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Q & A

Size of Stern Gland Packing

1. How do I determine the size of stern gland packing. The shaft on my narrowboat is 30 mm dia. but the gland does not appear to have any marking to indicate size of packing required. Apart from taking off the for'd cover and measuring the clearance how do I know which size packing to purchase?
2. Is it necessary to cut the new packing into circles before fitting, rather than fitting in 1 piece in a spiral, which might provide a better seal.

Asked by: Peter McLaren  | 12.23pm, Tuesday 17 November

WW says:

Unfortunately the only way to be sure of the packing size is to remove the compression piece and measure the gap between the shaft and the inner face of the stern gland. Very little water will leak into the boat while the gland is apart, unless it is severely worn. There are packs containing three common sizes of stern gland packing available for this very reason.
It is best to cut the packing into circles and position the joints such that they are not coincident. If the packing is fitted as a spiral, the voids at each end and the angle cause the distortion of the packing when the compression piece is tightened. It will thus be more likely to leak.

Rupert Smedley  | 2.48PM, Tuesday 17 November

Also, when repacking, it is sometimes worth removing the old packing- though you might need to use an improvised "hook" to pull it out- if you add more packing onto old, the packing towards the aft bearing can become hardened, which can score the shaft and lead to issues.
It is possible to replace the packing while afloat, though having the packing pre-cut can be very useful, as well as a full battery to run the bilge pump!
When replacing the packing, do not overtighten the gland facing, as you don't want to over compress the packing- when running, you need at least one drip every second to enable cooling of the bearing- too tight and it will run hot- though you will need to retighten slightly the gland after the first few hours cruising.

Mark Langley  | 4.09PM, Tuesday 17 November

Readers say:

Many thanks. Peter

Peter McLaren  | 3.05PM, Tuesday 17 November

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