The 580 however got my attention as I see it as a very good shallow water Performace Cat. It is basically a Nacra 5.8 with hulls that are modified in a few ways. The bows are a bit slimmer. The dagger board trunks are replaced with large trunks to accommodate a very nice centerboard design.
The rear of the hulls, aft of the rear crossbar are tapered to accomodate the same sterring system that is found on the Inter 20.
It's a great boat that is narrower than the F18. I think that it is a few inches wider than a Nacra 5.8.
Nacra 5.8 is 8' beam, and F-18 is 8' 2.5". I've been intrigued by the 580 as well; it looks like a fun bay boat, especially with the spinny option.
PS: Checking Cathouse's 580 page, it's listed as having 8'6" beam. There are some pics too.
http://cathouse1.com/N580.htm
