3d printing technology in boat building ?

You know if I was still working I would be desperate to see this work.
But I've seen too many "exciting" developments which are really just an attempt to get enough money to do the development to make something actually useful.
Actually I've been a part of some of those - and you wouldn't believe how many pitfalls needed to be crossed to have a chance for a useful development.

 

You'd foam it for exactly that reason. It greatly increases the stiffness and reduces the required strength since it supports the skins. Inflatable boats get there using fairly soft materials but increase stiffness with inflation. Foaming does much the same thing. I don't think you can get there without foaming it, the fundamental material properties aren't there. And since this was a stunt we don't know if the foamed areas were sufficient or oversized.

 

You could also print infill structures like honeycomb or tetrahedrons or computer generated infill to support specific loads.

 

Foam in the apparent quantities is very heavy.

Printed honeycomb, etc, seems most appropriate, unless it fills with water. The same thing that happens (at times) with aerospace honeycomb.

Again, foam increases the stiffness (reduces buckling/ deflection of walls) but doesn't increase strength. Sorry about being a nitpicker, but we need to talk about the right problem to achieve solutions.