1. What is the Propeller Speed Calculation?

The propeller speed calculation estimates a boat's speed based on engine RPM, propeller pitch, and slip factor. It helps compare theoretical versus actual performance and optimize propeller selection.

2. How Does the Calculator Work?

The calculator uses the propeller speed equation:

Where:

• \( RPM \) — Engine revolutions per minute
• \( Pitch \) — Propeller pitch in inches
• \( Slip\ Factor \) — Efficiency factor (typically 0.9-0.95 for good props)
• 1056 — Conversion constant (inches to miles, minutes to hours)

Explanation: The equation calculates theoretical speed then adjusts for real-world inefficiencies via the slip factor.

3. Importance of Propeller Speed Calculation

Details: Proper propeller selection maximizes engine efficiency, prevents over-revving, and ensures optimal boat performance. Comparing calculated versus GPS speed helps diagnose propulsion issues.

4. Using the Calculator

Tips: Enter accurate RPM at wide-open throttle, exact propeller pitch (marked on hub), and typical slip factor (start with 0.9). All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical slip factor?
A: Well-designed props have 5-10% slip (0.90-0.95 factor). Poor props or hull issues may exceed 15% slip.

Q2: Why is my actual speed lower than calculated?
A: Additional factors like hull drag, weight, trim, and water conditions affect real speed beyond just propeller slip.

Q3: How does pitch affect speed?
A: Higher pitch increases theoretical speed but requires more power. Too much pitch bogs the engine.

Q4: What's the 1056 constant?
A: It converts inches-per-rev and revs-per-minute to miles-per-hour (12 in/ft × 5280 ft/mi ÷ 60 min/hr).

Q5: Should I use this for propeller selection?
A: This provides theoretical comparison only. Always consult with propeller experts for actual selection.