Propeller Drop is distance,drop due to its own weights.Let us start about it in brief:-
In the after peak tank the propeller shaft is fitted with inboard and outboard seals.
These seals contain nitrile rubber or viton lip seal which fits shrunk around the cast iron propeller shaft to seal against the bronze liner.It creates grooves on them after a few years and naturally looses sealing and sea water can find its way within easily.
This reduces the lubrication effect, and if the bronze liner creates wear.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.
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