Lower rudder bearing - grease or not?

[garvellachs]

I have the spade rudder out of our Dehler 372 currently. It has an alloy stock. The lower bearing is a stainless sleeve epoxied onto the shaft, inside a tall plastic bearing fixed into the stern at the bottom of the rudder tube. It was greased when I removed it - should it be? or should it rely on water alone? There's a small screw cup greaser into the grp tube well above the bearing, but my guess is that is to keep grease in the upper bearing to stop water slurping up into the stern. Any thoughts please?

 

[Neil_Y]

Probably not, but it depends on the material being used, if it's open to the water with no seal then it should be a water lubricated material. We would use a Maritex Aquarius grade for rudder bearings which have dry lubricants and also resist marine growth. But it all depends on the material you have. The clearances will also vary depending on the material being used as the swell characteristics can be quite different.

 

[Bosun Higgs]

It depends! If your local waters had lots of sediment in them I might be inclined to leave it ungreased - sediment can turn the grease into a grinding paste. If the waters are clear I would grease - I dont like stainless under water and the grease might help prevent the stainless corroding as it rubs in the bearing.

I have never greased any of my shaft bearings - they have all run in nylon bushes quite happily.

But in truth, I don't know the answer so I'd suggest asking an "authority".

Let us know the result.

 

[oldharry]

Three things: One it is well known that Nylon expands in water, and a number of owners who have used Nylon to replace rudder stock bearings have found after 6 months or a year the nylon has swollen enough to jam the rudder completely. Subsequent removal to rectify has been - er -difficult!

Secondly Stainless below the water line is prone to crevice corrosion if it is in an anaerobic environment - i.e oxygen free. A submerged greased stainless bearing would be just that, so is risky. I have seen a stainles steel prop shaft seriously corroded round the cutless bearing where over enthusistic stern gland greasing had filled the stern tube and worked its way into the cutless bearing in only 9 months service.

Thirdly, grease in the lower rudder bearing can attract sand and silt, converting it in to a very effective grinding paste, unless there is a means of repalcing the grease regulalrly and pushing the contaminated grease out. Water is a very good lubricant in its own right.

 

[garvellachs]

Thanks for your thoughts - the bearing sits just out of the water when at rest in still water. Otherwise water will slurp up into it when on the move.

 

[PaulR]

probably same as on our dehler 34 and we used to grease it but following advice now don't - our concern with greasing was that grit and bits washed out of cockpit floor could go down open rudder shaft tube and be lodged by the grease- our main bearing has clearance grooves in it which we guess is to allow grit to wash down if small enough?