Using an inflatable PVC boat as a mold to lay up fiberglass?

Discussion in 'Boatbuilding' started by DocGil, Nov 23, 2017.

  1. DocGil
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    DocGil New Member

    I have an idea...famous last words, I know.

    I have a 16 foot inflatable boat that is made from PVC and was wondering if it would be possible to flip it over, clean it, apply generous amounts of mold release and then lay up resin, chop strand, fabric etc out to gel coat? This way, the old boat form would become the inside of the clone and I could flip it and reinforce and finish the inside.

    Am I crazy or could this work?
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    Do you have a picture of this inflatable ?
     
  3. DocGil
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    DocGil New Member

  4. Blueknarr
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    Blueknarr Senior Member


    Welcome.
    It should be possible to create a boat like floating object that could be propelled with substantial effort. The inflatable boats I am familiar with do not have the most efficient hull shapes.
     
  5. DocGil
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    DocGil New Member

    I should point out that the only thing it will be used for is floating downstream in a maximum of Class 1 rapids. It won’t be motorized, just rowed.
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    I don't know what a "class 1" rapid is, but if there is the likelihood of hitting rocks, it could be a problem.
     
  7. CDK
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    CDK retired engineer

    What at first glance seems a brilliant plan may be a waste of time and materials. The resin hardens with an exothermic reaction that changes the shape and size of the PVC inflatable, it may even rupture during the process.
     
  8. Blueknarr
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    Blueknarr Senior Member


    I looked at the link you provided, the boat appears far more sophisticated than I originally suspected.

    However, as you plan on using the new one as a row boat, efficient pulpution would be high on my list of requirements.

    For almost the same effort and materials a proven design and construction method should provide a better solution.
     
  9. ondarvr
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    ondarvr Senior Member

    The short answer is yes...but....

    The typical inflatable needs to be a compromise of the best design for the hull and it's intended use, and a shape that can be made in an inflatable, with the inflatable part trumping design. So while it may work, the shape you get won't be that good, and it won't be much less work, or maybe none at all, compared to building a good design in the normal way.

    Drift boats are designed for this purpose, you can easily find plans online, and since they're simple you could even make the design yourself without too much research. These designs require only flat sheets of plywood, then some glassing, you can make it very simple, or a piece of art, that's up to you, both options function the same.
     
  10. kapnD
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    kapnD Senior Member

    Just wondering what the motivation for this is?
    Does the inflatable have outstanding characteristics you want to capture in a rigid hull?
    Keep in mind that even a direct copy of the hull will perform differently as a rigid boat, when the “flex factor” is removed.
    It is very likely to be heavier, and will involve A great deal of work to bring it to a fair finish, both in and outside.
    Might be a better idea to copy the lines and build your boat by traditional means.
     
  11. Bzidro
    Joined: Apr 2019
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    Bzidro Junior Member

    KapnD
    I have an inflatable pvc with 3.60m and most of my navigation is done in rivers, reservoirs and lakes and I often encounter many floating debris from trees. I have a similar idea (Using an inflatable PVC boat as a mold to lay up fiberglass? https://www.boatdesign.net/threads/using-an-inflatable-pvc-boat-as-a-mold-to-lay-up-fiberglass.59493) and want to use the same process, which is to make a fiberglass hull only up to 3 quarters the height of the floats with holes to pass fixing straps, so that I can sail without the risk of drilling, and even dock on the banks with vegetation that could easily pierce. Find it a feasible idea?
    My boat is not like the one DocGil showed on the link, it is almost flat bottom with a sligth inflatable keel.

    The Main motivation is both the low cost of all this and the very high price of a rigid boat with a similar size, otherwise would have bought a rigid initially.

    Thank you !

    Bzidro.
     
  12. kapnD
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    kapnD Senior Member

    How about a picture or even a rough drawing of the vessel in mind?
    So far we know it has an almost flat bottom with a slight keel, not very hard to do in plywood and glass.
    Which is what I’d highly recommend doing over laying glass on a non-rigid surface that is constantly changing with temperature fluctuations, and not likely to hold still while being worked on.
    I foresee much sanding and filling, and possible weakness in the lamination due to unstable mold surface.
     
  13. Blueknarr
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    Blueknarr Senior Member

    it is almost flat bottom with a sligth inflatable keel.

    The Main motivation is both the low cost of all this and the very high price of a rigid boat with a similar size, otherwise would have bought a rigid initially.

    Bzidro

    I agree with KaptnD, there is probably a lot more work, sanding and expensive supplies than you think.

    I use an inflatable 2.5m sit on top. It is a PVC bladder with a very heavy nylon cover. I have improved its rigidity by placing a thin plywood incert under the bladder. Still fits in my closet.

    Covering an inflatable with glasswork robs it of its most desirable qualities (cushion and roll-up storage) without improving its inherent lack of performance.

    I predict that your bladder will chaff against the partial shell.
     

  14. Bzidro
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    Bzidro Junior Member


    You missed all up.

    Especially the part in which I mean that it is a protection that will have holes to pass fixing straps which means that it is removable.
    I do not live in an apartment and I have around me and my house, Ten thousand square meters - One Hectare, to keep my boat.
    I'll send photo of boat and a sketch of what I intend to do. Thanks for your opinion.
     
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