make homemade super-sized fiberglass/wood ply for super-sized stitch&glue?

Discussion in 'Materials' started by Squidly-Diddly, Apr 18, 2020.

  1. Squidly-Diddly
    Joined: Sep 2007
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    Squidly-Diddly Senior Member

    Stitch&Glue is nice, but you always gotta work around fairly short 8' or 2M plywood size, then making less than optimal joints. It bugs me, especially for a small boat, that then you supposed to then locate framing at the joints.

    So I'm thinking, for something like Sharpie, that fabricating big flat or gently curved full size panels of fiberglass and regular non-ply wood stringers, then assembling as if they were precut stitch&glue might have advantages.

    I'm thinking it would be easy to fab fiberglass/wood panels when laying flat, and unlike plywood I'd be able to use diff Schedules of fiberglass/wood in diff areas.

    Then again, I've heard the main advantage of fiberglass is the structural strength it gets from being a complex rounded shape, much of which would be lost making big flat or at least developable panels to Stitch&Glue.
     
  2. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    I have started to build a 12' two part nesting dinghy with two chines made from laminated fibreglass sheets (just a CSM/WR/CSM combination).
    It will be almost symmetrical fore and aft, with the aft end being a bit fuller, so that the bow section can sit inside it comfortably.
    The fibreglass panels are all stitched together with cable ties before laminating the joints, in similar fashion to a plywood dinghy.
    I made up the panels on a sheet of galvanised steel plate (bought from a roofing company here, before they put corrugations in it).
    I stitched the panels together some years ago; I just have to finish it now.....
    But I think it will work well. And as you mentioned above, I can use different (additional) lay-ups in different areas as required.
    The aim is to try to make it as light as possible.
     
  3. Squidly-Diddly
    Joined: Sep 2007
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    Squidly-Diddly Senior Member

    Nice tip on the metal roofing. Might be able to form gentle curve so panels aren't over stressed with bending to join, especially if panels have embedded wood stingers for strength and stiffness.
    Another thing that bugs me about stitch&glue (never actually done one) is where the sharp edges meet. Maybe I missed it but I'd want to bevel the edges so they have at least thickness of the material wide flat contact. If I was gonna make my own panels of fiberglass and wood, I'd put angle cut wood stringers on the edges of where the panels would be joined, for lots of contact, and figure out right type of fastners or whatever.
     
  4. Rumars
    Joined: Mar 2013
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    Rumars Senior Member

    Possible, yes. But it does not make much sense if we are talking flat panels. A properly scarfed plywood joint is perfectly fine structurally. Curved panels are either done directly on the hull mold and then it's called "cold molding", or on a separate mold in one piece or in sections (cylinder molding, constant camber).
    Making your own plywood is expensive, you need a lot of veneer plus glue. In the absence of a heated press the glue must cold cure at low pressure, usually meaning epoxy. There is no advantage whatsoever to normal cold molding.
     
  5. Dejay
    Joined: Mar 2018
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    Dejay Senior Newbie

    I've been thinking of something similar, weather it would be possible to vacuum infuse your own plywood panels. Not for stitch and glue but for a type of SIP, or structural insulated panel for a cabin. Something like 3mm thick wood strips, maybe 40mm wide. Then XPS with flow channels cut in using some sort of big hot wire cheese grater. Vacuum infusing 10m x 3m walls with cheap materials and little work would be awesome.

    I plan to do some experiments when I finally get by workshop sorted. The question is if the resin would flow in between and around those veneer strips (probably not). This would probably work just fine using hand layup and vacuum bagging. My main concern is really building large thick insulated walls in one go and without endless sanding and painting.

    But then like Rumars says you'd then need to source those veneer strips. Or make them yourself by building some type of oversized planer. That is how straight veneer is made after all. Theoretically I imagine you'd get much cheaper material costs using 2 inch thick rough sawn boards or 2x4s.

    For the stitch and glue idea I'd laminate only on the outside though so you don't compress the fiberglass laminate on the inside.
     

  6. DCockey
    Joined: Oct 2009
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    DCockey Senior Member

    Scarfing plywood to create panels of any desired length is a standard operation.

    Here is a 54 foot, Sam Devlin designed stitch and glue boat.
    Blue Fin 54 https://devlinboat.com/blue-fin-54/


    Who says joints should be located at panel joints?

    A sharp plane can bevel the edges of plywood quickly. Sam Devlin now recommends beveling panel edges at 45 degrees for about half the panel thickness.
     
    bajansailor likes this.
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