LVL Crossbeams

Discussion in 'Multihulls' started by goodwilltoall, May 20, 2018.

  1. goodwilltoall
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    goodwilltoall Senior Member

    Curious to know if you guys think these would work well. They are basically laminated ply just like plywood, have seen them used in construction in length up to 50' (wow). The engineered capacities are all speced, available in just about any size, and basically $6 a BF. Would guess they use WP glue as well.

    Encase them in a layer or two of glass and epoxy should be good togo
     
  2. fallguy
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    fallguy Senior Member

    Ungodly heavy for the return of strength/inertia.
     
  3. upchurchmr
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    upchurchmr Senior Member

    Right, you don't want solid wood (even laminated - actually laminated is worst) for cross beams.
    Of course if you just want the ultimate strength and low cost, get a steel beam.
     
  4. goodwilltoall
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    goodwilltoall Senior Member

    The laminations I would guess go in one direction since it is a beam.

    If box beams are whats needed you can make it from these, they are very stable.

    Maybe on a typ. 7000# boat you need 500# for crossbeams (lets say 40'L × 20'B), 3 main crossbeams, probably each beam would suffice with a double 2"x12". Thats 720# so an extra 220# on a cruising cat is acceptable. Btw, if recalled correctly, they are 6$ per ft for 2"×12".

    $720 for an off the shelf item that will attach to a wood bulkhead like no other material.
     
  5. UpOnStands
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    UpOnStands Senior Member

    Missing a link?
    Hollow Al. sections might suit (at least the fwd. beam). Must be a lot of scrap in the Caribbean from last year.
     
  6. fallguy
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    fallguy Senior Member

    A double 2x12 lvl is 12# per foot and way overkill in yy. Each beam would weigh about 240 pounds before glassing.

    LVLs have no rating in the x direction that I know of, but assuming the smallest lvl box beam of say 7" square; the thing would still be heavier than 240# before glass. Glass would be needed to keep the beam from splitting on a glue seam.

    I think your idea has merit, but not with conventional lvl widths or thicknesses, and byt hen you are back to AL.
     
  7. trip the light fandango
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    trip the light fandango Junior Member

    Epoxy saturated ply absorbs the resin so it doesn't swell, but building laminates , while the glue is waterproof, will still swell up. aluminium I beam would be wonderful with suitable struts and bracing. if you don't have time to make ply epoxy saturated beams. Money or time , I'd probably use donor woven glass cut to get the basic shapes required., although a roll of 3 inch glass tape is pricey[you can cut up matt of course] and it is time consuming to go down this path, first find a suitable wreck,.or mast section using the tracks to take the ply.... my 2 cents worth...
     
    Last edited: May 21, 2018
  8. fallguy
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    fallguy Senior Member

    Why does the Al mast section need ply?

    Straps.
     
  9. trip the light fandango
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    trip the light fandango Junior Member

    I was thinking 2 mast sections running parallel with ply slotting into the tracks to make the beam, with ply it is critical that the cuts/ edges are well sealed,this is where it mainly wicks moisture. Saturated in epoxy ,the west system is best. I tried a thinner for epoxy, tolulene but the type of epoxy I used didn't accept it, beyond my google search /chemistry capacity, West system worked it out. There may well be a Chinese copy now, I don't know.
     
  10. fallguy
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    fallguy Senior Member

    You can make a mechanical connection to the beam. You don't need to epoxy plywood to it.

    The ply in track is a bad idea for reasons you alread allude to..
     
  11. goodwilltoall
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    goodwilltoall Senior Member

    Aluminum complicates and adds costs for attachments at hulls, deck, and structures above.

    Box then has to be the easiest
     
  12. trip the light fandango
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    trip the light fandango Junior Member

    Scrap mast section can be cheap but you wouldn't want to build over it so as it couldn't be eyeballed, box ply has really good longevity if it has been painted with an anti fungal, I read here and elsewhere.
     
  13. upchurchmr
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    upchurchmr Senior Member

    Making a crossbeam doesn't work by guessing.
    Lots of early boats broke because the engineering wasn't done, and they underestimated the forces in a heavy storm.
     
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  14. trip the light fandango
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    trip the light fandango Junior Member

    Amateurs can do their homework. There are so many examples of well made craft and how to make sound joins, weight distribution and other discussions, i.e. due diligence. Engineers aren't gods. Proven designers/engineers are by far the safest, value for money/effort, but only if they build in proper flotation.
     
    Last edited: May 23, 2018
    dsigned likes this.

  15. trip the light fandango
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    trip the light fandango Junior Member

    Just as previous boats that were engineered broke up, hit something , or sunk, pushed too hard in a storm, or all of the above .
     
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