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Replacement of stern tube and propeller shaft

In brief:- Back in May 2009 the stern gear of my narrowboat was replaced. On 2nd May 2011, I took my narrowboat in for blacking and asked for the stern tube packing to be redone as we were getting a lot of water ingress and using a lot of grease. I was advised that the stern gear was worn significantly and needed to be replaced again. Surely this is not normal. I have written to the boatyard that did the original stern tube replacement and they don't want to know. Do I have a case to persue the matter further?

Asked by: Richard Facer  | 12.07pm, Friday 20 May


WW says:

Mark Langley writes:
This is quite a difficult one to answer, unfortunately. Stern tube wear could be caused by misalignment of the engine (which could easily occur during the two-year period) or by damage to the prop (causing imbalance), or even by grit in the water working its way through the packing.
I presume that your tube is the conventional type, with rope packing, and a daily greaser. I would also presume that you are continuing to use the correct grease. It would be unusual for a stern tube to be significantly worn after 2 years, even with fairly heavy use.
Water freezing in the tube can also cause distortion, although this is fairly rare. Most damage comes from misalignment of the engine, or excessive fore-aft movement of the shaft- the latter is unlikely with modern engines.
When the stern gear was replaced, did the boatyard realign the engine, and use proper locking nuts? Are the engine mounts in good condition (i.e. is the engine still aligned properly). if flexible mounts are used, are they showing signs of degradation? Is there a flexible coupling fitted, and/or a thrust bearing- and if so, are these aligned properly or showing wear?
It is almost impossible for us to give legal advice- it does depend somewhat on what the original boat yard did, and how you have looked after the engine/drive train over the intermediate two years. I am, however, surprised by the "significant wear" of the sterntube, and it does suggest that something is not right- be it the alignment, or the (angular) fitting of the sterntube and components such as bushes.
If you have any more information, please let us know and perhaps other contributors might be able to help.

Richard Fairhurst  | 11.56AM, Tuesday 24 May


Readers say:

There are several factors that can cause a stern tube to wear so quick. Misalignment being the most common, Inside the inner gland where the packing is, there is a bearing, behind the packing, assuming this is where the wear is, in order for it to wear there must be friction ie the shaft is rubbing on the bearing a simple check would be to feel for heat around the gland,do this with the packing gland loose. This would indicate misalignment or worn or bent shaft. the best way to check alignment is to unbolt the shaft coupling from the gearbox and slide the shaft back about 1/8 of an inch. Note, alignment should always be checked with the boat in the water as they change shape on hard standing.
No lubrication, if its a grease fed tube with a non ferrous bearing is the grease getting into the bearing.
The ingress of water could mean the shaft is worn around where the packing lies this can be checked by removing the packing when out of the water, of coarse, and feeling for wear. this is caused by over tightening the packing or long term use, did they replace the shaft as well?
There should be no need to replace the whole stern tube the inner gland is removable but can be a bit of a nightmare to do.
The fact that the yard do not want to know about your problem would indicate they know where the fault lies. It would be worth your while and a little money to get the alignment checked by a independent body and have a written report done, to-do it properly they MUST split the couplings. I will put money and my reputation of fitting stern gear in many commercial and pleasure crafts of all sizes that the engine is not lined-up properly. Let me know how you get on.

Steven Miller  | 8.37PM, Friday 9 September

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