I've long been wanting to build a boat, and now that I live in a place with a lot of waterways I have no reason not to.
But I don't have a garage/workshop, and even if I had I'm obsessed with the idea of modularity, so I have the following idea:
- make multiple short foam-filled modules, each buoyant on its own;
- put a couple of boat-long centerline ropes through these modules, tension them to squish modules together;
- add a bunch of shorter ropes near the edges of the modules, connecting each pair to counteract any flexion/torsion;
- add a few dowel pins in-between modules for a bit of extra stiffness;
- have rubber gaskets at the connecting faces of the modules for water tightness.

In my imagination this should be viable for a 6m boat. And even if I fuck up some of it, each module is small and cheap enough to just re-do it from scratch, so I should be able to experiment and iterate on it without burdening myself too much.
Tell me why this idea sucks.