The actual world scenario about 18 foot skiffs rules is divided in two:
on one side we have the "European 18 Foot Skiff Association Rules" adopted for the European Grand Prix championship and on the other side we have the Australian League, UK Fleet and the Americans that adopt the "International 18 Footers Class Rules" during their events.
The European Association is born in the end of 2000 and it has been founded by the group of sailors that partecipated last year to one race of the SPT at least. Martin Blum, then Patrick Chanez have been elected as secretary of the class and all the votings and decisions have to be made by e-mails from the members. The Association has voted as first thing the rules to adopt for the class. You can find them later.
The European Grand Prix will be under this new European Rules. The UK Tour, all the events organized by the Australian League and Americans will be under the International Rules. The biggest difference and most important one between the 2 sets of rules is that the Eurpean Association opens (under certain recstrictions) the drawing and the bulding of the hull to everybody and the International Rules accepts only new boats made from Murray projects (build in Sydney and by Ovington (UK)) and the old grandfathered boats.
You can download and read everything here: