Wayne -

An excellent question, as I'm not sure what a good "minimum standard of rigidity" would be. Establishing such a recommendation is really tough, particularly as it depends so much on the final design and construction of your boat. For example, on my baidarka, eack piece is *very* flexible - the keel is even split into three pieces! However, when arranged in the boat, the pieces that would normally bend reinforce each other - in order for the boat to flex upwards, the keelson must stretch (which it does at the joints, but not much) and the coaming must compress.

Careful design could allow you (theoretically) to build a very rigid boat out of almost any material, no matter how flexible. Geodesic Aerolite boats uses an ultra-lite wood framework (strong in compression) and a spectra or kevlar string to put the hull in tension, and make it more rigid. Needless to say, the string isn't very rigid. The problems I see with PVC is the difficulty of making it strong in tension (because of the press-fit joints). I'm sure it's adequately strong to end-loading, so long as the pipe stays perfectly straight. Unfortunately, once it starts to deflect, say goodbye to your integrity. (Think putting a heavy book on top of a straw.)

Overall, I think the sacrifices you'll need to make to make a conduit-framed kayak far outweigh the cost benefits you might achieve. Your boat will be floppy, and if you put enough pipe in it to make it rigid, it will be unacceptably heavy. Also, the more framework you include, the more difficult it is to set up, and the bigger the bags you have to carry it in... you get the idea. Wood has been used very successfully in folding kayak frames (Klepper); I'm hoping that I can figure out a clever and efficient design using wood, Easton aluminum tubing, and some carbon/glass structural elements. I think the expense of such materials is justified - if my kayak stinks and paddles like an banana, who cares if it only cost $50?

Of course, having said all this, I'll bet someone shows me their beautifully engineered, 35 lb. 19' expedition folding kayak that they built for $20. If they do, I'll feel dumb... but not dumb enough not to go build one myself.

Good luck - think wood. It's more fun to work with anyway.

: Nathan,

: I appreciate your response to my query. Your main concern seems to be safety
: (yes!), and in particular the ability of the PVC conduit pipe to stay
: rigid. I'm curious, what would be a good minimum standard of rigidity? In
: other words, if a material of length X could support Y pounds of weight
: then what is an acceptable amount of flex (Z)?

: For example, if supported say 4 feet of PVC conduit with sawhorses at either
: end, and weighted it with 50 lbs., how much downward flex could be
: considered "safe enough"? Or 6 feet of length and 100 lbs?
: Opinions?

: Again, thanks for your thoughts,
: Wayne