Could your propeller pitch be destroying your boat’s engine?

You’ve loaded the boat for a big day out. As you get out onto the water you open the throttle, but you’re underwhelmed. Your boat just isn’t doing what you think it should do. It could be all about the propeller pitch. Choosing the right propeller is critical to maximising your boat’s performance. If the pitch is right, the motor is able to run at the recommended RPM range and apply its maximum horsepower in the water, all while consuming less fuel in the process.

Get the propeller pitch wrong, and you might not just have performance issues – you might be unwittingly destroying the engine.

What is propeller pitch?

Pitch is basically how far a propeller would move in one revolution if it were moving across a solid surface – similar to the rotation of a tyre or a screw turning through wood. Pitch is measured in inches, so a 21-pitch propeller would theoretically move forward 21 inches for every revolution, assuming there is no prop slip.

Every inch of pitch equates to about 200 rpm. A lower pitch provides better acceleration and pulling power, while a higher pitch enables the boat to go faster.

Common mistakes in choosing propeller pitch – size matters!

Many people think switching to a large pitch prop will make the boat go faster, but that’s only as long as the engine has enough power to keep in the optimal RPM range.

If the propeller pitch is too large, and the engine doesn’t have enough horsepower to turn the prop, the RPM drops, the engine becomes bogged down and the boat ends up going slower. Even worse though is that this can cause heavy wear on the internal engine parts as the motor loads up and plugs become fouled.

Going too small can cause similar problems, with the engine exceeding the recommended RPMs and becoming damaged.

The idea is to find a propeller pitch that allows the motor to reach the maximum RPM recommended by the manufacturer, without going over. So if your engine is running below the optimum RPM, you may need a propeller with less pitch. If the engine is over-revving, you may need to increase the pitch.

How do you get the right balance?

When buying a propeller, it’s important to understand how it translates to real-world performance. The type of engine and horsepower, the weight of your boat, hull style, and, importantly, how you want to use your boat, will all influence which propeller is best. A family taking a weekend trip to the islands will have different needs to the mates who’ve loaded the boat with gear and eskies for a big fishing trip. This is where our on-staff marine mechanics can help.

Whether you’re unhappy with your boat’s current performance, or simply want to get started the right way, our marine mechanics are specialists in their field who can help you figure out what you need, and get the right propeller pitch for the job.

For helpful advice on choosing the right propeller pitch for you boat, contact Holt Marine today!

This entry was posted in Boat Maintenance, News & Information, The Boating Lifestyle. Bookmark the permalink.

Comments are closed.