Prop Pitch
Calculate boat propeller pitch from speed or determine boat speed from prop pitch. Analyze propeller slip, gear ratios, and optimize your marine propulsion system.
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Why: Understanding prop pitch helps you make better, data-driven decisions.
How: Enter your values below and results will compute automatically.
Run the calculator when you are ready.
Enter Parameters
Calculation Mode
Boat Speed
Engine & Drive
Propeller Slip
For educational and informational purposes only. Verify with a qualified professional.
What is Propeller Pitch?
Propeller pitch is the theoretical distance a propeller would travel through a solid medium in one complete revolution. Think of it like a screw - the pitch determines how far it advances with each turn. A higher pitch means more distance per revolution, resulting in higher top speed but slower acceleration.
High Pitch
More distance per revolution, higher top speed.
21"+ pitch
Best for: Speed boats, light loads
Low Pitch
Less distance per revolution, better acceleration.
13-17" pitch
Best for: Heavy loads, pontoons, towing
How is Prop Pitch Calculated?
Prop pitch relates boat speed to engine RPM through the gear ratio. The formula accounts for "slip" - the difference between theoretical and actual propeller travel through water.
🔬 The Formula
Pitch = (Speed × Gear Ratio × C) / (RPM × (1 - Slip))
When to Use This Calculator
Use this calculator when selecting a new propeller, optimizing boat performance, or troubleshooting speed/RPM issues.
📊 Common Pitches
🎯 Use Cases
- New propeller selection
- Performance optimization
- Speed verification
- Troubleshooting RPM issues
- Comparing prop options
Frequently Asked Questions
What is propeller pitch and how does it affect boat performance?
Propeller pitch is the theoretical distance a propeller would travel in one revolution through a solid medium. Higher pitch (17-21+ inches) provides better top speed but slower acceleration, while lower pitch (13-17 inches) offers better acceleration and pulling power but lower top speed. The right pitch depends on your boat's weight, hull design, and intended use.
How do I know if my propeller pitch is correct?
The correct pitch allows your engine to reach its recommended WOT (Wide Open Throttle) RPM range. If RPMs are too low, you need less pitch. If RPMs are too high, you need more pitch. Most engines perform best at 90-95% of their maximum rated RPM at WOT with a normal load.
What is propeller slip and what causes it?
Propeller slip is the difference between theoretical and actual propeller travel through water, expressed as a percentage. Typical slip ranges from 10-20% for most boats. Higher slip can indicate propeller damage, incorrect pitch, or hull drag issues. Lower slip (under 10%) suggests efficient operation.
How does gear ratio affect propeller performance?
Gear ratio determines how many times the propeller rotates per engine revolution. Lower gear ratios (1.5:1 to 2:1) provide more torque and are better for heavy loads. Higher gear ratios (2.5:1 to 3:1) allow higher propeller RPMs and are better for speed. The gear ratio affects the relationship between engine RPM and propeller RPM.
Should I choose a higher or lower pitch propeller?
Choose higher pitch (19-21+ inches) if you prioritize top speed and your engine reaches maximum RPM easily. Choose lower pitch (13-17 inches) if you need better acceleration, plan to carry heavy loads, or tow water skiers/tubers. The goal is matching pitch to your engine's optimal RPM range.
Can I use the same propeller for different boats?
Generally no. Each boat has unique characteristics (weight, hull design, engine power) that determine optimal propeller pitch. A propeller that works well on one boat may cause poor performance on another. Always test propeller performance and ensure your engine reaches its recommended RPM range.
What's the difference between pitch and diameter?
Pitch determines how far the propeller advances per revolution (speed), while diameter determines the propeller's size and affects thrust and efficiency. Larger diameter propellers move more water but require more power. Both pitch and diameter must be matched to your engine and boat for optimal performance.
Official Data Sources
⚠️ Disclaimer
This calculator provides estimates based on standard propeller theory and formulas. Actual boat performance may vary significantly due to hull design, weight distribution, water conditions, propeller condition, engine tuning, and other factors. Propeller slip values are estimates - actual slip depends on many variables. Always consult with marine professionals and test propeller performance on water before making final decisions. Results are for planning purposes only and should not replace professional marine consultation or on-water testing.
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