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What is Propeller Pitch?

Sunday, June 12, 2016

A propeller is a mechanical device which is formed by blades that spin around a shaft to produce a propelling force. Several technical terms can be used to describe a propeller's characteristics: pitch, diameter, hub, disc area relation, etc. let us talk more about a prop pitch.

When talking about a propeller, diameter simply refers to the distance across the circle made by the blade tips. This diameter is determined by the RPM, rotations per minute, of the propellers. Propellers work a lot like a car's axle ratio: basically, the lower the ratio, the more pulling power when at a standstill.

When a propeller makes a 360 degree spin, it also makes a displacement so that a 40-degree propeller pitch set in a solid surface would advance 40 inches per every complete spin. In water, the displacement would not be as effective.

This pitch concept works in many other mechanical devices: for instance, the screw mechanism works the same way. A screw with 10mm pitch advances 10mm each time a screwdriver gives it a complete turn.

When buying a pitch, keep in mind that every inch of pitch equals 200 RPM. Should you want to lower the RPM all you need is to lower pitch and to increase RPM do the opposite. A high pitch increases top speeds but it also lowers acceleration and if fitted onto a low horsepower engine, a high pitch can wear down internal engine parts.

If you are changing a prop, the trick would be to find one with good acceleration and top speed. Qualified dealers or marinas have a lot of experience with props and can help you pick out the right one for your gadget.

Some useful information when shopping for props includes: type of engine, horsepower rating, type of prop you want- versus the type you are currently running, boat's weight, hull style, etc.

When a boat is running while carrying a load, you need to check the RPM at wide open throttle. If you carry a lot of diving equipment on your boat, then you should be looking more into low pitch. On the other hand, if your performance goals are set higher, then your fixed blade props will have to be set to deliver.

You can not have low end torque and high speed: you have to choose one. Choose high pitch if your boat is light and you like speed.

Take a look at the Deep Blue Yacht Supply propeller guide, as that will be able to help guide you towards the perfect pitch for your engine.  If you have any questions, reach out to the experts at Deep Blue Yacht Supply.