Stern Seal failure: Separating facts from hearsay

[Tranona]

We have had tales of the Volvo seal splitting in the way of the rear clamp. One chap said it fell into pieces with radial splits and flooded his boat. There is a report of this type of split nearby at the moment. Perhaps the lip seals jam and put unfair stress on the rear of the unit? They should be changed every 500 hours.

Difficult to imagine how it could split there. The rubber wall is about 6mm thick and fully clamped over the whole surface. In front of that is a 50mm or so water lubricated rubber bush running on the shaft. Equally can't imagine how the lip seals would "jam" to the point of putting stress on the rubber housing.

Perhaps you can get photographic evidence of the split one "nearby" to share with us?

As to life - the one sitting in my garage spent 14 years in my boat and is in perfect (visual) condition. Volvo suggest 5 years replacement, but I have seen charter boats with several thousand hours on them still with the original seal.

 

[prv]

Failure of the bellows is similar to failure of the hose in a stuffing box design.

Of course, as mentioned upthread, a "proper" stuffing box doesn't have a rubber hose.

Needs either a solidly mounted engine (vibration) or an Aquadrive type coupling (expensive) to achieve though.

Pete

 

[Tranona]

Of course, as mentioned upthread, a "proper" stuffing box doesn't have a rubber hose.

Needs either a solidly mounted engine (vibration) or an Aquadrive type coupling (expensive) to achieve though.

Pete

Not necessarily. A good flexible coupling like the one on my boat as pictured on Vyv's website will work. Although I have a Volvo seal, the inboard housing has a bearing so the shaft is fixed and a conventional stuffing box could be fitted as that is what it had originally.

 

[doug748]

Difficult to imagine how it could split there......
Perhaps you can get photographic evidence of the split one "nearby" to share with us?
.....

Sorry I don't keep a scrapbook I only read the stuff thats posted.

here is what Chris Robb wrote last year:

"Volvo Shaft Seal - Life span

I Tried to do a search on this, but no luck - sure its been discussed before.

The Manual says change every 500 hours. I have done 500 hours this year alone - greased every 100 hours. Since I have had the boat it has done 1000 hours. I don't know how old it is, but the previous owner left all the servicing to Volspec so they probably had changed it at some point.

Its not showing any sings of dripping or wear, It runs just warm to touch, and seems to need burping on a regular basis as air always comes out from it."

and Martin J:

"What was surprising was that although mine looked perfectly sound after about seven years use.... there was quite a deep crack around about a third of the circumference... just forward of where the jubilee clips were.... The crack was just visible when trying to flex the seal by hand in every direction.. but once removed was very very visible.

Maybe not so easy to describe.. I'll take a picture later.. Very difficult to find the split as well when installed but once I knew it was there it was so obvious."

Perhaps he has his photo?

 

[Robin]

Of course, as mentioned upthread, a "proper" stuffing box doesn't have a rubber hose.

Needs either a solidly mounted engine (vibration) or an Aquadrive type coupling (expensive) to achieve though.

Pete

I had one like that on one of my first boats and my teeth have still not recovered from the vibration! Every boat since had the stuffing box fitted into a flexible hose.

 

[Tranona]

"What was surprising was that although mine looked perfectly sound after about seven years use.... there was quite a deep crack around about a third of the circumference... just forward of where the jubilee clips were.... The crack was just visible when trying to flex the seal by hand in every direction.. but once removed was very very visible.

Maybe not so easy to describe.. I'll take a picture later.. Very difficult to find the split as well when installed but once I knew it was there it was so obvious."

That does sound possible because that is the point at which it flexes, being fully supported by the stern tube aft (assuming the stern tube is long enough to come right up to the end of the clamp) and by the shaft forward. Even then there is a bulge immediately forward of the clamp to reinforce that area. It may well be that the tube was not long enough. The clamp is not a jubilee clip as standard but a single length clamp with two clamping screws.

BTW no trying to defend the Volvo seal over others - just that often when you really get into a failure you find the cause is nothing to do with the design or manufacture but improper fitting or lack of maintenance - as demosntrated by many of the examples quoted in this thread.

 

[yodave]

Apologies: I don't want to hijack, but given the experience availble in this thread may I ask for advice on the risk of a catastrophic failure please?

We recently picked up our new boat. It had around 100 hours on the replacement Lombardini engine. On the day we were leaving the Netherlands [nice timing] the broker told me that the stern gland leaks when the engine is running, and I'd need to pump the bilges every two or three hours. In the end, we had to run the engine for four 24 hour days to get back home, and pumping the bilges seemed to do the trick. There has been no further leaking since we popped her on her [drying] mooring.

I don't know the make of gland/seal. The broker reckoned that I'd need to replace the 'rings' at the end of the season.

So the question is: is it safe to wait, or should I panic?

 

[prv]

I don't know the make of gland/seal. The broker reckoned that I'd need to replace the 'rings' at the end of the season.

So the question is: is it safe to wait, or should I panic?

Hard to definitively identify the item from what you say (got a picture?) but my money's on it being a conventional stuffing gland. (Mention of leakage being considered normal and seasonal replacement of "rings" ie packing.)

I wouldn't panic. Depending on how quick the water comes in (can you count the speed of the drips?) I'd look at tightening the gland (without making it so tight it gets HOT, slightly warm is ok) or adding a little more grease if it has the facility to do so (usually by turning a screw to force more in). If the water doesn't inconvenience you (pumping's not onerous and your bilge is deep enough to contain it) then maybe not do anything at all for now.

Pete

 

[Bosun Higgs]

there is no simple answer yodave. Whilstever the seal doesnt leak on the mooring and only leaks the same amount in use, then it sounds as if you can wait for a suitable time to lift out the boat and cure the problem. If the seal has "rings" then it sounds like the conventional stuffing box and not only do they all leak in use but they are meant to do so. But just a drip or two per minute which is a lot less than yours sounds to be doing.

Personally I would hoik the boat out and mend the gland right now, but then I am picky. I dont think there should be anything in your bilges but dust.

 

[vyv_cox]

Yodave: I suggest you have a look at the various types shown on my website at http://coxengineering.co.uk/Sternglands.aspx If yours is a packed gland type it probably only needs to be taken up a little, not unlikely after re-engining. Instructions are on the site and there is a link to another with detailed instructions for a variety of packed gland designs. If it is something else then I suggest you ask for further advice.

 

[yodave]

Thanks prv, Bosun Higgs, & vyv cox.

Not sure I'd put too much weight on the brokers input. He initially told me that the gland only needed burping and then tightening, but our hired Dutch skipper couldn't see any way of tightening it.

Then later the broker said that the 'rings' / 'seals' would need replaced. Please keep in mine that his first language wasn't English, so I'm not putting too much faith on the terms he used.

Umm... I don't want to pollute this thread any more and risk upsetting jfkal, so I'll take some photos over the next couple of days, compare those with vyv cox's website info, and possibly start a new thread. If I start a new thread, I'll return here and add a link just in case anyone wants to follow.

Thanks again

- - -

Here's the link to the new post:

http://www.ybw.com/forums/showthread.php?p=2943899#post2943899

 

[prv]

Not sure I'd put too much weight on the brokers input. He initially told me that the gland only needed burping and then tightening, but our hired Dutch skipper couldn't see any way of tightening it.

Then later the broker said that the 'rings' / 'seals' would need replaced. Please keep in mine that his first language wasn't English, so I'm not putting too much faith on the terms he used.

With all this, I retract my suggestion of a stuffing gland without too much wrong with it. Could be anything, and while it could be fine it's definitely worth further investigation. Post a photo or two here once you've taken them.

Pete

 

[yodave]

As promised: here's the link to the post specifically related to my stern gland:

http://www.ybw.com/forums/showthread.php?p=2943899#post2943899

Anyone who's interested will find photos in the link on the first post.

Thanks

 

[Ubergeekian]

However, what reports you have confirms my own (mostly secondhand or observation) experience - that face seals and rubber bellows are perhaps not good ideas in this application.

I get the impression that intermittent use is the problem - maybe not surprising for systems which depend on water as a lubricant and can dry out between uses.

When I got Jumblie the conventional stuffing box was in a bit of a state. I asked here if a modern alternative was worthwhile and was advised against it. That seems to have been good advice. One drop of seawater every twenty seconds seems a small price to pay for reliability and longevity.

 

[doug748]

I get the impression that intermittent use is the problem - maybe not surprising for systems which depend on water as a lubricant and can dry out between uses........

I read this as well, a few years ago.

As my stern gland was of the face type in question I have attempted to dry it out over the winters ashore and to make the faces sticky. No luck so far.

I would guess that lip seals would retain even more moisture.

 

[lukecsmith]

My stern gland hose split recently. I was away from the boat for a couple of weeks and on returning found a couple of feet of water inside. Once dried out the damage to the stern gland hose was obvious. It had split next to the jubilee clip and water could just poor straight through. I have to admit though - I didnt know what a stern gland was until it bit me on the arse. My boat is an old 30ft half-tonner and Ive been slowly working on her over the past year or two with no previous knowledge of owning a boat, nor friends/family with boats. In fact most of my learning has been done via books and the internet, and through this forum.

So I'd replaced the obvious things, like sea cocks and connections, but I just wasnt aware of stern glands and how they need to be maintained - til it was too late. It was rather a setback to my work inside - particularly to wiring, which has had to be replaced everywhere that was underwater, so engine-battery connections, etc. Luckily I'd taken my lovely new upholstery off the boat, so that wasnt damaged, and my shiny new starter motor had not yet been fitted. And its all good as new now and a new PSS shaft seal is on the way.

Theres an image of the old stern gland that Vyv cox has put up on his fine site : http://coxengineering.co.uk/Sternglands.aspx . Its the third photo down under the heading 'problems with packed stern glands'. The rip was just on the underside of the hose in the picture, about an inch long. As Vyv says, its not a proper stern gland setup really - theres the packing nut / lock not apparatus and stuffing inside, but its all covered in a basic rubber hose, probably a piece of exhaust hose or similar. An accident waiting to happen really. Lucky I wasnt out at sea and it split more thoroughly. With my kids on board. Etc. Phew!

 

[doug748]

My stern gland hose split recently.....


There but for the grace of God.

Mine was iffy for many years but I got away with it, hope you have better luck with the new kit.

 

[Tranona]

I read this as well, a few years ago.

As my stern gland was of the face type in question I have attempted to dry it out over the winters ashore and to make the faces sticky. No luck so far.

I would guess that lip seals would retain even more moisture.

Unfortumately it won't show up on a photo as the thing is like a black hole, but the Volvo seal I removed from my boat has - looking from the end nearest the engine. Grease, lip seal, grease, lip seal - then the water the aft side of the second seal. There is no apparent wear or damage on these seals and they are still covered with greas except the aft face of the second seal. Aft of this is a fluted rubber bearing which has no grease (can't get past the seals). This is the bit that needs the water, just like a cutless bearing - indeed very similar to the Stuart Turner stern bearing. That is also the bit that makes the noise if you do not expell the air.

Think it is the the rubber bearing supporting the shaft that ensures there is little load on the seals and all they have to do is keep the water out.

On the face sticking issue, it may well be connected with water quality as in some waters there is a lot of calcium like deposits that build up during periods of inactivity. I have seen cutless bearings seized up because the flutes are full of deposits. Only a theory, but one of the problems with failures like this is that they are small in number and poorly reported so difficult to get enough data to draw any reliable conclusions.

 

[snooks]

a, Volvo Seal IIRC
b, Split during the 2001 Fastnet, off Portland
c, Wrapped sail ties around it and finished the race
d, Water ingress stopped
e, NA

 

[jfkal]

Storm in a tea cup

I now have summarized all the information given and here are the results from the submitted responses:

1. None of the boats was sinking
2. All could manage (as expected) to control the, whatever, water ingress
3. All reported cases are either caused by:
a, Carelessness (ie T-Shirt wrapped around shaft)
b, Neglect
c, External factors (ie rope around prop)
d, Installation errors

Verdict: If installed properly, kept clear of T-Shirts and such, inspected once in a blue moon a mechanical seal is safe, reliable and drip free.

Happy motoring.