We had quite a discussion of boat weight last summer. It included equations for kinetic energy and, if memory serves me, phases of the moons of Jupiter. I think the final conclusion was that, within any reasonable limits, weight has next to no effect when on the water. It is far more noticeable when carrying the boat to and from the water. And that you can save more weight by lightening the paddler and loaded gear than you can ever save during boat construction.