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.
I have designed, built, or sailed with several versions of what could be referred to as a “Code 0”, “Asymmetric 0” or “Masthead Genoa” since 1992 and I have done this within both Symmetrical and Asymmetrical measurement rules.
For asymmetric, when constricted with a 75% girth restriction, the sails are effective but not very much fun. Generally you need to run a upwind sufficient cloth for the body of the sail but a lighter false leach (attached to your designed shape leach) which will allow the sail to measure but then generally flaps when sheeted hard for tight reaching or even upwind.
This is fine on bigger boats like a TP52 but it is not so flash (or legal) in one designs where there are generally spinnaker cloth restrictions (I have not looked but I am sure laminates and heavy nylon are not legal in the F18 guidelines).
The best example of this is to find a photo of the W60 Tokio from the 1993 Whitbread before Code 0s were legal.
All-up, I think this would be aweful on a F18...
