PROPELLERSChoosing the right propeller is the single most important decision you can make to get the best performance from your boat and outboard! It has a direct effect on acceleration, cornering, pulling power and fuel economy.WHAT TO CONSIDERSeveral characteristics affect how a propeller will perform. Especially important are propeller diameter and pitch. Look for a number like 14 3/4 x 21. The first number is the diameter, the second is the pitch.The diameter is the width of the circle described by the tips of the rotating blades. Propeller diameter determines the amount of power a propeller can apply to the water - how much load the propeller can push.Pitch is the theoretical distance a propeller will travel in one complete revolution. For example, a 14 3/4 x 21 propeller would ideally move 21 inches forward with each revolution. In practice, the actual distance travelled is less than the pitch because of "slip" which is necessary to produce thrust.WHAT PITCH?Lower pitched propellers are like the lower gears on a car. A low pitch allows engine RPM to build up quickly, which gives faster acceleration and more pulling power.Higher pitched propellers are similar to high gears. A high pitch puts more load on the engine, which reduces low speed pulling power and acceleration, but usually provides more top speed.THE RIGHT PROPELLERAll Evinrude and Johnson outboards have a recommended full throttle operating range. This means that, at full throttle, engine RPM must never be below or above this range. Usually this range is between 4500 RPM and 5500 RPM (check your Operator's Guide).By increasing the pitch by one, RPM will decrease by approx. 500 RPM - losing some acceleration and power, gaining top end speed.By decreasing the pitch by one, RPM will increase by approx. 500 RPM - gaining acceleration and power, losing top end speed.
