When using a kicker motor to troll or for the main propulsion on a heavy boat such as a sailboat, it is often necessary to use a low pitch propeller specifically designed for thrust, not speed. We have had great results with the Solas Amita 4 High Thrust propeller which is available for most "kicker size" motors (8hp, 9.9hp, 15hp, 20hp) and most motor manufacturers (Honda, Mercury, Tohatsu, Suzuki).
The blade size and style of the Amita 4 High Thrust is great for the kind of low end push that is required to move a heavy boat or to keep trolling speeds down. The ease of maintaining low end speed without cavitating while trolling or the power and maneuverability required while docking a sailboat increases dramatically when switching from a traditional 3 blade propeller to the Amita 4 High Thrust.
Due to their weight, sailboats will almost always run the 5 pitch prop. When using on a kicker motor, the 7 pitch is more popular, but if your boat is fairly heavy, you may need the 5 pitch.