rudder bearings-new technologies? advice pls

[Vic]

We are considering the selection of the rudder bearings for our new design 30' performance cruiser. The steering systems suppliers offer usually Acetal (Delrin) roller bearings.
These bearings are firstly expensive. Moreover we feel that in the view of the current technologies it's likely that the more simple and reliable solutions might be available.
We were adviced to use the maintenance free plain bearings with lead-PTFE sliding layer and the bronze backing (thus seawater resistant), also available with the thrust flanges nad washers.
We are interested with any experience with the application of this sort of bearings or any other type of the modern sliding bearings.
Any advice will be helpful.


<hr width=100% size=1>Victor

 

[dickh]

Vic,
Definately go for low tech plain bearings, plenty of materials around from MOS² filled nylon to Tufnol; make sure you calculate the clearances correctly as most swell slightly when immersed. Be careful of some bearings as they may create a corrosion problem with dissimilar metals in seawater.
Good Luck

<hr width=100% size=1>dickh
I'd rather be sailing... /forums/images/icons/smile.gif

 

[Vic]

Dick,

Thanks.
Please tell me what the abbreviation MOS stands for ?



<hr width=100% size=1>Victor

 

[ex-Gladys]

MoS2 Molybdenum Disulphide.... Slippery as snail snot

<hr width=100% size=1>Larry Botheras

Anderson 26 "Amber"

 

[philwebb]

Hi Vic, I agree with Dickh. My rudder bearings were worn out and were made of white
nylon. I replaced them with nylon loaded with molybdenum disulphide ( from RS
components) which I turned up on a lathe. I had problems of tightness after about
a season`s use and had to ream out the bearings. They are now working well. You have
to make them with a generous tolerance as they seem to take up more water than
the specifications and swell. In retrospect making them a tight fit in the housing did
not help matters. If you are interested I have some of this material left over -it is around
100 mm diameter.
Regards Phil

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[Vic]

Phil,

Thanks a lot for the information and your readiness to help.
I know that PTFE and Nylon take a water and therefore Delrin / Acetal is widely used as it does not swell so much.
I wonder if the combination of Delrin/ MOS would be available on the market.
Could you give any indication upon your experience on the required tolerance asessment ?
Who are RS components ?

Kind regards,


<hr width=100% size=1>Victor

 

[beneteau_305_553]

try IAC plastics 01706 212225

They supply a range of filled plastics for submersible use.

Plain nylon expands greatly with moisture. UHMW polyethylene is a possibility.

My beneteau has a bronze sleeve approx 60 mm bore, 75 mm high, and wall thickness of 2 mm. Its split so that shims can be added between the collar and the grp housing in the hull to get the right clearance. It runs against a stainless steel collar attached to the rudder shaft. Its such a large bearing area it doesen't wear. The rudder top bearing looks to be delrin (acetal) and has worn but I havent got round to replacing it yet. Sometimes the traditional materials are still the best.

<hr width=100% size=1>Richard

 

[snowleopard]

plain bearings work well within their limits, providing you allow for water absorbtion and swelling. for higher performance and bigger runnershaft loads, especially with spade rudders, you need to go up to roller bearings. that is what whitlock advised for my 40 ft cat.

further up the performance scale there is the possibility that side loads on the rudder will make the shaft bend thereby making it bind in the bearings. to prevent this requires spherical bearings which are mind-blowingly expensive.

the best way to get by with cheap simple bearings is to use a skeg to support the bottom of the rudder.

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