Stern Gland head scratching!

[BigStu]

I was after a quick bit of advice on a new boat I have purchased. I have the stern gland off the boat (Westerly Longbow) and was surprised to find that there are no ‘dogs’ to stop the torsional shear force on the rubber coupling. It his a traditional glad with two bolts to 'nip up' and tighten.

I could now look at other stern gland options- I’ve always preferred the traditional type as you can ‘nip up’ the gland if there is any leakage. However, I certainly don’t like the thought of not having ‘dogs’ on the shaft or gland which ultimately could sink the boat of the coupling fails with shear forces. However, a surveyor said to me- not a problem just use heavier duty rubber (and an engineer has suggested exhaust hose- commented that this is ideal but people don't use it as it is very expensive).

What do I do here I wonder?- go with the traditional (which I like) with a heavier duty rubber, or try a new type like a Volvo seal (but I'm not sure that will work as only about 1.5cm of stern tube is available for fixing it to and not sure you can use Volvo seals with semi flexible couplings).

Any help appreciated!

 

[NormanS]

I was after a quick bit of advice on a new boat I have purchased. I have the stern gland off the boat (Westerly Longbow) and was surprised to find that there are no ‘dogs’ to stop the torsional shear force on the rubber coupling. It his a traditional glad with two bolts to 'nip up' and tighten.

I could now look at other stern gland options- I’ve always preferred the traditional type as you can ‘nip up’ the gland if there is any leakage. However, I certainly don’t like the thought of not having ‘dogs’ on the shaft or gland which ultimately could sink the boat of the coupling fails with shear forces. However, a surveyor said to me- not a problem just use heavier duty rubber (and an engineer has suggested exhaust hose- commented that this is ideal but people don't use it as it is very expensive).

What do I do here I wonder?- go with the traditional (which I like) with a heavier duty rubber, or try a new type like a Volvo seal (but I'm not sure that will work as only about 1.5cm of stern tube is available for fixing it to and not sure you can use Volvo seals with semi flexible couplings).

Any help appreciated!

I too, prefer the traditional packing gland, and it seems that thousands are simply mounted on rubber hose, without any problems. Personally, with several boats over the years, my packing glands have always been solidly attached to the stern tube, but the modern tendency is to use beefy rubber hose, with or without locating dogs.

 

[vyv_cox]

My advice is not to use exhaust hose. The correct stuff is available from several suppliers.

Best way to avoid possible hose damage is to nip up the packing bolts gently, checking that the shaft rotates with minimal torque at each stage.

 

[AndrewB]

A sore point for me because I was nearly sunk in the middle of the Pacific by damage to this hose. Dead calm, so I'd motored all day in hopes of reaching the trade-winds. I turned the engine off when it started rattling, suspecting it had come out of alignment. At midnight the bilge alarm went off. Stupidly I assumed a fault in the alarm, and turned it off, but a little while afterwards water started to cover the floorboards. Panic! Would we have to take to the liferaft 300 miles from the nearest land? Was my grab-bag sufficient?

But first, where was the leak coming from? A major job checking: stores would have to be shifted and floorboards raised. While I rushed around seacocks, by a stroke of good luck SWMBO guessed right first time. The stern gland was now so deep under water you couldn't see water coming in, but she stuck her arm right down and felt the gush. I couldn't see the hose, and thought it had gone altogether. But feeling down I could tell it had just partly split and come off the gland. Pushing it back on reduced the flow to a trickle, and at least we were able to bail, fortunate that it was a dead calm. Then when the level was low enough, I wrapped the whole thing in a glass-fibre bandage secured with great splodges of epoxy glue and hose clips, which held, though I didn't dare use the engine again except for the last quick burst into a marina where I was able to get a lift-out.

Incidentally, this was exhaust-hose.

 

[Tranona]

I too, prefer the traditional packing gland, and it seems that thousands are simply mounted on rubber hose, without any problems. Personally, with several boats over the years, my packing glands have always been solidly attached to the stern tube, but the modern tendency is to use beefy rubber hose, with or without locating dogs.

Very simple answer to that - the use of the heavy hose is to allow the engine and shaft to move. If you have fixed inner bearing in the stern tube, either you need a solidly mounted engine or a flexible coupling. In other words if you want a flexibly mounted engine you heed to isolate the engine movement from the shaft. Attaching an old fashioned stuffing box with a flexible tube was the quick fix compromise before better methods of sealing the stern tube and shaft were developed.

However there is no reason why you cannot replace a solidly mounted stuffing box with a superior modern shaft seal. I have done it on one boat and am just about to do it again on another

 

[LittleSister]

It's a perfectly normal and very reliable way of mounting a stern gland.

BUT, it is essential to use the proper hose sold for the job. (See Vyv's post above.) This is not a part to save a few bob on!

p.s. - Also replace the existing hose if you have any doubts about it.

 

[penfold]

The helical metal wire reinforcing of exhaust hose tends to give it a permanent curved set and it is very stiff; this is not suitable for use with a stern gland.

 

[vyv_cox]

The helical metal wire reinforcing of exhaust hose tends to give it a permanent curved set and it is very stiff; this is not suitable for use with a stern gland.

And the wire will fatigue if only a short length is fitted. My exhaust hose perforated due to broken wire ends in the length between the silencer and skin fitting, about 6 inches. Took me a very long time to find that leak!

 

[NormanS]

Very simple answer to that - the use of the heavy hose is to allow the engine and shaft to move. If you have fixed inner bearing in the stern tube, either you need a solidly mounted engine or a flexible coupling. In other words if you want a flexibly mounted engine you heed to isolate the engine movement from the shaft. Attaching an old fashioned stuffing box with a flexible tube was the quick fix compromise before better methods of sealing the stern tube and shaft were developed.

However there is no reason why you cannot replace a solidly mounted stuffing box with a superior modern shaft seal. I have done it on one boat and am just about to do it again on another

Or you have a properly engineered installation, like mine, where the thrust from the prop shaft is taken by a thrust bearing, and there is an Aquaflex (or similar) coupling between the bearing and the flexibly mounted engine.

 

[Tranona]

Or you have a properly engineered installation, like mine, where the thrust from the prop shaft is taken by a thrust bearing, and there is an Aquaflex (or similar) coupling between the bearing and the flexibly mounted engine.

Indeed but very few boats do, including the boat in question. You have to deal with what is not what you would like it to be.

Oh and by the way the sort of installation you have is not the only "properly engineered installation" saying that is an insult to the engineers that have developed alternatives that do not require a thrust bearing or an Aquaflex. Yours in only one solution to the problem and not now commonly used.

 

[NormanS]

Indeed but very few boats do, including the boat in question. You have to deal with what is not what you would like it to be.

Oh and by the way the sort of installation you have is not the only "properly engineered installation" saying that is an insult to the engineers that have developed alternatives that do not require a thrust bearing or an Aquaflex. Yours in only one solution to the problem and not now commonly used.

Please don't try to put words in my mouth. Nowhere did I suggest that the installation with thrust bearing, and flex coupling was the ONLY properly engineered solution, but it's certainly better engineering than something flopping about on a bit of rubber hose, which in your own words, was "a quick fix compromise".

 

[Tranona]

Please don't try to put words in my mouth. Nowhere did I suggest that the installation with thrust bearing, and flex coupling was the ONLY properly engineered solution, but it's certainly better engineering than something flopping about on a bit of rubber hose, which in your own words, was "a quick fix compromise".

The "quick fix" compromise if you read what I said was to adapt a stuffing box the a flexibly mounted engine/shaft arrangement, since largely superseded by other simpler arrangements that do not use stuffing boxes - nor do they need the complication, cost and space of a thrust block or an Aquaflex.

 

[NormanS]

The "quick fix" compromise if you read what I said was to adapt a stuffing box the a flexibly mounted engine/shaft arrangement, since largely superseded by other simpler arrangements that do not use stuffing boxes - nor do they need the complication, cost and space of a thrust block or an Aquaflex.

Well, maybe, but the OP has the quick fix, and like thousands of others, it'll be fine. It just won't be as good as a properly engineered solution.

 

[Tranona]

Well, maybe, but the OP has the quick fix, and like thousands of others, it'll be fine. It just won't be as good as a properly engineered solution.

In what way not so good? The only weakness is that the stuffing box leaks whereas the alternatives available now don't. There is no need for the sort of complicated arrangements such as you have.

 

[penfold]

At the low power end of auxiliaries the gearboxes all have thrust bearings, there's little difference between those and yours other than existing at a different point on the cost/NVH curve. All work, all have been signed off by classification societies.

 

[NormanS]

In what way not so good? The only weakness is that the stuffing box leaks whereas the alternatives available now don't. There is no need for the sort of complicated arrangements such as you have.

Well, for example, my engine and prop shaft don't move fore and aft, when engaging gear.
Very little skill is required to avoid a packing gland from "leaking". They are designed to have a regular drip when the shaft is rotating, but leak - no.

 

[Tranona]

Well, for example, my engine and prop shaft don't move fore and aft, when engaging gear.
Very little skill is required to avoid a packing gland from "leaking". They are designed to have a regular drip when the shaft is rotating, but leak - no.

So what? Can't see any advantage of the shaft and engine not moving, after all any movement is catered for in the design of the power train. Whether you call it a leak or a drip there is no need to let water into the boat from this source.

If you want a really well engineered solution that avoids the problem of having a shaft going through a hole in the bottom of your boat and absorbing the thrust evenly over the whole of the boats structure then fit what the majority of sailing boats with under 70hp now do - a saildrive.

 

[NormanS]

So what? Can't see any advantage of the shaft and engine not moving, after all any movement is catered for in the design of the power train. Whether you call it a leak or a drip there is no need to let water into the boat from this source.

If you want a really well engineered solution that avoids the problem of having a shaft going through a hole in the bottom of your boat and absorbing the ithrust evenly over the whole of the boats structure then fit what the majority of sailing boats with under 70hp now do - a saildrive.

Have it your own way. ?

 

[Keith-i]

So what? Can't see any advantage of the shaft and engine not moving, after all any movement is catered for in the design of the power train.

I can, namley less vibration and greater longevity of the cutless bearings. Admittedly this doesn't have much significance on the choice of stern gland. Personally, I have a Python Drive thrust bearing and a Lasdrop Gen 2 shaft seal. No drips/leaks and very little vibration.

 

[penfold]

How about arguing about how many AWBs can be fitted on the head of a pin?