Propeller Slip Calculator
Propeller slip is the share of a propeller's push that is lost in the water instead of moving the boat. Enter the pitch, the engine speed and the boat speed to see it.
- Free
- Works offline after your first visit
- Saves on this device
- No sign-up
- Updated
How it works
Pitch times revolutions per second gives the speed the propeller would move the boat if it met no slip. The boat's real speed is lower, and the gap, as a share of that no-slip speed, is the slip.
Some slip is normal for a working propeller. More slip means more of the engine's power goes into churning water rather than moving the boat.
Worked example
A propeller with a pitch of 15 in at 2,600 rpm would move the boat at 32.1 kn with no slip. At 26 kn, the slip is 19%.
Questions
What is propeller pitch?
Pitch is how far a propeller would move forward in one full turn if it screwed through a solid. The figure is usually printed on the propeller or in its listing.
How much slip is normal?
It varies with the boat, load and conditions. This calculator shows the sum for the numbers you enter, and it does not give a target figure.
What makes slip go up?
Heavier loads, rough water, a fouled hull or a pitch that does not suit the boat can all raise it.
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