Cary-

Check out Murray's- They have them both in the Cat section and windsurfer section as I recall or you can "make your own" out of webbing and webbing straps (see mine on the Taipan in attachment above post). On my old 18 sq. (same hulls as yours) we mounted them on the top edge of the hull (so the leeward one doesn't "drag" in the water), back them up REALLY well w/ SS fender washers or (better) SS plates or Aluminum plates and 3M 5200 or epoxy (better) to spread the load out on the hull. Use a rear port to get access to the inside of your hull-



Kirt