Right now boat hulls (and cabins) are produced in a variety of forms…
- Cored fiberglass
- Cold molded
- Epoxy coated
- Cement (Ferro-cement)
Most of these involve individual pieces/components that are fastened together via weld, chemical bonds or physical fasteners. Others tend to be more monolithic but are more out of the reach of home builders (fiberglass molded hulls, etc.) Not that it can’t be done, but its a big time and effort investment. The molds required also make this a difficult to justify expense for one-off builds and "experiments". Once you have a good hull design, you use the mold as long as possible. Molds are passed between companies (sold, etc.) and used for totally different craft that share hull similarities.
I wonder how long it will be before technology comes along that can "print" a boat hull. Using either cement (a return to ferro-cement???) or some types of plastic, I think the technology is going to get there to have a monolithic hull, deck and cabin "printed" or "sprayed". Then you could fit it out as you wished. I guess you could have furnishings and all built in as you went… not much "home building" to this anymore, but some designs that can’t be reasonably built now could certainly be explored.
Check some of these sites for information on this technology in the homebuilding and small part fabrication world today: