My father just bought a new Yamaha 225 outboard for his 21' Seaswirl. Yamaha printed him a performance graph using a 15 1/4 X 17P which showed the best performance for his boat. Can someone give me some recommendations for ocean going cruising. At 4000rpm we averaged around 34-37 km/h using a 14.5X17P prop depending on trim and trim tabs. This prop is 3/4 smaller than the Yamaha perf chart. Anyone ?
