Curved beam?

Discussion in 'Fiberglass and Composite Boat Building' started by andysailor, Jan 10, 2018.

  1. andysailor
    Joined: May 2017
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    andysailor Junior Member

    I plan to make a curved beam to have in the aft of my trimaran to hold an aft trampoline.
    One way would be to use foam and put about five layers of 10 or 12 mm overlaying each other. between each layer of foam putting carbon fibre/kevlar/or fiberglass. And in the end wrap the beam with cloth.

    Another way would be to build a box beam and wrap it with kevlar/carbon/or fiberglass. Would I stiffen it up also by adding cloth to the inside of the beam as well (before closing it)?

    Beam needs to be about 8 meter long and I guess somewhere around 15 cm high.

    How would you do?
     
  2. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    It is necessary to know the loads that this beam must support in order to establish the proper lamination schedule.
     
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  3. jorgepease
    Joined: Feb 2012
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    jorgepease Senior Member

    Me: 2 half molds, infuse, glue together, don't know about laminate, would get an engineer to do that side of it.
     
  4. TANSL
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    TANSL Senior Member

    First and most importante is to know the loads that this beam must support.
     
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  5. andysailor
    Joined: May 2017
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    andysailor Junior Member

    Well, you are right, of course it''s all about the loads. I just don't know the loads. The beam will extend from stern of the main hull to the akas.

    The beam will be holding a trampolines outer edge (about 3,5 meter) and the area of the trampoline is about 3.5 sqm. Using a 50% openness net.
    The maximum calculated load will probably be breaking waves over the trampoline.
     
  6. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    Can you provide a sketch with dimensions of the whole arrangement, and the displacement of your boat too?
     
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  7. andysailor
    Joined: May 2017
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    andysailor Junior Member

    Don't have the exact measurements here but here is an old sketch I found. It would be option #2, but curved. Measures is something like.
    Length: 3 meter
    width: 2 meter
    outer edge (the beam) 3.5 meter
    [​IMG]
     
  8. Ad Hoc
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    Ad Hoc Naval Architect

    Thanks....but not really sufficient to answer your question properly.
     
  9. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Lets start from the beginning. What's the make, model and year of the boat, with related options?
     
  10. andysailor
    Joined: May 2017
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    andysailor Junior Member

    It's a one off, built in the mid -80's
    46ft long, 28 ft wide, weighs about 7-8000 lbs. Hull, Ama, and the underside of aka is foam and glass. Deck and aft part of the aka is ply.
     
  11. jorgepease
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    jorgepease Senior Member

    Why all the info needed, the loads are for what the trampoline must support, no? Won't that just be live loads, you and your crew? ... The beam is not there to support the boat in anyway, right?
     
  12. luff tension
    Joined: Aug 2010
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    luff tension Junior Member

    Why not just do a wire support edge on it like the front tramps
     
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  13. TANSL
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    TANSL Senior Member

    There can be relative movements between the main hull and the amas that cause efforts on the new beams. The designer may want to consider them or not. If it's just about supporting the crew (which I do not think is correct), the solution is simpler. In any case, you must define the supports of the beams at their ends.
     
  14. andysailor
    Joined: May 2017
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    andysailor Junior Member

    The beam will be attached to the main hull and the aka (not Ama). The beam and trampoline needs to handle, crew and breaking wave impact. The movements between aka and hull should be minimal. The aka's includes box beams, reaching from port to starboard side.

    Wire, instead of beam could work, but it would feel safer and a more usable area if adding the beam. But, you are right, it could be a much easier way to go.
     

  15. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    I am only going to be the dumb guy here. Just a boat builder. I don't quite understand the need for the curve. Maybe you could redraw/explain so that others can help you better. And be more specific about the intended attachment points. Are you curving down toward the aka or in toward the aka from the aft portion of the hull? Perhaps others here understand better out of the gun, but not me. I assume the curve is in, but why when you show straight lines?
     
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