Home » All Calculators » Engineering Tools » Propeller Slip Calculator

Propeller Slip Calculator

Photo of author
Published on

Navigating the waters efficiently is paramount for mariners and boat enthusiasts alike. A crucial aspect of this efficiency is understanding and calculating propeller slip, a concept that might seem complex but is made accessible through the use of a Propeller Slip Calculator. This tool demystifies the process, allowing for improved performance and fuel efficiency on the water.

What is a Propeller Slip?

Propeller slip refers to the difference between the theoretical distance a boat should cover under ideal conditions with each propeller rotation and the actual distance it covers. It’s a measure of how much propulsion efficiency is lost due to the propeller moving through water. In simple terms, it helps you understand how effectively your boat’s propeller converts engine power into forward motion.

How Does the Propeller Slip Calculator Work?

The Propeller Slip Calculator uses a specific formula to determine the slip percentage, which is:

Slip (%) = ((Theoretical Distance - Actual Distance) / Theoretical Distance) * 100

Here’s a breakdown of the terms used:

  • Theoretical Distance (TD): This is the distance your boat would theoretically travel in one hour if there was no slip at all. It’s calculated based on the propeller’s pitch, the revolutions per minute (RPM), the gear ratio, and a conversion factor to adjust from inches per hour to your desired unit of distance (e.g., nautical miles, kilometres).
  • Actual Distance (AD): The distance your boat travels in the same period, which can be measured using GPS or known distance markers.

Required Inputs

To calculate propeller slip, you’ll need:

  1. Propeller Pitch (in inches)
  2. RPM (Revolutions Per Minute) of the propeller
  3. Gear Ratio of the engine-to propeller setup
  4. Actual Distance travelled (in the same unit as the theoretical distance)
  5. Conversion factor for inches per hour to the desired unit of distance

Step-by-Step Example

Let’s use the calculator with the following inputs:

  • Propeller Pitch: 24 inches
  • RPM: 3000
  • Gear Ratio: 2
  • Actual Distance travelled: 10 nautical miles in one hour
  • Conversion factor for nautical miles: 0.0000124274

First, calculate the Theoretical Distance:

TD = (24 * 3000 / 2) * 60 * 0.0000124274

Then, calculate Slip (%) with the actual distance known:

Slip (%) = ((TD - 10) / TD) * 100

Relevant Information Table

Propeller Pitch24inches
Gear Ratio2Ratio
Actual Distance10Nautical Miles
Conversion Factor0.0000124274Nautical Miles


The Propeller Slip Calculator is an invaluable tool for optimizing boat performance. By understanding and adjusting for propeller slip, mariners can ensure their vessel operates at peak efficiency, saving fuel and improving speed over time. This calculator simplifies a complex calculation, making it accessible to professionals and hobbyists alike, ensuring that every journey on the water is as efficient as possible.

Leave a Comment