The F in the F17 is to distinguish the boat as a racing class.

(Just because you build a boat with certain dimensions... does not mean that the sailing public will buy in... eg I17R with a fixed spin size. The term class means that you have a reasonable size group of people who agree to race the boat under a set of rules which determine the configuration)

The formula has to do with crew weight and the size of the chute you are allowed to carry. Since its a single handed boat... the class has worked out the rules to minimize performance differences down wind.

It is much the same as the F18 Class which specs out two size jibs and chutes for teams below certain weights.

granted.. the F18 and F16 formulas allows for multiple builders... and it is owner controlled. The F17 Formula is basically a SMOD with options for the sail size of the chute. Since its SMOD... you can't change out foils or use sails from different sailmakers... Many would argue that these limits are serious and violate the spirt of the term "formula" as understood by the majority of the sailing community.