I have researched this further and there were 2 Hobie 18 Formulas. One was the predecessor to the SX, built in Europe with a 1 1/2' taller mast and mylar sails. The other was US built and had white powder coat but otherwise is a standard 18. The Formula 18 is still rated under portsmouth, inactive classes. The European 18F had no wings and was allowed to race with a spin, just like the SX. I still plan to use the number generated here but the H18F is a valid portsmouth rating and could be applied to my frankencat. And I did learn that I finished second in open class at Catfest without racing the second day. In looking at the times I would say my cat is substantially faster than a standard 18 but not as fast as an F18.