first I want to announce that my 1984 Hobie 18 has been on her first sailings, in last three years, during last weekend. It was a lot of fun and I'm so happy about it. Anyhow, during the sailing sessions I pointed out that the hulls are moving pretty much up and down when I pearce the waves. I realize that a hull which is builded between two aluminium tubes can't be/isn't too stiff but wheres the limit? They move now about 15 to 20 cm from the front. (when the other hull goes up, the other goes down.) Is there some places which I should check, make tighter etc.?

1. Tighten all external fittings (stainless steel bolts that pass through the gunwhale lip and fasten under the Hobie 18 lip).
2. Tighten the trampoline as tight as possible.

This thread may help. But I would use 2 layers of Saran wrap (which is extremely thin) around the dophin striker at the main beam, as it goes in the seat.
http://www.catsailor.com/forums/sho...page=&view=&sb=5&o=&vc=1