Steel stern tube mystery?

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AlanR

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I posted this a few days ago, and to my surprise have had no comments. So here it is again,surely someone has some ideas?

The surveyors report on my sons 36 year old Van Der Stadt steel yacht said that there was about 2mm of play in the stern tube bearing, and it needed replacing. So off with prop and out with the shaft. We dug around with a file and saw to remove the bearing. No bearing, it appears that the shaft has been running on the steel stern tube, which is welded into the boat. Surprisingly the shaft is in good condition and will not need replacing. We expected to find some sort of bearing material supported in a bronze tube or some sort of solid bearing material a press fit in the hole with a wall thickness of about 2 to 3mm. But nothing?

Has anyone come across steel on steel for a bearing and how best to repair it?

Alan
 
It's a bit mysterious, the tube seems small for the shaft, I've never heard of steel on steel for this. The clearance is hardly enough for bearing material between. Is the tube only 2mm bigger than the shaft all through, or is there a sleeve at the end, (that used to hold a cutless bearing, or similar, I once had one with a remote lubricated bronze bush)?

What is the bearing on the inboard end?

Are there threads on the end of the tube, and clearance between it and the prop, where there once was a bearing carrier?
 
This site has some graphics and descriptions of stern shaft arrangements http://www.tb-training.co.uk

There is one description which might support what you have. The stern gland arrangement has an internal and external bushing which provide the support and not a cutless or aft bushing.
 
Thanks for you comments.

There appears to be nothing missing from the outer boss which is about 2.5 inch dia and sticks out about the same. On the inner end is the usual rubber tube attached to a conventional stuffing box gland which has a threaded end with screw in nut adjusted with a 'C' spanner. It looks similar to the assembly shown in one of the articles suggested. There is certainly no room for a bearing as most of the play is up and down as would be expected.

Has anybody heard of steel on steel?

Alan
 
No, steel on steel is just asking for scuffing problems. There has to be some sort of bearing material, either non-metallic or maybe a bronze. If steel-on-steel was a possibility everyone would use this combination.
 
I do agree with you about scuffing, when we first looked it I though; Ahh non metallic and proceeded to scrape away with a file to find the sleeve. It turned out to be rust with no apparent support tube.

Alan
 
Could a cutless bearing have worn away and the bits dropped out? The build up of rust would make the aperture smaller. Bit of a job to fit another. Perhaps you could slide a new bearing and carrier on the shaft, then weld a flange to the tube to bolt it to? Maybe shorten the outboard end of the tube to make room. I don't know if that would be good practice.
 
Your arrangement sounds more like one designed for a boat with a P bracket with a cutless bearing supporting the shaft further aft, close to the propeller.

If you have no P bracket, then the prop should be quite close to the end of the stern tube and this sterntube would normally have a bearing in the outer end. However 2mm is not sufficient clearance to house a bearing and you say there is no evidence of an internal sleeve, being the remains of a bearing, nor an overhanging bearing housing which would be fitted over the outside of the sterntube.

If there is no P bracket, we are left with the possibility that you have a makeshift arrangement with no facility for fitting a bearing. Steel on steel would not be a satisfactory long-term engineering solution, due to the lack of a provision for taking up wear. You would expect quite a lot of vibration when running under power with 2mm clearance in the shaft bearing.

If the steel tube has a sufficiently thick wall, you may be able to open it out carefully at the end with a drill and reamer to house a standard cutless bearing which would have a wall thickness of about 3mm.
 
I have seen a steel shaft in a steel tube......on a steel boat-therefore no galvanic problems.
It had a few millimeters of play, due to waer on the shaft, but it had done 28 years, and been around the world 2 1/2 times!!

They like plenty of grease, right down the tube.

You could machine up a steel or whitmetal bush, after opening up the tube a bit (reaming).

You may have to weld some brackets on to do this.

Keep clear of bronze though.

Edit...this seems a repeat of the above posts, but my two year old was helping me to type slowly!
 
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Seanick said:
I have seen a steel shaft in a steel tube......on a steel boat-therefore no galvanic problems.
It had a few millimeters of play, due to waer on the shaft, but it had done 28 years, and been around the world 2 1/2 times!
Click to expand...

Seanick - this is triggering a memory of looking at one of those Bruce Roberts "Spray" design yachts which was out the water. I am pretty sure I noticed that the stern tube was hollow, noticeable because of the gap, not what was expected at all.

http://www.bruceroberts.com/ Bruce Roberts can be emailed at this web site and he might provide some guidance.

AlanR have you tried contacting http://www.stadtdesign.com/ directly.
 
There are some brilliant ideas coming now, thanks all. I'm most interested in that there does seem to be steel on steel bearings out there. Any more ideas?

Thanks Alan
 
Having had 3 steel boats never heard of steel on steel.Most steel pleasure craft have a steel tube welded into the hull going thro. the keel.Inside this is a bronze tube thats bolted at the prop end and fits into a split type of clamp.the prop end is tightened and then the split clamp.The stainless prop shaft goes inside the steel tube.Mine has a cutless bearing at prop end and another halfway down the bronze tube. If you look in a Vetus catalogue there is usually one shown.As suggested probably best to contact the makers of the boat.
 
nedmin said:
Having had 3 steel boats never heard of steel on steel.Most steel pleasure craft have a steel tube welded into the hull going thro. the keel.Inside this is a bronze tube thats bolted at the prop end and fits into a split type of clamp.the prop end is tightened and then the split clamp.The stainless prop shaft goes inside the steel tube.Mine has a cutless bearing at prop end and another halfway down the bronze tube. If you look in a Vetus catalogue there is usually one shown.As suggested probably best to contact the makers of the boat.
Click to expand...

Sorry, can't agree. Most steel boats have a steel stern tube welded in, with either a flexible inboard bearing/stuffing box as the OP, and either a plain steel bearing, removable white metal bearing, or a cutlass phenolic bearing.

Bearing in mind the age of the boat and its designer, it is quite likely that a plain steel bearing will last as long as it has. It is a sailing machine, not a narrow boat.

If the prop is balanced and has no fouling there is very little loading on the bearing surfaces, especially as it should be well greased.

Most Vetus gear is cheap toot and should not be used on a boat like this.

A pic of the outboard end might inspire some more suggestions.
 
That tube looks like it's tapered, so there's more room further in. Scrape around and clean up the outside end you may find some set screw or other fastenings, some sort of collar holding the bearing which is or was up inside the tube. Mine has a collar screwed to the end of the bearing, bolted to the end of the tube. What's the shiny bit we can see on the end of the tube?
 
The shiny bit is flash reflection. I scraped of the paint to see that is is steel. Next time we go we will have a look for a set screw or other fastening.

Thanks Alan.
 
I would guess it's a white metal bearing. It is still possible to find metalwork shops that can recast the bearing.... no idea of cost however. If it's anything like mine you'll struggle to fit a modern stern tube into the space of the old one.
 
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