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Narrowboat Magazine

Q & A

Narrowboat Stern Tube Packing

As the stern tube packing wears away it is possible to insert another piece of square section rope after removing the flange. This seems simpler and dryer than removing all the old packing and replacing it. What are the pros and cons of the two approaches?

Asked by: Colin Wilks  | 8.19am, Thursday 20 November


WW says:

The pros of doing it your way are that it is easier.

The pros of doing it the other way are that you can sleep at night.

Graham Booth  | 9.59AM, Tuesday 25 November

Well, if you want to repack, then I would consider having a look at

http://www.tb-training.co.uk/10sgear.htm#bmn31

This is part of Tony Brooks Training notes- he covers this in his courses and they are very useful. However, if you are technically minded at all, they are not difficult to follow.

Am not quite sure I like the idea of packing something around the aft end of the shaft while replacing the gland packing. Water does come into the boat, but if you have everything prepared (such as the new packing prewound onto the shaft) it shouldn't be too much trouble, that a good bilge pump can't shift!

If you keep on ramming packing in, the old stuff often hardens, which may mean that you have to disassemble the whole gland when the boat comes out of the water. In the worst case, it might cause localised heating, scoring and damage to the shaft and/or bearing surfaces.

As Graham points out, doing it properly does allow you to sleep better!

Mark Langley  | 1.29PM, Wednesday 26 November


Readers say:

Graham appears to think that inserting a further piece when space allows (which is not my way by way, just one of two approaches I've been recommended) is cause for serious concern, although he doesn't explain why.

Clearly safety is paramount, but I'd like to make an informed choice.

Is it safer to try to replace all the packing with the boat still in the water or to add additional pieces until the time comes for the boat to come out of the water for re-blacking?

I have been told that a sausage of plasticine or similar goo which is wrapped in cling film and then squished in around the external prop shaft is a reasonable method by which to make the stern gland watertight temporarily, whilst the old packing is hoiked out and replaced.

I'm new to boating and there seem to be as many opinions about things afloat as there are boaters! I was hoping for a wise explanation from the grey beards at WW, rather than just another opinion.

Colin Wilks  | 5.48PM, Tuesday 25 November

I'm assuming here that you have already read Tony Brooks very informative web pages.

So much will depend upon the present condition of the propshaft in way of the gland; if the propshaft is worn badly, or badly scored, even new packing will have a much shortened life and leakage will soon reoccur.

The same problem will also occur if the stern bearing is worn as the propshaft will move radially when rotating which will result in further wear of the metal parts of the gland to the point where the gland itself will require eventual replacement.

Hardened packing, especially if further compressed, *will* cause wear on any propshaft and adding additional packing to 'cure' leakage should only ever be considered as an emergency stop-gap procedure.

Scoring and/or pickup on the shaft will quickly tear new packing; this will often result in uneven compression around the shaft and localised hotspots that can further damage the shaft, or cause a small shaft to be displaced radially, and the shaft ought to be withdrawn and either repaired by metal spraying, or replaced.

To return to the question, a gland in good condition should not allow much water to leak past whilst you are replacing the packing. Any water which does enter the hull should be contained in the engine spaces but, if considering pumping this over the side, make certain that the bilge is not full of oil first!

If this is not possible then collect the water in some form of container and ask yourself why there isn't already a dam built six inches forward of the gland to collect any drips.

Excluding preparation, the job should not take very long at all once the old packing is removed; in any case, leakage will quickly be reduced once the first packing ring is place and don't forget to count the number of rings you are removing!

A few hints:

# Pull out the old packing with a blunted tool (to prevent damaging the shaft), if you have the access available then an old bottle opener is useful, or get hold of a hooked dental 'pick' from your local tool store; if you are handy then you can even make your own from a metal coathanger - I'm not so sure about Tony's 'screw' suggestion as it can, especially in inexperienced hands, damage the shaft.

# Always prepare the new packing before removing the old and test the fit on a clean length shaft in front of the gland.

# Use individual rings with a scarfed (ie diagonal) joint and use a *very* sharp knife to cut these cleanly.

# Fit the rings with the first joint at 12 o'clock, then at 6 o'clock, 12 o'clock, etc.

# Use the compression part of the gland to carefully move each ring back into the gland as you fit them, use hand pressure only until the gland is fully packed.

# When the last piece of packing is installed then fit the nuts and washers and gently tighten them down, equally on each side of the gland, until the gland has been nipped up.

# Test the result alongside by running the engine in gear, ahead and astern. The gland needs to be just tight enough not to leak more than a, very occasional, drip but not tight enough to become hot ('warm', on a decent run, is fine).

# Check your work during the first few hours running; you may need to re-tighten the gland a little as the packing settles down.

# Finally, remember to grease the bearing - but not too much as forcing grease into the packing will prevent it from doing its job properly!

middledogwatch  | 3.29PM, Saturday 29 November

Many thanks to all for the advice and explanations. It all makes sense now and I shall be replacing all the old packing, with the boat still in the water, when I am half an inch away from running out of room to nip up the gland's pusher any further.

Colin Wilks  | 6.45PM, Monday 1 December

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