you need to do some homework if your going to play boat designer. large dia pvc pipe is flimsey and heavy. a simple calculation will show that a 22: od pipe x 12'(the biggest i could find specs on) will support a maximum of 1915 lbs. Unless you want some really bad handleing and loading characteristics, a round pontoon shouldn't be loaded over 50% that limits you to 957 lbs, from that you subtract 60 lbs for the pipe, 30 lbs for the ends (a guess), and probably another 100 lbs or more for mounting the pipe. The stuff really is flimsey so it needs a lot of support. So far you have a 767 lb available payload on a pontoon that weighs 190 lbs. Not a good ratio. And you still have to do something about protecting the pipe from bottom contact or internaly bracing it so it doesn't break in half when you ground out on a log.
: I have this idea about using large diameter pvc pipe for pontoons. I'm thinking about 18"-24" dia. pipe roughly 12' long capped off on the ends. What problems do you forsee with this idea? Any input would be helpful. Also, have you an idea what this size pipe costs/ft. ? Thanks.