Replacing a PSS Shaft Seal with a Stuffing Box?

[skipperpete]

Originally Posted by Jim Cate

Pete, what has been the failure mode on these?



Jim

Hi Jim , mostly related to the hose clamp closest to the front of the bellows, as the assembly ages, owners try to apply more pressure to the bellows which puts one of the hose clips under and in contact with the “rubber” and the hose clamp wears a hole into it, this is usually not too terrible and results in a nasty leak. The worst fails have been the shearing of the bellows where it’s attached to the prop shaft, the hose clamps squeeze the rubber collar until it’s micro thin and finally it tears, sometimes evenly right around the edge of the hose clamp and other times the part where the hose clip screw is stays attached and the body of the bellows gets torn. They have the same sticking issue between the carbon and the mating surface as the PSS and if it’s not noticed before engaging the gearbox the bellows again is the weak point and tears. The bellows compound seems to be affected by oil and I’ve found some that have softened and swollen, not dramatically like a Yanmar 2 or 3GM front engine mount when folks bleed the fuel system at the injector pump and wet the engine mount but still definitely affected. If this was only happening with marina boats that went out infrequently, I’d be ok with that, just tighten up the sealing clamp and get towed back to the marina but my customers are often departing on ocean passages and losing propulsion ability because of a bad shaft seal that requires the shaft to be somehow locked solid so the safety seal doesn’t become the next failure point is simply too much of a gamble ( a folding or feathering prop might soften my attitude). The path of least resistance is to install a more robust seal at the same time as the engine change or out of water service. I don’t have any sort of vendetta against whatever brand those seals are, I just replace them if the opportunity arises as a safety measure.
PeteJ

[reflectionsv37]

I have never been a fan of the PSS seals and I wouldn't own one. Every cruising boat I know that has them has had problems. Sometimes serious problems requiring emergency haulouts. And all of them complain about dripping caused by something getting caught between the plates.

20 years ago I replaced a standard stuffing box with a custom made shaft seal made by a machine shop in New Zealand. It has worked exceptionally well in 30K miles of travel and over 3000 engine hours. It has 3 lip seals inside. Between the outer seal and the inner seal (the inner seals are stacked) is a gap and the housing has a zirc fitting to allow the gap to be filled with grease to keep the front 2 seals lubricated. On the prop side of the last seal is a water injection port. In 20 years and all those hours I've replaced the seals 3 or 4 times during regular haulouts. I always carry a complete set of seals and a couple extra of the outer seals. In a remote location I could back the shaft out, replace the outer seal with a new one and not worry about a flood of water rushing into the boat. I've never had to do that. I just replace them every 5 years or so or when I start seeing a small drip.

If I ever need to replace this unit, I would take it to a machine shop and have another one made. The one I have has a nylon housing and I would probably try to have new one made in bronze. It is really a very clever design and has worked fantastic over the years.

If I were to replace it with any commercially available option I like the the Tides Marine seal. Having a spare seal already mounted on the shaft for an in the water replacement is a great feature. I believe you can stack up more than one of the spare seal housings if you have room on the shaft.

[gulfislandfred]

I've had both types of shaft seals. I can live with the 'dripless' kind, but I much prefer the old style stuffing box, with new style packing.

[Ka Hale Kai]

I had a PSS shaft seal while my boat was living in a marina and being used for day sails only twice a year on the SF bay. I dove and cleaned the bottom on a Sat morning and hand spun the prop to clean my 2 blade. When I returned Mon I found my 500 gph rule bilge pump running almost continuously! I hauled and returned to an Algonquin packing gland. The insurance adjuster that examined her stated that I was the 3rd catastrophic PSS failure he had seen that month! I will never use one again.

[sinnerman]

Originally Posted by AKA-None

I wonder if you could use a wax toilet bowl ring rather than a rag to temporarily seal the shaft

Cleanup should be easy

These wax toilet rings are always good idea to carry on the boat to plug a leak in an emergency.

They make a "marine version" of this as well:
https://www.stayafloatmarine.com

cheers.

[Bowdrie]

Depending upon the layout of the stuffing box/hose arrangement it's often possible to have a grease fitting that allows pumping in grease just aft of the packing gland.
Quite common not all that long ago.
In boats that used a pipe/tube that mounted both the stuffing box and the Cutless bearing you could fill the whole thing with grease should you desire.
The prop shaft never got any corrosion and the tube never got filled with nasty sea monsters.
With such a set-up one can have the packing running with little compression and it won't leak and it'll last almost forever.
It's an old idea that works well, but of course their "had" to be new devices invented to sell that are expensive and can lead to really serious problems.

[saillr]

Smart idea.Be sure to use teflon Packing when you change.
Our Island Packet 40 is 27 yrs old and the first thing I did was put Teflon packing in the stuffing box. Tighten by hand and check after a few hrs running. Tighten by hand again until drips stop. It will run cool and will not leak at all. After 27 yrs still does not leak to this day.

[skipperpete]

I,m fairly happy with most of the propshaft seals on the market, lip seals, carbon ceramic, flax rope but the recurring failure mode is lack of maintenance, not just of the seal, the engine alignment and shaft vibration can damage any type of shaft seal. It’s important to know what type of stern seal you have and what specific peculiarities your type has.
Volvo seals are pretty good but need to be greased regularly
Lip seals in bronze carriers eat up the garter springs even if greased often
Dripless seals need burping after haulout and correcting the “sticking” fault needs care.
Flax packing will not tolerate overtightening and often happens when owners “harden up” the adjustment for winter layup but forget to release it after layup ( often “releasing”it requires unpacking a couple of rows and fitting new flax)
On some boats it’s not even possible to see or access the stern gland if a Vee drive is fitted or a long propshaft puts the shaft seal under the cabin sole in the aft cabin.

[Greg K]

Originally Posted by markxengineerin

Walter Schulz (of Shannon) summarized dripless shaft seals very well when he called them "a solution to a problem no one ever had"

100%

[FuzzyFeat]

Another vote for a stuffing box. With the advent of Teflon impregnated packing it's a no brainer. For me 12 years of cruising, no drip, shaft in great shape and zero maintenance. Well maybe a little tightening of the packing gland.

Aside from the hose, nothing to wear, crack or pick up a bit of dirt. No springs, no moving parts or parts that are not supposed to move. In this case simple is better.
If you already have a mechanical seal, fine wait until it fails, then decide for yourself.


Oh, did i mentioned cheaper? Especially if you pick up a used one.

[Tanqueray]

I went with a Volvo dripless shaft seal when I replaced my shaft and coupling. The old stuffing box was OK, but it would drip, even with a Teflon impregnated packing. It also ran hot if I tightened it enough to stop drips in the slip.

I am very impressed with the simplicity of the Volvo seal. A squirt of grease at launch time in the spring is all I have to do to it…no leaks, dry bilge. Not much not to like.

Here is a good comparison of my old stuffing box and the Volvo.

https://youtu.be/L99fV8eREjY?si=oV8qE936Kt2IIl_L

3 seasons on the Volvo, and I am very happy with it.

Greg

[Bowdrie]

Originally Posted by FuzzyFeat

Another vote for a stuffing box. With the advent of Teflon impregnated packing it's a no brainer. For me 12 years of cruising, no drip, shaft in great shape and zero maintenance. Well maybe a little tightening of the packing gland.

Spot on.
In a way it's kind of comical, (tongue in cheek).
Hull to deck leaks, leaky portlights, leaks into core materials, leaky keel bolts, leaking water systems and heads, leaky engines, water from the anchor rode, water leaking thru the mast step, the shower drain, or even bringing in water from wet clothing, the list goes on.
But it's "Oh no, a disaster, the packing gland is passing a few drops of water when we're motoring", this must be stopped by any means, (lots of money,) necessary.
It's ok, just trying to inject a little humor.

[sesmith]

Originally Posted by sailorboy1

I am not going to explain or debate the coupling issue and leave it to each boater to look up etc. I did say it you want to do it right.

Agreed.

Concerning the coupling, if you ever did anticipate having to try and replace a pss seal in the water, I'd replace the coupling with a split coupling. That would take care of all the headaches of trying to remove a rusted solid coupling and trying to tap it back in place while the water sprayed in.

[pbmaise]

In the video posted by Roniszoro at 3:40 he mentions a vessel that had the PSS slip owing to the set screws. This is exactly the same failure on my vessel the very first time I moved the vessel after purchasing it. I was in the middle of trying to dock the vessel when I learned water was pouring into the engine compartment.

Fortunately I had other sailors nearby who were able to come to my rescue and knew exactly what was going on.

The PSS on my vessel began to drip after it had been installed about 12 years. It dripped mostly when under engine power. Sometimes not very much, some times quite a lot. I never could predict how much. The water collected in a small space which didn't drain into the sump below the engine. This means I had to manually empty about 2 gallons (5 liters) of water about every 10 hours. It gave us an excuse to go down into the engine room and have a look around but was still a pain.

Note: Once I found a very very thin fishing line wrapped around the shaft while cleaning the vessel. I suspect that fishing line worked its way into the shaft seal and was causing it to stay open. After I pulled the line out it stopped dripping. Perhaps later on is when it started to drip under engine power.

[pbmaise]

Originally Posted by skipperpete

A frequent issue is leaking under full power against soft engine mounts, the movement can be substantial and can’t always be accommodated by over adjusting the bellows tension.

Oh wow! You just described both the situation and the solution for my vessel. I think under engine power we had to manually empty the space where water accumulated about 100 times. That was a constant pain.

I realize now I should have come on the board and described the dirty laundry I was dealing with. Someone might have been able to explain to me how to fix the issue.

What do they say about learning to live with someone hitting you in the head with a hammer?