Understanding Boat Propeller Pitch

All commercial marine propellers take into consideration two basic dimensions: diameter and pitch. Most propellers feature these measurements on their surfaces and present them as the diameter measurement x the pitch measurement. Diameter is simply how large of a circle the propellers make as they rotate, from the tip of one blade to the tip of the blade opposite of it. Understanding boat propeller pitch, however, is a bit more complex.

Identifying the Pitch

The propeller’s pitch is the number of inches the propeller moves forward in a single rotation while moving through a soft solid. So, for instance, a 17-inch propeller would move 17 inches every time the propeller makes a full rotation. For boaters, the best comparison may be that of a car’s axle ratio. The lower the ratio, the easier it’ll be to accelerate and get moving after starting from a stopped position. However, this comes with the price of a lower maximum speed because your propeller reaches its maximum number of rotations per minute quicker. Higher pitch propellers do the opposite in that you’ll see a greater top speed but a slower acceleration time.

Selecting a Propeller

Another aspect of understanding boat propeller pitch is the pitch’s effect on the boat’s engine. Picking the incorrect pitch will put extra stress on the engine. You’ll eventually wear it down, which will either necessitate costly repairs or kill your vessel outright.

You can’t go wrong if you replace your propeller with one that is the same exact model. But if you’re looking for optimization, you should speak with professionals at any qualified dealer or marina that will have an understanding of what pitch is most appropriate for your vessel’s engine. If you’re shopping for a propeller on your own, take into account your boat’s engine, how much horsepower it has, the boat’s weight, and the hull style. Reference your owner’s manual for the finer details.

Goals for Performance

What does optimization mean for your boat? Determining the purpose and function of your vessel will help you define goals for how you want it to perform. This will help guide you towards the correct propellers, as there’s no such thing as a propeller that has both high-end or low-end torque and speed. For example, a towboat’s function is to guide much larger ships safely through a harbor, so its priority is to have the torque necessary to move these ships. The towboat doesn’t require high speeds when trying to maneuver around a harbor. However, a pleasure craft isn’t a workhorse ship and might instead prioritize speed for greater enjoyment.