Do you have the correct propeller on your outboard motor?

Posted on: 1 November 2018

If you purchase a new outboard motor for your boat you must consider several factors to ensure that the outboard motor you choose is compatible with your boat. If you make the wrong choices then you could be placing your life at risk with an unstable boat that could be dangerous if you attempt to use it at speed. Of all the decisions you must make, the size and style of the propeller is one of the most important. It will play a major part in determining whether your outboard motor will reach its peak performance and operate safely. Finding the right propeller will also stop your engine over-revving while allowing it to achieve the minimum r.p.m. at maximum horsepower.

The propeller you select will be dependent on the usage you will make of your outboard motor. If you will be operating a ski boat then your chief concern is going to be top-end speed so you will need to select a propeller which possesses a higher pitch. By contrast, the owner of a houseboat or cruiser will be more concerned about how the motor performs at displacement speeds and therefore they should choose a propeller with a lower pitch which will offer better low-end power.

If the original propeller supplied with your outboard motor does not offer the performance you need then you will need to choose an alternative propeller with a different pitch. Start by reading your user manual to locate the right open throttle RPM range for your engine. Next, you must work out the open throttle RPM and speed you are achieving with your present propeller. You may need to adjust your trim to reach the maximum speed.

If your propeller does not allow you to reach the needed RPM within the range quoted in the owner's handbook, then you must adjust the propeller pitch until this goal is reached. If you need a larger pitch then adding one inch to the pitch will lower your RPM by around 150-200RPM. Conversely, removing an inch of propeller pitch will increase your RPM by a similar amount.

Finally, the majority of outboard motors are fitted with aluminium propellers as standard. If you seek greater performance from your motor then swapping to a stainless steel propeller can be a cost-effective way of improving your speed and acceleration. You can learn more about your options by contacting outboard motor suppliers.