HULL , BOAT SPEED
I do not know a simple formula for a cat. As you know the catamaran is not restrained by displacing water - which the simplistic formula is based on. The ability to plane in a catamaran frees you of all that stuff. I suppose a much more complex formula based on drags (hydro and aero) and power is possible but it would be less general in nature i.e. requiring very specific measurements for your boat.