Wouldn't the problem be solved by having a tiger rating that is slightly higher than the F18 rating ?
Afterall they are sailing with a full complement of the big sails without corrector weights and at a lower minimum weight. Ergo the one-design rating can never be lower than the F18 rating ?
For some reason I think that in this case nobody will want to run on the Tiger OD rating then. Call me clearvoyant !
Wouter