I don't think you can do an Ocean racer smaller than the Mini6.50 not on account of the boat but on account of seaworthiness and safety. You have some guys doing the Pogo 2 in America and the boat is not expensive for an Ocean racer.
Regarding the material that's another story. That's a CFS (Carbon Fiber Stone) material and the first I herd about CFS was on the Salona shipyard. In fact they use the material, not with volcanic stone but with granite that seems even strange to me. In fact if you order a Salona (any of them) in IBC specifications (infusion based carbon) the bulkheads are made in CFS, using granite. Take a look at the movie and stop exactly om 1.00 minute and you will see. All bulkheads are made with that material. It is not painted black it is just its color:
I saw the material there, it comes in big panels and its weird, black as the night, very light and very strong.
I looked at the time on internet searching for the material and I found very little. It says well from Salona since they are using it on top performance boats for years. Maybe because they are a small subdivision of a huge plastics and fibers manufacturer they have access to information and top materials in what regards the plastic/fibers development.
You should see my face when they asked to me if I wanted granite bulkheads on my boat
Some more information:
Towards a new Stone Age
PS: that boat can have also an interior made of a lighter material (and more expensive) but it seems to me that it is a normal interior. The mast, boom and wheels are carbon but it has also teak decks so it is not a top racer. Some guy that wanted a fast but comfortable boat.