What is propeller drop?
The propeller shaft in the aft peak tank is provided with inboard and outboard seals. These seals contain nitrile rubber or viton lip seal, which seals against the cast iron propeller shaft. After a few years it creates grooves on them and naturally looses sealing and sea water easily find its way inside. This reduces the lubrication effect and creates wear in the bronze liner. Now there is enough clearance the shaft will come down by certain amount because of propeller weight. This drop in propeller shaft is termed as propeller drop.
>Usual propeller drop = 1mm/160mm shaft dia
>Water cooled bearing clearance = 8mm.
>Oil cooled bearing clearance = 2mm.
Propeller drop Measurement Procedure
> 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.
> So 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 know more or have doubts Please Comment Below
The propeller shaft in the aft peak tank is provided with inboard and outboard seals. These seals contain nitrile rubber or viton lip seal, which seals against the cast iron propeller shaft. After a few years it creates grooves on them and naturally looses sealing and sea water easily find its way inside. This reduces the lubrication effect and creates wear in the bronze liner. Now there is enough clearance the shaft will come down by certain amount because of propeller weight. This drop in propeller shaft is termed as propeller drop.
Must Read:> What is Rudder Drop? How to reassure it?
How measure propeller drop?
This propeller drop is measured using poker gauge. >Usual propeller drop = 1mm/160mm shaft dia
>Water cooled bearing clearance = 8mm.
>Oil cooled bearing clearance = 2mm.
Propeller drop Measurement Procedure
> 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.
> So 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 know more or have doubts Please Comment Below
Can you take the propeller drop even after the propeller is removed?
ReplyDeletei think no... In some ships i have seen markings on the housing in that case you can take...
Deleteyes, because after removal of propeller, shaft remain on that very weared condition.
Deleteplease note that the propellor clearance is not because of the nitrile rubber rings but actually because of the propellor shafts movement in liner and with bearing causing the bearings to wear down which can be measured indirectly from propellor drop as there is not other way (easy way to measure this two diameters) hence according to me if you can directlly measure the dieamters of liner and bush it should be accepted measurement for propellor drop
ReplyDeleteWhy do we take poker gauge reading from bottom
ReplyDeleteIt is not necessary to take the reading from bottom but when we take it from both the sides viz. top & bottom, we get to know the exact wear down with no place for doubts. Because the amount by which the clearance has increased on the top would be the same amount by which the clearance has decreased on the bottom side. Please correct me if I have got this wrong.
Deletewell said...
Deletecan anybody explain the 2nd and 3rd point of taking prop drop?
Deletewhere we will fix the poker guage exactly
ReplyDeleteAfter reading the post and comment I guess I should clear the doubt about the propellor drop fully.
ReplyDeletePropellor drop is taken to determine the stern tube bearing wear as due to weight of the propeller and movement of propellor the bottom part of the bearing is liable to get wearer out with time.
Now to take the propellor drop it is required that propellor will be in place or else what's the use of taking propeller drop as the shaft vl be not in a loaded condition which is a normal senario.
Third the drop is taken between the water side seal and the oil side seal. But before that oil is drained and before putting the poker gauge u have to remove a copper washer present on the plug removed to put the poker gauge.
Fourth , yes we have to take reading both top and bottom as we have to be sure that the bearing is actually worn down and not because of any other reason.
This comment has been removed by the author.
ReplyDeleteShaft dia =455 mm
DeleteBearing inside dia= 456.2 (apparently )
please anybody explain how to set the pocker gauge and how to take the reading.
ReplyDeleteThe reading is taken every dry dock and/or in-water survey in lieu of dry-docking and recorded. In order to take the measurement, we need to have access through the rope guard.
DeleteThere are different access plates (open/accessible, bolted, and welded). Also, Special equipment needs to be provided from the Chief Engineer onboard, since each vessel has specific customized tools (poker gauge). This poker gauge is used to measure the propeller shaft drop.
1.how will u read poker gauge reading?
ReplyDeletePoker gauges normally comes customized,each vessel having different gauges... I think it's normally measure in mm
Delete> The poker gauge is placed between the last and second last stern tube seals (aft- near the propeller).
Delete>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.
> So 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.
a hole is provided only on top of the seal, or both bottom and top ?
ReplyDelete