When you see your prop described by two numbers, such as 13 x 21, what does that mean? The first number is the diameter. Diameter is two times the distance from the center of the hub to the tip of any blade. The diameter of the propeller affects your engine’s speed and efficiency. For example, a large diameter propeller can push more water than a small diameter propeller, creating more power. The diameter is usually predetermined by the manufacturer for a family of products.

The second number is the pitch. The pitch is the theoretical distance in inches that the propeller would travel forward in one single revolution. For example, a 21-pitch propeller would move forward 21 inches in one revolution. Think of your pitch as the gears on your car. A lower gear gives you a quicker start but less top speed. A higher gear gives you slower acceleration but a higher top speed. With your prop, a lower pitch will give you a better hole-shot whereas a higher pitch will give you a higher top speed with slower acceleration.

Prop Pitch

As you can see, selecting the right combination of diameter and pitch can be complex. If your propeller is not properly matched to your motor, serious engine problems could result. Likewise, you want a prop that delivers acceptable acceleration and top speed and is compatible with your boat’s intended use. The experts at Ace Propeller can help guide your choice. Provide your details in our Sizing Request Form or call us at 1-866-621-7767 and our technicians will respond with the optimum selection.