1. What is Prop Slip?

Prop slip is a measure of the efficiency of a boat's propeller. It represents the difference between the theoretical distance the boat should move based on propeller rotation and the actual distance it moves through water.

2. How Does the Calculator Work?

The calculator uses the prop slip equation:

Where:

• Actual Speed — Measured boat speed through water (knots)
• Theoretical Speed — Speed calculated from propeller pitch and RPM

Explanation: The equation calculates the percentage of "lost" motion due to propeller inefficiency in the water.

3. Importance of Prop Slip Calculation

Details: Prop slip helps evaluate propeller performance, diagnose propulsion system issues, and optimize boat speed and fuel efficiency.

4. Using the Calculator

Tips: Enter actual boat speed and theoretical speed (calculated from pitch × RPM × 60 ÷ 6080). Both values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is a good prop slip percentage?
A: Typically 5-25%. Lower values indicate better efficiency. Outboards usually have 10-15% slip at cruising speed.

Q2: Why does prop slip occur?
A: Due to water not being a solid medium - some propeller thrust is lost to water movement rather than boat movement.

Q3: How does prop slip vary with speed?
A: Slip decreases as speed increases up to a point, then may increase again at very high speeds due to cavitation.

Q4: Can prop slip be negative?
A: Normally no, unless there's measurement error or unusual currents affecting actual speed measurement.

Q5: How can I reduce prop slip?
A: By choosing the right propeller size/pitch, maintaining clean hull/propeller, and proper engine trim.