Interestingly enough, non-US areas are much less hung up on being featherweights when sailing the F18's. In fact F18's are raced hardest by crews in the range 150-165 kg (330 - 365 lbs), which are predominantly all male crews. But overall the fleet covers a very wide weight range, from 125 kg to 175 kg and most are doing pretty well. So I don't you have much to worry about.

Pretty much all current F18 designs carry weight well.

Wouter