Good pick-up on the rolling shear issue. That thought occured to me but, truthfully, the Reinell
is such a small yacht and the rudder accordingly so lightly loaded, I dismissed it out of hand. Perhaps I should not have but I don't think its an issue.
As for the weight of a laminated plywood
rudder per Amgin's observation, I think that AA Marine
Grade (or Aircraft Grade) ply can fairly safely be assumed to weigh in at roughly 32-35PCF. Assuming that only approximately 50-60 percent of the rudder is immersed (depending upon the rudder's shape of course) it would not seem that there should be much up-lift due to buoyancy. Moreover, I would expect that there should be a "keeper" on, at least, the upper grudgeon to hold Spooky's rudder in place. If up-lift does prove to be a problem, however, he/(she?) could simply bolt two slugs of elllipticly shaped lead weights to the bottom of the blade without ill effect and perhaps even to some advantage when the yacht's heeled.