Skin material for skin on frame kayak

Discussion in 'Boat Design' started by Hultis, Aug 29, 2014.

  1. kerosene
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    kerosene Senior Member

    Have you tried sail making shops. At least here in Finland there are no retail resellers of dacron but people who want to make their own projects buy from sailmakers. It seems that they don't markup the price that much.

    There are several small sailmakers that omport their own material in large quantities, there must be a bunch in Sweden too.
     
  2. rwatson
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    rwatson Senior Member



    What got me wondering is the longevity of the job. eg.

    "Peel Ply is either Dacron or Nylon fabric. It is placed in the layup anywhere you want the laminate to separate and or on any surface you want to do secondary bonding to."
    http://www.kayakforum.com/cgi-bin/Building/archive.pl/bid/11/md/read/id/48906/sbj/using-peel-ply/

    I have seen 6oz fg/epoxy separate from underlying 'supporting' fabric after impact.


    For this system to work, you are going to need some very specific type of fabric, not just any old 'dacron' . It probably wouldnt work on old sails for example.
     
  3. upchurchmr
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    upchurchmr Senior Member

    Kerosene,

    You typically use dacron which has not been "heat set". Sail cloth has been heat set and coated to help it not stretch.

    You want the dacron to be able to shrink with the application of heat to take out wrinkles and not be coated so that the fibers will shift when you try to drape around the complex contour of a kayak or canoe. Any boat, in fact.

    Sail cloth will require darts just like the fiber reinforced PVC shown at yostwerks.com
    And it will look the same way, if you care.

    Watson,

    You are again telling someone who has done it that it can't be done.
    Why don't you ask what kind of dacron was used instead of telling him it won't work with old sails.

    Can you describe the application where you saw the separation?
     
  4. kerosene
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    kerosene Senior Member

    Ah, then nevermind
     
  5. rwatson
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    rwatson Senior Member

    Where did I say it couldn't be done ????

    Where did I say it wouldn't work ?????

    What I said was it was ^&*^%% hard to find any concrete explanation of the process, especially in the forum that you said had the info.

    I still haven't seen links to any definitive build or description of the process.

    What I did say, and what I linked to, was that at least 1 type of Dacron could act as peel ply -which would be a disaster.

    What you need to do is stop being so defensive, and supply some precise details of the technique, with the materials, and some actual long term examples.
     
  6. griff10
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    griff10 Junior Member

    peel ply

    Yes peel ply does exactly what it says it'll do, it'll peel away from a glass/epoxy layup. With my method though there is no way to start a peeling process, so it doesn't happen. The glass/epoxy encapsulates the Dacron (trademark).

    Again, I use normally uncertified aircraft Dacron fabric, it's much less expensive than the certified fabric and it's unlikely you'll fall from the sky if it fails. The fabric is designed to be heat shrunk which gives a snug covering and it's also designed to be coated after it's shrunk. I precoat with epoxy first which bonds well with the fabric then apply the glass/epoxy once it's set.

    Perhaps some here work full time in the boatbuilding industry, I no longer do that, this is a hobby now, I have a few more irons in the fire that take up most of my free time, so I haven't taken the time to write up a full building process journal. Perhaps sometime in the winter when there are less pressing matters for my time.

    Bill H.
     
  7. Jeremy Harris
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    Jeremy Harris Senior Member

    I've been using offcuts of aircraft fabric (Stits and Ceconite) as peel ply for years. It works very well as peel ply, as it doesn't bond at all well to epoxy and just rips off leaving a nice smooth surface.

    I've also built a skin on frame boat using heavy duty Ceconite. Worked well, but even the heaviest weight Ceconite is really too thin to be durable on a SOF boat, as it has very poor abrasion resistance, even with multiple tapes over all hard points (exactly as you'd do when covering an aircraft with the stuff, and my background is in building aircraft).

    I protect the keel of my Ceconite covered SOF boat with polyurethane prop tape, which works OK at minimising abrasion, but needs regular replacement and isn't cheap.

    I have seriously thought of adding a Kevlar epoxy skin to my SOF boat, but because I know beyond any doubt that the bond is very poor between the polyester (Dacron) cloth and epoxy resin I'm very wary about doing it. I'm near certain that the bond will just break down and it'll delaminate, just from my years of experience of using this same cloth as peel ply.

    If I do try it, then I think that what I'll do is make loads of holes in the polyester skin, after it's been heat shrunk, then lay up the kevlar epoxy on the outside and add a thin layer of epoxy glass on the inside. With luck all the small epoxy "rivets" through the holes will help prevent delamination if they are big enough. I know the pores in the fabric aren't big enough to provide the same function, though, so the holes will need to be larger than that. I was thinking along the lines of making a pricker roller that could be run over the cloth to punch thousands of holes in fairly quickly, perhaps slightly tearing the edges of the holes in the polyester to improve the mechanical bond. I've not got around to trying it, but it's on my list of things to try one day.

    BTW, there are photos of my SOF boat in this thread, start here and read on to see the photos: http://www.boatdesign.net/forums/boat-design/beautiful-skeleton-37456-2.html#post455306
     
  8. Wavewacker
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    Wavewacker Senior Member

    A cheap alternative is to go to a swimming pool dealer, get a PVC pool liner or better a heavier PVC pool cover, it is reinforced webbing in the PVC and flexible. Cut and glue it, trim neatly for better appearance. The pool covers can be tuff stuff. Might find one in the trash that has enough material to cover your kayak that has no issues at all. Free!?
     
  9. latestarter
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    latestarter Senior Member

  10. bpw
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    bpw Senior Member

    If I remember correctly George Dysons early boats had a fiberglass skin. I think he would wrap the boat in some form of shrink-wrap/plastic film and then glass over that.

    A soft flexible skin really is better though since it allows the boat to move a sit should, and can be much lighter. Dyson talks in his books about dragging the early boats up the beach on rollers since they where heavy. His later soft skin boats are very light in the 30-40 lbs range.
     
  11. Petros
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    Petros Senior Member

    the big banner signs are made from pvc covered polyester, even the lightweight stuff is suitable for a kayak. Go to a sign and banner shop and ask for their mistakes (their trash will be full of them), or old banners after the the events they advertized.

    it does not stretch much, so you will need to put darts and more seams than normal, but the fabric will be free, watertight and tough. If you carefully designing the hull below the water line so it can be flat wrapped, you will only need one seam below the water line, at the prow and stern. A seam at the gunwale level is not as critical, but using solvent adhesives or heat would make a really water tight seam. No sewing required.
     
  12. rwatson
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    rwatson Senior Member

    So what does he use now, and why ?

    Its a great theory, but as i noted earlier, the fg warps when curing, so if the underling support is flexible, you can end up with permanent wiffles on the surface.
     
  13. rwatson
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    rwatson Senior Member

    That sounds realistic - the problem I have encountered were small delaminations that held moisture, sort of small bubbles of water spotted over the surface ( not a boat hull) that stayed there for a long time, and made the cover noticeably heavier.
     
  14. bpw
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    bpw Senior Member

    When I was building my boat to his design 15 years ago or so he was using various cordura nylons coated with hypalon for skins. They are tough and work very well.

    Don't know much about the early fiberglass boats but his book "Baidarka" has pictures of quite a few of them and they look nice and fair, so there is some way to make it work. He paddled the FRP boats up to Alaska and back a few times, so they certainly stand up to hard use in tough waters in reality, whatever the theory may say.
     

  15. rwatson
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    rwatson Senior Member

    I have seen the latest ballistic Nylon impregnated with Polyurethane.

    I dont know what could be better in lightness, impermeability and strength - it seems to have it all
     
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