- When the vessel is moving ahead the propeller exerts pressure on the water to create the forward motion.
- Propeller slip occurs because water is not a solid medium and there is some slip related to it.
- Slip may be considered as the difference between the speed of the vessel and the speed of the engine.
- It is always expressed as a percentage.
- The calculated value of slip will be increased when the wind and sea are ahead and if the vessel has a fouled bottom.
- The differing values of slip are especially noticeable after a vessel has been cleaned in drydock.
- Theoretically a vessel should never have negative slip, but this may occur in one or more of the following conditions:-- A strong following sea.
How to find the Propeller Slip
Mean Apparent slip = Distance run by propeller - distance run by ship per day
Distance run by propeller
Distance run by propeller in nautical miles = Pitch(m) x total engine revolution per day