Actually, I'm told that the force on a normal touring stroke is about 3 lbs. I would guess the force with a C-to-C is on the order of 30 lbs.

Blade size and shaft length would make a huge difference in how much or little the blade accelerates through the water.

: Probably a lot more than that if you do an eskimo roll. I'd do the stress
: analysis of a C-to-C-type of roll. Assume that one blade is fixed against
: the hull, the other blade is fixed on the water (assume the load is at the
: center of the blade), and your hand is pulling down at the grip on the
: water side. For a force value, I'd use the weight I could do flyes with.
: Do a little free-body-diagram to find out what the max stress is, multiply
: by a good safety factor of at least 3, and build to that.

: Dean