Inspired by Ernst Z’s boxsection trimaran, the old Real size battleship citadel-design and the Fender guitars:
What if the box sections acts as a core for loads and you add some foam to the deck and the bottom? Those box sections are very easy to make and shaping the foam attached to the box section is much easier and you get good looking round shapes without having to strip / planket etc. Also if you make the load bearing structures attached to the box sections ( the citadel), you can easily try out different underwater hull forms, just cut off the old foam and reshape the new foam!
Also if you varnish the citadels carefully, you can cover the foam sections with solar-film or similar lightweight material. I dont believe that this method would make the boats heavy, its more vice versa. Also you could use more hours ( designing, details, torsional stiffness, beams, weight saving etc ) to the “vital” parts of the boat, as they will be fully recyclable for your next experiment / boat.
Also on monohull you could make the hull citadel with keel, rig and rudder attachments and radio compartment from plywood / balsa and then add some foam around it and go sail. No tank tests, no complicated calculations, just make an innovation, and try it 4 hours later 
And if you make the citadel right, you can also add wheels, skates / whatever to it and go try the other ways to sail.
- HJ
“Expertice is gained trough mistakes. However repeating
same mistake is not learning but stupidity.”