The rule generally regarding carbon vs aluminum is that the wall thickness that works for aluminum (say 3mm) will work for carbon – all geometry the same. The Marstrom and Lindahl A-class have carbon beams that are just under 3mm thick. If strip planked you could subtract from that a little. I would especially like to see the beam striped in halves with carbon put on inside, halves then joined then outside carbon applied. I think you could get away with 1mm inside and 1 mm outside with 6mm thick spruce strips. 75% unidirection 25% braid or biaxial or woven for hoop strength. Striped up you could increase geometry toward the center, tapering as you get to the hull (can’t do that with extrusions or pultrusion) but you could with a strip version – especially applicable to the forward beam. In addition to function, it would look cool too. (This was actually done in some of the early C-class by Hubbard and A-class boats like the Loca. The aft beam should be lighter than the forward beam. You could also add to the outside if under built – the way to do it if you’re pushing the envelope.