1. What is Propeller Slip?

Propeller slip is the difference between the theoretical distance a propeller should advance in one revolution and the actual distance it advances through the water. It's an important measure of propeller efficiency.

2. How Does the Calculator Work?

The calculator uses the propeller slip formula:

Where:

• Actual Speed — Measured speed of the vessel through water (knots)
• Theoretical Speed — Speed the vessel should achieve based on propeller pitch and RPM

Explanation: The formula calculates what percentage of the theoretical speed is lost due to slip.

3. Importance of Propeller Slip

Details: Monitoring propeller slip helps identify propulsion system efficiency, potential hull fouling, or propeller damage. Optimal slip is typically between 5-25% depending on vessel type.

4. Using the Calculator

Tips: Enter both actual and theoretical speeds in knots. Both values must be positive numbers. The result is expressed as a percentage.

5. Frequently Asked Questions (FAQ)

Q1: What is a normal propeller slip percentage?
A: For most vessels, 5-25% is typical. High-performance boats may have higher slip at low speeds.

Q2: What causes excessive propeller slip?
A: Common causes include hull fouling, propeller damage, incorrect propeller size, or heavy loading.

Q3: How is theoretical speed calculated?
A: Theoretical speed = (Pitch (in) × RPM × 60) / (1852 × 39.37), converting to knots.

Q4: Can slip be negative?
A: Normally no, unless there's measurement error or the vessel is benefiting from currents.

Q5: How often should slip be monitored?
A: Regular monitoring helps detect changes in performance. Check monthly or when performance seems abnormal.