Steel stern tube mystery?

Much better practice to have the steel tube clear of water.Thats why there is a bronze tube supporting the cutless bearing at prop end and the seal at the g/box end.I wouldnt like to have a steel tube open to sea water.How do you protect from corrosion?I also dont agree that Vetus equip is no good.Over the years I have been very satisfied.
 
Thanks folks there comments are really helpful. A few comments ago a bronze bearing was not recommended. Can you tell me why? And what should the bearing material be?

Thanks Alan.
 
AlanR said:
Thanks folks there comments are really helpful. A few comments ago a bronze bearing was not recommended. Can you tell me why? And what should the bearing material be?

Thanks Alan.
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I can think of no reason why a bronze bearing should not be OK. Assuming from the previous posts that there is no rubber cutless bearing there then a leaded tin bronze is probably the next best choice. The link posted earlier by Blowing old boots shows lots of these components, which they describe as 85-5-5-5, which is Cu-Sn-Zn-Pb, but all are intended to have a cutless rubber bearing inserted. If going for a tube with no cutless bearing it would be safer to increase the lead content, so a 75-5-20 (Cu-Sn-Pb) would probably be best, followed by 77-8-15 and 80-10-10.
 
Hi Vyv
85-5-5-5 is this 'Naval Brass" and is it good for use underwater on a steel craft and if so what would be good bolt material to use with them please?
 
AlanR said:
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
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Ball and roller bearings are steel on steel. However, how short is your stern tube? If, for the sake of argument, the stern tube was just 4 inches long and the shaft was supported by bearings inside the boat, then I dont see why there would need to be any bearing inside the stern tube. And the fact that there hasnt been any shaft wear suggests either that the shaft is supported in this way or the bearing has just dropped out. Steel on steel would give definite witness marks / scuffing.
 
ean_p said:
Hi Vyv
85-5-5-5 is this 'Naval Brass" and is it good for use underwater on a steel craft and if so what would be good bolt material to use with them please?
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The 85-5-5-5 material is a leaded bronze. It has a small zinc content that is mainly there for deoxidation purposes, whereas Naval brass is a 60/40 brass (60 Cu/40 Zn) with a small tin addition. The bronze is excellent underwater.
Bolts for underwater use should be tin bronze with good tensile strength. Phosphor bronze is often used (e.g. Blakes seacocks) copper with between 2.5 and 8.5% tin and 0.1 to 0.35% phosphorus. Silicon bronze is also good but bolts in this material seem to be less commonly available. I find this site useful for reference.
 
I did ask Van Der Stdat if it was one of theirs, and they said no. It is a well designed and clearly a yard built boat that has been built for serious off shore sailing. For instance the saloon sear backrests are designed to double as lee boards.

Does any one know whose design it might be? It was built by Van Der Vliss in Holland in 1973. See photo
 
AlanR said:
I did ask Van Der Stdat if it was one of theirs, and they said no. It is a well designed and clearly a yard built boat that has been built for serious off shore sailing. For instance the saloon sear backrests are designed to double as lee boards.

Does any one know whose design it might be? It was built by Van Der Vliss in Holland in 1973. See photo
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It could be a Cumulant 31, built by Van der Vliss at that time.
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That photo is most interesting. Very similar. Who or what is 'Cumulant? Is it a design, if so who did them (there seem to a number of other similar boats around) There also seem to be Cumulants in steel in larger sizes.

Thanks Alan
 
The photo came from an advert here where there are more pictures.

I've googled Van der Vliss and Cumulant on various Dutch web sites. Some say Van der Vliss was the builder and designer of the 31, some say they are designed by Van der Stadt (None of them were referring to The Stig!)
More recent Cumulants were built by different yards, but were still designed by Van der Stadt.

Even if Van der Stadt did design it, it is quite possible that details like the prop shaft were either left to the builder, or the builder chose to ignore the design.


I guess this is yours. It lists is as a Cumulant I!
 
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Yes, so right you are! Actually its my Son's Ian, he's just bought it. Apart from lots of hard work the vital repairs are to the prop shaft bearing and the mast step which is rusted through on one side. We spent the last week of last year getting the mast down and the engine out to get the prop shaft out. Fortunately although the Taylor diesel was a bit temperamental it kept us nice and warm.

Alan
 
Here is an update and a question?

It turns out that the stern bearing is a tight fit in the stern tube held in by a grub screw. During boat building this screw had been welded over as the tube was fixed to the hull. It came out with a few blows of a mallet on the end of a long bar.

The bearing mystery solved itself when we came to bore the housing out to fir a new bearing, its made of cast iron which having a high free carbon content can be an excellent bearing surface. (Think of the pistons in the cast iron cylinders of an engine.)

Attached are some pics. (The bar is not the prop shaft its an old piece of tube.)



Now the question. We have the opportunity to replace the stuffing box with a water lubricated bearing fed from the water pump and also to use a composite stern bearing. If we do this will the anodic protection provided by sacrificial anodes on the outside of the hull also protect the inside of the stern tube?

Assuming we refit the existing stuffing box, probably with PTFE impregnated cord, do you think there would be any problems if we still fit a composite outer bearing? It will be lubricated by a mixture of grease and water.

Cheers Alan
 
Wtare lubricated bearings don't like greae as the grease blocks the water channels and the water film becomes boundary and heat can build up as grease is a poor conductor of grease.

Water is an excellent lubricant and coolant, over greased stern glands where the grease finds its way back to the bearing can result in prematurely failed bearings.

Grease is only good for slow moving high load bearings, shafts like water or oil.
 
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