Propeller pitch is the theoretical forward movement of a propeller for one revolution, assuming that there is no prop slip. For example, a 21 pitch propeller will theoretically move 21 inches for every revolution. The second number listed in a propeller size is the pitch (Ex. 14 1/4” X 21”).
When selecting a propeller pitch for your boat, it is important that the propeller runs at the upper end of your engines wide-open-throttle RPM range. If you want your RPM’s to increase, go down in pitch. To decrease RPM’s, go up in pitch. As a general guide, for every 2″ of pitch, RPM’s will change approximately 400 RPM’s.
Most boaters would look at their propeller and think nothing of a small ding out of it. However, a small ding which may only be an ounce of aluminium on the outer edge of a blade that is running at wide open throttle now gets multiplied, causing an imbalance issue. Even though you do not feel a vibration one does exist. It is causing unnecessary vibrations in your outdrive or lower units gears and bearings, causing premature wear. This condition is far worse with larger props, stainless props or higher rpm units.
Believe it or not over a year your prop can become out of balance, even if you have not hit anything your propeller could be out of balance. On inboard drives or v-drives with propeller shafts, prop balance, as well as propeller shaft balance, is important. An out of balance prop can cause severe vibration, premature wear on strut bearings, v-drive or transmission bearings and shaft alignment issues. It can also cause the shaft coupler bolts to break and you could loose a shaft!
The most important part of propeller repair is the workshop that does your work. A welding shop is not a propeller repair shop unless they have all of the proper equipment. We have seen many occasions where someone had a propeller fixed at a welder and they have severe vibration or lost performance, and here is why. North Coat Boating has the proper machines to balance your propeller so that there is virtually no vibration. Our skilled mechanics have the knowledge to know how a propeller performs, the technology behind it and often how to tune it so that it will perform better for your needs. We also have the knowledge to advise you if you wish to change the performance of your boat by using the various types of propellers in the market.