connect two foam torsion boxes

Discussion in 'Fiberglass and Composite Boat Building' started by fallguy, Jun 29, 2018.

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  1. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    I want to build two floating,removable cockpit catamaran panels as torsion boxes. They will be about 70-80mm high with about 50mm in the middle and 12mm laminates on each side.

    I need to attach them at the middle and I'd like the attachment to be failproof. That is, if the connections come loose, the panels won't fall into the sea.

    Each panel is about 4' wide by 8' long with the join on the 8' side.

    I have a few different ideas, just wondering if anyone else has a better one.

    I would prefer to avoid flush mounted deck hatches if possible. If you had one every 2'; you'd need 5 which would be unsightly.

    A removable panel over the seam would be a possibility, but no ingress would be allowed as the torsion boxes also serve as service conduits for electrical and hydraulics.

    tia
     
  2. SamSam
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    SamSam Senior Member

    Well, it would work better if you posted your ideas to see if anyone's got a better one. Otherwise, people could post 3 or 4 hundred ideas, and then if it turned out yours was best, everybody would have wasted a lot of time posting useless ideas.
    Sorry, but I get no clear idea of what you're attempting. Maybe post some photos and clearer info. I'm wondering things like what is attached at the middle of what to what and where every two feet and 5 hatches comes into the picture. What is this 8' join you speak of ? Assuming the panels and hull are built similarly, aside from the laminates and resin, a person almost has to know what the core is made from. Is this panel an afterthought to be added to an existing boat or is this a future project in it's design phase?
     
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  3. SamSam
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    SamSam Senior Member

    Alright, I see in the title the core is foam. When information is only in the title, you have to scroll for it and I'm very lazy so I often miss it.
    Since you want them removable, bolts sound promising, since it's foam core, localized reinforcements would be necessary.
     
  4. fallguy
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    fallguy Senior Member

    Thank you for the criticism SamSam. I was a little worried I wasn't providing enough detail and you affirmed my concern.

    This is a project under development. I will provide a crude drawing and a picture of one of the ideas (one I don't like). I am not so great with drawings, but will try.
     
  5. fallguy
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    fallguy Senior Member

    Here is a vee shaped channel mock up. Upside is all connections from above and a loose bolt would not fall into sea. AF75D8E5-74C9-4163-BA2A-8786866E2D02.jpeg Downside is they'd need covers and use a lot of foam on the edges. Foam at bolt would be high density (not in mock up due to cost). The stuff is like $15/sqft.

    Of course, this is only one side of the box and the bolt wouldn't be an unwashered pan head, etc.
     
  6. fallguy
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    fallguy Senior Member

    Here is a crude drawing with explained dimensions. Not to scale..this shows a couple of deck hatches where you'd open them and do the bolting and close them again, but for 8' it'd probably be a lot of deck hatches.

    My other idea is not drawn, but I had wondered about putting a removable panel over the seam say like 6" wide; the boxes would be opened, then joined, then the removable panel screwed down, but that panel would need to be over a section of the torsion box that would drain as the panel would need to come off and on. That panel would use more high density foam and a little worried about the holes getting stripped for the cover easily.


    torsion box picture.jpg
     
  7. fallguy
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    fallguy Senior Member

    Also, the reason for the torsion boxes is they would be stiff, and allow for service conduit to the helm from the engines for hydraulic steering and electronics for the engines, throttles and shifting, and depth finders, etc.

    The boat is demountable if I didn't mention early on (thought I did). So the panels need to be light enough to move by hand onto the truck or into the cabin for moving the rig to seas. And this is why we would build two panels and connect them. Handling an 8'x8' panel would be tough. It wouldn't fit in a doorway for moving, etc.

    Thanks for any replies.
     
  8. rwatson
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    rwatson Senior Member

    I'm still "taking in" the design, but one point that is obvious immediately

    "Foam at bolt would be high density foam ....."

    I would replace that spec with "Bolt connection will be 1/2" solid fibreglass.
    You don't use foam at joins , even for hull/deck connections.
     
  9. fallguy
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    fallguy Senior Member

    FYI
    The other side of the cockpit panel is the hull and that side of the hull is HD the length of the cockpit panel. The original cockpit panel was spec'd with AL angle. I can add more fiberglass to the inside of the hull at that location once we determine the location better. The AL angle or a metal strip will be getting laminated into the torsion box now. We can also laminate AL angle into the torsion box connection side. I did not put that in the mockup, but it could be in it on the edge. The inside of the hull at the panel can also get a strip of metal or be heavily washered.

    I have to be able to pick the torsion boxes up at the end of the day, so half inch thick glass on each side (box and hull) might get a little difficult. None of the above fyi means I disagree, but I need to make it manageable..

    I will update the drawing to reflect the AL angle.
     
  10. fallguy
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    fallguy Senior Member

    some type of aluminum strip or angle can be laminated into the sides of the box to go along with the fastening method and the metal can replace or be an adjunct to the HD foam

    torsion box picture.jpg
     

  11. rwatson
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    rwatson Senior Member

    No, no - I don't mean 1/2" glass for the whole side of the box - just the fastening area, perhaps 6-12 inches around it.
     
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