Foam Boat - Beginner Advice

Discussion in 'Boatbuilding' started by Sammy F., Feb 6, 2018.

  1. Sammy F.
    Joined: Feb 2018
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    Location: Australia

    Sammy F. New Member

    Dear All,

    I've been wanting to build a small boat (2 to 3ish meters) for a while, however I want to do so in an easy and cheap way with minimal tools. Rather than using plywood, complex ribbing and strip planking, or foam composite techniques to create a hull, what's stopping me from getting a large slab of foam, shaping it, and (assuming I'm magic and can shape it perfectly) simply laminating the entire thing with a several sheets of fibreglass and epoxy, fairing it, priming then finally painting it? Assuming my foam does not deform during this process, is this a viable approach? Wouldn't most of the rigidity come from the epoxy/fibreglass exterior? Essentially I'd end up with a monolithic hull. I'd love to hear your thoughts. What drawbacks would there be? My alternative approach would be to 3D print a light honeycomb-like hull with a thin skin, then perform the above approach instead of foam.

    Kind regards,
    Sammy
     
    Last edited: Feb 6, 2018
  2. rwatson
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    rwatson Senior Member

    So, have you priced your "large slab of foam", and the cost of enough f'glass to make it strong enough ?

    This method has been suggested nearly a dozen times over the last 5 years on this forum, and the sums didn't ever add up that I remember.
     
  3. Sammy F.
    Joined: Feb 2018
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    Sammy F. New Member

    Surely I could buy some cheap insulation foam panels and stick them together? These are quite inexpensive at the hardware store. There's a boatbuilding store in my city which sells 280gsm (I think this is 10oz equivalant) fibreglass fabric for $12/m or heavier 400gsm triaxial stuff for a similar price. Would any of these be suitable? Then a few litres of epoxy resin for $150ish. In total maybe $400?

    I'm more interested really in the type and thickness of the fibreglass fabric I'd need. 0-90? Bi-axial, tri-axial weaves? Possibly with a small 10-15hp outboard motor!

    Thanks,
    Sammy
     
  4. gonzo
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    gonzo Senior Member

  5. Sammy F.
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    Sammy F. New Member

    I had something like this in mind:

    [​IMG]
     
  6. ondarvr
    Joined: Dec 2005
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    ondarvr Senior Member

    Is building a boat the desire, or being on the water for a low price? Either one is fine, but wil change the responses you get.
     
  7. gonzo
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    gonzo Senior Member

    That is expanded foam, not insulation foam. Your plan has a contradiction. Easy and cheap with minimal tools would be satisfied by building in plywood. You can build with a saw, a drill and a grinder. Plywood form fair curves and is cheap; particularly the 1/4" (6mm) from the building supply. 3D printing a honeycomb can be done, but you can buy a new 20 footer with a motor for the same price. If you want easy and cheap, don't start by restricting materials and techniques. However, if you want to build starting with a big block of foam, then you will have to spend whatever it costs in materials and tools to achieve that.
     
  8. rwatson
    Joined: Aug 2007
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    rwatson Senior Member

    "cheap insulation foam panels"
    Well, 1240 cm x 410 cm x 60 mm = $60,
    A 6 metre boat would take 4 sheets long, 2 sheets wide, 20 high = 160 sheets @ $60 = $9,600

    yeah, really cheap.
    Now carve it up and waste 2/3rds of it

    Then try to figure out how much it will cost to coat it with Epoxy and glass to keep it from breaking on impact, and keep the water out for more than 6 months ( its not sealed foam nor is it high strength)

    Do yourself a favour, get yourself some plans and save yourself a lot of grief and expense, and end up with something you can safely let your kids out on.
     
  9. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    The tricks with foam composites are the foam density and fabric costs. Most of the big box store foam isn't high enough density to take very seriously, unless you layer on a bunch of fabric and resin, which absorbs any savings from the cheap foam. If you use 5 pound foam, which is the minimum density from a structural stand point, then the foam costs go way up, but you can save some labor and fabric costs, though usually not enough to make this as viable as other methods.
     
  10. rasorinc
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    rasorinc Senior Member

     
  11. rasorinc
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    rasorinc Senior Member

    go to GLEN-L and look at out boards. they have many 8' 9' 10' good plans simple builds and low cost
     

  12. Sammy F.
    Joined: Feb 2018
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    Sammy F. New Member

    Thanks for all your responses. So perhaps foam isn't the best option! Perhaps my 3d printer idea would be more viable, you see I already own a self-built 3d printer with a large enough build volume to build 0.5m segments of a boat. Hypothetically though, assuming cost isn't a factor now, how many layers of 6 or 10oz fibreglass fabric would you expect is required in order to make a stable structure for a small 3m boat, be it foam, or thin 3d printed structure. Thanks for you help, very interesting feedback!
     
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