What is Propeller Drop ?
Propeller Drop is distance,drop due to its own weights.
Due to the weight of propeller and the clearance developed due to wear , the shaft will come down by a certain amount. This drop in propeller shaft is termed as propeller wear down or propeller drop.
Propeller drop is measured by POKER GUAGE.
When it is measured ?
Ans:- during dry dock
Let us start about it in brief:-
The forward end of shaft is connected to the main engine and at the aft end we have a propeller,which is fitted on it. Basically it is a cantilever beam with one end fixed and other end free on which the propeller is fitted and the weight of propeller would attempt to pull the shaft down.
At a point where the propeller shaft passes through the hull into the sea to prevent sea water entering into the engine room, a sealing is provided.
I.e In the aft peak tank the propeller shaft is fitted with inboard and outboard seals that is called lip seal.
These seals contain nitrile rubber or viton lip seal which fits shrunk around the cast iron propeller shaft to seal against the bronze liner.
To prevent heat build-up and harm the sealing, lubrication is provided between liner and sealing.
Naturally after few years , grooves are created on liner surface of shaft due to the loss of seals and sealing and sea water can find its way within easily.
This reduces the lubrication effect, and creates wear in bronze liner on the propeller shaft.
Now as there is sufficient clearance, due to the weight of the propeller ,the shaft will come down by a certain amount.
This drop is called propeller drop or “propeller stern shaft clearance” or “propeller wear down”. in the propeller shaft.
Before taking the measurement,
●we have to remove the rope guard first.
●Also make sure weather the vessel has the poker gauge or not. This poker gauge is use to measure the propeller shaft drop (known as propeller wear down).
●After dismantling the rope guard, make sure to turn the blade to one position refer to the marking.Normally, we take top measurement and bottom measurement.
Procedures to measure Propeller Drop :-
● The poker gauge is placed between the last and second last stern tube seals (aft- near the propeller).
● The reading is taken every dry dock and recorded.
● A hole is provided on top of the seal which is closed by a plug.
● This plug is removed, the poker gauge is inserted and a reading taken.Since, the propeller is connected to the shaft and the poker gauge measures how much the shaft has ‘dropped’ due to the wear down of the bearing on which the shaft runs.
If you have any problems ,then do not forget to comment.
People also ask
Which of the following instruments measures propeller drop?
4.None of the above