PROPELLER PITCH
Propeller pitch greatly a ects boat performance, so it’s a worthwhile topic for boaters to review.
Propeller pitch is one of numerous key physical properties of your boat’s prop. Pitch is probably the characteristic most frequently changed by boaters looking to enhance performance. Propeller pitch is also one of the harder prop characteristics to understand. Because pitch changes along the length of a propeller blade, the stated pitch is an average. Diameter, blade area and other prop traits can be measured readily. While pitch and its e ects cannot be described fully in a single-page magazine article, what I hope to provide is a solid foundation of the importance of propeller pitch to your engine’s, and thus your boat’s, performance.
SCREW THEORY Pitch can be described by its e ect on the prop instead of by directly measuring the prop. e above photo shows that pitch is the distance a propeller will travel through a solid in one revolution. An equally valid way to describe pitch is to think of it as a key propeller characteristic that, along with mum horsepower the propeller can absorb. is is why the best prop for most engines is the one that lets it rev at or near its maximum-rated rpm.
Too little pitch can allow the engine to over-rev. While a lower-pitch prop might increase hole-shot speed, allowing the engine to over-rev can cause damage. Top speed will also su er when the engine is propped too low. Fuel economy will also be a ected negatively.
TOO MUCH PITCH Too much pitch will not allow the engine to reach its maximum rpm. An engine not capable of turning its max speed will lug throughout the rpm range and can even be damaged as a result. Fuel economy will su er, and the boat will be slow to plane.
PITCH BY NUMBER A rule of thumb that has proven useful is changing pitch by 1 inch results in about a 150 to 200 rpm di erence. For example, for an engine that achieves 5,600 rpm at wide-open throttle, decreasing prop pitch by 1 inch will allow it to turn 5,700; increasing pitch by 1 inch can see it turn 5,500.
PITCH AVAILABILITY Propellers in a series of the same material, diameter and number of blades can be available in pitch increments of ½ inch, 1 inch or 2 inches. If the pitch you seek (for achieving the engine’s max rpm) is not available in the series of props you use, try choosing a prop from another series.
CUSTOM PITCH For those seeking the utmost in performance, e ciency and quiet operation, propellers can be repitched and otherwise customized by some prop shops and companies, such as BBlades (bblades.com).