I wanted to follow up on something Eric touched on. Aluminum is much stronger than wood, so the advantage is that we can us thinner sheet material. But the disadvantage is that the thin material is not as stiff as the thicker wood.

Maybe some of the engineers in the crowd can help us out by comparing the tensile strengths of the two materials. If we built an aluminum boat to equal the strength of a wood boat I would expect the panels to be very thin and lack stiffness. Building the aluminum boat to equal the weight of a wood boat would still yield thin panels. If we built for equal stiffness I suspect we would have a heavy boat. Another factor to consider is the particular kayak design choosen. The more curvature in the panels, the better they would fare in a thinner material.

A Guillemot-like design, with it's compound curves, might work better in aluminum than a stitch'n'glue. But that completely changes the building technology required from welding flat sheets to forming them over a mold.