: . . .Making some engineering evaluations of the material is what I'm after, in
: addition to its favorable prototyping qualities. I'm looking at this
: project as a test bed for my design, as well as for using foam as a
: building material. I will probably be involving students in the project
: for independent study, so it's also a teaching exercise. I plan to
: document the whole thing, so I guess I should be finalizing my design
: instead of arguing about material selection. . .

Carl, I fyou have not yet seen Ray Jardine's log of how he constructed several kayaks, including one from foam and glass, take a look at them.

http://www.rayjardine.com/adventures/kayak-construction/index.htm

You should like them, and they should be good info sources for your class, as well.

: I assume that, as usual, the
: design will indicate fairly immediately if the materials are not up to the
: job by breaking in half and dumping me in the sound.

Or, it could break in such a way that the first paddler is trapped in the cockpit, while the boat folds up and pinches him in place. Keep plenty of people around for a safety crew, and do your test launches in very shallow water (5 to 6 inches deep). Once you have some feeling for how strong, or flimsy, the craft is, you can head out to deeper water and more challenging tests, or head back to the shop for mre reinforcement.

Keep it safe and enjoy the design and building process.

PGJ