Stern Gland Packing - help!!

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raro3

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I'm hoping for some advice. I've just returned to my boat (Frances 26) after 6 months during which time she has been in the water (in the tropics); prior to my departure everything was fine. On my return, she started immediately, and the engine was running smoothly. When I put her in gear, however, there was a bloody awful grinding noise both in forward and reverse. The prop is clean, and the gearbox has oil; there seems to be no play in the cutlass bearing. I think the cause may be the packing in the stern gland which may have dried out - is this possible? There was no water at all in the bilge even after 6 months, but I used to get a significant drip from the shaft where the prop was turning, and it appears that this is still the case (although I didn't want to run it for long). I believe the packing was last changed when the engine was overhauled about 18 months ago. Assuming I have to change the packing, can this be done whilst she's in the water? (I'm miles from any haul-out facility). I'm very concerned about the volume of water which will come in when I remove the packing nut (the stuffing box is the type with one big packing nut and locking nut), always assuming I can get it undone - the nut is 56mm and there's not a lot of room to wield a spanner. Any suggestions to mitigate the flow of water, and on the job itself would be appreciated (I do have Nigel Calder's book). I also need advice on the packing material itself - the prop shaft is 1 inch diameter: any suggestions? Thanks for any help.
 
The packing is what stops the water coming in the boat. So if you remove it you are relying on the constriction of the outer bearing to restrict the water flow. I wouldn't do it but I'm sure that someone posted a while back that they had done it! It just seems to me that there is no plan B. You are hanging upside down working in a restricted space. You have to rake out all the old stuff and carefully replace it. You won't know the water flow until its out and then getting it back quickly if there is a deluge is pretty unlikely. When replacing the packing, any pressure from the water trying to get in isn' going to help do a good job.

On the grinding noise. Have you looked at in action. I would not have expected a grinding noise - rumble, vibration yes After all it's just a polished metal shaft spinning in dry and presumably shrunk packing - are you grease or water lubricated? How about squeezing a lot of grease in there - as much as you can turn every day for a week and then tightening the shaft nut? If water lubricated, is it getting through?
 
You may have marine growth in the flutes of the cutless bearing or further inside the stern tube.- whatever version of barnacles grow in your ocean.
It could be a rusty bearing inside the gearbox, but I think thats less likely.
If too much water comes in when you open the packing gland, run some plastic and insulation tape, or cling film or similar round the outer part of the stern tube and propshaft to slow down the flow. There may also be a water connection inside to the sterntube from the engine cooling.
If you remove the first couple of turns of packing, it should feel reasonably soft and greasy, able to be straightened without cracking. Remember to stagger the ends when you replace each turn.
 
raro3 said:
. Any suggestions to mitigate the flow of water, and on the job itself would be appreciated (I do have Nigel Calder's book). I also need advice on the packing material itself - the prop shaft is 1 inch diameter: any suggestions? Thanks for any help.
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Under normal circumstances you would not get a grinding noise from your stern gland unless the whole assembly is dry . you say that not a drop has come in but you do not say if youu have a grease lubricator.

It is remotely possible that the gland assembly is dry and that gases have built up in the water so creating a waterless area behind the packing which would normally be water lubricated.

The best way to sort this is to either pump in a fair amount of grease into the gland space using the lubricator which is standard on most boats or to slacken the gland nut to a position where the air bleeds out and water is able to reach the places it needs too. Then re tighten till there is just a drip.

Folk often add a turn of packing while afloat however you are trying to do more. I would not advise trying to repack afloat unless you have good access to the gland and have several turns of packing of the RIGHT size pre cut to fit.
 
Thanks for the useful replies. I should have mentioned, the shaft is water-lubricated, there is no grease pump. Most comments confirm my concerns about the idea of removing the packing and the risk of flooding. Expanding on one of the ideas, what do you think if I put a heavy duty plastic bag over the prop and secure it tightly around the shaft log with gaffer tape or string?
 
Think it highly unlikely that it is dry packing. I think you have a Vetus stern tube which has "ears" covering the water inlet to the tube at the outer end. It is quite possible for these inlets to get blocked with marine growth as well as growth in the cutless bearing. First job is to dive and check this area. As already mentioned you can also check if water is getting in by undoing the lock nut. Water will not rush in , but flow will increase as you take pressure off the packing. You may also be able to see how much grease there is in the bearing.

You may also have something wrapped around the shaft between the prop and the bearing housing.
 
tillergirl said:
The packing is what stops the water coming in the boat. So if you remove it you are relying on the constriction of the outer bearing to restrict the water flow. I wouldn't do it but I'm sure that someone posted a while back that they had done it! It just seems to me that there is no plan B. You are hanging upside down working in a restricted space. You have to rake out all the old stuff and carefully replace it. You won't know the water flow until its out and then getting it back quickly if there is a deluge is pretty unlikely. When replacing the packing, any pressure from the water trying to get in isn' going to help do a good job.

On the grinding noise. Have you looked at in action. I would not have expected a grinding noise - rumble, vibration yes After all it's just a polished metal shaft spinning in dry and presumably shrunk packing - are you grease or water lubricated? How about squeezing a lot of grease in there - as much as you can turn every day for a week and then tightening the shaft nut? If water lubricated, is it getting through?
Click to expand...


I have changed my stern gland packing when afloat, and it was completely non-dramatic, in my experience no different from doing it out the water. I first squeezed a big quantity of greese into the gland to try to force it down into the cutless bearning and around the shaft. Not a drop of water came out. I certainly wouldn't want to have paid/gone through the hassle of a haul out just to do that, when it was just a ten minute job costing a fiver for the new packing.

However, I tend to agree that a grinding noise doesn't sound like a stern gland packing problem. I'd be thinking grinding means metal on metal, eg if the engine has (somehow??) moved on its mounts. Disconnecting the shaft from the gearbox (as already suggested) would certainly be pretty high on the list of things I'd try (well above the stern gland packing)
 
How about a build up of barnacles on the shaft rubbing against the stern tube? Try turning the shaft by hand with the the engine off and out of gear. Have a listen where the grinding is coming from.
 
Sterngland

Are you in tidal waters? If so can you dry out enough to inspect/repair without leakage into the boat. Have you looked at the engine bearers? Has anyone had access to your boat whilst you have been away, perhaps they could shed some light on the situation.
 
I doubt if it's the packing that's making the noise. I wonder if before you left the boat for six months, you pumped an excessive amount of grease in, and it has caused the rubber in the Cutless to expand, and fire onto the shaft.
Your idea of the plastic bag round the prop and taped to the ouside of the sterntube would let you safely remove the packing to check it. It wouldn't let you try turning the shaft, while the packing was out, though.
 
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