Bronze stern tube in Steel Hull

[machone]

Welders are welding like mad - we're under time(it's money!) pressure. A slow steel yacht with a low hp highish tq engine and big prop. It has a shaft through the hull stuffed and remotely greased. This worked well but leaked a little and the steel in the hull is showing signs of wear - flaring. There were some funny noises on the last trip before laying up.

I'm thinking of replacing the old system with a Vetus(Volvo) water lubed shaft. This comes with a bronze stern tube. What I am worried about is the galvanic corrosion between the tube and the steel - is there an effective way to isolate the parts and what is best? I don't want to coat the bronze with anything that will act as a wick.

Also, from anybody who has done it, is it worth the swap?

Advice welcome.

Thanks

 

[Neil_Y]

Surely much cheaper and easier to get a steel tube fabricated and install bearings in this at one end and some form of gland seal at the other? ideally water fed to allow clean water to the bearing. This sort if thing is commonly fabricated on commercial boats often changing from greased/oil white metal bearings to water lubed.

 

[rogerthebodger]

Fabricate a steel stern tube and P bracket if your design needs one.

On my steel boat I have tried to have as little bronze as possible to such an extent all my skin fittings and sea cocks are stainless steel and I have even fabricates my prop in stainless 316.

The only bronze I now have is my bow thruster leg.

 

[machone]

Got it, thanks.

I liked the idea of the tube that let the shaft move a bit with elastomeric bearings but sounds like bronze is a no-no. I have a brass skin fitting for the webasto but that's above the water line. Not sure how I can fit a new tube for a volvo type seal without the fancy lining. Not sure I trust a single bearing. Priced up labour and skill for a bearing option and it gets pricey pretty quick.
Looks like the best option is to get a new prop/shaft and tube and stick with the grease.

 

[Neil_Y]

Elastomeric bearings when compared to hard bearings have shown greater wear and vibration, they allow the shaft to bend and flex which increases vibration, hold the shaft straight and allow the engine to move is the preferred option. I can give you independent feed back from a commercial boat if you like. If you are still at the design stage you can use modern bearing materials as very thin wall greased bearings to save bearing material costs. A new steel tube and a water feed and a hard bearing would be the easiest cheapest and probably best option, water is a great lubricant and coolant. You can use this calc to work out clearances http://www.h4marine.com/Downloads/Maritex AQUARIUS General Calculator REV 20100519.xls