Prop Pitch Calculator
Calculate propeller pitch or boat speed using engine RPM, gear ratio, and slip percentage
Propeller Calculations
Maximum boat speed at full throttle
Engine to propeller shaft ratio (typically 1.5:1 to 3:1)
Engine speed at full throttle (typically 5000-6000 rpm)
Typical slip: 10-20% (higher for heavy loads)
Propeller Pitch Results
Formula used: Pitch = (Speed × Gear Ratio × C) / (RPM × (1 - Slip))
Conversion constant (C): 1056 for MPH
Effective slip: 10% = 0.10 decimal
Example Calculation
16" Pitch Propeller Speed
Propeller Pitch: 16 inches
Engine RPM: 5500 rpm
Gear Ratio: 2:1
Propeller Slip: 10%
Speed Calculation
Speed = (16 × 5500 × (1 - 0.1)) / (2 × 1056)
Speed = (16 × 5500 × 0.9) / 2112
Speed = 79,200 / 2112
Speed = 37.5 mph
Propeller Basics
Diameter
Circle diameter of propeller blades
Larger = more water displacement
Pitch
Theoretical advance per revolution
Higher = more speed potential
Slip
Efficiency loss in water
Typical: 10-20%
Pitch Selection Guide
Lower Pitch (8-14")
Better acceleration, heavy loads, water sports
Medium Pitch (15-19")
Balanced performance, general boating
Higher Pitch (20-24")
Top speed, light loads, racing
Understanding Propeller Pitch
What is Propeller Pitch?
Propeller pitch is the theoretical distance a propeller would advance in one revolution if it were moving through a solid medium, like a screw through wood. It's measured in inches and directly affects your boat's performance characteristics.
Why is it Important?
- •Determines maximum boat speed potential
- •Affects acceleration and hole shot performance
- •Impacts engine RPM and fuel efficiency
- •Influences load-carrying capacity
Pitch Calculation Formula
Pitch = (Speed × Gear Ratio × C) / (RPM × (1 - Slip))
- Speed: Boat speed in mph, kph, or knots
- Gear Ratio: Engine to propeller shaft ratio
- C: Conversion constant (1056 for mph, 656 for kph, 1215.2 for knots)
- RPM: Engine revolutions per minute
- Slip: Propeller slip percentage (typical: 10-20%)
Note: Actual performance may vary based on hull design, weight, and water conditions.
Propeller Slip Explained
Propeller slip is the difference between the theoretical distance a propeller should advance and the actual distance it does advance. This occurs because water is not a solid medium, and some efficiency is lost due to turbulence and water displacement.
Efficient Performance
10-15% slip indicates good propeller efficiency and proper sizing
Acceptable Range
15-25% slip is acceptable for most recreational boating applications
Poor Efficiency
Above 25% slip indicates oversized pitch or damaged propeller