I put my Camano's numbers into Victoria Propeller's prop calculator, and the answer came out remarkably accurate for how my engine and propeller perform. That's a free and easy way to get an independent evaluation starting point. Data: 200 hp turbo, 20x18 four blade prop, 3700 to 3900 rated max WOT, actual recent 3/4 fluid load, actual max SOG both ways of 14.4 kt at 3750 WOT - 2 year old bottom paint, cleaned by diver 2 months before. Model suggested something like 14.7. Model said to achieve 15 kt. I needed 25 more hp. My purpose was to see if I could go to a 20x20 prop and get more speed, but evaluation convinced me to stick with what I have. Will check again after May haul out.
See what Victoria Propeller's model tells you, and determine your next step.
Build me straight, O Worthy Master,
Stanch and Strong, A Goodly Vessel,
That can laugh at all disaster,
And with wave and whirlwind wrestle. (Longfellow)