I had this book a number of years back. It has a Hobie 18 flying a hull on the cover with 2 girls out on the trap and one was looking over her shoulder to smile back at the camera. There was a guy sitting on the tramp with the tiller.

Thanks for the help. Someone just had one of these on ebay also.

I think the book is called "This is catamaran sailing" by Barth and Enzman.

That looks like it. I have just found it - haven't looked at it for years. From 1983 - lot of photos of different cat classes. The foreward is by Francis Prout.