[Paddlewise] Skinning a Folding Kayak

I am building a double folding kayak, a Blandford PBK19, per plans from 
Clarkcraft. This will be primarily used in lakes, Long Island Sound, and 
until tested in warm water within swimming distance of shore (FYI the bottom 
is essentially done including endposts, the first two crossframes, and 
stringers and gunwales installed for the front quarter of the boat.) I am 
looking ahead to skinning and have three possible routes to follow. They are 
in order as follows:

1. Plans call for a rubberized fabric, preferably canvas and rubber ply. The 
hull is done in one piece, being stretched along the gunwales and sewn up 
along the endposts. I imagine this is done similar to that shown at the 
Folbot page at
http://www.folbot.com/tour3.htm
Notice the Folbot uses a thick hypalon material that I believe is not 
stretchy, which is why they use sponsons (like other manufacturers). Folbot 
and others connect the gunwale to the top stringer with little plates as 
shown at
http://www.folbot.com/anatomy.htm
which give the sponsons something to push against to tighten the hull. The 
pbk19 does not have these. If I follow this route I have to either find a 
stretchy material, or use non-stretchy material and somehow add sponsons to 
tighten.

Questions for this route
a) Since the pbk19 has a flat plywood bottom, can I put a sponson there?
b) Does anyone know of a source for stretchable rubberized fabric? I have 
samples of PVC and neoprene fabric and none seem to stretch.

2. From the baidarka mailing archives, cut strips to match the keel, chines, 
and gunwales, glue and then heat to remove wrinkles. This can be found in 
detail by searching the archives at
http://robroy.totalsports.net/baidarka/wgindex.html
and searching for "hendrix mixture", will return two hits including "cutting 
the skin" which is what you want. This was done for the kayaks at (excellent 
site by the way!) 
http://robroy.totalsports.net/baidarka/slideshow/index.html
by Hendrik Maroske. His brother Gerald advocates sewing as well, as 
mentioned in the other hit returned. I believe Hendrik used Stamoid PVC for 
his single aluminum kayak. I have a sample of 15 oz seems thin but smooth 
both sides, and looks like it would glue nice. Other samples I have, 
basically have one smooth side and the other side shows the fabric weave 
which I believe would not glue as easily, as when gluing an overlap. 
Additionally some PVC has special coatings, which must be cleaned before 
gluing.

Questions
a) Blandford advocates no seams below the waterline, and this route has a 
lot. Hendrik and his brother have had luck with this but is this really such 
a good idea?
b) The neoprene fabric sample I have is 16 oz buff free(no coating), a 
little thin but looks fairly tough. Does anyone have any recommendations 
for/against neoprene fabric? Is there any particular flexible glue that 
should be used?
c) Any recommendations for a particular PVC source? I have samples from 
Seattle Fabrics, of PVC, and neoprene (special order fabric). I am waiting 
on 16-oz hypalon sample (again special order). They have been very helpful. 
I also have Weblon samples, but they have coatings on them.

3. George Dyson, author of Baidarka, sells plans for aluminum kayaks that 
are skinned with one-piece nylon fabric. The skin is then heat shrunk and 
hand painted with thinned hypalon, to saturate the skin to the inside. It is 
then painted with neoprene, and finally finished in hypalon. Since this is 
sewn in one piece similar to route 1 above the question arose from another 
pbk19 plans purchaser if this could be tried.

Questions
a) Dyson’s method is meant for a non-folding boat so there is quite a thick 
layer of coating on this boat. I seem to recall that folding something this 
thick would result in cracking since much of the coating is on the surface. 
Is there anyway of getting by with just using thin coats of neoprene? I 
believe this is more flexible than hypalon, but Mr. Dyson used thin coats of 
hypalon because it thins easier  than neoprene.
b) Is there some way of covering the woodwork so that the paint that soaks 
through will not stick to the woodwork? I recall reading that removing skins 
painted in polyurethane results in wood coming off with it.
c) Some boats done this way use polyurethane instead of hypalon/neoprene. Is 
polyurethane flexible enough for a folding kayak?

4. Okay I am sneaking in a forth route, basically meaning other. This 
assortment comes from Jim Heter’s
really neat PakYak site at
http://robroy.totalsports.net/boats/PakYak/
He uses multiple layers in his latest prototype, nylon pack cloth, a foam 
layer and a bottom liner. The pack cloth is waterproofed with urethane on 
one side and then he coats the outside with Thompson's Water-Seal. I’m not 
sure if there are seams below the waterline. He mentions that he has used 
cordura in the past.

Questions
a) Multiple layers sounds interesting. Some inflatable boats use two layers. 
Okay how about making an unsupported vinyl hull (no fabric) glued up as in 
route 2. Then sew up a nylon skin as in route 3 over the vinyl and coat with 
thinned neoprene?
b) Thompson's Water-Seal? Can this be used on plain old canvas?

Has anyone actually read this far? Feel free to offer any suggestions or 
comments. Thank you in advance, Paul.
kayaker37_at_hotmail.com



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