18SE is the term Hobie went to after the SX came into existance. Standard 18 with 28' mast. SX has a 29'6 stick and mylar/dacron radial cut sails. The Tiger spin is a more current assymetrical shape, faster than the SX chute. I am not a racer, just a guy that likes to race every once in a while. I just want to be sure I represent the boat correctly to the race committee. I don't understand the portsmouth number system, is a higher number better or worse? Formula 18 never took off so open class is the only option I think. I got a little carried away with this conversion. Wanted a spin, got one that is white, gray and black. Thought about how good it would look in front of a smoke main, got one. Didn't want to cut the sail down so needed a taller stick, got one ( SX ). So here I am. Been sailing with the 28' stick and spin for about 2 months now and love it!!!!! Just now repairing corrosion damage on the 29'6 stick and will have it done this weekend. Will need to cut down a 18 boom since the foot of the Tiger is smaller. I would be happy to race and not be placed at all in the end, don't want to effect others season results. Just curious about overall speed and racing is the only way to compare. I feel the boat will be substantially quicker but not sure.