Free · Physics models
Boat Propeller Pitch and Slip
Relate boat speed, engine RPM, reduction ratio, propeller pitch and fractional slip using advance per revolution.
- Formula & worked example
- Private in your browser
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Calculator inputs
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How to use this calculator
- Enter the known values in the units shown. Results update as you type.
- Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
- Use the worked example to check the method. Reset restores the starting fields.
Private by default
Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.
Formula and method
propeller pitch = 277.77778 mm.
Pitch (in) = speed (mph) × gear ratio × 1056 / [engine rpm × (1 − slip)].
Worked example
Enter these known values and leave the other values blank.
- Boat speed
- 30 km/h
- Gear ratio
- 2 : 1
- Engine/crankcase speed
- 4000 rpm
- Propeller slip
- 10 %
- Propeller pitch
- 277.8 mm
Assumptions and limitations
- Relate boat speed, engine RPM, reduction ratio, propeller pitch and fractional slip using advance per revolution.
- Gear ratio is engine speed divided by propeller speed. Slip is the fractional shortfall from ideal advance; it ranges from zero up to but excluding 100%.
- This is a kinematic estimate, not a propeller performance or load model. Inputs must be positive and refer to the same operating point.
- Inputs and inverse outputs share the displayed unit selectors. Clear a known field to solve for it, and lock quantities that must remain fixed. Singular inverses may have no finite result.
Common questions
What does 10% slip mean?
The boat advances 90% of the pitch distance per propeller revolution.
Does pitch alone determine speed?
No. Propeller RPM and operating slip are also needed.
References
Relate boat speed, engine RPM, reduction ratio, propeller pitch and fractional slip using advance per revolution. Gear ratio is engine speed divided by propeller speed. Slip is the fractional shortfall from ideal advance; it ranges from zero up to but excluding 100%. This is a kinematic estimate, not a propeller performance or load model. Inputs must be positive and refer to the same operating point.