What does the stern greaser do?

[stuart]

As the title says What does the stern greaser do? / how does it work?

[jmj]

Starting from the front, there's an engine, then a gearbox, on the back of the gearbox is the propellor shaft and on the end of this is the propellor.

 

Clearly the engine and gearbox are in the boat and the prop is in the water. The prop shaft starts in the boat and ends in the water, so it has to go through a hole on the hull, and something has to stop the water comong in through this hole.

 

Surrounding the propshaft is the propshaft outer - a tube with seals at the end - the shaft runs through it, and the tube is welded to the hole in the hull.

 

Because the shaft is rotating, the seals can't be 100% watertight so the tube is filled with grease.

 

That's the background, now the answer to the question.

 

Gradually grease leaks out of the shaft, so the stern greaser is there to top it up; when you turn it round, it squeezes a bit of grease into the tube.

 

Sorry if the first part is more simple than you need, but if you don't understand that, then the last bit wouldn't make sense.

[timboharticus]

The idea is that every week or so or more if you are cruising you give the greaser half a turn to pump a bit into the prop seal/bearing

 

This lubricates and stops water leaking in.

 

It is usual to put a container by the prop tube to catch any drips of water that do come through.

[maffi mushkila]

I seem to remember someone here saying that he had fitted a gizmo from Volvo that eliminated the need for a "greaser". Anyone remember?

[John Orentas]

Maffi.

 

You can buy a contraption that does away with the need to screw your greaser in regularly. It's supposed to contain enough grease to last about a year. I have seen them in use in idustrial applications too, though I havn't heard much about them for a while.

 

The Volvo type is a complete stern tube assembly, it takes lubricant (oil) from a small bottle which you have to top-up as required.

 

John Squeers

[nbtafelberg]

My boat is quite strange because although I do the "stern tube thing" regularly there is NEVER any water in the Bilge.

 

Is this the same experience for everyone?

 

Paul

[Jus73]

I have a Vetus water lubricated stern gland that supposedly needs no maintenance. So far so good! Apparently these type of glands are used frequently on sea going boats?

[John Orentas]

I get about a pint per year out of my stern gland, there is no reason why they should leak water. some people who should know better will say that they should drip every minute or so to aid cooling or lubrication. Often when they have sold you some worn out stern-gear.

 

Many of the stern tube systems produced for sea boats tend to suffer from the gritty conditions of the canals causing premature wear and failure.

 

John Squeers

[weeble]

John,

I was going to start another thread on this, but it leads on directly from your reply!In order to achieve such dry conditions, how often do you tighten the stern bearing packing, and how tight do you adjust it?

 

I was told that you should be able to turn the shaft freely by hand, but I find I have to adjust mine pretty tight in order to totally stop ALL dripping when cruising, so I normally back off both adjusting nuts by a turn and put up with a small amount of the wet stuff -- pint + or so per cruising day. As this is caught in a container I just treat emptying it as part of the "after flight" checks, along with turning the greaser!

 

Got no flexible drive coupling so if the shaft is out of kilter is it possible to check it without taking the boat out of the water?

 

Cheers.... mike

[John Orentas]

Mike.

 

I happen to have a rather different stern tube to most boats, bought it from Calcutt Boats many years ago. Instead of the two studs and nuts to tighten the gland, mine has the sleeve which compresses the gland threaded into the stern tube housing, a locking ring prevents it from loosening. Both threaded sleeve and locking ring are notched for the use of a 'C' spanner though in pratice I use a blunt punch and heavy hammer to tighten it. I consider this type to be far superior.

 

You were correctley advised, you should loosen the two lock-nut and then evenly and gradually tighten the two nuts, at the same time rotate the propshaft by hand. When a significant resistance is exerted on the staft tighten the locknuts carefully whilst not allowing the main nuts to move. At this stage no water leakage should be occuring and the gland adjustment is complete.

 

If you carry out the above and you cannot exert a resistance on the propshaft or the gland continues to drip water, the gland will need re-packing.

 

The shaft and/ or stern tube will be in need of repair or replacement if.

 

1) You need to carry out the above exercise repeatedly.

 

2) You can continue turning the greaser, (make sure it is totally filled), feeling little resitance and without grease comming out of the gland.

 

3) You can detect more than very slight play when puhing and pulling the propellor at right angles to the shaft, check up and down and side to side with as much force as you can. This can be checked when the boat is dry-docked or usually but with more difficulty through the weedhatch.

 

In practise 2 or 3 of the above syptoms will be apparent.

 

I will discuss alignment later !

 

John Squeers

Edited October 16, 2004 by John Orentas

[weeble]

Mike.

 

snip

 

You were correctly advised, you should loosen the two lock-nut and then evenly and gradually tighten the two nuts, at the same time rotate the prop shaft by hand.  When a significant resistance is exerted on the staft tighten the locknuts carefully whilst not allowing the main nuts to move.  At this stage no water leakage should be occurring and the gland adjustment is complete.

 

snip

 

What's your interpretation of "significant" John. Should the shaft turn freely using one finger, one hand, both hands? I know that if I tighten the packing sufficiently I can obtain an absolute watertight seal, but there really is a "significant resistance" when I get to that point and I'm concerned I'm overdoing it -- i.e. if the shaft is slightly out of alignment it would probably exacerbate the situation. The packaging was replaced when I purchased the boat (year ago) and there's plenty of adjustment yet available, the nuts are probably not more than 25% down the thread.

 

The adjustment system on your boat does sound superior in that it more or less guarantees the sleeve is always parallel to the bearing housing, and also less prone to damage during adjustment. Wonder why this method wasn't adopted by other builders.

 

Thanks again for a very informative reply. I'd still be interested to hear from other users how much water they get in their bilge in a normal cruising day.

 

Cheers.... mike

[John Orentas]

Significant resistance.

 

I can virtually 'spin' my proshaft before I have tightened the gland, I tighten the the gland to the point were I can stiil comfortably turn the shaft with one hand, griping only the shaft.

 

That's the best I can do.

 

You say you have no flexible coupling, I assume it is a vintage type slow running engine and you don't have any form of flexible mounts on your engine. Ideally oak bearers to give a noise barrier.

 

John Squeers

[weeble]

Thanks for the info John, it gives me some sort of yardstick to check against when I next visit the boat.

I might have misled you about the engine. When I say there is no flexible coupling I meant that there's nothing in line between the gearbox and prop. The engine is a BetaMarine (28hp) on antivibration mountings, but of course nothing to compensate for any minor misalignment.

Cheers.... mike

[John Orentas]

Mike.

 

Now you have really got me worried, is there nothing that looks like it can allow some movement of the engine?, and yet the engine is on soft mounts ?

 

John Squeers

 

 

 

 

Edited for rubish punctuation.

Edited October 18, 2004 by John Orentas

[weeble]

Mike.

 

Now you have really got me worried, nothing that looks like it can allow some movement of the engine and yet the engine is on soft mounts ?

 

John Squeers

<{POST_SNAPBACK}>

John,

Thinking about it of course you're right -- maybe that's why is so ruddy noisy stood on the rear deck. But I could swear there was rubber around the mounts..... I'll check next week-end when I visit the boat and get back to you.

 

Cheers.... mike

[John Orentas]

Mike.

 

Your Beta engine (Kubota based) should be fixed on soft mountings and by definition it must have a flexible coupling in the drive chain, it must allow linear AND angular movement of the engine.

 

Problems in this area will not only give stern tube wear and leakage, it will put extreme loads on the gearbox leading to premature failure.

 

John Squeers.

Edited October 18, 2004 by John Orentas

[Guest whould be dhutch]

also, i dont think it been mentioned that stern tube gland greasers dont create grease!!

 

- as you do a turn a day, or a turn a week, or what every feel you need, you will eventauly get to the bottom of the greaser, then you have to unscrew the whole thing off the base, wind the ram all the the way back out, and fill it full of sturn tube grease and put it back

 

- as for how much it leaks, if it leaks alot and you have no more room to tighten it, you will need to "repack" the gland, which is a job that might be best left to a yard to to for you the first time (watch the man do it, and you can do it next year)

 

- as for leakage, you shouldnt get much, and if your leaving the boat for a lond time (a week or so) - you can put few extra turns of grease untill its sealed

 

danel

 

-

[weeble]

Mike.

 

Your Beta engine (Kubota based) should be fixed on soft mountings and by definition it must have a flexible coupling in the drive chain, it must allow linear AND angular movement of the engine.

 

Problems in this area will not only give stern tube wear and leakage, it will put extreme loads on the gearbox leading to premature failure.

 

John Squeers.

<{POST_SNAPBACK}>

 

Hi John,

 

Sorry, I forgot to get back to you about my drivetrain. As far as I can see, the situation is as I suspected and therefore probably needs looking at.

 

At the risk of asking another idiot's question, could you shed some light on what the assembly is between the engine and gearbox -- i.e. where (normally) the "clutch" should be, there's some sort of a drive plate. Is there any flexible alignment performed by that unit, or is it just a means of coupling one device to another?

 

As an aside, following your comments I tightened the gland nuts slightly more than I usually do and it's more or less stopped all water intake -- So I guess I must have been too conservative with it before.

 

Cheers.... mike

[John Orentas]

Hi Mike.

 

Yes there is a driveplate in there, it's function to allow a tiny amount of misalignment and also a kind of 'cush drive' arrangement as you would have on a car or motor bike, smooths out those imperceptible changes in engine speed as each cylinder fires. Some of these driveplates have given trouble over the years, they can get very rattley.

 

Please do something about your drive-chain. You will be storing up all kinds of expensive problems.

 

John Squeers.

[Rick]

Before our Beta Marine engine was fitted I contacted Beta to ask about couplings and preferred types.

 

Their comment was that it was up to me, they didn't consider one necessary. We had a Python drive fitted to reduce transmission noise. We were going for the Aquadrive but there wasn't room to get it in.

 

Richard

[John Orentas]

Rick.

 

In other words we sit the engine on soft mounts which will allow this vibrating mass to float around. Then at the far end of the gearbox we fix a 1.5" dia propshaft and clamp that rigidly to the boat through the stern tube.

 

We can only imagine the loads imposed on the gearbox output shaft and the stern tube.

 

I can only think you may have been talking to the wrong chap.

 

John Squeers.

[David Schweizer]

Don't have soft Mountings, don't have flexible drive, don't have any problems.

[ChrisPy]

Whatever happened to those flexibly mounted stern glands?

 

The prop shaft was conventionally supported in a cutless bearing (fibre or bronze) at the aft end ot the stern tube. This acted as a fixed pivot point. The stern gland was connected to the front of the stern tube by a short length of reinforced rubber tube which provided all the flexibility needed. The system worked OK in conventional boats, but maybe only because there was a greater length of propshaft which could flex slightly between the vibrating mass of the engine and the fixed pivot at the aft end.

[Rick]

We can only imagine the loads imposed on the gearbox output shaft and the stern tube.

 

I can only think you may have been talking to the wrong chap.

 

John Squeers.

<{POST_SNAPBACK}>

 

I can only think that you are very probably right. Happily I didn't take much notice.

 

Richard

[Amicus]

Was there a happy outcome to this thread?