I don’t know about you, but propellers have always mystified me. They still do. A lot of my boating buddies would swap one for another and back again, and I never could figure out what the heck they hoped to accomplish. They were probably just as much in the dark about as I was.
So I picked up the phone and made some calls. I wanted to try to put together something quick and easy to digest that would help Boat Trader readers understand more about propellers without getting mired in deep theory and mucky details only an engineer could understand. So here goes nothing.
If you want to go fast, go stainless. It’s stronger than aluminum, which means manufacturers can make thinner blades, increase efficiency, and reduce drag, according to John Scherrer, manager of propeller and hydrodynamics engineering for Mercury Racing. It also increases the variety of propellers you can buy.
“Once you go to stainless, you get all these different model lines,” Scherrer said. “There’s an ability to tune your boat for what you want to do.”
One rule of thumb is that if you are going from a three-blade propeller to a four-blade, you may have to drop down in pitch. Likewise, when going from a four-blade to a three-blade, you may have to go up in pitch. Mercury offers a prop selector tool on its website based on the type and intended usage of your boat, along with other factors.
Three-blade aluminum: Nonperformance prop, usually comes with the boat; thicker construction, few pitch options.
Three-blade stainless: Up to 2-mph gain over aluminum three-blade; accelerates better because blades are thinner, holds better in turns, blows out less.
Four-blade aluminum: Nonperformance prop, smoother than three-blade aluminum; thick construction, few pitch options.
Four-blade stainless: Most popular performance propeller, up to 2-mph gain over aluminum four-blade, smoother than a three-blade, better acceleration, holds better in turns, blows out less, lots of pitch options.
Five-blade stainless: Smoother operation than four- and three-blades; gets on plane better, enhances midrange performance, but probably no gain in top speed.
To help you figure out what pitch propeller you need, Mercury Marine has a couple of nifty features on its website to help: