Constant drip stuffing box shaft seal

[skyflyer]

My boat has this type of shaft seal. 3 rings of square section braided ptfe “cord” get squeezed by a large nut and thus form a seal against the prop shaft (I believe the exact same system is used in garden taps!).
in order to prevent friction and heat build up, the pressure on the nut is adjusted to allow a small ingress of water, 4 or 5 drips per minute whilst shaft is turning. This reduces to about 1 per minute (or less) when engine is stopped.
My question: is this an unusual arrangement In the UK? (It’s a US built boat) My prospective purchasers surveyor had never seen such a system without some other form of lubrication?

 

[Tranona]

Sounds like the surveyor does not know what he is talking about. While the actual make of the stuffing box may not be the same as he is familiar with it is standard fitment on most UK boats pre 2000 (and even later). There are many variations on the housings and methods of adjustment but they all work in the same way. See here for details coxeng.co.uk/stern-gear/stern-glands/ You might want to print it off and give a copy to the broker and surveyor for their education! I have just done away with one the same as in Pete Caterrall's photo and replaced ot with a modern dripless seal - not that I am suggesting you do this if you are selling the boat!

BTW same with his comments on moisture readings. They only indicate moisture levels and almost nobody gets panicky about them nor spends the £10k to do what he suggests.

 

[Graham376]

My boat has this type of shaft seal. 3 rings of square section braided ptfe “cord” get squeezed by a large nut and thus form a seal against the prop shaft (I believe the exact same system is used in garden taps!).
in order to prevent friction and heat build up, the pressure on the nut is adjusted to allow a small ingress of water, 4 or 5 drips per minute whilst shaft is turning. This reduces to about 1 per minute (or less) when engine is stopped.
My question: is this an unusual arrangement In the UK? (It’s a US built boat) My prospective purchasers surveyor had never seen such a system without some other form of lubrication?

All mine on 4 boats have had greasers which I would have thought is standard. Doesn't yours have one?

 

[skyflyer]

All mine on 4 boats have had greasers which I would have thought is standard. Doesn't yours have one?

Nope. See above reply. 1800 of these boats were built all with the same design and I’d be surprised if the manufacturer used a different system in the slightly bigger and smaller models so at a guess 10000+ using these seals. As I say, maybe it’s a US thing

 

[Praxinoscope]

I have never come across a stuffing box with no form of ‘greasing’, normally supplied by a tube from the grease reservoit, but as can be seen from Viv Cox’s site there is a type where the grease reservoir is part of the stuffing box.
Surely there must be some form of greasing, otherwise the stuffing would run dry and wear very rapidly?

 

[Buck Turgidson]

I have never come across a stuffing box with no form of ‘greasing’, normally supplied by a tube from the grease reservoit, but as can be seen from Viv Cox’s site there is a type where the grease reservoir is part of the stuffing box.
Surely there must be some form of greasing, otherwise tge stuffing would run dry and wear very rapidly?

Yes but it does have a greaser. Not seen one without.

 

[ean_p]

My boat has this type of shaft seal. 3 rings of square section braided ptfe “cord” get squeezed by a large nut and thus form a seal against the prop shaft (I believe the exact same system is used in garden taps!).
in order to prevent friction and heat build up, the pressure on the nut is adjusted to allow a small ingress of water, 4 or 5 drips per minute whilst shaft is turning. This reduces to about 1 per minute (or less) when engine is stopped.
My question: is this an unusual arrangement In the UK? (It’s a US built boat) My prospective purchasers surveyor had never seen such a system without some other form of lubrication?

There are many types of packed gland as there are many types of packing. Not all of them need to use grease as a lubricant. If the correct packing is installed in the correct way and with the correct surface pressure then the use of water to maintain an equitable temperature is all that is required. In fact the introduction of grease or excessive amounts of grease can cause temperature rise as it reduces the passage of and so the cooling effect of the water. Have a chat to Beldam or Klinger tech people for advice as to the best packing rope to use in your greaseless application. There are by the way many types of 'PTFE' ...some impregnated with Graphite some impregnated with other materials. The base 'rope' too has a great influence as to the heat generated by any particular compound of materials ! A quick chat with the above will soon sort out which is best for you! On a slightly different note, have repacked more glands then I can remember over the years the low number (3) of coils seems very low. Don't think I've ever come across less than 4 and more generally 5+. If you've been in there yourself are you sure you never left one or two behind, very easily done?

 

[skyflyer]

Ok lets go over this again:

1) I am quite happy with the design and operation of my shaft seal
2) The same design has been fitted to at least 2000 boats and probably 10,000 by one manufacturer and as it is not their own design, I suspect to thousand more boats from different manufacturers.
3) The correct number of rings is 3 - there is no room for more and the owners manual states that three is correct
4) There is no problem with the seal. The packing is GFO which is a PTFE/Goretex woven braided material - not graphite; once again IAW manufacturers directions
5) There is no form of externally added lubrication - it doesnt need it because it is not a "dripless" seal; it must be set (easy) to allow 5-7 drops per minute when shaft is turning. this ensures lubrication and stops overheating (much like a cutless bearing)
6) My only question was "is this type of shaft seal unusual in UK because the surveyor _ no spring chicken - had clearly never seen one before

The answer to 6 is - evidently - yes.

Thanks all

 

[ean_p]

sometimes you just know your wasting your time.............?

 

[Tranona]

Yes, it is unusual in the UK - but that is because for some reason in the past packing material was not so good and the seal tended to leak so grease was added to the tube to act as a secondary seal to keep the water from dripping when the shaft is not turning - not to lubricate the packing. The packing does not require lubrication as that is provided by the minute flow of water that causes the drip. As ean_p explains too much grease is bad as it is a poor conductor of heat.

Of course the best thing to do is to get rid of it completely and fit a modern seal which does much the same thing without the drips! But as you say it is a proven bit of kit.

 

[Praxinoscope]

I bow to those with greater knowledge of stuffing box stern glands, obviously some designs do not require grease, I have just never seen one in almost 50 year's of mucking about in boats.

 

[Tranona]

I bow to those with greater knowledge of stuffing box stern glands, obviously some designs do not require grease, I have just never seen one in almost 50 year's of mucking about in boats.

There are lots of things in boats that we consider "normal" when there is no rational reason for them being that way now. Greased stuffing boxes is one of them!

 

[Fr J Hackett]

Here you go Leo to the rescue with a perfect and visual explanation. The surveyor and what he has written isn't worth tuppence. God knows how he ever became one.

About 10. 40 in

 

[Seaway Channel]

No it is not unusual in older boats.

 

[rib]

Here you go Leo to the rescue with a perfect and visual explanation. The surveyor and what he has written isn't worth tuppence. God knows how he ever became one.

About 10. 40 in

Great video... Learn something every day

 

[Refueler]

Most boats I have seen have the 'stuffing box' version of seal. I would suggest it is not a US or UK thing at all ... as its a universal seal design used not only for drive shafts - but also to seal valve stems ... pump shafts .... many uses in fact due to its ease of service and success.

The 'packing' used normally is impregnated with 'persistent water proof grease' .... plus the addition of a greaser unit.

As mentioned above - the seal is set so it drips about 1x every 20 secs or so WHEN SHAFT IN USE .... this provides the 'cooling' ...
When shaft is stopped - its common practice to use Greaser to introduce more grease to reduce drip to a minimum. In fact once you get to 'know' your boat - you can actually inject just enough to stop the drip. Once shaft is in use again - that 'extra' grease is soon dislodged and drip starts again.

When changing packing ... its easy to see if improper use has been ... not enough or too much grease ... if its the white packing - then it will show 'burnt brown' where its had lack of water / grease ..... (a small trace of brown is normal).

 

[Porthandbuoy]

No greaser on my Neptuinian 33 shaft. The shaft seal drips about 3 drips per minute when stopped, about double that when rotating. No idea when the packing was last replaced and won’t be doing so myself unless the drip count increases dramatically.

 

[scottie]

Did Morse known for controls not market this way back in the last century as an alternative to the traditional weight of bronze units

 

[Refueler]

No greaser on my Neptuinian 33 shaft. The shaft seal drips about 3 drips per minute when stopped, about double that when rotating. No idea when the packing was last replaced and won’t be doing so myself unless the drip count increases dramatically.

I know people who has modified their units by drilling hole ... tapping a thread and then screwing in the greaser connector. Pipe up to grease holder connected and that's it. If its the usual T handle that screws into the greaser reservoir - it just needs a couple of turns each outing .....

 

[Sandy]

My boat has this type of shaft seal. 3 rings of square section braided ptfe “cord” get squeezed by a large nut and thus form a seal against the prop shaft (I believe the exact same system is used in garden taps!).
in order to prevent friction and heat build up, the pressure on the nut is adjusted to allow a small ingress of water, 4 or 5 drips per minute whilst shaft is turning. This reduces to about 1 per minute (or less) when engine is stopped.
My question: is this an unusual arrangement In the UK? (It’s a US built boat) My prospective purchasers surveyor had never seen such a system without some other form of lubrication?

My French built boat has had this type of arrangement for the last 36 years and has not sunk.