Weight/Layers of glass to 'harden up' Okoume

Discussion in 'Boat Design' started by abosely, Aug 10, 2015.

  1. abosely
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    abosely Senior Member

    When using 6mm Okoume beach launched rowboat, what weight and or how many layers would be good to prevent the soft Okoume from being dented easily?

    Or will it take such heavy glass fabric and or layers to get a harder surface that it would be lighter to use Hydrotek Meranti plywood and use a lighter glass cloth for basic abrasion resistance?

    Cheers, Allen
     
  2. FAST FRED
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    FAST FRED Senior Member

    AS the ply will flex a good deal Dynel ,

    one layer, in epoxy with flex hardener should take care of beach rash.
     
  3. PAR
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    PAR Yacht Designer/Builder

    Dynel is an option, though Xynole is better at abrasion, for the same cost and laminate effort. Both will make a hard, abrasion resistant sheathing. You don't need, nor is it desirable to use a flexible hardener, which will decrease it's effectiveness at both abrasion and hardness. A regular, room temperature cure resin/hardener combination will do just fine.
     
  4. philSweet
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    philSweet Senior Member

    It depends on the beach and on the loadings. What does the rowboat weigh? and is the beach stony or does it have a lot of coral? Will the boat be dragged?

    So there are two issues - abrasion resistance, and ding resistance, and they are a bit in opposition to each other. For ding resistance, you want a hard, stiff coating that will bridge the weaker okoume. 6oz woven glass in a deck epoxy (hard stuff, 100% solids) will do pretty well for that. Add a 3" tape of 9 oz glass to all chines first, fill this with more epoxy, and feather this out completely, then drape the hull. At least that's how I do it. If it carries more than 15hp, you might want to bump the bottom skin up to 9-10 oz glass.

    The above is not adequate for dragging, though. If dragged, add sacrificial Dynel/Xynole in epoxy to the keel after doing the above. Anything thicker than the above is basically wasted because you will split the inside of the ply before you puncture the skin. A veil if glass on the inside is always a good idea for improved water resistance and scuff wear. But often not practical. I put more dings on the inside of my skiff than I ever did on the outside.

    Add hardwood rubbing strakes for heavy duty. A 3/4 x 3/4 mahogany strip can take an amazing amount of abuse, and you can screw and bolt stuff to it. Good luck.
     
  5. abosely
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    abosely Senior Member

    I'm thinking about building Fisher 16' Swampscott to be a tender for the Narai.

    It can be built with 9mm ply at 250lbs and or 6mm ply at 160lbs or so, I'll build it with 6mm.

    He has a clinker ply glue & tape version. I like the looks of the best.

    The beach's are lava rocks, lava sand & regular beach sand.

    Will put a layer of glass on inside and probably use Ipe skid strips on bottom since I have some already and that stuff is tough.

    Would Hydrotek Meranti be a better choice than Okoume? It's a little heavier, but harder & stronger.

    Cheers, Allen
     
  6. PAR
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    PAR Yacht Designer/Builder

    Use meranti on the garboards and broad strakes, as these seem to get beat the most. You can't sheath a lapstrake, so just sheath the garboards. It's the edges of the laps that will get bashed. Rub strips on a lapstrake just look awful, so maybe just harden up the corners of the exposed laps. Fabrics will not make these turns, but some thickened epoxy can be used to fair the edges.
     
  7. abosely
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    abosely Senior Member

    Well that's kind of embarrassing... I know a clinker ply hull can't in glass or Xynole! Duh! Don't know what I was thinking or rather why I wasn't.

    With that said I would build it as a stitch & tape, so the hull can be sheathed in Xynole. Fisher has both options in the plans.

    The stitch & tape version looks similar to the clinker ply hull in that the planks are narrow like the clinker ply build so will look close to clinker ply look, just not as defined as the lapped joints, but will still look "salty".

    Cheers, Allen
     
  8. PAR
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    PAR Yacht Designer/Builder

    To a novice, the build you describe might look okay, but to anyone with some experience they look awful.

    You can sheath the garboards, before the broadstrakes go on. I just did this with a glued lapstrake build and it hardens up the bottom. The radius of the fillets necessary to permit the fabric to lay down nice, without puckers and kinks is pretty big, but you can do this too. There's a lot of difficult fairing and smoothing necessary to make this look good, so you might as well put more fairing compound on the lap edges so you can sharpen them up in the fairing and smoothing process.

    For a rowboat, I don't see any of this as necessary, except for the garboards and maybe some keel protection (rub strip) if you have one projecting below the planking. Rowboats are light and usually manhandled around, so damage will be scratches and dings, with nothing of significant impact being common. Will you get dents and scratches, yep, you sure will, but dragging boats over beaches, seashells, rocks, etc. is just the nature of it's life. If you don't have sheathings on the planking, it'll be fairly easy to repair (a little filler and some paint), if you do sheath, you'll have the additional effort of fixing the sheathings too, which can also trap moisture under deep breaches in the skin. Simply put, don't make more work for yourself and keep it simple, painted planking.
     
  9. abosely
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    abosely Senior Member

    OK, thanks PAR, that makes things simpler. Since not sheathing the hull, will use Hydrotek Meranti instead of Okoume since it's a bit harder & tougher.
    Would the extra weight be worth it since won't be sheathing hull?

    I haven't used Okoume but from what I understand it's pretty soft compared to Meranti.

    Cheers, Allen
     
  10. PAR
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    PAR Yacht Designer/Builder

    Meranti is a bit tougher and a little harder to bend. It's also about 20% heavier, but if you do only the bottom planks, with okoume above the LWL, you can save some weight. Considering you'll need maybe 5 or 6 sheets for a typical row boat, you're looking at 80 to 100 pounds in okoume and 95 to 120 pounds if all meranti. If you do the bottom in meranti and the topside in okoume, you're looking at 90 to 110 pounds of planking. Maybe these numbers have you worried, but I wouldn't be. If 10 - 20 extra pounds is going to kill you . . . Of course the first time you have to drag this puppy a long way, I'm sure I'll be the one you'll repeatedly curse, as your back pain kicks in. I can take it . . .
     

  11. abosely
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    abosely Senior Member

    LOL If it's to heavy for me being built with Meranti, it will be my responsibility, since I'm the one that made the choice. I don't believe in blaming someone else if I take their advice or suggestions and I'm not happy with the way something turned out. I figure they gave me information and it's my responsibility to make sure it is a good choice for me & my situation. No whining allowed. :)

    Even if building with Meranti added 30lbs, I think it would still be worth it. Don't need to drag it any distance really as she will be a beach launch tender. I prefer the ruggedness over saving a few pounds.

    Cheers, Allen
     
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