The specifics of a propeller are all determined based on its RPM performance on your engine when running at wide open throttle (WOT). This appropriate range will be listed in your owner’s manual.
Every design feature of a propeller will affect its performance in a number of different ways. Because the variations are so complex, manufacturers have specified which engine models are designed to work with their particular propeller.
If you use the Prop Selector on our page, you will likely be given more than a few different propellers that will fit your particular engine. You will then be able to select different style variations based on your preferences.
These factors can vary slightly with every motor, all depending on what you decide to use your boat for. You can go through our Prop Finder to find out which propellers will fit with your engine, and then choose one of the suggested pitches and diameters based on your preference.
Larger diameter is generally better for pushing heavy loads and maneuvering at low speeds as well as getting excellent hole-shot because of the expanded grip on the water.
Smaller diameter propellers will spin faster making them a good choice for performance boats that need higher top end speeds.
A V6 outboard prop would range 13”-16” while a 10 horsepower propeller would be around 8”.
Pitch is the distance a propeller
travels in one revolution
Definition: The distance (in inches) a propeller travels in one revolution if there is no slippage. Pitch affects the performance of a propeller more than any other aspect.
**Sustained operation with a pitch that is too low or too high will cause damage to the engine.**
High Pitch: (Lower RPM) Boats go faster at the top end speeds. A high pitch is typically used on larger boats.
If the pitch is too high for your engine, it will "lug" the engine, reducing both top speed and performance.
Low Pitch: (Higher RPM) Increases acceleration, fuel efficiency and pulling power. Low pitch is typically used on smaller boats.
If your pitch is too low, it will cause the engine to exceed its specified RPM at top end speeds.
When you have the right propeller and it is working properly, your boat’s engine will run within the manufacturer’s designated RPM when running at Wide Open Throttle (WOT). If it doesn’t, then you need a new propeller.
Make sure your gas tank is full but the overall load in your boat is light (do not go out with the maximum number of people on board).
Run your boat for at least 5 minutes to ensure your engine is properly warmed up.
Find a wide open piece of water with little or no other boat traffic.
Give your engine full throttle and get it up to maximum speed.
When at maximum speed, note and record your RPM.
If the RPM at full throttle and speed is outside (either below or above) of the manufacturer's recommendation, it is time to shop for a new propeller.
Cavitation is any erosion, pock marks, or irregular edges on the surface of the propeller. This is mainly caused by the impact of air bubbles when a pocket of air forms on the backside of a propeller blade – usually when the propeller is turning too fast for its design.
How to Avoid
The most important factor is to choose the correct propeller pitch for your engine.
You can also reduce the likeliness of prop cavitation by choosing stainless steel, or by adding a cupping design on the blades.
Shallow Waters / Hard Obstacles
Aluminum propellers are more susceptible to damage than stainless steel props, but are cheaper to replace. They will also absorb the shock of an impact better than stainless steel, which actually protects the lower unit from incurring extremely costly damage. This is the reason they are recommended for shallow water where rock collisions are more likely.
Silt and Sand
The damage from soft material can lead to cavitation, reduced fuel economy, and reduced overall efficiency. A stainless steel prop will hold up to silt and sand exposure very well.