stern gland

ghostlymoron

ghostlymoron

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my mirage 28 has a stern gland without the usual rubber tube. i.e. the gland itself is screwed onto the fitting at the end of the stern tube. This seems a superior arrangement as there is no danger of the rubber splitting and leaking. Why are all boats not like this?
 
There is no allowance for engine movement if you have rubber engine mounts fitted to reduce noise and vibration.
 
They often have a white metal bearing inside them that keeps the whole shaft rigid. Therefore only of use if the engine is solidly mounted.

Not sure that split hoses is a common problem and easy to check. Leaks are more often caused by wear on packing and shaft, particularly bronze shafts.
 
I remember many years ago when I first began messing about with yacht propulsion systems, I asked an ex ship's engineer colleague a few questions about my stern gland. He could not believe that there was no bearing at the centre of the shaft. All ships engines are rigidly attached to the hull bedplates, the aft bearing likewise, and a Plummer block bearing supports the shaft in one or maybe more places. Shaft run-out is regularly monitored.

It was only with the requirement for low transmitted engine vibration that soft mountings came into use, meaning that rubber cutless bearings, flexibly mounted stern glands and no centre shaft bearing became the norm. Engines are now free to wobble about to their hearts' content, within the constraints of the shaft to stern tube clearance, and shaft runout is of no concern except during original alignment. Until the problem of high thrust became apparent, when the Aquadrive and similar designs entered the scene.
 
My engine does seem to be noisy - although it is my first boat with an inboard diesel so I have nothing to compare with - would this be improved by fitting a 'rubber hose' type stern gland. I'm not sure whether I have rubber mountings on the engine.
 
Would I be right in thinking you have a horizontal single cylinder Yanmar YS8 or 12? In which case it will be solidly mounted and I expect the stern gear is Stuart Turner.

Yes it will be noisy compared with more modern flexibly mounted engines, particularly 2 cylinder. However, and probably no consolation, better than many of its contemporaries! Good insulation of the engine box might help if you have not already done that, but not a lot else you can do.
 
The engine is a fairly new < 5 years Yanmar 2GMF fitted by the previous owner. Not fitted any sound deadening yet as the engine compartment is cluttered with water pump, calorifier, Eberspacher etc so fitting would be a nightmare.
 
The rule of thumb is that you can have any two of the following three flexible but one must be a solid connection

stern gland

engine mounts

shaft coupling

all three allows uncontrolled flexing

although some would say that an R+D coupling is solid enough to count as solid
 
A 2 GM should be very quiet and smooth. It should have flexible mounts and will almost certainly have a flexible coupling (probably an R&D) between the gearbox output and the shaft. Easily recognised as a white plastic disc. This will allow the engine to move even though the shaft is fixed.

I have a very similar installation but with a 1GM, also using a rigid shaft like yours. However I replaced the R&D coupling with a more sophistcated (and therefore expensive) Bullflex. However, biggest improvement in refinement is insulation. A waterlock and possibly a silencer in the exhaust line can also help.

As I said a flexible stuffing box is not going to help as the shaft is held rigid by a bearing and flexibility would lead to bearing wear. There is a way of introducing some flexibility into the stuffing box area but a re-design and machining involved and probably not worth it.
 
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