In the early 1970s I worked at a canoe shop in Chicago, and a couple engineering students came in looking for design info. (This event has been around that long!) As I remember, the maximum length specified then was 14 feet and I seem to also remember that it was specified as "ferrocement" construction, which meant iron/steel reinforcement was required. I suggested chickenwire (reasonably light), but didn't have any idea how to actually form one one-off. With fiberglass allowed, I guess the "ferro" part isn't followed any longer. I handed them off to the boss, and we never heard back from them that I heard about.
A little googling around led me to this, the rules for this year's competition:
I went to Michigan Tech, back in the dark ages. It was a Civil Engineering department thing - MTU entered every year, and I think they still do. I never saw it (I was an ME).