Do not guess or use someones numbers. You need to evaluate your boat. They want to know the diameter of your shaft. The type of end on the shaft. The distance between the shaft and the bottom of your boat. Additionally the engine data, and the transmission. All of this goes into building the prop that will fit "YOUR BOAT" not just any boat.
A Campbell Sailor from WestbyNorth.com is a good choice for power and above adequate for sailing. If you are concerned about racing you might look at the cost of a fold able prop. They can optimize your sailing by minimizing the drag of the prop in the water.