Ultimate-Boating.com - Choosing the Correct Boating Propeller

SELECTING THE CORRECT BOATING PROPELLER

So you need a new prop but you don't think you can pick it out. Sure, there are plenty of service professionals that can help but this is actually a task you can perform, with success, but you have to have a basic understanding of what a propeller does.

Start with your engine. It will have a recommended WOT (wide open throttle) rpm range. For example, if it's an 18' boat with a 125hp engine, the range will probably be 4500 to 5500 RPM's. Typically, when you purchase a boat it already has a prop on it. For this example we're going to say it had a 21 pitch prop. Under WOT you've noticed that the engine runs at 4900 RPM's. It's a great prop for the life of the engine because you are in it's rpm range. But are you getting the best performance? Here's how to tell.

It's a very easy rule. Every 2" of pitch causes rpm's to change around 400 rpm's. So if you drop in pitch the rpm's increase and if you go up in pitch the rpm's go down. So in this example if you want the rpm's to go up you've got to lower the pitch of the prop. We are currently at a 21 pitch so if we drop to a 19 pitch it, we'll run around 5300 rpm's. Result? We'll gain some more speed and get through the hole quicker.

Although the 2" rule isn't an absolute it is a good guide. Different prop brands and manufacturers will affect the performance.

So as a recap, less pitch equals more rpm's, more pitch means less rpm's. If you want your boat to perform at it's peak you've got to run the engine at the top end of the rpm range. So that's it. Propeller brands will affect your handling and lift and that's where a service professional will help. But now you can "speak" the basics.

For improvement under loads do this. If you have 2-5 people on board or you're going to tow a wakeboarder or innertube get another prop that is 2" lower on pitch that your regular prop. This will help compensate for your added weight and make a vast improvement to yoru performance. Just remember to watch the RPM's for best engine performance.

To locate the size of your prop check on the side or in the hub. Use this as your starting point. If you're happy with the performance, that you're running the right pitch. Otherwise, go up or down depending on your needs.

Happy boating!