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 expressed as a percentage and indicates the efficiency of the propeller.

2. How Does the Calculator Work?

The calculator uses the propeller slip formula:

Where:

• \( theoretical\_speed \) — Speed the vessel should theoretically achieve (knots)
• \( actual\_speed \) — Speed the vessel actually achieves (knots)

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

3. Importance of Slip Calculation

Details: Monitoring propeller slip helps assess marine propulsion system efficiency, detect hull fouling, and identify potential mechanical issues with the propeller or engine.

4. Using the Calculator

Tips: Enter both theoretical and actual speeds in knots. Theoretical speed can be calculated from propeller pitch and RPM. Actual speed is typically measured via GPS.

5. Frequently Asked Questions (FAQ)

Q1: What is a normal slip percentage?
A: Typically 5-25% for displacement hulls, 10-50% for planing hulls. Values outside this range may indicate problems.

Q2: Why does slip percentage matter?
A: Higher than normal slip indicates inefficiency - possible causes include hull fouling, propeller damage, or incorrect propeller sizing.

Q3: How is theoretical speed calculated?
A: Theoretical speed (knots) = (Pitch (inches) × RPM) / (1215.2 × Gear Ratio)

Q4: Can slip be negative?
A: Normally no, unless there's an error in measurements or calculations. Negative slip would imply the boat is moving faster than theoretically possible.

Q5: Does slip vary with speed?
A: Yes, slip percentage typically decreases as speed increases up to a point, then may increase again at very high speeds.