Bit of a leak at the back

Canal Boat - - Back Cabin -

QI have a leak from the prop­shaft/ stern gland on my boat. Some­one has told me one piece screws into the other and it must have come a lit­tle loose and that’s why it is leak­ing.

What I need to know is which bit screws into which and can I do this with­out tak­ing the boat out of the wa­ter. Also, how do I tighten it (which tool)?

DEREK THOMP­SON, via email

ATONY REPLIES... In the pic­ture, A is the stern gland as­sem­bly and pre­vented from turn­ing by the two bolts hold­ing it onto the trans­verse plate welded to the hull. This has a fe­male thread at the stern tube end; B is the stern tube proper and it is male threaded on both ends; C is a fe­male-threaded steel boss welded into the hull.

The stern tube might or might not have a bear­ing in­side it and if it does they are some­times se­cured in place by a hole in the tube, es­pe­cially if the bear­ing is a white metal. Some­times, as the bear­ing wears, the metal in the hole be­comes loose so it leaks.

The first thing to do is to dou­ble check that this is not what is hap­pen­ing. If it is, then wrap a piece of sheet “rub­ber” around the tube and se­cure with a worm drive hose clip. That will stop such a leak un­til you can get the boat out of the wa­ter for new parts to be fit­ted.

You can get leaks from the thread at ei­ther end of the stern tube but it is not nor­mally a sim­ple case of tight­en­ing it. If you do, then the whole gland as­sem­bly will need to turn and it will not then line up with the holes in the steel plate. If the holes in the gland are still on the plate, you could drill an­other set of holes to se­cure the gland. When this sort of leak hap­pens it is of­ten the case that the sealer used when assem­bling the stern tube has failed or that it has suf­fered a shock that dam­aged the sealer. To rec­tify such leaks, you need to fully un­screw the leak­ing parts, clean the threads, seal and re-tighten.

You might even have to source a large cop­per washer that fits around the shaft but into the fe­male thread so, when the gland as­sem­bly is tight­ened onto the tube, the cop­per washer takes up some slack. I have seen or­di­nary and gas PTFE tape rec­om­mended or var­i­ous pipe joint seal­ers. I would not use Boss­white and hemp though.

The stern gland

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