1. What is Prop Slip?

Prop slip is the difference between the theoretical distance a propeller should move a boat forward in one revolution (based on its pitch) and the actual distance it moves. It's expressed as a percentage and indicates the efficiency of the propeller.

2. How Does the Calculator Work?

The calculator uses the prop slip formula:

Where:

• \( RPM \) — Engine revolutions per minute
• \( Gear Ratio \) — Transmission gear ratio
• \( Pitch \) — Propeller pitch in inches
• \( Speed \) — Actual boat speed in mph
• 1056 — Conversion constant

Explanation: The formula calculates the theoretical speed based on propeller pitch and compares it to actual speed to determine slip percentage.

3. Importance of Prop Slip Calculation

Details: Prop slip helps evaluate propeller efficiency. Typical slip ranges are 5-25% for planing hulls and 15-50% for displacement hulls. High slip may indicate incorrect propeller selection or hull issues.

4. Using the Calculator

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

5. Frequently Asked Questions (FAQ)

Q1: What is a good prop slip percentage?
A: For most planing hulls, 8-15% is excellent, 15-20% is good, and over 25% may indicate a problem.

Q2: Why does prop slip occur?
A: Slip occurs because water isn't a solid medium - the propeller blades "slip" through the water rather than getting perfect grip.

Q3: How can I reduce prop slip?
A: Proper propeller selection (diameter, pitch, blade count), maintaining clean hull/prop, and optimal engine trim can reduce slip.

Q4: Does slip vary with speed?
A: Yes, slip is typically highest at low speeds and decreases as the boat planes, reaching minimum at optimal cruising speed.

Q5: What's the 1056 constant in the formula?
A: It's a conversion factor accounting for units (inches to miles, minutes to hours) and propeller efficiency assumptions.