developable surfaces

Discussion in 'Boat Design' started by metin_mehel, Jul 31, 2013.

  1. metin_mehel
    Joined: Jul 2009
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    metin_mehel mech.eng.

    Hello,
    As you know hard chined boats are designed by the 3d programs such as rhino,
    Than flat patterns are done by unrol developable surface etc.
    I wonder what happens if those flat plates epoxy coated, and one surface is coated by fabric. Then the plates are mounted to each other?
    the normal manufacturing is first those plates are connected to each other with for example stitch and glue then epoxy coated and fabric too.
    I mean maybe while those plates are laying down the floor, the glassing and grinding for getting smooth surface is easier than the traditional way?
    what are the comments?:?:
     
  2. gonzo
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    gonzo Senior Member

    That has been done when the sheeting is only for waterproofing. If the laminate is structural, it may end up being too rigid.
     
  3. PAR
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    PAR Yacht Designer/Builder

    Bending a previously faired surface will likely make it unfair, possably popping out your filler materials too, so a waste of time and materials. Pre-coating the plywood with epoxy is a common practice, but pre-fairing and smoothing will be self defeating.
     
  4. metin_mehel
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    metin_mehel mech.eng.

    Par, I meant pre-coating but not ony epoxy, I meant coating with glass fibre.
    How about junctions of two adjacent glass fibered plywoods while they are mounted to construct the hull?
    the connection become weak? it needs additional glass fibre to reinforce the junction?
    Thanks
     
  5. PAR
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    PAR Yacht Designer/Builder

    My comments were directed toward your intent to pre-sheath, with fabric set in epoxy. A straight epoxy coating is acceptable, sheathing isn't.

    In repairs you have no choice but to use some sort of joint on the hull (or where ever). You have a few options, a scarf, a butt block a Payson butt joint, etc. The Payson butt joint will require some fabric in or over the joint to insure its integrity. Without the fabric, the joint will just crack out.

    You'd be best advise to download the free user's guide from westsystem.com and the "Epoxy Book" from Systemthree.com. These will cover the appropriate techniques when working with epoxy set fabrics and reinforcements.
     
  6. rwatson
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    rwatson Senior Member

    In support of the previous very pertinent comments - . The benefits of pre-finishing even a full size panel before bending to shape are a bit marginal, compared to the very real difficulty of forcing fibreglassed plywood or other materials to form.

    Often getting the plywood to conform to a curve is difficult enough ( especially near the bow area for example ) without the added pressure of a layer of glass on it.

    Also, any high quality finish would be at risk during the laying of the big finished panel on whatever formers you are using.
     
  7. SamSam
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    SamSam Senior Member

  8. gonzo
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    gonzo Senior Member

    It works with foam core. We used to make hardtops with panels glassed and faired on one side. Plywood would get too stiff.
     
  9. rwatson
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    rwatson Senior Member

    I know foam does too - once it gets one layer of glass, especially if its a final external layer of glass like the OP is suggesting, its not very flexible.
     

  10. groper
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    groper Senior Member

    I think it would work, just need to account for how much curvature there is and whether material can take the bend you need it to. I would also fair it roughly, not completely, as some unfairness can creep in. A lot will depend on the stiffness of the joints- I would guess that a scarf would produce uniform stiffness joint whereas a payson butt joint not so. If you try to bend a jointed panel with different stiffness in its joints, it won't bend fair. That's your main consideration....
     
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