I may be wrong but last I heard, Hobie Tiger was the only F-18 to be granted ISAF International status. Therefore the NACRA F-18 can not race an offical 'World Championship' but can race an 'Intercontinental Championship' which is not recognised buy ISAF.

Minor details though.

As far as I know, Tiger makes up somewhere between 50 to 60 % of the International F-18 fleet. NACRA are the next largest with the rest no where close.