Stern Seal failure: Separating facts from hearsay

[jfkal]

I am trying to get to the bottom of this. So I am kindly asking for your contribution of FIRST HAND experience only. Did your boat or did you have been on a boat experiencing a so called catastrophic seal failure.

Definition of catastrophic: Fast water ingress which would result in sinking if left unattended for less than 24 hrs (approx).

Please indicate:
a, Type of seal in question: Stuffing box (make/model), Halyard Seal, Deep Sea Seal, PSS Seal, Volvo Seal, others.
b, Short description of failure
c, Action taken to stem water flow
d, Action under c, did prevent boat from sinking or boat actually sunk
e, If boat sunk please indicate whether at sea or at mooring/anchor/marina etc.

Many thanks for your help and I look forward to your contributions. I will gladly summarize the results and re-post them.

 

[jimking]

Two failures of PSS seals, one on my boat, one on a friend's.

On my boat I was in Las Palmas, Gran Canaria, on the day before setting off to cross the Atlantic. I started the engine and put the boat into gear. A loud clunk was heard. A few minutes later the bilge alarm went off. The two faces had stuck together. The bellows had partially come off the spigot and had a tear in it, luckily the bilge pump was able to cope with the water inflow. The bellows was re-fitted and the tear temporarily repaired with self-amalgamating tape. The seal was about 3 years old. I now always check the seal if the engine has not been used for a week and, depending on the length of time, I find that there is some stickiness between the faces. I am in Caribbean waters and wonder if the very quick growth in the waters contributes to the problem.

On my friend's boat, also in Caribbean waters, the boat had not been moved for a few months. He was cleaning the prop and rotated it. The bellows tore with a fast inflow of water, it was temporarily repaired with rescue tape. The bellows was about 10 years old.

I think that the water ingress was a lot slower on my boat as it is a Westerly Conway and the prop shaft exits the boat through a shaft log rather than having the P bracket arrangement.

In both cases the boats were hauled out for repair.

 

[The engineer]

Not a fun experience

Volvo type seal on extended rubber tube, control cable wraps around tube and rips it open. Solution wrapping stretched inner tube round the rupture to stop the rapid ingress.
face contact type seal that I cant' recall the make of (US) got a load of fishing line between the faces. I rescued the boat when the floorboards were floating and most things submerged!

 

[Porthandbuoy]

PSS seal. Carbon (?) face disintegrated. The engine, a Yanmar 1GM10, continued running until I stopped it just before air inlet was submerged. Vigorous pumping gained on the leak and we were able to do a bodge that got us to our destination.

The bodge: We gaffered the two faces together and removed the jubilee clips holding the bellows to the shaft. Waterpoof grease let the shaft spin without tearing up the rubber. It still leaked, but occasional pumping kept the level down.

This was the port engine in a cat which was bulkheaded off from the rest of the hull. We wouldn't have sunk but it was quite exciting at the time.

 

[Tranona]

Disappointing not more responses - which either suggests failure is not the issue that hearsay suggests - or maybe this is not a good time to poll on the subject.

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.

 

[jfkal]

Volvo type seal on extended rubber tube, control cable wraps around tube and rips it open. Solution wrapping stretched inner tube round the rupture to stop the rapid ingress.
face contact type seal that I cant' recall the make of (US) got a load of fishing line between the faces. I rescued the boat when the floorboards were floating and most things submerged!

On the second mishap. From where did the fishing line enter the seal (inside/outside) and how did you rescue the boat?

 

[penfold]

My old man had a Volvo seal come off the stern tube; the tube itself was GRP and had been damaged and bodged with a bit of PVC tubing by some cretin so there was no external sign of a problem. It occurred in the Dorus Mor, which was quite exciting. Fortunately the leak was spotted as the water came over the floorboards, and the prophylactic action of grabbing the seal(gearbox in neutral), pushing it back into position and holding it in place solved the problem long enough to get back to Ardfern.

There was no problem with the seal itself, although it was replaced with a new one when the tube had been repaired properly.

 

[Robin]

Disappointing not more responses - which either suggests failure is not the issue that hearsay suggests - or maybe this is not a good time to poll on the subject.

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.

Our last boat did 10,000 miles on a DeepSea seal before we bought it and immediately replaced it because the bellows was starting to split. The same happened in just 2,000 miles with the Deepsea replacement. We then switched to a PSS seal that was completely drip and fault free for over 18,000 miles.

I suspect 'sticking' of face seals can be avoided if the seal faces are kept lubricated with water, as is the case with the water injected ones. In our case the UK PSS dealer told me that the best option was to install the water injected version but instead of feeding it with pumped water (as required for a high speed application) take the tube well up above the waterline as a continuous air bleed. This would keep a small head of water always above the PSS faces and keep them lubricated, plus it removes any need to 'burp' air from the seal after a long period dried out ashore.


I would be very happy to use a PSS seal again. Our boat is sold and we are looking at USA trawler yachts to live on, most of which have the PSS seals and I am entirely happy with that.

 

[vyv_cox]

Disappointing not more responses - which either suggests failure is not the issue that hearsay suggests - or maybe this is not a good time to poll on the subject.

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.

Earlier PSS seals did not have the vent that current ones do, and therefore required 'burping' as Volvos do to this day. I understand that unburped Volvos make a good deal of noise that would alert the user if he failed to do it. PSS seals will not do this, so total failure could occur unnoticed.

Current PSS seals have no burping requirement and if installed correctly will run unattended for very long periods.

Photos of all types under 'stern glands' on my website.

 

[Poignard]

I have an old fashioned stuffing box type so have had no catastrophic failures, but a friend of mine with a similar boat set off for France from Gosport and his patent seal failed after a few miles and he had to race back for an emergency crane out.

Another, often overlooked, advantage of the stuffing box is that your on-board spares kit only consists of a foot or so of packing. Very cheap and available anywhere in the world.

 

[Tranona]

Earlier PSS seals did not have the vent that current ones do, and therefore required 'burping' as Volvos do to this day. I understand that unburped Volvos make a good deal of noise that would alert the user if he failed to do it. PSS seals will not do this, so total failure could occur unnoticed.

Current PSS seals have no burping requirement and if installed correctly will run unattended for very long periods.

Photos of all types under 'stern glands' on my website.

There is a variation on the Volvo seal made in Italy with a vent, but I have not seen it here. You could also (if there is room) have a longer inboard tube end with a vent in there. The noise (which I have heard) is excruciating and is caused by the fluted rubber bearing running dry rather than the seals - although presumably if run for some time heat could damage the seals.

 

[Bosun Higgs]

Failure of a Volvo seal when I accidentally allowed a shirt to wrap itself round the shaft ( long story) which in turn dragged some electrical wire into the seal itself. The shirt and wire stopped the seal from sealing. Temporary cure during tow in by using duct tape. Once I had pulled the melted insulation and shirt out of the seal it looked undamaged but I replaced it anyway with another Volvo seal.

I have no doubt that there would have been the same problem with an old fashioned stuffing box

Had an earlier failure with a deep sea seal, one of the earliest versions of that design, and as a consequence would not consider one nowadays. In fact I gave away the new replacement seal that Deep Sea gave me rather than use it

 

[NormanS]

I don't see how a traditional packing gland / stuffing box could ever fail catastrophically. The dubious method of attaching any type of sealing system to the sterntube, with a bit of rubber hose, and jubilee clips, can easily lead to catastrophic failure.

 

[Bajansailor]

We had a failure here recently of a bellows on a yacht fitted with a PYI shaft seal - the Owner was fortunate that it happened in daylight hours, and the boat was observed to be sitting rather low in the water at her mooring. Quick action by the folk ashore who saw her sinking stopped her from going to the bottom.

I started a thread about it here - http://www.ybw.com/forums/showthread.php?t=265732

 

[vyv_cox]

I don't see how a traditional packing gland / stuffing box could ever fail catastrophically. The dubious method of attaching any type of sealing system to the sterntube, with a bit of rubber hose, and jubilee clips, can easily lead to catastrophic failure.

Yes. In refineries mechanical seals or a better system like dry gas seals are universal on every type of pump except one - fire pumps. The thinking is that a mechanical seal failure can conceivably prevent a pump from operating at all, whereas it doesn't matter if a packed gland is leaking like a sieve. Even when a packed gland is at its worst the majority of the water is still going down the fire main with little reduction in pressure.

 

[charles_reed]

Earlier PSS seals did not have the vent that current ones do, and therefore required 'burping' as Volvos do to this day. I understand that unburped Volvos make a good deal of noise that would alert the user if he failed to do it. PSS seals will not do this, so total failure could occur unnoticed.

Current PSS seals have no burping requirement and if installed correctly will run unattended for very long periods.

Photos of all types under 'stern glands' on my website.

Having had one of the PSS seals for nigh on 10 years now, I can assure you that, if un-cooled, it definitely makes a noise - a very loud squealing.

I have had the seal leak twice - both times after a rope wrap round the shaft, forcing the prop away from the boat and pulling the shaft part-ways out of the clamp. This movement forces the stainless rotor up the shaft and when the forward drive is re-engaged the shaft moves back into its clamp and the rotor no longer bears on the carbon block.

The leak can in no way be described as "catastrophic" - just a return to the commonplace drip of the stuffing box seal.

 

[Bosun Higgs]

Yes. In refineries mechanical seals or a better system like dry gas seals are universal on every type of pump except one - fire pumps. The thinking is that a mechanical seal failure can conceivably prevent a pump from operating at all, whereas it doesn't matter if a packed gland is leaking like a sieve. Even when a packed gland is at its worst the majority of the water is still going down the fire main with little reduction in pressure.

I once did the Tilbury tenerfire trip on a container ship of SAF lines. It was fitted with lip type seals on its two monstrous shafts. Seems to me that the only thing keeping old fashioned stuffing boxes going is conservatism. Bit like wooden boats really.

P.S. Bet your fire engine didnt have stuffing boxes on its shafts. Or its built in pumps.

 

[Bosun Higgs]

The dubious method of attaching any type of sealing system to the sterntube, with a bit of rubber hose, and jubilee clips, can easily lead to catastrophic failure.

How do you attach a stuffing box? I've only ever seen it done with hose.

 

[vyv_cox]

How do you attach a stuffing box? I've only ever seen it done with hose.

Lots of examples on my website. Problem is that if it isn't on hose some alternative flexibility needs to be built in, like a flexible coupling.

 

[PCUK]

Deep Sea Seal. Rev counter stopped working indicating no charge. Checked engine comp' and found foot of water. Seal had a bit of grit in it and had filled the bilge very fast. Pumped out, cleaned seal face and and pushed rotating part further down shaft to increase pressure. Always leaked after that until changed for Halyard seal.