I currently have a 13 x 9 three blade fixed prop and am wondering if a move to a 15" prop will gain more speed. Engine is yanmar 2GM20F, 2 cylinder, 18 hp and I would really like to gain more boat speed under power. Currently get 5.0-5.3 knots at 3,000 RPM with no wind or current (which never happens) and would like to get close to 6 knots. Not sure what size prop most Catalina 310's are using?