I replaced a 3 blade fixed, 16", on our 34'' with the autoprop and am very impressed. We went from avg. motoring speed of 5.2 @2300 rpm to 6.2. We now run at 1900 to 2000 rpm and maintain 6K. Light wind performance under sail has improved dramatically. It was a little more $ than max. but feel it was worth it to get curved blades.