Jake,

The Inter 18 was designed by Morelli and Melvin to compete as a Formula 18 from the beginning. In the U.S., most opted for the optional carbon mast, and later, larger sails. The carbon masts never went to Europe, not being legal in Formula 18. Those in North America who bought the Inter 18 were racing single manufacturer one-design, as the North American Formula 18 Class Association had not been formed until the Nacra F18 hit the market. The carbon mast (with F18 legal sail plan) was grandfathered into the NAF18 for a year or two, but is outlawed now.