I don't like how Nacra keeps calling its boats FXX to confuse people. There is no such thing as a Formula 20 or Formula 17 box rules. There are Formula 18 (the infusion is a nice Nacra representative of the class) and Formula 16 box rules. F17 and F20 don't mean squat these days (yes, there used to be some try to make a Formula 20 class, but it fizzed out).