Building a ply design with balsa instead?

Discussion in 'Boatbuilding' started by Newickspark, Aug 27, 2019.

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  1. Rumars
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    Rumars Senior Member

    I said you can save some weight by going carbon but you can not save "a lot". So if you look for shaving two thirds of the weight of the design it will not work


    Okoume (gaboon) is a hardwood. Average weight of the plywood made out of it is 450kg/cum.
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    The boat has to sit on its lines, so unless there is some imperative to make the hull lighter, like a load that will always be carried, why obsess about lightweight construction.
     
  3. Newickspark

    Newickspark Previous Member

    I was just researching plys, looks like Okume for price, quality and weight.
    With skins it will be more then okay.

    I suspect that a lot of ply rot issues come from people covering ply with epoxy, that’s not properly dry.
    Getting humidity down and making sure the ply is dry before epoxy and glass will be important to me.
     
  4. Newickspark

    Newickspark Previous Member

    I wouldn’t say I’m obsessed, it’s more just trying to avoid unneeded weight
     
  5. fallguy
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    fallguy Senior Member

    You need to match elongation character or your hull will fail.

    In general terms, carbon is best with ply. Probably room for lotsa polemics, but the reason some people are willing to mismatch is for weight; not overall hull quality.

    The boats with foam and carbon are generally considered disposables.

    Elongation of epoxy, foam core, and S glass are very similar. The hull is a system; not a buffet.

    Elongation of carbon and ply are close, but the weight advantage vanishes.
     
  6. Newickspark

    Newickspark Previous Member

    Thanks for the info, so if you where building this boat, which would you choose?
     
  7. Mr Efficiency
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    Mr Efficiency Senior Member

    I can understand why someone might want to make big weight savings in hull weight, as in for instance a planing motor boat where a diesel engine is desired, but the extra engine weight might cruel performance, otherwise I can't see the point in delving into exotic or difficult to work with materials.
     
  8. fallguy
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    fallguy Senior Member

    Well, it is easy for me to decide.

    I have no experience with carbon. I ordered a piece today to make a fancy dash.

    I am building a Woods Skoota using Silvertip epoxy, Gurit Corecell M, and S glass using wet bagging.

    The way I would build the boat you want is plywood and s glass and epoxy.

    The reasons are simplicity of build and time to build, and cost.

    I also hate balsa core. I bought a rotten balsa boat a few years ago. Someone installed a bilge pump and wrecked the whole boat most likely. Balsa core is NOT robust.

    Some high number like 80 percent of amateur builds never finish. The builder finds they don't have time, or money, or required abilities.

    If you have a lot of money; develop new scantlings with ply and carbon. You could probably thin the plywood down. The elongation of the epoxy won't matter much if the carbon and ply are close. (This is an semi-pro opinion).

    Carbon likes to pinhole I am told. So, plan to deal with it. I don't know how carbon an ingress relate, but to avoid ingress; you need about 12 oz of glass. You might need to neat coat the carbon layups for the pinholes and ingress both (I am guessing for sure!).
     
    Last edited: Aug 28, 2019
  9. fallguy
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    fallguy Senior Member

    By the way, my build has used 227 gallons of epoxy to date. The cost per gallon is about $100. Foam building with epoxy is outrageously costly because the glass is thick. In order to reduce the weight, we vacuum out excess epoxy and throw it in the trash at a rate of like 20%+. Do the math. 5k in trash

    The glass for plywood is much thinner which will reduce the epoxy cost. A lot.

    Carbon is VERY costly and harder to laminate.

    Keep these in mind.

    If you really hate plywood; plan on lots more build time and money. Foam can be used in a monocoque hand laminate, but generally not.
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    You didn't like pre-fab epoxy/glass panels, fallguy ?
     
  11. Newickspark

    Newickspark Previous Member


    Thanks for the input. I Just received another email from Dudley Dix, btw this guy is awesome. He reply’s always, and is very str8 forward.

    He basically told me his black cat is ply with just epoxy on the outside. 6 Atlantic crossings and 23 years, still going strong. Good enough for me!

    Very basically said, the trick to keeping these ply boats going is coating the entire outside area. I like the kiss mentality, which I lose to easy.
    Did say a thin glass coat will help with minor abrasions, and I would do that no doubt,

    The sglass has a better abrasion. Resistance, lighter. Not sure on how it’s better for fairing and painting, I hope it finishes better then e glass. Not sure

    Again, I’m ordering study plans, after seeing his prompt reply’s I’m impressed, and will build the 29 retro.

    So at this point I’m pretty well settled on

    Okum’ ply hulls and deck
    Epoxy ( haven’t looked into the best yet for water protection)
    And a thin sglass skin, just so I can sleep a little better!

    So what’s the consensus on

    The best epoxy for outside of the hull below and above waterline.

    Best epoxy based primer

    I want to use roll and tip Alex top coat.
     
    Last edited: Aug 28, 2019
  12. fallguy
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    fallguy Senior Member

    Silvertip.

    Epifanes epoxy primer.

    Mr, E, the problem with my build is throwing away 5 grand in epoxy plus consumables. And wet bagging is slow and artsy. Do it over and ply would be easier, but ply wasn't ever an option for this unique design (demountable powercat). Do over and I learn panel infusion at least.
     

  13. Mr Efficiency
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    Mr Efficiency Senior Member

    I meant pre-made panels like duflex. Not sure how that would cost out, but the joins are a bit of an issue.
     
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