Just a side-note: Zeke Smith in "Understanding aircraft composite construction", refers to a builder (Molt Taylor) who used paper extensively when building airplanes. I dont know the Young modulus for cellulose, but I see that Flax have a breaking strength of about 100k psi. Common E-glass 500k psi and kevlar49 700k psi. I guess the Young modulus fallows approximately the same trend.

So, it's quite possible to build a boat with flax and epoxy as matrix, but it would need to be heaver than the same boat buildt in carbon or glass.

I think it's cool that boats are buildt in different and 'new' materials. Who knows what we might learn.