It's been a little while since I reviewed the rules, but that code 0 could also trickle it's way to F18 as I don't believe the rules stipulate anything about spinnakers other than the area measurement.
From F18 Class rules
C.4.4. SPINNAKER
4.4.1 Definition of a spinnaker
All triangular sails not complying with the definition of a mainsail or a jib are spinnakers, on
condition that the girth at mid-height is equal or greater than 75% of that of the foot.
The Tornado class has a max girth requirement but no min girth. I think this girth requirement means any F18 gennaker will not look quite like the Tornado ones (which look like they have a shorter girth). An F18 class legal gennaker will probably be less efficient than the Tornado designs when the sail is sheeted hard up wind (the larger shoulder will be unstable).
Chris.
