Coating for plywood boat

Discussion in 'Materials' started by Daan, Sep 20, 2020.

  1. Daan
    Joined: Sep 2020
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    Daan Junior Member

    Hello everyone,

    I am building my own plywood boat and it is nearly comming to an end but I have one thing I haven't figured out. What do I use to coat my boat with? I was thinking of using fiberglass sheets and resin but I've also seen people using marine epoxy.
    What do you guys think is the best material to cover my boat with?

    Thanks in advance!
     
  2. bajansailor
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    bajansailor Marine Surveyor

    Hello Daan,
    Please do use epoxy - definitely not polyester resin!

    Can you tell us a bit more about your boat please?
    Perhaps even post a few photos of her?
     
  3. hoytedow
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    hoytedow Bananas

    Use fiberglas with whichever you choose. Epoxy is more waterproof but uv rays damage it. Polyester holds up to sunlight but is less waterproof. It is not nearly as good as epoxy. Whatever you choose make sure wood is completely protected or it will rot, destroying your hard work.
     
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  4. Daan
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    Daan Junior Member

    I will be able to post some pictures at the end of this week.
    Why would you choose epoxy over polyester resin?
     
  5. bajansailor
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    bajansailor Marine Surveyor

    Epoxy is more expensive than polyester - but when you compare the difference in relation to the total cost of building the boat it is a 'no brainer' re using epoxy.
    Epoxy is an adhesive, polyester is a laminating resin, and epoxy will be far superior in every respect., and well worth the cost differe1nce.
    Yes, you will have to paint it, but you would have to paint or gelcoat a polyester sheathing as well.
    The use of fibreglass with polyester resin for sheathing plywood hulls harks back to the days before epoxy, when this seemed to be the best choice available - but now that epoxy is widely available, it is definitely the way to go.

    Excellent re how we can look forward to seeing some photos in due course!
     
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  6. Daan
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    Daan Junior Member

    I was already planning on painting the boat so that won't be a problem. But would you recommend using fiberglass with epoxy or only use epoxy?
     
  7. bajansailor
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    bajansailor Marine Surveyor

    You would get better abrasion resistance if you use a suitable glass cloth with the epoxy, rather than just coating the hull with epoxy.
    It will use more epoxy resin, plus the cost of the cloth, but it would be well worthwhile doing.
    You could put additional layers in way of the keel, especially if you will be beaching the boat.
    How big is she? And what type, sail or power?
     
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  8. Daan
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    Daan Junior Member

    The boat is 330 cm long and the total width is 100 cm and it is going to be a power boat if everything works out.
    I have found some epoxy resin and suitable glass cloth that I will be using so thank you for the information about that.
     
  9. bajansailor
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    bajansailor Marine Surveyor

    OK, this all sounds rather optimistic - 3.3 m. long and only a metre (3' 3") wide, and you want to install an inboard engine with a shaft drive propeller........ you will also need to have a rudder - will this be tiller steered, mounted on the transom?

    I would be rather worried about the stability of this little boat, with only a metre of beam.

    Can you not simply take a photo with your camera of the boat and post it on here?
     
    Last edited: Sep 21, 2020
  10. Daan
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    Daan Junior Member

    I am not staying at the place where I am building the boat. I will post a picture as soon as I have the time for it.
     
  11. Daan
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    Daan Junior Member

    This is what I have so far. As you can see I still have the sides and the back left to do.
     

    Attached Files:

  12. Mr Efficiency
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    Mr Efficiency Senior Member

    What is joining those panels of ply together ? People have spoken of this thing being "tippy", but when I see that veed bottom, I think they are quite correct. Where did you get this idea from ?
     
  13. bajansailor
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    bajansailor Marine Surveyor

    I think that the panels are simply butted on the frames - which is not ideal, as there is not much contact area re the overlap.

    Another question - why have three sections of plywood with butt joints along the hull length, when you could have used two sections if you use standard 8' x 4' plywood sheets?
     
  14. Mr Efficiency
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    Mr Efficiency Senior Member

    That would make me nervous on anything more than a duck pond, I think it needs a thorough audit. Certainly on appearances it does need sheathing with some reinforcement and epoxy, to assist in holding it together.
     
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  15. bajansailor
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    bajansailor Marine Surveyor

    Daan, did you build this boat with good quality marine plywood, or ordinary furniture plywood?

    If the former, then before you spend extra money and effort on sheathing the hull with epoxy, it might be a prudent move to splash the hull on your nearest duckpond (or swimming pool) and test it out for stability by climbing onboard - I have a feeling that you might find that she is rather wobbly.
    Proper marine plywood can cope with having some water flung at it briefly.
    However furniture plywood will pretty much fall to pieces fairly quickly if it gets wet.

    Have you already glued (with epoxy) the panels to the frames? Or are they just attached with screws?
    If they are just screwed on, then before you spend more money on materials (like epoxy and cloth), it might be worthwhile disassembling the hull, using the plywood panels for something else, and buying a set of plans for a boat that is proven to do the job that you want it to do.
    And then starting from the beginning again.
    Apologies for being so harsh, but I do have serious doubts about your hull, both in terms of the design and the construction.

    Edit - a left field suggestion - if you cut this hull in half longitudinally, then you could create an assymetric catamaran hull form which would certainly have enough stability. But it would probably cost at least 50% more in additional materials.
     
    Last edited: Sep 23, 2020
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