Enter the theoretical speed of the propeller and the actual speed of the propeller into the calculator to determine the propeller slip percentage; this calculator can also evaluate any of the variables given the others are known.

## Propeller Slip Formula

The following formula is used to calculate the propeller slip:

Slip = (N - S)/{N} *100

Variables:

- Slip is the propeller slip percentage
- N is the theoretical speed of the propeller
- S is the actual speed of the propeller

To calculate the propeller slip, subtract the actual speed of the propeller from the theoretical speed of the propeller. Divide the result by the theoretical speed of the propeller, and then multiply by 100 to get the slip percentage.

## What is a Propeller Slip?

Propeller slip refers to the difference between the theoretical distance a propeller should move in one revolution and the actual distance it does move. This discrepancy is due to the fact that water or air is a fluid medium, and when a propeller rotates, it pushes against this medium to generate thrust. However, the fluid medium also offers resistance and tends to “slip” around the blades of the propeller, causing the propeller to move less distance than theoretically calculated. The amount of slip is influenced by several factors, including the design and condition of the propeller, the speed and load of the vessel, and the condition of the fluid medium. It is usually expressed as a percentage, with 100% slip meaning the propeller is not moving the vessel at all, and 0% slip meaning the propeller is moving the vessel exactly the theoretical distance per revolution.

## How to Calculate Propeller Slip?

The following steps outline how to calculate the Propeller Slip.

- First, determine the ship’s speed through the water (knots).
- Next, determine the ship’s speed over the ground (knots).
- Next, subtract the ship’s speed through the water from the ship’s speed over the ground.
- Finally, divide the difference by the ship’s speed over the ground and multiply by 100 to get the Propeller Slip percentage.
- After inserting the variables and calculating the result, check your answer with the calculator above.

**Example Problem:**

Use the following variables as an example problem to test your knowledge.

Ship’s speed through the water (knots) = 10

Ship’s speed over the ground (knots) = 12