Bimini made from PVC pipes + Fiberglass/polyester resin

Discussion in 'Boat Design' started by mariobrothers88, Oct 18, 2020.

  1. mariobrothers88
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    mariobrothers88 Junior Member

    Hi I was thinking of making a solar panel arch type structure for my solar panels out of PVC pipes reinforced with fiberglass and polyester resin, and maybe a top coating of epoxy as well. I know PVC doesn't bond well with epoxy, which is why I would use the polyester resin. This would be in place of stainless steel pipes. Has anyone done anything like this? I plan to build a frame for solar panels like in this youtube video (the frame is made out of stainless steel in the video):




    Has anyone done this before? Is there a reason why this wouldn't work? I feel like the fiberglass will give the PVC enough strength and stiffness to support the weight of the solar panels, but please correct me if I'm wrong, thanks!
     
    Last edited: Oct 18, 2020
  2. kapnD
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    kapnD Senior Member

    What’s wrong with building it on a more traditional aluminum or SS tubing frame?
    The PVC/FRP frame will be heavy and quite costly, not to mention very labor intensive.
    How will you address fittings?
     
  3. bajansailor
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    bajansailor Marine Surveyor

    Mario, all else being equal, epoxy should bond better to PVC pipe than polyester resin - but the PVC pipe still has to be abraded / 'scuffed up' well first.

    I appreciate that a tubular S/S bimini / solar panel frame would be relatively expensive - building it in aluminium should be less expensive?

    And if you try to build it in PVC pipe, I think it would look rather 'agricultural' - and it certainly would not be anywhere near as strong as an aluminium or S/S structure.
     
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  4. Blueknarr
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    Blueknarr Senior Member

    SS tubes are used for bimini frames because they are the cheapest.
     
  5. mariobrothers88
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    mariobrothers88 Junior Member

    Hi guys thank you for all the replies! I am familiar with working with PVC pipes and fiberglass/polyester resin and epoxy so I can do all the labor myself. I am NOT familiar with working with stainless steel or aluminum, but I am willing to learn! Are there any good resources other than youtube? I did a search on youtube, found some decent content, but I am still confused, especially places to buy them, what would be a good price, how to work with them...etc. I already have a ton of PVC, fiberglass and resin left over from previous projects as well.

    Where I am, I can get 10' PVC pipes 1" 40 schedule for about $3. Fiberglass and resin are relatively inexpensive and I already have plenty of left over. I originally thought stainless steel, aluminum, and the equipment to work with them would be more expensive. But please correct me if I'm wrong!

    Setting aside cost, I disagree that SS and aluminum is stronger- it would really depend on how many layers of fiberglass you wrap the pipes with. I think if you only wrap it with one layer of thin fiberglass, then SS and aluminum would most likely be stronger. But if you wrapped it with multiple layers of thick fiberglass? I'm pretty sure you can get it to be stronger or at least just as strong.

    For fittings, I would usually regular PVC T and corner fittings and wrap them in multiple layers of fiberglass.

    In terms of weight, SS has a density of 7.480 g/cm3, aluminum has a density of 2.7 g/cm3, PVC has a density of 1.38 g/cm3, and fiberglass has a density of 1.52 g/cm3 so I would think the PVC/fiberglass structure could be less heavy actually (it really depends on how many layers of fiberglass, so it's really hard to compare abstractly).

    Are there any reasons why this would not work? I think 1" PVC with at least 2 layers of fiberglass with polyester resin and epoxy as the final coat would be strong enough to hold up the solar panels, but please correct me if I'm wrong :)
     
  6. mariobrothers88
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    mariobrothers88 Junior Member


    Thanks for your reply Bajansailor! When I search google, I see a lot of information that epoxy doesn't bond well to PVC but polyester resin will. When I did some testing myself with epoxy (from Raka) to PVC, it didn't bond well, but when I tested it with polyester resin, it bonded well. Do you have personal experience where you were able to bond epoxy successfully to PVC? Or do you have sources that claim that epoxy bonds better to PVC than polyester resin? Thanks again!
     
  7. bajansailor
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    bajansailor Marine Surveyor

    I must admit that I am baffled as to why polyester should stick to abraded PVC better than epoxy resin.
    Polyester is 'sticky', but it is not a glue / adhesive - it is a laminating resin.
    I have used epoxy with stitchmat to sheath PVC covered foam boards to build a couple of wheelchair ramps - this was 10 years ago, the ramps are in daily use, by heavy people, and no sign of any delamination yet.

    Are you planning on having a canvas awning attached to your bimini framework as well?
    Or maybe a rigid awning?
    If rigid, would it be built from fibreglass?

    If the structure is only going to be used to support the solar panels (how heavy are they ?) then the term 'bimini' is a bit mis-leading, as it usually refers to an awning to give you some shade in the cockpit.
    If it is just going to be used for the solar panels, then it could be called a gantry or goalpost type of mast across the back of the boat.
     
  8. ondarvr
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    ondarvr Senior Member

    Yes polyester bonds well to PVC, what's the epoxy outer coating for?

    This sounds like a disaster in the making. Have you ever tried to wrap glass around a 1" pipe, its not quick and easy to do it well.

    You didn't say how big this will be, but if this is a typical full sized bimini frame, wrapping will take a lot of time.

    You'd be better off buying aluminum or SS tubing and fabricating it. A tubing bender and fittings will give you a much better finished product far quicker.
     
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  9. mariobrothers88
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    mariobrothers88 Junior Member

    Yes I have wrapped glass around a 1" pipe, it's a little tricky but after a few attempts, it's pretty easy to get the hang of. It doesn't take that long either.

    I don't have a problem buying aluminum of SS tubing, I just don't have any experience. Outside of taking a course, are there good tutorials on the web or youtube to explain to a complete beginner? I know with aluminum it would involve welding correct? I've never welded before, but if I can find a good tutorial somewhere I'm definitely willing to try.

    However, other than potentially taking longer to build, what other disasters could there be? I think with enough fiberglass, it would be strong enough not to break with the weight of solar panels alone. The solar panels are 50 lbs each, and I plan to have 4 of them. The structure would be 4.5m x 2.5m and about 2.5m tall.


    Thanks again for all the replies, they are super helpful!!

     
  10. mariobrothers88
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    mariobrothers88 Junior Member


    Hi Bajansailor, you are right, gantry or goalpost type of mast across the back might be a better name rather than bimini. I plan to make the general shape similar to the solar panel frame in the video of my first post. I don't plan to add a canvass or rigid awning, it would be just the solar panels.
     
  11. messabout
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    messabout Senior Member

    Blueknar, Stainless tubing is NOT less expensive than aluminum. Aluminum is the material of choice for gazillions of Bimini tops.

    PVC pipe is a poor substitute and as Bajansailor says, it will look "agricultural". The difference in cost between the framing for a Bimini between PVC and aluminum is no justification for using the cheaper stuff. The problem, if any, is that PVC is available at big box stores like HomeDepot and alloy tubing is not. The ally is less convenient to buy but not at all a deterrent.
     
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  12. ondarvr
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    ondarvr Senior Member

    I used to make FG pipe and ducting.

    You would be given the blueprint, make all the pipe, then cut and assemble it.

    We would also line the inside and/or the outside of existing pipe and tanks.

    Getting even a half decent surface on the fiberglassed pipe will be time consuming and costly.



    You don't need to weld anything, a tubing bender and fittings are easily sourced which will allow you create and assemble just about any shape you'd like.
     
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  13. Mr Efficiency
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    Mr Efficiency Senior Member

    Way too flexible, regardless of all else, forget the PVC/GRP, Ondarvr's idea makes ample sense, pop riveted together.
     
  14. mariobrothers88
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    mariobrothers88 Junior Member

    Thank you for your suggestion. What do you recommend for the best source for the SS or aluminum tubes, fittings, and bender? There seems to be quite a few companies online, but I have no idea which ones are good quality or not.

    I think the PVC is flexible, but with two or more layers of fiberglass, it should be pretty stiff and strong, enough to hold up solar panels I would think. Am I overestimating how strong fiberglass is?
     

  15. Mr Efficiency
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    Mr Efficiency Senior Member

    GRP tube is very flexible, look at fishing rods. You will end up with something that is a heap of work, and not giving the best results.
     
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