Dumb Newbie Questions - need typical layup for 10' 1-person fiberglass boat

Discussion in 'Fiberglass and Composite Boat Building' started by Bill Brasky, Jul 14, 2010.

  1. Bill Brasky
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    Bill Brasky Junior Member

    Hello, new here, been looking over the site for a while. I'm building a small, 1 man fiberglass boat from a male mold I built. It will be fiberglass only, with no interior support or stringers, roughly 10' by 4', with a deck on it. Just wondering what will give me the maximum strength with minimum weight/cost. Ie: how many layers of cloth or mat, what weights...

    I appreciate any help you can give me. Thanks.

    Cool thanks. Great bunch of guys.:rolleyes:
     
  2. J3
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    J3 Junior Member

    There's strength and there's stiffness; you say you don't have any stringers or frames or bulkheads in this small boat but (I suspect) it will be hard for anyone to answer without knowing how the shape contributes (v bottom, flat bottom, rounded, tunnel; are there hard chines, strakes, etc. what are the unsupported panel sizes) what is the design speed range, horsepower to be applied, etc.
    Mat is for bulk and to avoid print through; it absorbs a lot of resin and thus is heavy; strength comes from the glass not the resin.
     
  3. Bill Brasky
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    Bill Brasky Junior Member

    Thanks J3. The unsupported panel is about 36 inches wide and curves up to the side, which has a 2" vertical edge. I've made one of these boats before, but we used materials from local hardware stores. I was going to save money by buying in bulk from US Composites, but the small packages of cloth and mat I bought from the store don't have weights on them, so I'm not exactly sure what I used last time. I was going to do a layer of 10 oz. cloth, a layer of 1-1/2 oz mat, and another layer of 10oz cloth. Would this be sufficient?
     
  4. Bill Brasky
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    Bill Brasky Junior Member

    Also, I've found bondo brand poly resin for $29/gal. Am I correct in thinking this is a good price? This is local so no shipping charge added.
     
  5. Bill Brasky
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    Bill Brasky Junior Member

    I would sure appreciate some kind of feedback on this so I can place an order with US Composites for the cloth/mat and get this ball rolling.
     
  6. tinhorn
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    tinhorn Senior Member

    I've made repairs to several dinghies this spring and summer, and the most common layup appears to be the equivalent of 2 or 3-oz mat, woven roving, more mat. An additional layer of Coremat is used on some where the oarlock sockets are mounted.

    BUT these boats have all utilized the seats to keep the sides from bulging out--either molded into the boat to provide flotation, or made out of wood and screwed to blocks that were laminated to the sides with a bit of mat (shudder). Your deck may very well provide the strength to hold the hull in shape. I've seen pictures of dinghies with decks that had the seats molded into them. Nice looking.

    If you buy an entire roll of glass you're gonna have a lot left over. Feel free to bring the leftovers to my house. Is there a marine supply store that will sell you only what you need? (And $29 is what I pay for a gallon of polyester resin.)
     
  7. Bill Brasky
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    Bill Brasky Junior Member

    I wouldn't be buying a whole roll, just by the yard. I figured I'd need about 17 yds of cloth and 8 yds of mat. My deck will keep the sides from bulging out, the worrisome part for me is the bottom, as its the widest unsupported part.
     
  8. tinhorn
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    tinhorn Senior Member

    Rats. I coulda used that extra 'glass.

    Me, I'd use mat, cloth, mat instead of the other way around. Not sure what your concern is about the bottom, or the shape of it. If it's flat and/or you're worried about a rock poking through, use mat, woven roving, mat, woven roving, mat on the bottom. Even with this thick layer, wear a life vest because some rocks are just plain sneaky.

    If your concern is simply rigidity (and not super-strength), a layer of Coremat is rigid as all getout between two layers of 3-oz. mat.

    If you use cloth or woven roving against the gelcoat you'll get print-through. If you use it as your final layer you'll have tons of hidey-holes for dirt to collect, and the resin WILL get scraped off the high points in the weave through simple wear and tear. Then you're screwed--if you try to cover it with more 'glass (or even just a new coat of resin), there's no way to sand out all the little hidey-holes to get a new-'glass-to-old-'glass bond. (According to an old-timer who claims to have worked with fiberglass since it was invented, if you let the woven glass go unprotected, all those strong fibers turn into moisture wicks.)

    You want your finish layer to be mat. I've never seen a final layer of woven roving or cloth that didn't have sharp fingers pointing out SOMEwhere waiting to snag an unsuspecting bit of tender flesh. It's most likely to happen when you're trying to impress someone in a bikini.
     
  9. Bill Brasky
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    Bill Brasky Junior Member

    That's a HUGE help. I thought the cloth would give me the better finish, not the other way around. So 1-1/2oz mat, 10 oz cloth, 1-1/2oz mat? I thought I read on here that mat doesn't have much structural integrity compared to cloth. Now I'm confused again.:confused:
     

  10. tinhorn
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    tinhorn Senior Member

    The characteristics are different between cloth and mat, sure. But if there's a piece I need to remove from an old dinghy, I'd much rather see it bonded in with cloth than mat--I can easily tear the cloth, and it doesn't take too much effort to tear woven roving. Resin has little structural integrity compared to the 'glass fibers, but if you made a panel out of mat AND cloth, I could build a panel out of mat that would be just as strong. Mine MAY just be a little heavier and thicker. Engineers (which I am not) will look at characteristics of different weaves and weights, compare those to the task required, and make recommendations accordingly. The laminate schedule for a huge yacht will be different than for a much simpler 10' one-man boat.

    Where superstrength and/or superlightness are desired, that's when we get into the realm of "advanced composites"--carbon fiber, Kevlar, 3D fabrics, epoxy resin, super-whiz-bang fillers, stuff like that. Somewhere between a 200-pound-three-layers-of-3-oz-mat-with-polyester-resin-puddled-in-the-bottom boat and a 20-pound-interwoven-carbon-fiber/Kevlar-skinning-3D-fabric-with-microsphere-filled-epoxy-resin-at-the-perfect-50/50-ratio boat lies your 10' project.

    I'd stay away from either extreme, of course. I'm not qualified to suggest the layup for your project, but I will share some observations: when I've cut up jet ski hulls, they appeared to be about 1/2" thick mat. (Applied with a chopper gun, but it's essentially the same thing as mat, just more resin-rich.) No sophistication, so they make up for it with mass. I'm currently repairing a sweet little canoe that appears to use your suggested 1.5 mat, 10-oz cloth, 1.5 mat. Very lightweight, and easily punctured. I've repaired older dinghies from 6' to 10' that were made with either 6 to 8 ounces of mat, or about 3 ounces of mat on each side of a layer of 24-oz woven roving.

    We need to know a little more about the tasks your boat will asked to perform, and we really ought to see a picture of the mold in order for the guys smarter than me to recommend actual materials.
     
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