Stern tube question.

[Jiggz]

Hi all

Pictured is the stern tube from a 1980's built Lambie lifeboat we are busy refurbishing in Cape Town.
On disassembly the tube contained apparently only old, hardened and very black grease, which seems odd but I have no real reason to disbelieve the man who dismantled it.

It is obvious though that there must be something in there, possibly in the obvious groove, that keeps the water out....

Does anyone have any advice, experience or knowledge as to the correct way forward to reassemble this please?

With appreciation....

 

[ribrage]

is there a twist style greaser fitted to the inside of it ? I have a variable pitch prop on a work boat that looks very similar to that and it is a simple greaser with no seals as such

 

[Tranona]

That is the outboard end and probably does not have a seal if the tube is water filled with a stuffing box or similar seal at the inboard end. There should be a bearing in the housing - and looks like there is from the photo. It could be either water lubricated rubber cutless type bearing or a composite.

Sorry, just looked again, and if it is totally grease filled then there could be an O ring in that groove. and the bearing could be either a composite or white metal.

 

[Poignard]

I have never seen one like that but there must have been some kind of seal (otherwise what is the point of the groove?), and the groove suggests an o-ring.

 

[Findhorn]

My money is on a traditional stuffing box with greaser..that bearing needs lubrication...usually water.An "O" ring at that end would stop the water getting to the bearing

 

[Poignard]

My money is on a traditional stuffing box with greaser..that bearing needs lubrication...usually water.An "O" ring at that end would stop the water getting to the bearing

Maybe the bearing is lubricated with grease (or thick oil)? A lifeboat may have to operate in shallow water and a water/sand slurry would rapidly wear out the bearing.

 

[RobinBirch]

Hi Jiggz

You might be better posting this question in the more mainstream PBO forum where some of the marine engineer pro's hang out.

For what it's worth it looks to me that you have a pretty standard stern tube/aft housing with a composite bearing which is lubricated by water passing by the grooves. There must be a greaser/stuffing box somewhere on the inboard side of the shaft. The hard black grease encountered on dismantling may in fact have been the product/mastic used to seal in the stern tube. If too much was used the excess resulting on tightening up the aft housing can block the grooved waterways of the composite bearing - resulting in excess wear of the shaft/bearing.

 

[ccscott49]

If it was a ships lifeboat, they are designed to run out of the water and would have been grease lubricated, with a lip seal or felt seal and retainer at the outboard end and a seal/stuffing box at the inboard end, similar to the RNLI lifeboats, which had white metal bearings, seals and recirculating water soluble oil in them. But as long as it has a bearing in the end which can be water lubricated and a stuffing box inboard, should be fine.

 

[Neil_Y]

I'm thinking that's white metal, and possibly a lip seal with grease or oil lubrication. You can replace the white metal with a composite bearing bedded on epoxy, but it will need oil/grease or water to lubricate it. Water is best as it conducts heat better and lubricates well.

 

[ffiill]

If its like mine bearing will be white metalled the same as car engine bearings.On the inboard end of mine there is a stuffing box with greaser.
If the bearing is worn there are specialist firms in the uk who can reline the bearing with white metal and ream out to size.

 

[mtb]

printers lead could be used to make new white metal bearings, I used to have a complete mod white metaling bearing kit which had inner and outer moulds. Once hardened you use blue to check for contact re high and low spots then using a bearing scraper take out the high spots until you get an even surface
These days you would machine the surface before final finishing.
I recon along with others it had a seal in that groove to allow initial start up before launching and the oil in the tube would be heavy 140 grade ish which over time could turn black
these people are very good http://www.tnorrismarine.co.uk/

cheers
mick

 

[captainboo]

It looks almost identical to my sterntube. Mine has identical groove just inside the end and then three grooves at 120 deg spacing parallel to the shaft. All these are in the 'white metal' that forms the cutless bearing. Mine has a greaser at the front end with a conventional stuffing box. Next season I intend to replace the front end with a PSS seal and replace the white metal liner with a modern composite bearing from h4marine rather than try to get it relined.

 

[itchenseadog]

As others have said, what you have there is a standard grease lubricated stern tube. We used to fit loads of these. There is a white metal bearing on the outer end with a grease cup and stuffing box inside. The solid black stuff is more than likely solidified grease. We used to recommend a turn of the grease cap prior to using the boat and a turn when back on the mooring. If using for long periods, a turn every 5 or 6 hours was reccommended. A nice and simple system.