Modern sheet material designs

Discussion in 'Multihulls' started by bruceb, Aug 6, 2021.

  1. bruceb
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    bruceb Senior Member

    Are any designs available that are using modern composite sheet materials instead of plywood? Here in the US, composites, like Coosa board or Thermo Lite, are not much different in price than wood, and are being widely used in powerboats. In my southeastern USA area even well built light ply boats start to come apart after two or three seasons when kept outdoors all year, so the composites have a lot of appeal. Some of the new small tri designs would be a lot more interesting if they could be built in something more durable than wood.
    What is out there?
    Bruce
     
  2. oldmulti
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    oldmulti Senior Member

    From Spiriteddesigns Boat Designs and Kits | Spirited News https://www.spiriteddesigns.com.au/news?blogstart=54

    "A client in WA has engaged us to customize this design to suit his particular requirements. He requested to build this boat using Polyethylene plastic sheet. Being considerably heavier than the standard Duflex material usually used for this design, the hulls needed to be re-designed to allow for the new material.

    The new hulls will carry this boat boat well with no sacrifice to freeboard or bridgeck clearance. The PE plastic sheet is welded together and has the advantage of not requiring fairing or painting, the material is supplied pre-coloured. PE has now been used extensivley in boatbuilding and has proven itself as a strong, tough and durable material. A local PE boatbuilding company will be carrying out this project for the client. The boat will be powered with an electric propulsion system and set up for extended cruising."

    Basic design before the above work Power-Sail Catamaran Kits and Construction Plans | Stow-Away 8.5 https://www.spiriteddesigns.com.au/stowaway8_5

    Also there are some power boat guys using Coosa board in transom etc instead of ply and in one case building smaller power boats in coosa covered with glass outside.
     

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    Last edited: Aug 7, 2021
  3. Heimfried
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    Heimfried Senior Member

    That's completely new to me.
     
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  4. Rumars
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    Rumars Senior Member

    You won't find any stock designs for Coosa & Co., it's too heavy to use as a general core, and not good enough to be used without glass.
    You can of course redesign any plywood boat to foam core, either flat panel or round bilge.
     
  5. guzzis3
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    guzzis3 Senior Member

    Yeah that's what I was thinking. Prices are different in the USA but here PVC foam from utek is cheaper than ply. They supply glass and all bagging materials at unbeatable prices. Of course with foam you can use vinylester or polyester to save more money.

    The only reason I can see that anyone bothers with ply anymore is a local cheap quality source and fear of working with something different.

    Goodness imagine building a V hull in foam. Instead of all that framing and joining you just glue a bunch of sheets together, cut to shape, use it as a template to cut 3 more hullsides and glass, build a table and infuse away. Do the same for the keel panels and bulkheads, set it up in a jig, fillet and tape. You'd be done in no time. Dory hulls wouldn't be much harder and if you want round bottom you only have to make 1 mold.
     
  6. fallguy
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    fallguy Senior Member

    Well, this has been covered before.

    coosa only available 1/2" lacks some of the properties of ply

    don't knock ply boats; they don't last two seasons if they are part of a well built composite and sheathe in epoxy and glass

    a ply boat requires much less glass and epoxy than a foam boat and is a far faster build than foam
     
  7. Russell Brown
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    Russell Brown Senior Member

    The cheapest foam, skins, and resin is more expensive than the highest grade Okoume plywood.
     
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  8. gonzo
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    gonzo Senior Member

    I am not sure where you got that information, but it is completely wrong. Plywood boats last for many years even if not maintained properly. I have built and owned many in the Southern USA.
     
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  9. Burger
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    Burger Junior Member

    Locally there are several ply boats (pre-epoxy, well-built and well-maintained) over 40 years old in perfect condition.
     
  10. guzzis3
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    guzzis3 Senior Member

    Not here. I can get foam glass and bagging supplies from china delivered for less than I can buy real marine grade ply alone let alone sheath it. As I have said many times here I can't comment on price and availability elsewhere. I am in Australia.

    The other problem with ply here is 1088 isn't an officially recognised standard here, so we get ply from asia with that mark but it's meaningless. Unfortunately most people don't realise until it's too late.

    I'll say it again. I cannot comment on costs in other jurisdictions. You need to make your own inquiries.
     
  11. Skyak
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    Skyak Senior Member

    I think the OP mistakenly believes that "Coosa board or Thermo Lite" are some new materials that designers haven't made use of. The real answer is that many designs exist in foam cored fiberglass. The way it is done is to cut, fit, fair, then glass. Or maybe cut, infusion on table...

    Boats aren't designed in these sandwiches simply because it is wasteful to build out of generic flat rectangles.
     
  12. bruceb
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    bruceb Senior Member

    A few points. "Coosa board", is now sold in thicknesses from 1/4" to 2", sheets up 4'x12' and in several different densities, the most popular being 26 lbs which is used as a direct ply replacement and is somewhat lighter than the ply it is replacing, and stronger. (The supplier's claim) . Search "Coosa board" and look at the material data sheets.
    Gonzo, I own two older ply/partial ply boats and I have been maintaining boats in my area for 40 years, and yes, ALL exposed wood has long term problems here. Our conditions are not extreme or unique, but they can destroy wooden boats fairly quickly without very intense upkeep. I love wood and wooden boats, but I know first hand its limitations. That is why I am asking about better materials, I don't want to argue about wood. Please!
    I am about ready to try some partial ply deck replacement on my 33'tri to get a feel for the material. If anyone has some hands on experience I would like to hear it. I have to drive about 350 miles one way to pick up a load unless I want to order a pallet's worth, if it seems reasonable, I am considering getting enough of the 20 lbs or 24lbs material to try a small tape and glue skiff.
    Bruce
     
  13. fallguy
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    fallguy Senior Member

    coosa does not compare in all engineering qualities; especially flexural rigidity or stiffness
     
  14. gonzo
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    gonzo Senior Member

    This is not about arguing, but defining what the characteristic of a material are. Wooden boats last for very long time with moderate maintenance. If you want something better, it is necessary to first define the material you think you are improving upon. Fiberglass, foam cores and exotic materials all have limitations too. For example, a foam core may fail from impact at a lower force than plywood. No material is absolutely better than another for all applications.
     

  15. bruceb
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    bruceb Senior Member

    Fallguy, thanks for posting. I notice you do have quite a lot of experience with wood, which grade of Coosa are you comparing to wood ply?
    My current need is for replacing 1/2" fir ply decking, which seems well within the material's abilities, and on my boat the decks are well supported and not too highly loaded. They are also the area that gets stressed most in our freeze/thaw/sun-baked weather and would seem to be an improvement from my current glass covered ply without much change in weight or strength.
    I have measured surface temps on my boats with overnight swings from 20 degree F at night to 80 degrees the next day in the sun, with seasonal ranges from 0 F to 140 F surface temps, we have high humidity all year so ventilation is not too effective. We use our boats all year so they are exposed to the whole cycle and it is not practical to keep a trimaran covered. The float decks are especially a problem, it is common for them to fail every 12 to 20 years on even the best built boats, much less if they are not well epoxy coated and sealed.
    Our conditions destroy foam core/glass decks too but the nature of the Coosa board seems as if it would be much less likely to have the same issues.
    Bruce
     
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