Another Plywood Thread!

Discussion in 'Boat Design' started by RagnarTheDane, Nov 12, 2016.

  1. RagnarTheDane
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    RagnarTheDane Swabbie's Boot Shiner

  2. RagnarTheDane
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    RagnarTheDane Swabbie's Boot Shiner

    Strength is a huge consideration (as well as trying to keep it as light as possible) I had no considered the pure strength would be greater. Thank you for the information.
    I had considered using regular construction plywood for the internals, but I figured keep it all the same.
    Something to think about.

    Thanks!
     
  3. RagnarTheDane
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    RagnarTheDane Swabbie's Boot Shiner

    I will, thanks!
     
  4. RagnarTheDane
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    RagnarTheDane Swabbie's Boot Shiner

    I am working on the details, pics of the scaled model I've made... but the long and short, this is going to be a hybrid Fish/Duck boat.
    The fishing I'm not as concerned about, as I don't do a lot of deep water, and I know the lakes here pretty well...
    But the duck part, the lakes here have brutal variances in the levels.
    It can go from walking field, to High speed deep water in no time (weeks/months) but the danger is stumps that rest just unseen.
    I'd never rip fast through uncertain waters, but either way, I don't want to pop a stump, and wind up with a great view of the bottom of the lake.

    There are some other things I'm into, hence the desire to customize the build, but consider it a workhorse, not a 'pleasure' boat.
     
  5. RagnarTheDane
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    RagnarTheDane Swabbie's Boot Shiner

    Awesome! Thanks for the share, I just can't watch enough of these builds.
     
  6. motorbike
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    motorbike Senior Member

    Don't mean to be offensive, a lot of people turn up here hoping to "big box" their build and think that it will be as good as marine grade materials. Sometimes you can get away with it, mostly not.

    7k is still not much, yet as a proportion the extra 340 is peanuts. Once you are into your build you cannot go back. In other words you can easily get 5k deep then end up wishing you spent the 340 but its too late.

    The fundamental materials should be the best you can afford for the purpose, the other added benefit is that good materials are much nicer to work with.
     
  7. RagnarTheDane
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    RagnarTheDane Swabbie's Boot Shiner

    If I misjudged the sentiment, i apologize.
    Keeping in mind, it's a modified flatbottom skiff hybrid (best thing I can think to call it) ... The motor is a Pro-Drive Surface Drive motor.

    My desire is to build the best boat that I can, and for it to last.
    But working with wood, metal, and in fabrication for quite a while, i've learned that there are some things that are hype, and some things that are absolutely unquestionable (like quality Toiletpaper)

    I just want to make sure that I'm spending the right dollars in the right places, and the internet is well.... the internet.
    I feel I've gotten my answer in this thread, and hopefully will get more as I go through the modeling process before I start my actual build.

    Thanks for looking out.
    Happy sailing (or um... motoring)
     
  8. Ilan Voyager
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    Ilan Voyager Senior Member

    No it's false. Exterior plywood even now is very far from a true marine one. First the number, quality, and thickness of the plies are very different. You cannot compare a 5 plies 1.2 mm each ply 6mm marine plywood with zero voids and zero defects on the faces, to a 6mm or 1/4 inch exterior plywood.
    True marine plywoods are made with a good wood. Light marine plywoods like those found in the States are made with non durable woods just good for making crates in the opinion of a French naval carpenter. Covered with epoxy that works, but the first choice is good heavy tropical wood.
    The second choice is a very good pine like the Finnish plywoods.
    The most important is the quality of the plies and no knots or voids with a waterproof glue (a phenolic one), a thing that do not understand most of the American plywood makers.

    A good marine plywood like those I know from the French like those made in sappelé wood or khaya mahogany for example can live 35 years in salt water with just old oil style paints.
    I have seem many plywood boats made in Europe in the fifties go to the late eighties, beginning of the nineties without major problem if carefully maintained. Some Asiatics and Indians make similar plywoods, the price to pay is the density around 700-750 kg/m3, and the price.

    I have used for decks of pro fishing boats plywoods in doucier wood with a density around 900 to 1050 kg/m3. Impossible to nail a 1/2 thick sheet. The termites die of hunger toothless. They kill all the drill bits you have to use before screwing, too much silica. Blade saws, and tools loose their sharpness in minutes. You can hammer without making a scratch. These special plywoods can stay easily ten years without protection as deck on a fishing boat with the sun, the snow, salt water, soft water, blood. nets etc...
    Unhappily these plywoods mean the devastation of the tropical forest.

    You're right. The glass for epoxying must be first class. In marine building except disposable holidays pram, you cannot go cheap.
     
  9. srimes
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    srimes Senior Member

    How do you decide which underlayment to use? I've had some good luck, but did get burned once. Small piece passed the boil test, but when I painted it there were many bubbles that arose where there simply wasn't enough glue. It sucked. Fortunately it was a simple 8' boat and we did get some good use out of it before sinking it in the pond.
     
  10. PAR
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    PAR Yacht Designer/Builder

    You do need to closely examine each sheet and yeah, it can be a crap shoot, but folks looking to do this typically aren't also looking for long term durability.
     
  11. brian eiland
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    brian eiland Senior Member

    consider KSS method, materials

    You just might consider an alternative to encasing your plywood boat with fiberglass, and build it of panels of foam sandwiched between fiberglass panels

     

    Attached Files:

  12. RagnarTheDane
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    RagnarTheDane Swabbie's Boot Shiner

    Kss

    Though this seems very light, and would hold up to water better. My concern is strength.
    There is a 100% chance of hitting stumps.
     
  13. PAR
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    PAR Yacht Designer/Builder

    The OP is concerned with costs, even considering construction grades of plywood as a result, so how is foam core to fit this equation? I did some cost analysis a few years back, comparing similar panels by strength, stiffness, thickness, etc. and the cost differences were quite dramatic.
     
  14. Squidly-Diddly
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    Squidly-Diddly Senior Member

    Tell her with the low quality Home Depot plywood you've been advised to increase your Life Insurance coverage, requiring a monthly increase in premiums of approx $90.

    But seriously, Exterior grade is pretty crappy stuff, full of voids, semi-voids and soft spots......so.....

    when you start laying out odd shapes on plywood that was meant to be nailed in full sheets to regular layout, you are bound to start hitting bad spots, so you'd probably end up needing more due to waste, not to mention stall in project, more shipping costs for an extra order, etc.
     

  15. RagnarTheDane
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    RagnarTheDane Swabbie's Boot Shiner

    The concern is not 'cost' as much as paying double the amount for something that is hyped.

    But, having viewed resources, considerations, and testimony from this thread, I don't see it as being hyped, and see it as being worth the money.
     
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