Now, determine your wide open throttle (WOT) RPM
For safety and efficient performance, it is critical that your engine operates within
the RPM range recommended by the manufacturer. Matching the right prop for the load
is the most significant factor of RPM adjustment.
Effect of Prop Pitch on RPM
A pitch change can increase or decrease the RPM’s and bring RPM’s into the recommended
range. A 2" increase in pitch (for example, from 21" to 23") typically
results in a decrease of approximately 300-400 RPM.
First, Determine Manufacturer’s Recommended RPM
Find the manufacturer’s recommended RPM range in the owner’s manual or ask your
dealer.
Test for Maximum RPM
Using the existing propeller or a new propeller, make test runs to determine the
maximum RPM and boat speed. Vary the trim angle for optimum performance.
RPM Higher Than Recommended
If the actual WOT RPM’s are above the recommended RPM range, install the
next larger pitch propeller to decrease your WOT RPM. Re-test the WOT RPM.
RPM Lower Than Recommended
If the actual WOT RPM range is below the recommended range, install the next smaller
pitch propeller to increase your WOT RPM. Re-test the WOT RPM.
When you combine all these factors, you have the information you need to select
the correct propeller for maximum performance, safety, and fuel efficiency.