For the benefit of the young man who started this thread building in aluminum
would be like pushing a boulder up a steep hill compared to plywood S&G. And the plywood boat would win hands down because of weight alone.
In the years I have frequented this site we never heard from the guy who had just learned to weld and was going to weld up a stainlees steel kayak. The same for the guy who was going to wind 20 yards of Kevlar around a styrafoam plug and get an instant ultralight boat. Oh, yeah, the bamboo stripper. Nobody's tamed that beast in their backyard, either.
There is a difference between following sound engineering evidence and trying to re-invent the wheel.

: All, well and good, Charlie, but you are only stipulating a single
: speicification in a vast pantheon of design material possibilites and
: benefits. If a light boat is all that you are after, then what are you
: doing messing with a wooden boat? Carbon and/or Kevlar extracted from a
: mold will be far stiffer and far lighter.

: Aluminum has a grouping of potent features on its side. All one needs is a
: design brief that brings that grouping into play and aluminum wins.

: It would be wise to keep one's mind open to all the design/build
: possibilities out there if one expects to arrive at the best material for
: any given design brief.

: Chris