One of the unused 18s on my beach has what appears to be either an old OEM or aftermarket gas motor mount made specifically for the Hobie 18. It has a very sturdy aluminum frame mounted directly to the inner deck lip about 15" aft of the rear cross bar via a pre-bent rear support bar. The forward end, which is cut in around the dead eye, is secured to the bottom-side of the cross bar with heavy duty bolts. I didn't bother to inspect the actual "bed" the motor sits on, but I believe that might be made of aluminum, too (with rubber side walls to help ensure the motor doesn't go for a swim)......

Underside......
