'Maintenance-Free' Stern-Glands

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Babylon

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\'Maintenance-Free\' Stern-Glands

Boat has what the original surveyor described as a 'maintenance-free' stern-gland; told me I need do nothing to it.

However two engineers who've now looked at the boat (engine, prop-shaft, etc need removing to install a new stern-tube - don't ask!) have said that the stern-gland ISN'T maintenance-free. There are two large locking-nuts at the forward end of the gland, however there is no grease-nipple nor a remote greaser, and access to the gland involves a 45 degree full-body dive over the top of the engine, so I cannot imagine how greasing or re-packing is normally intended to be done. (This certainly isn't a job I can imagine a beginner doing first time on land - let alone at sea!)

Given that the engine is coming out this winter, I'm considering fitting EITHER a remote greaser to the existing gland OR replacing it altogether with a Volvo (Deep Sea?) maintenance-free seal.

However I've also been advised that a potentially dangerous snag with such maintenance-free types is that IF they do fail offshore, then there's no way to fix them.

If I keep the existing unit, then the engineers will re-pack it etc as part of the job - then how often do I need to dive in there (a) to tighten the nuts, and (b) to re-pack and re-grease the whole unit?
 
Re: \'Maintenance-Free\' Stern-Glands

I have had the Volvo shaft seal on the last two boats - absolutely great bit of kit. Never yet had a leak of any sort. Replaced the last one at the start of last season after 10 years (Volvo say if should be 5 years) on the boat - never leaked in all that time. Easy job to do - took about an hour.

No, you can't do it at sea but I can't imagine any type that you could do that with.

Hope this helps
 
Re: \'Maintenance-Free\' Stern-Glands

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There are two large locking-nuts at the forward end of the gland, however there is no grease-nipple nor a remote greaser, and access to the gland involves a 45 degree full-body dive over the top of the engine, so I cannot imagine how greasing or re-packing is normally intended to be done. (This certainly isn't a job I can imagine a beginner doing first time on land - let alone at sea!)

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Sounds like one where one 'nut' pushes the grease up the shaft. Need to tighten when it drips excessively - maybe daily depending on how much motoring you do.


[ QUOTE ]
However I've also been advised that a potentially dangerous snag with such maintenance-free types is that IF they do fail offshore, then there's no way to fix them.

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Personally I think these risks are over-exagerated. The benefits/risks of something like a PSS seal for me outway the hastle of a grease seal.
 
Re: \'Maintenance-Free\' Stern-Glands

Would recommend change to a Volvo seal if you can. It will not drip, last for years. Remember to grease it annually and "burp" when you relaunch to get water into the stern tube. Will not fail catastrophically. When you get it you will see how robust it is - and it is cheap compared with other designs.

Do not confuse with "Deep Sea" or other face type seals. These are a very different concept and have never really made much impression on the market, partly because of the potential for failure.
 
Re: \'Maintenance-Free\' Stern-Glands

[ QUOTE ]
If I keep the existing unit, then the engineers will re-pack it etc as part of the job - then how often do I need to dive in there (a) to tighten the nuts, and (b) to re-pack and re-grease the whole unit?

[/ QUOTE ]
I'd change it for something a little more confidence-inspiring but if you do choose to keep the existing one then I'd get it re-stuffed with a teflon 'wax' packing as these are almost maintenance-free and don't rely on grease to keep the packing waterproof or water to lubricate the seal. (This is assuming that the seal IS a traditional packed gland.)
 
Re: \'Maintenance-Free\' Stern-Glands

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"Do not confuse with "Deep Sea" or other face type seals. These are a very different concept and have never really made much impression on the market, partly because of the potential for failure."

[/ QUOTE ]

Or because they succumbed to the Volvo legend and by the time they discovered that astronomic prices were not synonymous with quality after all they were hooked!

I have owned several boats with PSS and Deap Sea seals and never had any problems or even concerns. And you do NOT have yo burp them after drying out - just fit a water feed off the exhaust.
This alternative to string and grease is so obvious that debate is superflous IMHO.
 
Re: \'Maintenance-Free\' Stern-Glands

Volvo is the way to go if it will fit - I had to opt for a Tides Marine Seal because of parameters. Tides would also be better if you are on a drying mooring as a Volvo seal needs to be burped everytime it is dried out.

Size issues discussed here
 
Re: \'Maintenance-Free\' Stern-Glands

Not sure where the "astronomic" prices come in. The Volvo seal is less than £100 in sizes up to 35mm - far cheaper than face seals. And, yes, we could get into arguments about reliability, but whichever way you look at it a face seal can fail catastrophically in a way that a radial seal will not be it either a Volvo type, a Tides or a conventional stuffing box. And there are examples - not long ago there was a post on here with a a 40ft Hunter in the States that had sunk in its marina berth because of failure of a face seal. I don't know any builder that uses them on new boats - although many have in the past.
 
Re: \'Maintenance-Free\' Stern-Glands

I work as Chief Engineer on Merchant ships. All equipment fitted on commercial vessels is fitted because it is tried and tested - shipowners are an extremely conservative lot and are reluctant to try anything which is not. On most of the ships I have worked on for the last few years the stern tube seals have been of the Simplex radial type seal with Oil lubricated stern tube bearings( Like a very large Volvo seal).

ALL our pumps however use face type seals - that's water pumps, oil pumps fuel pumps etc etc. Both types are very reliable in service if properly fitted. Neither type requires any specific maintenance. However both are susceptible to failure under certain circumstance. Radial seals are very intolerant of fouling by rope or twine and something as simple a a bit of fishing line can totally destroy the seal. They also, over time, will wear a groove in the shaft where they seal against it. When this groove becomes excessive they will no longer seal and either the shaft must be sleeved or a new shaft fitted. On Simplex seals they actually seal on an expendible liner which can be moved relative to the shaft so that the seals will run on a new part of the liner. These liners can be machined up to a given tolerance to remove the grooves but when they reach that tolerance they must be renewed. Face seals do not wear the shaft.
Face seals are susceptible damage from fine foreign particles entrained in the water, particularly if they are pressure lubricated. All types are susceptible to failure by dry running, face and lipseal types in particular (hence the need for 'burping' or venting). Neither is better than the other in all circumstances. If you are on a drying mooring or frequently use your boat in heavilly contaminated water I would tend to fit a radial type seal with a vent, or a packed gland. In all other circumstances I would fit a face seal ( as I have on my own boat). Or just stick with a packed gland and accept that it will need greasing from time to time and the gland follower will need adjusting every so often when it starts dripping. In any case I would repack the gland every time the boat has been ashore for a significant period if using ordinary tallow packing or every 2 - 3 years if using a PTFE packing.
 
Re: \'Maintenance-Free\' Stern-Glands

Thanks for this detailed explanation. The chances of any line getting to an inboard bearing/seal are pretty remote. The only issue is providing adequate water cooling and lubrication to the rubber bearing behind the lip seal - not the lip seals themselves as they are lubricated by grease. As I know to my cost forgetting to burp quickly shows itself by an excruciating noise of dry rubber - fortunately no damage if dealt with quickly. Some designs of lip seals have water feeds, particulalry for use with high horsepower engines such as the Tides fitted to many new powerboats such as Fairlines. However, unecessary for small auxilliaries.

The problem with face seals on propshafts in modern boats is keeping a constant pressure on the faces. Normal fore and aft movement of a shaft on a flexibly mounted engine is about 6mm, but on some very soft mounts it can be up to 10mm. Hard in reverse and a poorly adjusted bellows can lead to the faces opening up. In other situations, such as one powerful crusier racer with an open type stern tube and shaft supported by a P bracket and the face seal type inner bearing - surfing down a wave water pressure was enough to open the faces and let large volumes of water in.

The other potential problem as you have noted is deposits on the faces causing wear or damage. More common on boats left unused in areas of heavy fouling.

You can see that manufacturers are aware of this by the detailed instructions on setting the bellows correctly to maintain pressure on the faces, or in the case of one design providing an emergency method of blanking off the seal if it fails. Does not inspire confidence!
 
Re: \'Maintenance-Free\' Stern-Glands

Provided you have reasonable access to the gland, there is absolutely nothing wrong with a normal (old fashioned) packing gland. It may occasionally need to be nipped up, and should be greased regularly, but will NEVER completely fail. The trouble is that it needs a little knowledge to pack it correctly. Ideally it will be adjusted to allow a few drips per minute when running, and none when stationary. I have been packing pump shafts and prop shafts for more than forty years, and have had more problems with fancy seals than I've ever had with conventional packing.
 
Re: \'Maintenance-Free\' Stern-Glands

Stern glands do not always need grease, water is a better lubricant and coolant. Packing can work well without grease, and runs cooler.

So check first it was not designed to run simply with water as a lubricant and coolant. You will not find boats in Western australia using grease in stern glands unless tey have come out from the UK,

To add some more information we have seen shaft foe and aft movement of up to 18.00mm with soft mounted drives/engines.
 
Re: \'Maintenance-Free\' Stern-Glands

This post is likely to attract more embroidered opinion than an anchor question.
i) Always remember that all stern glands can fail, and they do. ii) All stern glands need regular inspection and attention.
I fitted a PSS face seal and have found it excellent, tho one forum member had problems with his single cylinder engine arrangement. The Volvo seal is also said to be good but does require burping and some arcane greasing proceedure. When I was looking it was not available in Imperial sizes but this may have changed now.
I should ignore the more florid specualtion particularly if it seems to lack balance or is not backed up in the first person.
Remember conventional stern gear works well but also has sunk more boats than the German Navy.
 
Re: \'Maintenance-Free\' Stern-Glands

Don't know when you looked for a Volvo seal in imperial sizes, but I bought my one inch over 10 years ago.

Given your comments about speculation and lack of balance I would be interested in your evidence to support your last statement!
 
Re: \'Maintenance-Free\' Stern-Glands

BoatUS News Room at www.BoatUS.com
FOR IMMEDIATE RELEASE
Press Contact: Scott Croft, 703-461-2864, SCroft@BoatUS
The most common cause of dockside sinkings were found to be the result of deteriorated or damaged or corroded fittings such as intakes, seacocks, and drains below the waterline. Stuffing box leaks were number two on the dockside list.
The complete study results are as follows:
Sinking at the Dock
Below waterline fitting 44%
Stuffing box leak 33%
Keel and centerboard 7%
Rain 7%
Head back-siphoning 3%
Above waterline fitting 3%
City Water hookup 3%
Sinking Underway
Strucksubmergedobject40%
Propshaftortrut16%
Belowwaterlinefitting16%
Grounding8%
Stuffingboxleak8%
Storm/knockdowns8%
Above waterline fitting 4%

further
Stuffing Box: On powerboats or sailboats with inboard power, if the stuffing box’s packing material that seals the prop shaft is not tight, a steady drip will slowly swamp a boat. Also remember that no stuffing box should leak when the prop shaft is not moving. Stuffing boxes need to be inspected routinely, regardless of the season.
 
Re: \'Maintenance-Free\' Stern-Glands

Intereresting "statistics" However meaningless without the size of the sample (I was unable to find any further details on the site). "Stuffing box" is also a generic term which covers a range of designs, and the subject of this thread is around the differences in design from a security perspective.

Also I was rather hoping that you could provide evidence to support your last statement - such as the number of ships sunk by the German navy and the number of boats that have sunk through a failed stern gland - of all types.
 
Re: \'Maintenance-Free\' Stern-Glands

Re Doug748

Your figures are totally meaningless in a debate as to the relative merits of different methods of sealing propeller shafts. Obviously the figures relate to seals of all descriptions. The words "shoot" and "foot" come to mind.
 
Re: \'Maintenance-Free\' Stern-Glands

Having had the benefit of a face seal type failing, due I was told, to the heavy contamination of mud held in suspension in east coast rivers, /forums/images/graemlins/mad.gif I fitted the replacement supplied, (under Protest), which failed in a similar manner a year later!
Having taken advice, I fitted the Volvo seal and ceased to have any further problems. I did grease & burp the seal on an annual basis, but, despite being on a drying mud mooring, did NOT molest the seal on a regular basis.. dry bilges for the 6 years of remaining ownership! /forums/images/graemlins/grin.gif But! did have a large Jubillee clip in residence on the seal ..Just in Case!
 
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