Material for rudder bushes

Definitely not Nylon. An acetal such as Delrin is commonly used, but you need to ensure you get it machined with correct clearance for the size of bearing.
 
1. Acetal - I bought my last lot from an eBay seller who has a branch in Crawley.
2. Vesconite - www.vesconite.com, a South African company with a branch in the UK, tel 0800 731 9745. If you call them they will send you a suitable size offcut. They have a machining guide on their web site to calculate the tolerances (very useful when you're pressing the bearings into a housing as that tends to shrink the bore). I have used Vesconite for several rudder bearings and sterntube bearings and they have much better wear resistance than off-the -shelf brass/rubber types.
3. Someone on here knocks up bearings from a material that I have no practical experience of. From the specs I have read it doesn't seem that much different to Vesconite (maybe a fraction less water absorption), but whether he will sell you an offcut you can machine yourself I have no idea.
 
Had the bearings for our Pegasus machined from acetal. Water absorbtion was a concern but now five months in the water and absolutely no sign of tightening up, we opted for a very light sliding fit on the 25mm shaft.
 
With a transom mounted rudder like the one on the GK29 it probably doesn't matter too much. I must say I don't remember any bushes at all on mine. It is so easy to replace them by pulling out the long rod that disposable ones would be perfectly OK. On my gooseneck I bushed the aluminium fitting that had become very worn and used pvc water tubing as the bearings, expecting to replace them annually. In fact they have been there for four or five years now, no wear at all.
 
If in any doubt about the water absorption of a plastic, leave it to soak for a day in water, then microwave it (with a cup of water alongside to avoid blowing up the microwave).

If the plastic warms up, it has absorbed water.

(Tip from a broadcast television antenna manufacturer.)
 
Graham_Wright said:
If in any doubt about the water absorption of a plastic, leave it to soak for a day in water, then microwave it (with a cup of water alongside to avoid blowing up the microwave).

If the plastic warms up, it has absorbed water.

(Tip from a broadcast television antenna manufacturer.)
Click to expand...

And if you weigh it before and after you can determine how much water was absorbed.
 
I made my rudder bearings from nylon loaded with molybdenum disulphide ( a very good lubricant). This material is available from
RS components. They have a catalogue on the internet. It is tricky to turn on a lathe as it is very slippery. I made the mistake of having the
tolerance too tight and had to ream the bearings after they were fitted. The end result has been very good and they have lasted around
15 years so far. The originals appeared to be white nylon and had lasted 20 years.
 
Plastic bearing - water absorption. So what!

Rogershaw said:
And if you weigh it before and after you can determine how much water was absorbed.
Click to expand...

I cannot perceive that water absorption on a rudder pin bearing is going to cause any problem at all. There is no way that a minor volumetric expansion would cause seizure. Given that a rudder pin is say 16mm diameter with a tiller arm of 800mm in length that produces a mechanical advantage of 100:1 so a 10kg load on the tiller would produce a 1000kg load on a 'seized' shaft. It's going to move!

I recently replaced the pin on my transom mounted rudder and considered using bushes but instead opted to replace the pin with a larger diameter pin and machined out the pin pivot brackets. Therefore, the rudder pivots without any bearings. However, next time the pin and/or bracket wears I will machine out the bracket to accept flanged phosphor bronze bushes but wouldn't hesitate to use nylon.
 
philwebb said:
I made my rudder bearings from nylon loaded with molybdenum disulphide ( a very good lubricant). This material is available from
RS components. They have a catalogue on the internet. It is tricky to turn on a lathe as it is very slippery. I made the mistake of having the
tolerance too tight and had to ream the bearings after they were fitted. The end result has been very good and they have lasted around
15 years so far. The originals appeared to be white nylon and had lasted 20 years.
Click to expand...
At last the answer (probably) to a question I posted ages ago when i wondered what the material was used in our rudder bearings. Google from your info gives me Nylatron. Is this the stuff? or should I get something without nylon. The bottom bearing is starting to get slack and will need replacing at some stage. The picture is of the top bearing.
 
johnphilip said:
At last the answer (probably) to a question I posted ages ago when i wondered what the material was used in our rudder bearings. Google from your info gives me Nylatron. Is this the stuff? or should I get something without nylon. The bottom bearing is starting to get slack and will need replacing at some stage. The picture is of the top bearing.
Click to expand...
If that is under water then do not use nylon. Use an acetal such as Delrin or Vescomite - the former is probably more readily available. The Delrin bearing in the rudder shoe on my boat has been there since 1992 with no wear. The material is water lubricated but needs machine with the correct clearance for the bore and housing diameter to allow for the small predictable amount of swelling.
 
Jaguar 25 said:
I cannot perceive that water absorption on a rudder pin bearing is going to cause any problem at all. There is no way that a minor volumetric expansion would cause seizure. Given that a rudder pin is say 16mm diameter with a tiller arm of 800mm in length that produces a mechanical advantage of 100:1 so a 10kg load on the tiller would produce a 1000kg load on a 'seized' shaft. It's going to move!
Click to expand...

Sorry, but this is bad advice. If you had ever machined components like rudder bushes from nylon to normal engineering tolerances and used them in a wet environment you'd soon find them seized solid. There is absolutely no point in wasting time and money using the wrong materials for a job like this, when the correct materials, proven by practical experience, are easily available.
 
I have recommended vesconite before and been accused of having a commercial interest which I don't only a happy customer.

I have used vesconite for my rudder and propshaft bearings with out a single problem I have also used it when I need a plane bush elsewhere

To show the swelling of nylon have a look at this

http://www.vesconite.com/prod/vesconite/DimenStable.htm

IMHO it is bad engineering practice to use nylon in any wet environment let alone below the waterline on a boat.
 
As others have said steer clear of nylon as it will swell when it absorbs water and it can absorb something like up to 6% against acetals less than 0.5%.

Acetal / Delrin / POM is easy to machine and makes an ideal material for bearings but there are also both loads of branded materials specifically for marine use such as Vesconite or you can get composite plastics which contain a built in lubricants but they are probably overkill for something as simple as a rudder bearing.

In case anyone complains I will happily state I do have a commercial interest as I make custom components fro marine and dive use.
 
Thanks guys for all the advice, a suitable piece of Delrin arrived in the post today and is of to a friend with a lathe to machine up. Trafalger Marine were kind enough to send me the drawing they had for the sizes.

Thanks Folks
 
You must log in or register to reply here.

Other threads that may be of interest

conks01
Hanse 301 Buying Advice
Replies
4
Views
204
TSB240
TSB240
bluey01
Anyone want to design a folding sailing dinghy with me?
2 3 4
Replies
66
Views
2K
bluey01
bluey01

Share this page

Top