Graphite epoxy rudder bushes

PabloPicasso

PabloPicasso

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As part of a rudder refurbishment I'm considering using epoxy with 10% graphite powder to make the bushes. Graphite should offer a hard, slippery, wear resistant surface perfect for bearing surfaces.


Will graphite cause galvanic corrosion problems for the stainless steel rudder stock?

Are there any other issues I might need to consider if I choose to proceed?
 
PabloPicasso said:
As part of a rudder refurbishment I'm considering using epoxy with 10% graphite powder to make the bushes. Graphite should offer a hard, slippery, wear resistant surface perfect for bearing surfaces.



Will graphite cause galvanic corrosion problems for the stainless steel rudder stock?

Are there any other issues I might need to consider if I choose to proceed?
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I've heard of that and even got the graphite.The stuff gets everywhere be warned.I'm curious about the advice.
 
Best solid material for rudder bushes is an acetal such as Delrin. Machined to proper clearances it is water lubricated and very long lasting. I fitted one on my boat in 1992 and still no wear on it. Can't see any benefit in what you propose.
 
PabloPicasso said:
As part of a rudder refurbishment I'm considering using epoxy with 10% graphite powder to make the bushes. Graphite should offer a hard, slippery, wear resistant surface perfect for bearing surfaces.


Will graphite cause galvanic corrosion problems for the stainless steel rudder stock?

Are there any other issues I might need to consider if I choose to proceed?
Click to expand...

I ve used the mix for centreboard bushes, but a lot more than 10%.. The attraction was it could be cast in situe. For what you want, Tranona's delrin is best. I get mine from www.directplasticsonline.co.uk but you need a lathe, or a friend with one.
Re the galvanic. a friend thought of mixing araldite with brass powder to build up the slip rings on a magneto, then machined them to size. Didn't work, as each bit of brass was encapsulated in the époxy, so non conductive.
 
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DownWest said:
I ve used the mix for centreboard bushes, but a lot more than 10%.. The attraction was it could be cast in situe. For what you want, Tranona's delrin is best. I get mine from www.directplasticsonline.co.uk but you need a lathe, or a friend with one.
Re the galvanic. a friend thought of mixing araldite with brass powder to build up the slip rings on a magneto, then machined them to size. Didn't work, as each bit of brass was encapsulated in the époxy, so non conductive.
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Yes it's casting in situ that I need. The GRP around the underside of the rudder tube (the bit the stock goes through). Has worn a bit. I thought an epoxy repair would be best, and why not cast the rudder bush/bearing into the mix at the same time.

Turning a bearing to fit the outside of the tube would mean boring upwards into the hull around the base of the tube.
 
I wouldn't expect epoxy to be durable enough for this. Wouldn't it wear fairly quickly? Only informed guesswork from the fact it is easy to sand down - does anyone actually know?

I would go down the Delrin route personally. Whatever you do, don't use nylon - it expands and jams the rudder solid! If it's a through hull mount you then have a real problem to extract the rudder.
 
Take a look at the properties of UHMWPE. According to the blurb on the Direct Plastics website some of its properties include:

Extremely low moisture absorption
Very low coefficient of friction
Self-lubricating
Has an incredible resistance to abrasion and can outperform almost any engineering plastic in this regard

It's also the most commonly used material in artificial joints and is also used in the gravel and aggregate industries. Because it has very low moisture absorption, it is also found in some high demand areas of marine applications.

I've made bearings for my rudder out of this. I also made a bow roller from acetal and one from UHMWPE for a friend's boat and the acetal one showed signs of wear in a season on a swinging mooring and the UHMWPE replacement didn't.
 
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oldharry said:
I wouldn't expect epoxy to be durable enough for this. Wouldn't it wear fairly quickly? Only informed guesswork from the fact it is easy to sand down - does anyone actually know?.
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I think you're right. Neat epoxy is not very wear resistant. It just depends what you mix it with, colloidal silica, microballoons, aluminium powders or other fillers like graphite alter the consistency. It makes epoxy a very versatile substance. Perhaps West are onto a good thing
 
PabloPicasso said:
Thank you. That is just perfect. One bushing is into the hull so casting in situ makes sense, one bush in the top of the rudder could be an insert, but no space in the lower rudder support to insert it as its on a plate in a slot so again, casting in situ makes sense there to.

I think I've made my decision
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I may have misunderstood here but you only need two bushes. One at the top of the stock just below the tiller and one in the bottom support plate. There isn't one in the hull below the waterline. All you need there is a flat disc slid onto the stock to prevent wear between the flat top of the rudder and the bottom of the hull. You won't be able to line up three bushes.
 
One further thought: It might be an idea to use a fresh bit of tube to cast your bushes. Any wear on your rudder stock will make it extremely difficult to withdraw the stock afterwards and might make it difficult to turn.
 
Dipper said:
I may have misunderstood here but you only need two bushes. One at the top of the stock just below the tiller and one in the bottom support plate. There isn't one in the hull below the waterline. All you need there is a flat disc slid onto the stock to prevent wear between the flat top of the rudder and the bottom of the hull. You won't be able to line up three bushes.
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Yes it is the flat disc that has been wearing into the hull. It's this bearing/bush that is the issue. It's worn a round groove into the hull, and the top of the rudder.
 
As a supplier of bearing materials, metalurgists and materials experts have been working for years to develop materials that give low wear rates for marine rudders and shafts.

Using epoxy essentially it is soft (it melts so creeps as it gets warm) friction induced heat even in sea water can warm up small parts of the bearing and it will deform. You also have to allow for the moisture absorption of the Epoxy and the thermal change to work out your starting clearance.

So yes you can probably make something that works but it will be no where near the current range of composite bearings. These don't typically use graphite unless we are looking for very low thermal expansion and dry running low friction. We supply bearings for a US submarine dive planes which have graphite and achieve very low thermal expansion rates.

UHMWPE and other polyacetal thermo plastics and polyester resin composites are out there with varying performances.

I'm biased but in rudder bearing trials for LLoyds, Maritex Aquarius (phenolic resin and fibre with two non leaching lubricants one temperature activated) achieved no wear of bearing or rudder shaft after a 1000hr test running last 200 hrs at 20Mpa.

Achieving low porosity through very high pressure molding is a key part of reducing wear and moisture absorption.
 
Neil_Y said:
As a supplier of bearing materials, metalurgists and materials experts have been working for years to develop materials that give low wear rates for marine rudders and shafts.

Using epoxy essentially it is soft (it melts so creeps as it gets warm) friction induced heat even in sea water can warm up small parts of the bearing and it will deform. You also have to allow for the moisture absorption of the Epoxy and the thermal change to work out your starting clearance.

So yes you can probably make something that works but it will be no where near the current range of composite bearings. These don't typically use graphite unless we are looking for very low thermal expansion and dry running low friction. We supply bearings for a US submarine dive planes which have graphite and achieve very low thermal expansion rates.

UHMWPE and other polyacetal thermo plastics and polyester resin composites are out there with varying performances.

I'm biased but in rudder bearing trials for LLoyds, Maritex Aquarius (phenolic resin and fibre with two non leaching lubricants one temperature activated) achieved no wear of bearing or rudder shaft after a 1000hr test running last 200 hrs at 20Mpa.

Achieving low porosity through very high pressure molding is a key part of reducing wear and moisture absorption.
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All fascinating, and to me sounds correct. My problem is that the GRP around the bottom of the rudder tube is wearing away. There is a ring between the rudder and the hull, so what do I fill the hull with?

The rudder is also worn around where the stock enters from the same ring.
It's this I want to fill and fare to make a wear resistant surface and seal against water greasing into the rudder
 
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