Bit of a leak at the back
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