Good luck,

  3. idkfa
    Joined: Sep 2005
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    idkfa Senior Member

    Thanks Upchurchmr for the standards posting.

    Frames flex with hull - good. Bulkheads are necessary evils!
  4. CatBuilder

    CatBuilder Previous Member

    While we are on this topic, I have a general question that I was unable to get my designer to answer:

    What is the minimum section of a bulkhead?

    As in... how many inches or mm from the skin of the hull, to the point where you can cut out your holes in the bulkhead?

    I ask, because Richard's post really makes me think I need to leave the one bulkhead I need to remove alone. But, I'd like to trim it back.

    Currently, it goes about 1/2 the width of the hull, with several very large cutouts.

    I could gain counter space by leaving 6" of this bulkhead where the counters are and allowing the bulkhead to go full width up top and down below, inside of cabinetry.

    Would a modification like that work?
  5. Richard Woods
    Joined: Jun 2006
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    Richard Woods Woods Designs

    It all depends on why the bulkhead is there

    In your case I assume it is the chainplate reinforcing bulkhead.

    So you have to decide, do you want more counter-space or a strongly attached rig?

    No contest obviously

    So you have to redesign the structure to get the rig loads taken safely into the hull

    Anything is possible, but only one way is the best way. Everything else will be second best or a compromise

    Really you'll have to wait until your designer is able to help you. Its too important a structural item to ask anyone else. But from Kurt's blog looks like he's still tied up with the USCG

    Richard Woods of Woods Designs

  6. CatBuilder

    CatBuilder Previous Member

    Thank you, Richard for the input. Yes, Kurt is tied up - up to his eyeballs, I'm sure with government regulations.

    Guess I'll save that for January's question. :)
  7. sorenfdk
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    sorenfdk Yacht Designer

    Sorry, but your reasoning doesn't make any sense! ...it just adds weight is pure rubbish!
    Of course, you should design the panel to be stiff enough in the first place, but if it turns out not to be stiff enough, then a frame actually is a quite effective solution to the problem! It is not always possible or practical to add a bulkhead.
    In this case, where the builder wants to change the design, a frame is IMHO the way to go.
    We need more information about the design to determine if the panel is stiff enough or not. I guess it is, but guessing is not good enough!
    And regarding weight: The thicker, heavier foam has already added quite some weight!
  8. CatBuilder

    CatBuilder Previous Member

    Can I give you more information? Please let me know what you need and I will supply it.
  9. sorenfdk
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    sorenfdk Yacht Designer

    I would at least need a lines drawing, a GA and a Materials Specification. But most of all, I would need some time, which you, unfortunately, can't supply :(
    I don't know Kurt Hughes, but I'm quite impressed with a lot of his work. This is about the structural integrity of one of his designs, so I honestly find it quite disappointing that he can't seem to find the time to answer your question!
  10. CatBuilder

    CatBuilder Previous Member

    Well, just in case the time opens up... :)

    The lines drawing is below. The bulkhead I am looking to replace with a hat section is the one indicated. The chainplate is attached to the hull where you see a round sink just aft of the indicated bulkhead.

    It is a composite chainplate, I think I will do, maybe the stainless one if I get lazy. I have both options available in the plans.

    Materials spec is as follows:


    1150g triaxial
    25mm, 100kg Corecell
    1150g triaxial
    (infused with infusion epoxy from MAS)


    18mm Lloyd's register, BS1088 African Okoume, produced in Greece

    50mm diameter epoxy cove joint holds bulkhead to hull - no glass taping or tabbing on this bulkhead, only on structural bulkheads call for glass taping or tabbing, meaning bulkheads that are part of a beam spanning both hulls.

    I am not sure what a GA is though. Pardon the ignorance there. :(

    Kurt gives you about one question a month to ask. I could fit this in for January or February. He is truly getting pummeled right now by the US Coast Guard government regulations, so we should cut him some slack. Yes, he does very good designs, which is why I chose him.

  11. rberrey
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    rberrey Senior Member

    It,s my understanding thet at least with the design I,m building ,if you use foam you do away with the frames. Bulkheads are something else , but the frames can be replaced with stringers. I would have to agree with Richard, if the panel is stiff enough you would,nt need the support. Rick
  12. CatBuilder

    CatBuilder Previous Member

    Ok, well for you and richard, why does Gunboat make use of hat section bulkheads (vertical frames)?

    Also, my design uses them as well in alternate interior plans for aft bulkheads. I did already say all of this, but it's not reconciling with your post or Richard's in that department.

  13. groper
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    groper Senior Member

    Cat, normally the scantlings of the HAT are the same as for the inside hull skin, its just the width and depth of the HAT section you need to figure out, obviously the taller and wider it is the more stiffness you add... you can build it over a PU or XPS foam forma which makes laying it up easy and cheap... but with all your counters and cabinets in this area, i would hazard a guess you shouldnt need anything else in this area provided you make some key parts of this cabinetry structural, especially near that chainplate...
  14. TeddyDiver
    Joined: Dec 2007
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    TeddyDiver Gollywobbler


  15. CatBuilder

    CatBuilder Previous Member

    Thanks for these last couple posts. Been very busy in the boat shop and away from the forum, but thank you.
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