Stuffing box or dripless shaft seals?

[malbert73]

I have a tides dripless. Lip seal gives 100s and 100s of hours. Much less complex than PSS. Can keep spare seal on shaft waiting for use

[NorthernMac]

Originally Posted by mvweebles

After 25-years, I'm going from a traditional stuffing box to a PSS. I totally understand the arguments for a traditional stuffing box, and I've used most of the modern materials. I seem to be constantly checking and sooner or later, even with a Tupperware container as a sump, my dream of a desiccated dry bilge is history.

I know the argument about catastrophic failure potential against PSS. I've even seen one and it was breathtaking to see how much water came in. The source was an the set screw on the pressure ring had backed off, likely due to improper installation. 5-mins later we were underway.

Of all the fretting about PSS failures, it's the only one I ha e first hand knowledge of. With all the proselytizing of simplicity and effectiveness of traditional stuffing boxes, the vast majority I've see are not adjusted properly. Can it be done? Sure. I've done it dozens of times. Will it stay that way without regular tweaking? Absolutely not. And oh-by-the-way, I have seen one traditional stuffing box fail, though not catastrophically - the bronze threads eventually dissolved. And I have seen a few scored shafts from improperly maintained studding boxes. That's a non-issue with PSS

I have no serious quarrel with traditional stuffing boxes. But they are far from perfect. Count me in the PSS camp these days.

Think it more a matter of not wanting a possible catastrophic failure while out to sea vs seeking perfection.

[CarlF]

I've heard of a few boats with longer shafts that had problems with shaft vibration when converted from the builder's spec stuffing box to dripless. The stuffing box had acted as another bearing for the shaft (assuming everything is well aligned).

[mvweebles]

Originally Posted by NorthernMac

Think it more a matter of not wanting a possible catastrophic failure while out to sea vs seeking perfection.

Discussion should differentiate between a catastrophic failure which involves destruction of a key part/component; and non-catastrophic failure which means the system can be restored underway or with an reasonable work-around.

Dripless systems have millions of hours of reliable operation. When they fail, the root cause is always because bellows lost compression because face-seal moved. This is alarming, but non-catastrphic (though admittedly, clock is ticking as bilge pumps likely won't keep up).

Classic probability/impact risk comparison. Given recommended maintenance in both instances:

• Dripless: probability of a catastrophic failure is extremely close to zero; but impact is extreme.
  Probability of a non-catastrophic failure defined as bellows losing compression due to face-seal moving is still very low and can be mitigated by placing a hose-clamp on the shaft

• Traditional: Probability of a catastrophic failure: effectively zero - it's extremely rare for a seized stuffing box to tear-off the connecting hose.
  Probability of non-catastrophic failure such as a scored shaft of a secondary issue masked by a wet bilge is medium, impact is low-medium; which can be mitigated with enhanced maintenance and vigilance.

Both systems need to be renewed periodically, though dripless probably needs renewal every 10-years vs traditional go 20+. For me, I see mitigating risk of catastrophic failure of a dripless system as "meteorite insurance." But that's a personal decision - we all define our own risk-profiles.

[LauraleeG]

Originally Posted by mvweebles

Discussion should differentiate between a catastrophic failure which involves destruction of a key part/component; and non-catastrophic failure which means the system can be restored underway or with an reasonable work-around.

Dripless systems have millions of hours of reliable operation. When they fail, the root cause is always because bellows lost compression because face-seal moved. This is alarming, but non-catastrphic (though admittedly, clock is ticking as bilge pumps likely won't keep up).

Classic probability/impact risk comparison. Given recommended maintenance in both instances:

• Dripless: probability of a catastrophic failure is extremely close to zero; but impact is extreme.
  Probability of a non-catastrophic failure defined as bellows losing compression due to face-seal moving is still very low and can be mitigated by placing a hose-clamp on the shaft

• Traditional: Probability of a catastrophic failure: effectively zero - it's extremely rare for a seized stuffing box to tear-off the connecting hose.
  Probability of non-catastrophic failure such as a scored shaft of a secondary issue masked by a wet bilge is medium, impact is low-medium; which can be mitigated with enhanced maintenance and vigilance.

Both systems need to be renewed periodically, though dripless probably needs renewal every 10-years vs traditional go 20+. For me, I see mitigating risk of catastrophic failure of a dripless system as "meteorite insurance." But that's a personal decision - we all define our own risk-profiles.

Great summary!!

[Greg K]

Originally Posted by mvweebles

...Dripless systems have millions of hours of reliable operation. When they fail, the root cause is always because bellows lost compression because face-seal moved...

No, not true. Another cause of failure is damage to the bellows itself. Friends on a steel boat were motoring in the Bahamas when a harness which was drying (near an engine side access open hatch) fell onto the shaft and ripped the rubber on the dripless stuffing box to shreds in seconds even though the engine was shut down immediately with no other damage. Very tough situation with serious water coming in in the middle of nowhere. They used cloths, tape etc... whatever they could get their hands on to minimize the water flow and had to sail back to Miami to get hauled pumping day and night. Could not use engine. Imagine that happening to you hundreds or thousands of miles from lift facilities

In fact, we had a similar mishap happen to us. A bilge blower hose got loose and fell on the shaft while we were under power. The sudden noise of the stainless steel wire bashing around was so great, I shut the engine down immediately. The hose wire was wrapped around the bronze stuffing box and the shaft and the box was leaking. I cleaned up the mess and examined the box for damage and, finding none, tightened it a half turn or so and we were on our way. Can you imagine what the consequences would have been if we had a dripless stuffing box?

Yes, engine access hatches should be closed underway, and bilge blower hose attachment points should be inspected frequently... but such accidents perhaps are more common than we think.

For that reason alone, I would never put a dripless stuffing box on a serious ocean going boat.

[LauraleeG]

Originally Posted by Greg K

No, not true. Another cause of failure is damage to the bellows itself. Friends on a steel boat were motoring in the Bahamas when a harness which was drying (near an engine side access open hatch) fell onto the shaft and ripped the rubber on the dripless stuffing box to shreds in seconds even though the engine was shut down immediately with no other damage. Very tough situation with serious water coming in in the middle of nowhere. They used cloths, tape etc... whatever they could get their hands on to minimize the water flow and had to sail back to Miami to get hauled pumping day and night. Could not use engine. Imagine that happening to you hundreds or thousands of miles from lift facilities

In fact, we had a similar mishap happen to us. A bilge blower hose got loose and fell on the shaft while we were under power. The sudden noise of the stainless steel wire bashing around was so great, I shut the engine down immediately. The hose wire was wrapped around the bronze stuffing box and the shaft and the box was leaking. I cleaned up the mess and examined the box for damage and, finding none, tightened it a half turn or so and we were on our way. Can you imagine what the consequences would have been if we had a dripless stuffing box?

Yes, engine access hatches should be closed underway, and bilge blower hose attachment points should be inspected frequently... but such accidents perhaps are more common than we think.

For that reason alone, I would never put a dripless stuffing box on a serious ocean going boat.

Yep, thats what happened to us. Water was pouring in and of course, as things do on a boat..the bilge pump also conked out. Joy joy. For four hours, one of us bailed, one of us sailed till we finally could get to port.
We got a new bilge pump and we changed that out, an mechanic then opened/compressed ( did something?) to the bellows so that we could continue our onward journey and get home. We had to make sure that the engine did not rev over 1200rpms to minimize taking on water. But since the new bilge pump could keep up with the intake, it wasnt as dire an emergency
I think we are going to go with the Volvo as people here seem to like it.

[mvweebles]

Decent article on dripless glands. Mentioned mechanical strike as a point of failure. Definitely something to think about.

https://www.passagemaker.com/technic...ss-shaft-seals

[sailorboy1]

Well one of those PSS seals almost sunk my boak when the bellows failed. It was pure luck that in middle of the week I decided to spend the night on the boat instead of going home that night from work. Lucky rescue tape wrapped around it stopped the leak.

So I'm totally aganist any shaft seal that is based on those bellows. We know they fail, which is why they are suppose to be replaced regularly, but of course that becomes a game of Russian Roulette.

There are seals that don't have the bellows and I went with a Next Gen II seal that has a "real" box hose and the seal is adjusted with a spring in the rotating half.

With that said that seal dripped for 3 years no matter what adjustment I tired. Then after an all night motor pounding it leaked more, but not too bad to cause a haul out. This went on for 2 years till 2 months before I was hauling out for bottom paint, when it ........................... just decided to stop leaking and hasn't now for 10 months.

I never am going to install another dripless seal again. I long gave up on the bone dry bilge so I don't really care if a packing box drips a little because it isn't likely to FAIL bad enough to sink the boat.

[LauraleeG]

Originally Posted by mvweebles

Decent article on dripless glands. Mentioned mechanical strike as a point of failure. Definitely something to think about.

https://www.passagemaker.com/technic...ss-shaft-seals

Great article!!

[NYSail]

Not all dripless have bellows. The volvo has a pretty tough rubber housing. Basic system.

https://www.generalpropeller.com/3819724

Additionally the cost is relatively low ($140 for mine) so I have a spare. And if there were a need to replace it I could do it while bot is in water with a relatively minimal amount of water coming in.

[sanibel sailor]

If the gland on a traditional stuffing box seizes to the shaft- from being tightened excessively/shaft scoring/overheating/loose items/whatever- it can tear or dislodge the hose. In that case, the traditional stuffing box will leak at the same rate as a drip less.
The grooves in the cutlass bearing are the water entry point and are a significant constriction. It is not like the entire diameter of the bellows is open to the sea. When I burp my drip less, it allows a decent amount of water in, but it is not torrential. I imagine if the shaft was turning, it might look much more impressive. It appears to me that my 3700 GPH bilge pump would be able to keep up. I hope never to prove it.

[mvweebles]

So I'm clearly in the camp of running a PSS that runs a bellows against a face seal. The alternative - such as the Volve, use a lip seal, similar to how main engine seals seat on the crank shaft.

That said, the bellows on a PSS is much more fragile than a stuffing box hose which is purpose built with many plies. It's pretty stout. Possible to tear it, but very unlikely.

As far as flow being stemmed by cutless, all I can tell you is the one time I saw the face seal backed off, the amount of water coming in was really startling. Maybe it was because I didn't expect it, and maybe I remember it as worse that it was. And maybe the engine in my friends Brewer 46 was deeper than typical. But it was one of those moments where everything was blurry except the gushing water. Niagara Falls comes to mind.

That said, I feel the risk of scored shaft and wet bilge outweigh risk of catastrophic failure. Once I figured out why my friends boat was taking on water, I had it fixed in just a few minutes.

[LauraleeG]

Thanks so much for your comments and feedback. We now have a course of direction. We are going with the stuffing box. KISS.

[Pete7]

Originally Posted by NYSail

Not all dripless have bellows. The volvo has a pretty tough rubber housing. Basic system.

https://www.generalpropeller.com/3819724

Additionally the cost is relatively low ($140 for mine) so I have a spare. And if there were a need to replace it I could do it while bot is in water with a relatively minimal amount of water coming in.

Indeed, we had had dry bilges for 12 years using the Volvo seal.

Pete