Propeller Choice: A Lesson in the Basics

The speed bug bites everyone, and it will bite you. Your boat does 48 mph and you want it to top 50 mph, if for no other reason than to be able to brag about it honestly.

Going from a three-blade propeller to a four-blade, or vice versa, might require changing pitch.

If you want your runabout to go faster, you will find a few mph with a stainless propeller. 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. Stainless props are more costly, but you also will notice an increase in 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’re 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, but don’t try to figure it out on your own. Mercury offers a prop selector tool on its website based on the size, weight, and power of your boat. Before you visit that site, check out the following list of materials, blade counts, and operating characteristics.

  • 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 mid-range performance, but probably no gain in top speed.

Now, at least when the speed bug bites, you’ll be prepared.

For more propeller information, check out these stories on our sister site Boats.com:

 

Brett Becker

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