: I'm interested in building a kayak.

Great. Welcome aboard.

:I like the look of the walrus kayaks I
: saw pictures of, but I'm a little uneasy about paddling around in
: something with a canvas hull. How strong are they? How easy would it be to
: get tear or puncture if it gets hung up on some underwater obstacle? How
: resistant is it to wear?

If you do not have George Putz's book yet, go buy it. He will answer some of your questions in the text. I'll give you a few other answers here.

Resistance to wear and tear and puncturing is related to the material used to cover the boat. Generally it is an intuitive process. Thick canvas is stronger than thin canvas. Thick nylon is stronger than thin nylon, etc. George Dyson sells a nylon fabric that is the weight and thickness of an automotive seatbelt. When waterproofed with a few coats of liquid neoprene or hypalon the stuff is extremely durable.

Take a look at the Klepper web site. (www.klepper.com) Klepper has been making collapsible, fabric covered boats for over 90 years. Their older hull fabrics, made from a latex covered canvas lasted about 25 years. they estimate their current hulls, made of hypalon over a synthetic fabric will have a life of 50 years. ( an aside: I have friends who have a Klepper. It is going through the transition between the 2nd and third generations of owners. Grampa bought the boat and gave it to his daughter, she and her husband let their sons use it, and now the kids have laid claim to it, so the parents have a hard time getting it back to use it when they want to. Through all this, the boat is holding up well.)

The tires on your bicycle, and even your car, are made of fabric covered with a durable rubber coating. Bulletproof vests are made of ballistic Kevlar. If you want puncture proof, consider covering the boat with Kevlar and Hypalon. When a tire is punctured the air inside escapes as it is under rather high pressre, something like 35 pounds per square inch for a car, and up to 100 PSI for a bicycle. With a single paddler, the covering on your kayak hull is resisting water pressure at about 5 pounds per square foot. Divide that by 144 to get a pressure per square inch of about 1/30th psi, or 0.035 psi.

Even if you get a puncture you will get a trickle of water in, not a gush. You'll have 30 minutes to an hour to paddle to shore. Longer if you have a sponge to bail with. A bilge pump will extend your trip for many hours. Patch with a piece of duct tape and get back on the water.

Durability has a lto to do with where you paddle, too. In open water there are not a lot of obstacles to hit. YOur greatest wear and tear will be at launchings and landings. In either case, if you get a severe tear, you are mere feet from shore. If you hit a snag on landing, fix it when you wish. If you tear something on launch, pull the boat out, duct tape the tear, and relaunch. The worst place to use these boats is shallow rivers with lots of snags. But remember, if you are in an area where the water is so shallow that you can hit the bottom with your boat, then you can stand up and walk, or pick the boat up and cover a rip with duct tape.

But, even with that said, there is another force that reduces damage in a flexible fabric hull more than in a rigid hull. When the fabric hull hits an obstruction its tendency is to bend. The flexing action absorbs or deflects a lot of energy from impact with rocks and logs. The skin covered hull "gives" rather than breaks.

: The idea I had was to make a stitch and tape hull and use canvas for the
: deck. I figure this would help cut down costs for epoxy and fiberglass,
: while still giving me a bit more peace of mind while I'm out paddling.
: Economy is the other main reason, I'm a student, and need to keep this as
: cheap as possible.
: Any comments or suggestions? Are there any compelling reasons why this is a
: bad idea?
: Alan

The fabric covered walrus can be built for about $200. Maybe less. Use the recalculated offset numbers I've posted and you'll save about $30 on plywood costs for the forms.

If you are thinking of a plywood boat, check the archives for the posts by Mike Hanks about his plywood Walrus. He has made a few changes to the lines of the boat, too. The basic idea is to build the building forms and set on the wood chines as Putz calls for. Then, you set a narrow strip of 1/4 inch plywood on the chines and mark the outline of the chines on the wood. Trim it to the lines and glue and screw it to the chines. Keep this up until you've covered the hull with plywood. Voila! One plywood kayak. At this point you can cover the seams with a piece of glass cloth tape and some polyester resin (cheaper than epoxy)

Then paint the hull and deck with marine paint.

If you plane the chines so the plywood fits it smoothly, and use waterproof glue along the length of the chine to plywood joints, you might be able to skip using glass cloth and resin completely.

hope this helps

PGJ