Diameter & RPM

The first number listed when describing a propeller is the diameter. It is equivalent to two times the distance from the center of the hub to the tip of the blade. It can also be described as the distance across the circle the propeller makes when rotating. Propellers are labeled diameter x pitch. (A 13x19 prop is 13" in diameter and is 19" pitch). The correct propeller size (diameter and pitch) will allow your boat's engine to operate at the engine manufacturer's maximum recommended engine RPM at full-throttle.

The right prop for the job

If your propeller is either too large in diameter or too high in pitch (or both), your engine will not be able to reach the maximum recommended RPM at full throttle, (assuming your engine is in otherwise excellent running condition). This condition will cause your engine to strain and cause poor performance. If, on the other hand, the propeller is too small, either in diameter or pitch, the engine can be damaged by excessive strain. Importance of Choosing the Right Prop Size

Choosing the correct propeller size is so important since it helps you attain:

  • Top speed
  • Best cruising
  • Better gas mileage
The kinds of activities you do with your boat are important in determining what type of propeller you will need. You may need to have more than one propeller if you use your boat for different types of activities. No single propeller will be able to give you top speed and handling under all conditions. The propeller that provides the best hole shot will probably not provide the best top speed for your boat. A propeller that will give you absolute top speed, will probably provide an uncomfortable midrange ride.

More than one prop

If you use your boat often under a variety of conditions, you will probably decide that you need more than one propeller for various things such as cruising, speed and one for pulling skiers, etc... Of course, if your budget only allows one good quality propeller, you will need to select the propeller that provides the best compromise between the characteristics for which you are looking.