Electrical PVC (gray) has some different qualities than plumber's PVC (usually white.) Although the electrical PVC is more flexible, it's not likely you're going to break it. The weight difference between 3/4" and 1/2" is not that great, and I'm leaning toward using 3/4". I've stood (198lbs) on sections of 3/4" anchored into sheetrock at 4' intervals. Given that in the frame they'll be like a bunch of sticks in a bundle, I would think the resulting strength to be quite durable. The trick is how to join the tubing to the stern and bow, and how to get the ribs (I'm thinking plywood here) to join to the tubing so that everything becomes integral.

: Okay, be gentle with me here. I continue to contemplate how a first-timer
: could build a folding kayak. The image of a klepper frame found on ebay
: suggest a rather straightforward (?) aluminum frame. Has anyone ever
: attempted this with PVC pipe? PVC is cheap, flexible, strong, and so I
: wonder about its candidacy for frame building. Also, it would be very easy
: to repair.

: That most dangerous of phrases has begun to reverberate in my noggin:
: "how hard could it be?"

: ad delirium contiuum,
: Wayne