The propeller or prop is a vital part of how your boat performs. Prop size is usually determined by the boat manufacture for the hull and power option. The prop that the boat manufacture recommends is usually the best all round prop for planning and top end performance. By changing prop pitch up or down, you can achieve a little more speed or a little more planning power. You have to be careful not to change pitch too much in either direction so not to damage the engine.
Prop pitch is measured in inches and is equal to the forward distance the prop will travel for one revolution. To determined which prop will work best, find out what the RPM range of your motor is. Then find the max engine RPM at WOT ( Wide Open Throttle) with the motor or drive at maximum trim. Compare your engine max RPM with the recommended RPM range to help in deciding if you can change prop size.