Stuffing box packing replacement

[StephenW]

I have a traditional stuffing box without greaser and have been replacing it each year when it's laid-up. Am I overdoing it and can it be left in for several seasons?

The arrangement, whilst very simple, seems very reliable and I make sure the engine is aligned and that there is a drip every 30 seconds or so to ensure lubrication as advised. I need to adjust every 25 hours or so and access is very easy to achieve this.

The boat originally had a greaser but this was removed and relpaced by a water feed when an onboard cutless bearing was discovered behing the stuffing box arrangement (cutless bearings need water, not grease, lubrication).

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[brianhumber]

From your description it sounds as if you have a stern tube bearing and shaft seal arrangement similar to what ships in the early 60s were fitted with, ie a water lubricated rubber bearing with a packing stuffing box. The water to cool the bearing was introduced in between the bearing and packing box and I am assuming yours is the same.
As long as you do not wind lots of grease into the stuffing box such that it carries through and blocks the bearing cooling passages with grease, I cannot see why you should not have a greaser on the stuffing box or why the turns of packing need to be replaced every year.
Has brought back memories of being sent to reduce the water pouring through the packing as a Young Engineerand getting totally soaked. This was a Lignum Vitae wooden bearing ship. I can also remember being in Hamburg drydock looking at the drawn tailshaft and bearing and being amazed the rubber could stand the weight of a single screw 19,000t ships shaft without wearing out in a few weeks as well as planning that nights excursion ashore. Happy days

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[StephenW]

Just to clarify, the original arrangement, that has since been modified, WAS propshaft running through a) cutles bearing, b) stern tube assembly with central greaser hole (squirting grease both through striations in cutless and towards packing material) and c) packing material held down in compression around shaft by brass ring assembly.

NEW arrangement is a) cutless bearing, b) central stern tube assembly with old greaer hole now providing water lubrication from tube connected to new water scoop skin fitting and c) traditional packing material with usual (PTFE?) lubricant impregnation and held down by compression ring.

Doi you have any idea whether the packing be good for more than one season(without greaser)?

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[tillergirl]

I have the same arrangement and have not touched the packing for a number of years probably five years. I was intending to have a look at the shaft next spring when I come out of the mud-berth which will be too late for you. But I have no signs of failure. Like you I have no opportunity to grease the packing as the water feed goes in where the traditional grease connection would be. I opten wonder just how much water goes down there!

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[brianhumber]

Packing as you would expect is made of different materials for different applications and shaft speeds. Older packing was a mix of hemp, asbestos and graphite grease but PTFE is used more and more these days for shafts with water and I would expect with an unworn shaft for the packing to last 5+ years dependant on how many hours usage. (We only used to repack a good shaft every drydock on pumps in use 24hours/day) Worn shafts would need more frequent attention but this is caused by over enthusatic tightening of the packing nuts to stop all water. The packing then becomes hot and tears itself amd wears ridges in the shaft.
You have been allowing a drop per minute so this should not have happened.


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[StephenW]

OK, thanks Brian, thats the guidance I was after. PTFE is what was used for the last packing material. The shaft was renewed last year so there should be no wear in it.

The shaft has a flexible Vetus coupling on and originally this created a bit of uncertainty about the most effective way to ensure engine alignment, but the easiest way seems to be to undo the four coupling bolts a tad and then use a feeler guage to check that the gap is uniform all round when the shaft is rotated. Thanks for your help.

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