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Marine Propeller Slip Calculator — result sheet
Estimate apparent propeller slip from engine speed, gear ratio, propeller pitch, and measured boat speed.
Inputs used
Results
Visual chart
Breakdown
Calculation steps
Returned data table
Formula and methodology
Formula: Propeller rpm = engine rpm ÷ gear ratio; no-slip speed (knots) = pitch(in) × propeller rpm ÷ 1215.2; slip = 1 − actual/theoretical.
Propeller pitch is the theoretical advance per revolution in a solid medium. This calculator converts engine speed to shaft speed, estimates no-slip speed, and compares it with measured speed. Apparent slip is a useful diagnostic quantity but is not a standalone measure of propeller efficiency.
This result follows the calculator's declared inputs, precision, validation boundaries, and model limits.
Input contract
- Engine speed — rpm; minimum 1.0E-6; maximum 10000000
- Gear ratio (engine:propeller) — ratio; minimum 1.0E-6; maximum 10000
- Propeller pitch — in; minimum 1.0E-6; maximum 100000
- Measured boat speed — knots; minimum 0; maximum 100000
Worked example
| Input | Value |
|---|---|
| Engine speed | 3000 |
| Gear ratio (engine:propeller) | 2 |
| Propeller pitch | 18 |
| Measured boat speed | 14 |
The propeller turns at 1,500 rpm, the no-slip speed is about 22.22 knots, and apparent slip is about 36.97%.
Assumptions and limits
- The gear ratio is expressed as engine revolutions per propeller revolution and the pitch is the nominal pitch in inches.
- Boat speed is measured through the water or is otherwise comparable with the pitch-speed estimate and is entered in knots.
- Hull resistance, cavitation, trim, propeller diameter, blade geometry, water density, and engine torque are not modeled.
Calculator note
Source and methodology
Use the official WorldCalculate methodology policy for the source, formula, precision, and boundary standards behind this calculator.
Planning estimate, not financial, medical, legal, or professional advice. © WorldCalculate — reuse with attribution. Built and curated by Hassan ALRowaie.
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