Flyfisher's Experimental Folding Kayak Page
I travel a lot. Much of the travel is by aircraft, for business and for pleasure. I began thinking about the possibility of building a handcrafted foldable boat as I was using a short little Sit on Top kayak on St. Croix during the fall of 2002.
A search of the web found a few others who had done this. One particularly interesting boat had been designed by Tom Yost. It was based on a Feathercraft Design. I was intrigued by the picture of his frame.
I was interested by this construction technique and determined to do a rough construction trial with copper pipe and a 10 mil truck tarp. I shared this with the kayak builder's group. They were less than excited by my plans.
Here are some of the comments:
Eric said: Copper tubes are definitely unfit for structural use: too heavy, lacking resilience. They'll bend and won't get back to shape. You may email Tom Yost, he once mailed me he gets aluminum very cheap. Truck tarp needs trimming into several panels, according to my laborious experience: yes, two for the deck, two for the bottom, two for the flares, six panels (considering you have a deck ridge and a keelson, a pair of sheer stringers, a pair of chine stringers). Don't try to simplify with a four-panels layout. It would get all wrinkled otherwise. Ask Timo Noko e.g on the Pouch Boats site about his experience in turpentine-diluted silicone. It's cheap anyway. Lace your skin from coaming to stern, in order not to take too much water in; grommets and velcroed overlaps on top. Or use a large, stainless or plastic zipper. Sorry for insisting, safety matter here.
Paul Jacobson, thorough as always, had this to say:
OK. return the copper. The lightweight (L) is too thin and when it gets wet it will stain your boat with green stains. Copper pipe has very little "bending memory" (I'm sure there is a technical term for this, like "modulus of elasticity", but I think you get the point)
Once you bend the copper pipe, it stays bent. It does not spring back to its original shape. Imagine an archery set with a bow made from copper pipe. Pull back the arrow and release it -- and instead of the arow flying from the bow, it drops to your feet, while the bow in your hand has a permanent "C" shape.
You don't want that kind of behavior from your stringers. Otherwise you would be tightening the skin more and more each time, as you bent in the frame from the previous use.
If you want to use plumbing materials, look at the schedule 40 PVC pipes. I think the 1 inch pipe would be what you would want. The 3/4 inch seems a bit too flexible to me, but it could be reinforced to make it stiffer. At a little over $2 for a 10 foot length (20 foot lengths are available to contractors, but hard to find) you'll spend a bit less than half of what the copper cost you.
Straight couplings are under 25 cents use as many as you need to connect short sections of the tubing. Glue a connector to only one end of a section of pipe and it won't get lost, but the next section can connect easily, and as long as the skin is on the pipe can not come apart. Of course you could drill holes in the pipes and fittings and add safety wires or cotter pins to ensure the connection, too. The ends of the stringers would need to be tapered on one side so they could attach to the stem pieces. "T" fittings and short sections of pipe can be used for cross bracing.
Umm, I think you got the wrong tarp, too. The two sided (blue/brown, blue/silver, etc) tarps they sell around me are heavier versions of the cheap blue (woven) polyethylene tarps. After a little weathering the blue ones shred into confetti. Long before that they leak. I suspect the thicker ones will, too, but just take longer. The "REAL" trucker's tarps are a woven Dacron or nylon fabric which has a solid plastic or synthetic rubber coating. It might be PVC impregnated, or PVC coated, or laminated between sheets of PVC, but it is VERY tough stuff. And the price is not too bad.
McMaster Carr sells similar material through their catalog. try www.mcmaster.com and search for "heavy fabric". That should get you two or three different materials. If you can navigate their site to get to the Adobe acrobat page where these are printed, you'll find several other options.
Some of the solvents/glues in the plumbing department can be used on this PVC fabric as well as on your pipe! Look for a universal solvent/glue. Otherwise, there are special glues for vinyl which will work, or the material can be heat sealed. You can sew a seam and then cover the stitches with a strip of vinyl material to waterproof the seam., too.
But if you are looking for a water based artificial rubber compound consider some of the RTV rubbers and urethane rubbers. Mix 'em, spread 'em, let 'em set up. Voila, one "rubberized" skin. There are a lot of places that sell neoprene plastics, but there is one site I like: Try Eager Plastics of Chicago http://www.eagerplastics.com/cast.htm
You can't order online, but they list lots of products and the specs on many of them. Call and ask their people for tech advice and hopefully you can get a line of a good product. You should not need more than 2 quarts to cover a kayak skin.
Meanwhile, back in the hardware store, you can head over to the roofing repair section and ask for an "elastomeric rubber" roofing material. This is a water-based, latex material for covering flat roofs with a thick rubber coating. It goes on like latex paint. If you thin it a bit with water it will saturate a canvas fabric on the first coat, and subsequent coats will build up nicely.
Snow-coat, one of the Snow Roof system products from http://www.kstcoatings.com is one I've tried. Elasto-seal can be used underneath it, or on its own, too.
It LOVES to be outside, and has an expected 20 year plus life under all day sunshine, so don't worry about protecting this from UV. In fact, the preferred way to apply this is to do it on a hot, sunny day so the heat and sun can speed the curing process. I did tests inside on a cold winter day, in a dark basement, and it dried just fine. If I remember correctly, when it is dry it supposedly is non toxic and can be used for holding tanks for drinking water. It worked over fiberglass, so if you want a VERY strong skin with no stretch, cover the boat with fiberglass cloth, or fiberglass window screen material -- which is what their roof patching fabric looks like -- and cover that with the elastomeric roofing materials.
At that point I was beginning to feel a little bad about dreaming about the project at all. It was beginning to look like it might not be as much fun as I had dreamed. I made my discouragement known and Paul was quick to buck me up:
Don't lose interest. If you have a folder (particularly a double) you will use it more and more. One big problem with a kayak (and canoe) is shipping it to where you want to use it. A folder, or a collapsible, which can be checked as ordinary baggage on an airliner travels cheaper than a bicycle. Packed into two bags it can be carried on backpack frames, and shlepped to any pond, anywhere, to provide transport for the pair who share the load. The fishing possibilities abound! Small planes can carry you (and your boat) to the middle of nowhere. If your dreams of "getting away from it all" include a waterfront location, a folding kayak will let you enjoy the trip.
The nice thing about building a folder is that it takes up little shop space. You build the smaller parts, which can be an ideal inside-during-the-winter project. Then you assemble the boat from these parts each time you use the boat -- so the assembly can be carried out outside, usually in a few minutes, and then the parts can be disassembled and carried back inside.
October 22 2002: So this week I put together the frame. It was remarkably easy going. I am trying out the 1 inch PVC pipe idea to see if it works. I experimented with the elastomeric roof coating on ballistic nylon and it worked very well. I have ordered some 8 oz material from Dyson et al for the project.
Here is a picture of my frame
The bow and stern are bolted together with bolts which can be removed with one's fingers:
October 28th I worked on the cockpit:
And the cockpit is supported by the ribs and the stringers.
The "ribs" are made from plywood and are held to the stringers with bungee straps:
At last, on 30 October, the cloth has arrived from Dyson and I will begin sewing the cover.
18 November, 2002
I have put this project off to the side for now. I worked on sewing the loops on the top of the kayak, but found that when I began to lace them, the area between the laces sunk in to the middle of the boat. It was ugly and it was not what I wanted. So for now, it is unfinished.
One of the other builders, Wayne, on the builder's board also built a folder in a similar way with nylon and elastomeric roof coating. He reports that on returning from the lake, the coating was coming off in sheets all the way down to the cloth. He only allowed 48 hours of curing, but this still seems pretty drastic.
Flyfisher's Kayak Page