Hi Nicholas:
I live in Western New York and we have a number of Hobie 18s. I have a Hobie Magnum and I wouldn't trade this boat for the world because it's extremely stable and the ride on the wings makes it very dry. I can go for hours without getting chilled.
Phil Berman authored an Hobie 18 Performance Manual and you should be able to find a copy someplace. I'll bet any Hobie dealership could track one down for you. The boat has not changed much except for the kick-up rudders that were added in the early 80's. Really check out those rudders, because if they are they old style, your gudeons will snap off when you hit shallow water.
You'll have fun with this boat because there are so many ways to improve the performance with power downhauls, ochen blocks, etc.
Keep on writing for more information, but get the book. You'll find everything you need to know.
Wyatt
Fleet 119, Angola NY