3rd class GK question

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ngineer
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3rd class GK question

Postby ngineer » Mon Mar 02, 2009 11:41 am

Hi,
I've been going through some notes while gearing up for the 3rd class general knowledege exam, and I was hoping for some clarification on a question regarding sterntubes.

How do you determine the wear down of an oil lubricated sterntube bearing, and what would a typical maximum wear down value be?

I have come up with answers for these questions involving water lubricated bearings using text books, but it is proving to be difficult to find definitive answers for the oil lubricated type.

Thanks

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The Dieselduck
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Re: 3rd class GK question

Postby The Dieselduck » Mon Mar 02, 2009 1:37 pm

Funny you should bring it up. I am going through that right now. Although we didn't do it right this time, you can measure wear between the tail shaft and its tail bush using a poker gauge.

The poker gauge is usually provided by the original installer of the shaft and seal to the vessel, and kept by the Chief Engineer. I did find it eventually, one for the port side, one for the stb side, and it looks like a depth gauge, but specific to the vessel and within the box was a record of previous measurement. (Sorry I did not take a picture for you, I will try to when I get back). It fits into the the seal housing, see picture for the plug furthest left (I believe).

Because we didn't do the poker gauge method of measuring, the yard just but a bottle jack under the propeller boss, and a a dial indicator at the TDC of the tail shaft, then pumped up the shaft, then released it. The total movement equals the clearance in the bush. Ours was .064" on one shaft, and .030" on the other. The largest clearance indicated a problem, and when the shaft was pulled, the bearing was found wiped and damaged, see picture.

I am not sure what a typical wear is, but I wasn't too worried with 0.030" neither was the Wartsila Tech. I suppose .020" might be better though. I believe there is a rule of thumb, but can't remember it right this minute - 1 millimeter for every 100 millimeter of shaft diameter or something like that.

You can check out http://www.bv-industrie.de/brochures/ for more info on stern tube seals and bush, although I did not find anything on your specific question.

Hope that helps,
Attachments
2009.02-William J Moore-Ile aux Coudres.ml.110.jpg
Tail shaft bushing with 0.030" clearance.
2009.02-William J Moore-Ile aux Coudres.ml.110.jpg (136.91 KiB) Viewed 7206 times
2009.02-William J Moore-Ile aux Coudres.ml.071.jpg
Tail shaft bushing with 0.064" clearance.
2009.02-William J Moore-Ile aux Coudres.ml.071.jpg (175.93 KiB) Viewed 7202 times
2009.02-William J Moore-Ile aux Coudres.ml.061.jpg
Stern tube sea side seal
2009.02-William J Moore-Ile aux Coudres.ml.061.jpg (133.28 KiB) Viewed 7194 times
Martin Leduc
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ngineer
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Re: 3rd class GK question

Postby ngineer » Tue Mar 03, 2009 6:47 am

Thanks for the info, that will be of great help!

Cheers

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Madzng
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Re: 3rd class GK question

Postby Madzng » Tue Mar 03, 2009 8:59 am

The poker gauge is the best way to measure the wear down, as this can be done with the vessel in the water, in a matter or hours.

Just remember to check if the washer was taken out for the first readings (it should of been), or you could give the super a heart attack. Remember it is not so much the actual measurement that is important, but the change from original/last reading taken.

Jacking the shaft up sounds a bit heavy handed, was done in the hope that it would not have to be opened up whilst in the dock?

Once the ship is out of the water with the seal and liner removed you can simply use a set of feeler gauges to take the clearance.

The actual bearing clearance will depend upon shaft diameter, lubrication type (oil/water) bearing material (white metal/synthetic or Lignum Vitae), and loading.

Dependant on the factors mentioned above and Class requirements the maximum bearing clearance will vary. Oil lubricated bearings will have a maximum recommended by the maker - controlled by design limitations, stress, alignment and loading.

Good luck

CapitalC
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Re: 3rd class GK question

Postby CapitalC » Sun Mar 22, 2009 3:58 pm

I know that it is answer 6-9 for this exam, is it a minimum of 60% for a pass?
And for a thirds standard when they simply ask to describe a component do they expect a sketch like you would for a 2nd class exam. Our would it say sketch and describe?

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JK
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Re: 3rd class GK question

Postby JK » Sun Mar 22, 2009 4:06 pm

It would be sketch and describe

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The Dieselduck
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A pic of a poker guage

Postby The Dieselduck » Sat Mar 28, 2009 11:50 am

Poker Guage.1.jpg
Poker Guage.1.jpg (58.45 KiB) Viewed 6991 times
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