Can I put fiberglass over a canvas kayak?

Discussion in 'Fiberglass and Composite Boat Building' started by green1181, Apr 24, 2008.

  1. green1181
    Joined: Apr 2008
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    green1181 Junior Member

    I am going to build a kayak in a couple weeks, it is a 12 foot canvas over
    wood. I was wondering if I could build it, then lay the resin and cloth over the
    canvas? Would there be any advantage?
     
  2. alan white
    Joined: Mar 2007
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    alan white Senior Member

    No. No advantage. If the kayak isn't solid-skinned (like a canvas canoe) everywhere, the fiberglass/resin will be too thin to stand up. Even a canvas canoe oughtn't have both canvas and glass.
    I'm assuming your building method will be skin-on-frame. My advice is to not reinvent the wheel. Get some building experience first. Along the way you'll see why things are done the way they are.

    Alan
     
  3. rwatson
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    rwatson Senior Member

    I have done the fibreglass over cloth, and I would say that it *does* have an advantage - IF the weight and strength of the fibreglass ends up being strong enough to be a structural addition.

    My experience was in modfiying the centre hull of a trimaran, and adding a 'pod' for increased accomodation in the centre hull.

    I made a frame of aluminium, with a few stringers fore and aft, and stretched a nylon material very tightly over the structure, much like a kyak would.

    I then applied a layer of cloth, a layer of matt, and another layer of cloth over the nylon fabric. In essence, the fabric was acting as a simple female mould. Once it was cured, I simply painted over the nylon fabric, and I used the trimaran for years.

    The only 'gotcha' is that as the resin cures, it tends to warp the fabric into a hollow. So, if you fibreglassed the bottom of the canoe, you would find that instead of being very flat, there would be a slight concave shape created. (a hollowing effect). Its a bit like an umbella looks when the wind is blowing hard on the fabric.

    This isnt neccesarally a bad look if the hollow effect is running fore and aft, unless you get a frame along the hull that then stands out like ridge at right angles to the keel, and makes an ugly and inneficient hull shape.

    However, if all the stringers in your canoe frames are attached to the outside of the frames (not rebated into them), then the hollowing effect will not be a problem. This is usually how fabric canoes are designed anyway.

    Dont forget, in the average fabric covered canoe, the fabric deforms inward when on the water with a load. The fact that fibreglass makes this concave effect permanent should not be a major problem.

    I would suggest though, that if you are going to fibreglass straight away, dont use canvas. Use some kind of Nylon material. Canvas is cotton based, so will eventuallly rot, and is a lot more expensive to buy than nylon.

    Stretch the nylon, drum tight over the frame before applying the fibreglass, to reduce the distortion that will occur.

    The other tip for new builders, is that when you go into the fabric shop to buy metres of nylon, get the same amount of taffeta. After you have laid the fibreglass cloth over the nylon skin, use rollers and brushes to push the resin into the cloth and matt, and then lay sections of taffeta on as a final layer, and smooth it on over the wet fibreglass. You will want to cut the taffeta into say, 1 metre x 1 metre squares, and overlap the edges a little. Its too hard to try lay large areas of taffeta smoothly over wet fibreglass.

    Once the fibreglass is 'set', you should find that you can pull the taffeta squares off the fibreglass to leave a really smooth and even surface for painting, and save hours of itchy, dusty sanding to get the final smooth finish. If you can afford it, get what they call 'peel ply' from the fibreglass shop instead of taffeta, to do the same job a bit more easily.

    If you are not familiar with laying fibreglass, make a couple of small test frames, and practice first. The biggest trap is having the fibreglass go hard before you are finished 'wetting out' because you dont measure the catalyst properly. A few test runs will make you more confident and give you a better chance of a nice looking job on the real boat.

    Even if you make a few mistakes, its a great learning experience, and will give you confidence for much bigger jobs. Have fun.
     
  4. alan white
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    alan white Senior Member

    Just a note:
    The weight of a kayak is critical to its performance. The addition of a fiberglass skin to a stretched fabric may be appropriate for one who can design to compensate (there are obviously already plans for this kayak), but a neophyte will quickly get into trouble parting ways with his plans.
    I still say its a bad idea, meaning not appropriate in this instance.
    A novice has enough on his plate just sticking to a tried and true method.
     
  5. rwatson
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    Location: Tasmania,Australia

    rwatson Senior Member

    The weight of a kayak is not rocket science. A 12 ft plywood canoe is a lot heavier than a 12 ft fabric canoe. But, from an operational point of view, it only boils down to whether you need wheels to move if to the waters edge, and has bugger all effect on paddling and seaworthiness because a fabric canoe is ridiculously light (and fragile) in the first place.
    A hull of fibreglass is not going to be much heavier than plywood, so weight is no big deal. It will not have a bad effect on bouyancy, balance or seaworthiness.
    The worst that can happen is that the builder completely &^*&%'s up $100 of resin and cloth and has to pull it all off again. Its a cheap lesson, and a great learning experience.
    If he was going to attempt a channel crossing, more thought is needed, but this is just a great toy for getting out on calm water, and having fun playing with materials and design. The best I can do is point out a few tricks I learned at that age, and let them go for it.
    Hell, my first canoe was made of paper mache - and worked a treat. I cant count the amount of fibreglass I buggered up till I managed to figure it out.

    Unless a few hundred doallrs is your life savings green11, have fun!
     
  6. alan white
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    alan white Senior Member

    Well, I guess he knows his choices, which is why he asked.
     
  7. green1181
    Joined: Apr 2008
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    green1181 Junior Member

    Thanks for all the advise guys!! I think I might stick to canvas right now, I am on a tight budget..I know for sure that once I get one my girlfriend will
    want one so mabey I could experiment a bit then, or just go with stitch and glue plans.
    Just a question on canvas, Will there be any seepage of water if all the joints are sealed up good?
    thanks rwatson for the idea of nylon and taffeta, I have done a bit of fiberglass work with rc boats and when I worked at the bombardier dealer
    and sanding is a real pain, that sounds like I could get a nice finish.
     
  8. Squidly-Diddly
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    Squidly-Diddly Senior Member

    I did that one a self designed/built kayak. Worked fine.

    The kayak was PVC pipe on ribs jigsawed out of cheap 5/8 ply, covered with waterproof nylon used for tents and such.

    I duct-taped the fabric to the PVC pipe.

    When I put it in the water the fabric bowed in a lot more than I figured and I was nearly awash.

    I just laid a layer of cloth and resin (first time using this stuff, I was about 14) and it added enough stiffening to make the boat usable.

    If I was to do it again I might double the fabric so the inner might stay watertight even if the outer, still fairly weak layer is holed.
     

  9. rwatson
    Joined: Aug 2007
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    rwatson Senior Member

    Sqiddly Diddly confirms what I was saying - using fabric to form a fibreglass canoe is very practical. Beats doing a full FG mould.

    Now Green11, re the fabric laying ...

    There should be NO JOINTS, except at the bow and stern, where you overlap and fasten the ends together.

    Get the canvas or cotton based fabric wide enough to go right around the hull with about 6 inches overhang on the edges. Most fabric rolls come in widths wide enough to go around most canoes. After you lay the fabric over the upturned hull, temporarily fasten the centre of the sheet at the bow and stern, (making sure you have it pulled really tight first). Then use cloths pegs to loosely hold the fabric to the edge of the canoe, and then turn the canoe right way up.

    To get really tight skin, use G-Clamps with bits of wood to clamp the fabric to the top stringer on one side, then pull it tight on the other side and hold it it place with another bit of wood and a G-Clamp.

    To get a lot of tension, do what upholsters do, and wrap a bit of wood in the edge of the canvas, roll it really tight against the edge of timber.
    It would be worth getting an upholsterer to show you how, if you are unsure.

    Start at the widest part of the boat, and work towards each end. You will need a lot of cheap G clamps and bits of wood to hold it all in place.

    Work your way to each end of the boat. With constant adjustment, and lots of tension, you will get a big percentage of the canvas placed without wrinkles.

    However, you will certainly get sections where no matter how you pull it around, there is a bit of a "flap" left. Especially near the ends.

    Let these flaps hang around, until you get the whole skin stretched. Then the trick is to sew these flaps back onto the tight fabric. A bit like hemming a bit of material. With a bit of thought, you can arrange the "flappy bits" to not look too ugly. Sew them tightly with strong waterproof thread (get a sailmakers kit from the yacht shop, and get your mum to make suggestions if she is a bit of a sewer)

    Once the whole skin is tight, sewn up and fitting like you want, start replacing the G clamps with brass screws, through the bits of timber, for a permanent fix. Try not to just nail or screw onto the canvas directly, you should have a thin bit of timber over the top of the canvas to keep it tight, and then screw through that. At least use thick plastic washers under each screw if the wood is too awkward.

    So you should end up with no seams, but a few bits that have the flaps sewn over.

    If you used waterproof canvas, then theoretically you just need some waterproofing over the holes made by sewing.

    My opinion is that you are better off painting the whole skin with a special waterproof paint. House paint will work for a while, but it will go brittle and flake off fairly soon. I have seen "rubber" paints, that end up looking very smooth and flexible. They work well for longer, but eventually start to crack and peel around tight edges near the stringers.
    If you dont mind a slightly matt finish, and probably black in colour, the "bituminous" water proofing finishes are by far the most waterproof and reliable. Have a talk to a few local hardware shops to see what is available in you area. You can paint over these 'tarry' finishes without creating waterproofing problems.

    The two main points are
    1) Makes sure you have smoothed all the timber into round edges where the canvas will touch. Paint the timber to make it last

    2) Dont start screwing the canvas down until the whole boat is covered, and everything looks like you want it. You will need to make a lot of adjustments.

    Have fun. It will work. I did my first one when I was you age, and have never forgotten the experience. 40 years on, I have finally gotten around to make a 'real' canoe out of strip plank and fibreglass.
    au.360.yahoo.com/greenwoodenfish

    Now *that* was a lot of work!!
     
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