"plastic" rudder shaft bearing

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andybussell

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\"plastic\" rudder shaft bearing

The bottom of my rudder shaft rotates in a cup-shaped white "plastic" bearing which looks like an old-fashioned ink well (walls and top flange 7 mm thick). The bearing has broken and needs replacing.

Does anyone know exactly what the material is likely to be and where to get a new bearing made? The boat is a Barbican 33.
 
Re: \"plastic\" rudder shaft bearing

If it is broken as in cracked, it may be poly-acetal. There are many brand names and colours ranging from black to white for this material.
 
Re: \"plastic\" rudder shaft bearing

The best material for this application has the trade name "Orcott" Do NOT use Nylon 66 widely available as it is fiercely hydroscopic and will swell up when wet.
 
Re: \"plastic\" rudder shaft bearing

We use "Oilon" or "Nyoil" for our rudder and stern bearings in the Albin Vega club. It is an oil impregnated nylon that will swell by maximum 3% in water. Allow for this when you make it. Available from all good platic suppliers and Farnell or RS. Easy to machine and lasts for ages.
 
Re: \"plastic\" rudder shaft bearing

My last and current boat had a similar problem. I cast a new bearing with West epoxy and a sintered filler. 30,000 miles later, still going strong ......
 
Re: \"plastic\" rudder shaft bearing

Actually Delryn is an acetal based product too and properly called Ertacetal H
If you can get it Ertacetal HTF is even better but for a rudder bearing WITH PROPER MECHANICAL SUPPORT either will do as neither are hydroscopic to the same degree nylon is. As Steve says, using any form of nylon you will have to leave the bearing a loose fit as it will swell. If you use acetal it has not got the mechanical strength of nylon and may crack (as yours has)
Orcott is a material we used extensively in my shipbuilding days but I can't find it on the internet now so it may not be available. I think it is also acetal resin but has fibrous reinforcement, not sure.
If you do use Nylon the stuff to avoid is bog standard 66 grade that will swell horribly.
 
Re: \"plastic\" rudder shaft bearing

Looked up Orcutt in some old design notes. I now think (not sure) it was a PEEK (Polyetheretherketone) plastic with glass reinforcement. The reason we used this originally was its high temperature resistance and almost zero hydroscopy. Obviously we used it for other things because we kept it in stock.
Frankly you will have to go with what a local machine shop has in stock or it will cost a fortune. Delryn is widely available so long as the bearing is a good fit in its outer housing and therefore supported Delryn should be fine.
 
Re: \"plastic\" rudder shaft bearing

Thordon is readily available around the world (in fact is a British product) and is very well regarded for water lubricated bearings in both the marine and land based (eg mining) industries.

It is expensive but, of course the quantity needed is small. Am slightly biased as we specified it for our rudder stock and propellor shaft bearings /forums/images/graemlins/smile.gif, but is widely used, certainly around this side of the world.

A google on Thordon throws it up.

John
 
Re: \"plastic\" rudder shaft bearing

Yes. In have used this too and its excellent. I think you will find head office in Canada rather than UK though. The company usually like to sell finished bearings rather than supply material in the UK. At VT we did use them for high load bearings such as the rudder stock on Mirabella V as the material is actually flexible. Its a fully cross linked thermoset copolymer in the urethane group similar to "Adiprene". Unfortunately it's virtually impossible to find a corner machine shop with this material in stock and it's therefore going to be a bit expensive.....
 
Re: \"plastic\" rudder shaft bearing

Hi Mike - yes agree 'tis Canadian, dunno what was on my mind there. Think it may have been as may have seen a big promo on use in UK naval vessels, perhaps /forums/images/graemlins/blush.gif.

Regarding the availablity of it here, the Thordon importer is just down the road from our home and I checked with him this morning regarding availability of profiles. Solid bar is readily available for machining free form bearings out of and if he doesn't have the wanted size in stock is usually only a weeks delivery from Thordon.

There is a distributor in UK - AND Group PLC I believe.

One of the users here is Henleys (the prop and related manufacturer) who you may have heard of as their props go to UK, they remanufacture it into some of their products. As I think I said, our own rudder and prop shaft bearings are Thordon, but I don't recall what exact grade.

Which leads to a question from me - from various posts on these forums I get the impression that Cutless type rubber composition bearings are widely used in the UK. I wonder why they are so popular given the problems with them (and seemingly indicated so by many posts), compared to better composites, due to their comparatively short life and damage from abrasive marine growth in them in boats not in continual service, silty water, etc?

John
 
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