Should I have a 3 or 4 Blade Outboard Propeller?

PowerTech, 2019, propellers

Should I have a 3 or 4 Blade Outboard Propeller? Or even 5?

We regularly help customers who call or come in asking for a outboard boat propeller with more blades because they want to go faster. Unfortunately, that’s just not how outboard boat propellers work. Here, we’ll walk through the applications for different outboard / sterndrive boat propellers based on number of propeller blades, and outline some considerations to make when switching from one to another.

Best conditions to run 3B: We recommend 3-blade boat propellers for most recreational boats with 3, 4, and 6 cylinder outboards and I/0 engines. 3-blade boat propellers generally run “faster” than props with more blades because you can use a higher pitch and be in your recommended RPM range for WOT. They can provide good hole-shot and top-speed performance. Without changing number of blades, you can often go up or down in pitch with a 3-blade boat propeller to achieve your hole-shot or speed goals within your RPM range.

Best conditions to run 4B: We recommend 4-blade boat propellers for specifically in towing applications, heavily weighed boats, or bass boats with very specific prop requirements. Those with high-performance hulls running high horsepower outboard engines can also benefit from 4-blade applications. The performance of a 4-blade propeller vs. a 3-blade propeller is very subtle yet the 4-blade is a little better out of the hole as well as smoother and quieter in operation, with less steering torque and less vibration at high speeds. Many of our recreational boating customers find that the four-blade performs okay but not great, as you’ll need a lower pitch to run similar RPMs to a higher-pitched, and therefore faster, 3-blade prop.

Conditions for running 5B: We typically recommend 5-blade boat propellers specifically for barefoot skiing, or in applications where a 5-blade prop has already been running successfully. Because most 5-blade options are small in diameter and the blades tend to be narrow, the pitch selection is generally the same for a 5-blade as a 3-blade to run similar RPMS.

Note: Most calculators will calculate pitch for RPMS assuming for a 3 blade propeller. When switching from 3 to 4-blades, generally a 1″ pitch decrease is required. So, a 21″ pitch 3-blade is replaced with a 20″ pitch 4-blade. Pitch is increased when switching from 4 to 3-blades OR 5-blades.

When you ask us to help determine what will work best for your application, we will ask for the RPM and speed you can reach at WOT with your existing prop, in addition to the dimensions of the prop, motor information, and performance changes you’re trying to achieve.
Do you have more questions? Contact Us at the shop or call us at 253-272-5065 today.