Propeller Slip Calculator
Calculate the efficiency of your ship's propeller by determining its slip percentage.
Input Data
**Note:** This calculator determines "apparent slip" which doesn't account for the wake fraction. The result is a good indicator of overall propulsion efficiency. High positive slip may indicate hull fouling or adverse weather. Negative slip suggests a strong following current.
About Propeller Slip Calculator
Understanding Propulsion Efficiency
Propeller slip is the difference between the actual speed of the ship and the speed it would have if the propeller were acting in a solid, unyielding medium (like a screw in wood). Monitoring slip is the primary way for Chief Engineers and Masters to evaluate hull cleanliness and engine performance.
Technical Formulas
1. Theoretical Speed (Knots):
V_theo = (RPM × Pitch × 60) / 1852
2. Apparent Slip Percentage:
Slip (%) = ((V_theo - V_actual) / V_theo) × 100
Interpreting Your Results
- 0% to 10% (Normal): Typical for a ship with a clean hull in calm sea conditions.
- 10% to 25% (Moderate): Suggests increased resistance, likely due to head winds, heavy seas, or moderate hull fouling.
- Over 30% (Poor): High slip indicates significant efficiency loss. Possible causes include severe biofouling, damaged propeller blades, or the vessel is operating in extreme weather.
- Negative Slip: Occurs when the vessel is being pushed by a strong following current or heavy following seas, making it move faster than its theoretical engine speed.
Role in Maintenance
Consistent increases in slip over time are a clear signal that the vessel may require underwater hull cleaning or a propeller polish to restore fuel efficiency and reduce carbon emissions (CII ratings).