1. What is Prop Slip?

Prop slip is the difference between the theoretical distance a propeller should move forward in one revolution and the actual distance it moves through the water. It's expressed as a percentage and indicates propeller efficiency.

2. How Does the Calculator Work?

The calculator uses the Mercury slip equation:

Where:

• \( RPM \) — Engine revolutions per minute
• \( pitch \) — Propeller pitch in inches
• \( gear\ ratio \) — Gear reduction ratio
• \( speed \) — Boat speed in miles per hour
• 1056 — Conversion factor (inches to miles and hours to minutes)

Explanation: The equation calculates theoretical speed based on propeller pitch and RPM, then compares it to actual speed to determine slip percentage.

3. Importance of Prop Slip Calculation

Details: Prop slip helps evaluate propeller performance, diagnose propulsion issues, and optimize boat setup. Ideal slip is typically 10-15% for most applications.

4. Using the Calculator

Tips: Enter accurate RPM, propeller pitch, gear ratio, and speed measurements. All values must be positive numbers for valid results.

5. Frequently Asked Questions (FAQ)

Q1: What is a good prop slip percentage?
A: Most efficient setups have 10-15% slip. Higher values may indicate incorrect propeller selection or hull issues.

Q2: Why does my prop slip vary with speed?
A: Slip decreases as speed increases until reaching optimal efficiency. Cavitation can increase slip at high speeds.

Q3: How does propeller condition affect slip?
A: Damaged or worn props typically show higher slip percentages due to reduced efficiency.

Q4: Can slip be negative?
A: No, negative slip indicates measurement error in RPM, speed, or other inputs.

Q5: Does hull type affect prop slip?
A: Yes, displacement hulls typically have higher slip than planing hulls at lower speeds.