Gluing fiberglass/epoxy skin to pvc core for cabin construction

Discussion in 'Materials' started by JATesvich, Feb 16, 2021.

  1. JATesvich
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    JATesvich Junior Member

    I've purchased factory made 0.032" thick smooth fiberglass/epoxy sheets and plan to glue onto 1" divinycell core to use for making wall sections in the construction of an enclosed flybridge on a motor yacht. I believe that having the finished outer skin would significantly minimize layup and fairing time and labor. I am thinking of using epoxy to glue the frp skin to the core. I was wondering if there is any experience of bonding thin laminates to cores using any other adhesives? Also, I was considering using a plastic laminate, like Formica, for the interior skin. Any suggestions to the relative suitability of this type of composite combo for use in a flybridge enclosure?
     
  2. ondarvr
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    ondarvr Senior Member

    What type of structure/framing is this being attached to?
     
  3. JATesvich
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    JATesvich Junior Member

    The framing will be 2”x 2” x 1/4” frp square tube, fastened to the fly bridge deck and the existing frp hardtop.
     
  4. ondarvr
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    ondarvr Senior Member

    You would probably be better off with wall panels made from a typical sandwich construction of the foam and laminate on each side.

    Fiberglass tubing tends to be heavy, expensive, and doesn't have the strength you'd expect considering the first two things I listed.
     
  5. bajansailor
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    bajansailor Marine Surveyor

    I think it would be false economy to use something like Formica for the inner skin, especially as you are already investing good money in fibreglass sheets, epoxy, foam sheets and FRP square tubes.
    Do you have any sketches of the proposed arrangement for this enclosed flying bridge?
    Or photos showing what the existing flying bridge looks like?
     
  6. JATesvich
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    JATesvich Junior Member

    88BAF5E9-20BE-452F-9E6F-EA54445BCBBB.jpeg E6592AD9-0A90-4531-983F-C2601A8F7F2B.jpeg
    The existing hardtop is cantilevered and supported by 4 braced SS tubes.
    My plan is to replace the soft enclosure with lightweight cored walls, traditional sloping windshield forward, and a mixture of fixed and opening windows on the sides and back.
     
  7. fallguy
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    fallguy Senior Member

    Well, forget the formica. More trouble than value returned.

    It is really more work to laminate the finished frp panel onto the core than build the core unless you get away with no finishing.

    What I would do is as follows, based on limited details.

    sand the inside faces of frp panels with 40-60 grit and remove sheen

    use something like a 10oz woven fabric for the bonding layer, no overlaps, epoxy to foam, let it kick to tacky plus maybe 15 minutes, same with frp, neat coat and let it kick to tacky; apply frp to panel like contact glue

    allow it to cure with some minimal weights or a caul of say 3/4" plywood on it; any errors are permanent

    then flip and either use the same method on reverse or glass it with 6oz woven...the glass inside allows you much more flexibility for bonding to structure

    this assumes the core does no structural work

    ps. You don't want to bond formica to the attachments as it may fracture and/but I know little about its use in composites
     
  8. kapnD
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    kapnD Senior Member

    The forward corners appear to be rolled, do you plan to bend your panels to match?
    I believe I’d look for a custom aluminum fabrication to fit the opening, as curves can be accommodated in both aluminum framing and glass or plastic window panels.
    If you’re dead set on composite laminated panels, there are many options available ready made, so you don’t have to engineer and build them from scratch.
     
  9. JATesvich
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    JATesvich Junior Member

    The 1/4" thick frp has some meat to it. If frp tubing is too heavy and not strong enough for framing, what are better options for a boat? Epoxy coated wood . . .or aluminum tube?
     

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  10. bajansailor
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    bajansailor Marine Surveyor

    That is a nice sketch JAT.

    My only suggestions would be -

    1) Don't rake the windscreen aft as much as you have shown - the angle of your current screen is steeper vertically. You will also appreciate a more vertical screen if you are helming at night on the flying bridge - the more angled back the forward windows are, the more reflections you will get from the lights on the bridge. Hence why most commercial boats have windows that are raked forward.

    2) You have a 'vertical' at the front of the windscreen, going down from the window to the flying bridge deck - this does not really 'relate' to any other vertical, ie it is on it's own.
    I think that the windows shown would look better if they have vertical sides, rather than raked aft - the rake makes everything look a bit too 'racy'.
    And these will tie in visually nicely with the vertical aft bulkhead behind the roof gantry support.
    But these are just my thoughts, and others will no doubt have different ideas.

    Be aware that a 'solid' flying bridge structure will really 'stand out' visually a lot more than your current canvas enclosure.
     
    Last edited: Feb 17, 2021
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  11. JATesvich
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    JATesvich Junior Member

    Thanks for your response. I planned on curving the side walls in slightly in order to blend aesthetically with the rest of the boat's curves, but the sidewall would meet the forward windshield in a sloped corner joint. I do not want straight slab walls on the flybridge for the same reason. In order to create curved wall sections having only the outer frp skin (no inner skin) and scoring the core if necessary provides a lot more flexibility in working the panel prior to attaching the inner skin. I've already considered aluminum fabrication but it is not what I really want.
     
  12. JATesvich
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    JATesvich Junior Member

    I appreciate and thank you for your input. 1) I'm well aware of the benefits of a more vertical windshield for the captain, but on a motor yacht, as an amateur designer, it is hard to say that the raked windshield doesn't look sleeker and racier on this boat, and that is the dilemma of the compromise. 2) The reason there is a vertical in front of the windshield is to conserve space up front because there is an existing sun-pad there so that after renovation there could possibly be a seating area or pad if pass through is provided in the windshield.
     

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  13. fallguy
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    fallguy Senior Member

    I think you are oversimplifying things.

    please don't pursue my advice; it was given without a full understanding and your sketch and I assumed you were just closing in the sides

    The structure needs to be engineered to support the windows, etc.

    It is not a complex engineering, but a needed one to make sure it supports your window choices. This cannot be done with frp panels and it requires significant work and strengthening of the laminates. Done right it will look very nice.
     
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  14. fallguy
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    fallguy Senior Member

    To give you a better understanding; the mullions or spaces between the windows need significant tabbing and that tabbing can go into recesses in the core. If you make a frp panel; all the tabbing would be on the exterior, for example.


    ps--take your drawings to someone who can spec the work for you
     
    Last edited: Feb 18, 2021
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  15. JATesvich
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    JATesvich Junior Member

    Your points are well taken. Strength is important. Taking engineering into account the framing between the windows (mullions) will be required to take most of the stress. My plan was to use two 2" sq tubes 1/4" thick in the mullions with the 1" cored wall section outside the framing. That is 3" thick wall section at the frame. I do not have the engineering data on the frp tubes but assume that it should be significantly stronger than a 2" thick wooden frame.
     
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