Delrin rudder bearing - what is it and where to get it?

Robert Wilson

Robert Wilson

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When I re-fix my skeg/rudder shoe I should insert a Delrin bearing (apparently)
What is Delrin?,
Where/how could I get a piece for a bearing?
How would I make one - flat piece or formed "cup"?

I don't think there originally was one inserted in the shoe, so why would I need one now?
The rudder hangs from two large nuts on a bearing-plate in the cockpit and the bottom of the stainless-steel stock (approx. 30mm diam) sits in the cup in the shoe; I don't know if it should hang free or sit touching the cup bottom/sides.
There is about 2mm-3mm play, but no obvious signs of wear.

All ideas, advice, warnings, sympathetic comments gratefully received :encouragement:


Or should I just pack the cup with grease. There isn't a grease nipple, but there is a small hole through the bottom of the cup (drainage?)
 
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Delrin is an acetal commonly used for rudder bearings. Important thing is that it is stable and does not absorb water. You can buy it on ebay, but you will need it machining by somebody who knows what they are doing. Suggest you contact H4 Marine (he posts here sometimes) who will make you a bush out of a similar material. You will need the dimensions of the stock and the housing so that he can machine it with the right clearances. Easy job for somebody who knows what they are doing.
 
'Delrin' is a trade name for a plastic often called acetal, and a good choice for rudder bearings. Widely available as sheet or rod. Many plastics supppliers will stock it - just ask Google.
It would need turning up on a lathe.
Skeg bearings often have drain holes to deter mud etc from settling and encouraging wear. You might want to enquire about the recommended set-up for your model of boat.

P.S. It's proper name is Polyoxymethylene, but you probably won't get very far with that at a trade counter ;)
 
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macd said:
'Delrin' is a trade name for a plastic often called acetal, and a good choice for rudder bearings. Widely available as sheet or rod. Many plastics supppliers will stock it - just ask Google.
It would need turning up on a lathe.
Skeg bearings often have drain holes to deter mud etc from settling and encouraging wear. You might want to enquire about the recommended set-up for your model of boat.
Click to expand...

Thank you.
Unfortunately the Javelin30 was built by Marcon who no longer exist, so getting technical help and advice is all but impossible.
If there ever was a bearing in the cup I have no idea where it went, or when. The boat is about 35 years old.
I'd be particularly interested to find out if the stock ought to hang free of sides and bottom, or whether it should be held by the cup. The 2mm-3mm play may be the cause of an infuriating rumble when motoring if the stock is sloggering within the cup. Or the rumble may be nothing to do with the stock/rudder!

PS. Polywallyoxymethsylene :eek: I'll stick with Delrin ;)
 
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Robert Wilson said:
Thank you, Mr Speedy!
There is only about 2mm-3mm difference between the inside diameter of the cup and the diameter of the stock, indicating a 1mm-1.5mm tolerance for the thickness of any bearing.
Should the stock have some play, or be held completely tight?
Click to expand...

That is a very thin bearing. It needs to be machined to be a push fit into the housing and a clearance to the stock. If it is done correctly there should be no play and the bearing should last effectively for ever! It is water lubricated, hence the need to get the clearance just right.

I fitted a delrin bearing in 1992, and there has been no wear at all. I had a spare made at the same time. Makes a good coffee table decoration or a conversation piece!
 
Well, Robert, I can tell you what Marcon did on my old Rival 32: a shoe of some sort of bronze held to the bottom of the skeg by three through-bolts. The shoe was both bearing carrier and bearing (I think: it was a while ago). The Rival had a full skeg, but no doubt the principle's the same. With a Rival I'd go to the owners' club site for info, but perhaps there isn't one for the Javelin?

There's no reason an acetal sleeve couldn't be made up as Tronana suggested (whilst I was typing post #4...he's on form this morning*). Trouble is, I fear that a wall thickness of around 1mm just isn't enough; and to make it thicker, the shoe would need machining. Any sleeve should retain clearance around any drain holes in the shoe.

Your shoe will probably bear witness marks telling you whether the shoe took its weight or not. Most rudders don't actually weight all that much when in the water, anyway: only the shaft has much by way of negative buoyancy.

* And I've just seen he still is. Good morning, Tranona :encouragement:
 
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An exact facsimile of the problem and its solution, although for a different boat, is shown on my website at https://coxengineering.sharepoint.com/Pages/Sadler34rudder.aspx That page was composed last winter, since then I have replaced the shoe and used the boat for a season, all rudder play now a thing of the past.

Any small machine shop will be fully familiar with acetal and probably carry it as stock.
 
Robert: done a litle checking on the Rival Owner's site. Machining out the shoe and fitting a custom bush has certainly been done to good effect on several (Marcon) Rivals.

And a suggestion: if you can't find a drain hole in the shoe, have a good poke about: they often get blocked with crud, or even antifoul when owners don't realise the hole is there or what its purpose is.
 
Thinking a bit more about it, you will have to do what Vyv has done and have the bronze machined to take a thicker top hat bearing as in his photo. Your current clearance suggests it is just wear in the bronze. Hope there is enough "meat" in the casting to bore out.
 
Belatedly, due to posting in a different thread. Doh! (Thank you MacD)

Gentlemen (and ladies).
Thank you for all the above, each and every one of you.
I have just spoken with Neil at H4 who was extremely helpful, knowledgeable and understanding. Thank you Neil

The existing tolerances in the cup are so small that Neil fears a bearing wall thickness of circa 1mm may be a problem for machining. He also echoed the advice regarding some buoyancy properties of the rudder.

So, with the age of the boat and myself I will seek out a rigger who should have some Delrin off-cuts, make-up a small "washer" to fit in the base of the cup and let the stock sit lightly on that washer while the main weight is taken by the top nuts and the water.

Good luck to all of you who have/had similar problems.

Back to the painting of Khamsin; just clocking-up 125 hours since starting to strip the old paint off her in April. After three primer-coats, three undercoats and three top-coats, ONE coat to go!
If you want your boat(s) stripping, filling, fairing, epoxying, sanding, undercoating, sanding, and painting/sanding, DON'T ASK ME image: http://www.ybw.com/forums/images/smilies/rolleyes.png
:rolleyes:​


​
Read more at http://www.ybw.com/forums/showthrea...or-the-rudder-stock/page3#tpBJFsur2ChjY46J.99
 
As all plastics are not the same dont save money for just any cut off otherwise you may end up with a sized rudder

You have had Neil's advice get him to make you one
 
scottie said:
As all plastics are not the same dont save money for just any cut off otherwise you may end up with a sized rudder

You have had Neil's advice get him to make you one
Click to expand...

If I've understood Robert correctly, I very much doubt seizure could be an issue: he seems to be talking about what is effectively just a shim under the rudder shaft. It will though, need to be very durable. And, as I've banged on before, if there's any drain hole in the shoe, the shim should not interfere with it (which is perhaps why he describes it as a washer).
 
Who gave you the "apparently" as a matter of interest?
When I re-fix my skeg/rudder shoe I should insert a Delrin bearing (apparently)
Read more at http://www.ybw.com/forums/showthrea...is-it-and-where-to-get-it#7iCQ2ywgZKk9sSho.99
Click to expand...
I got a recommendation like this from a surveyor years ago on a bearing with no space for Delrin. On questioning, he imagined the gudgeons being rebored to make it all work. Took no notice and all is well. My boat has galvanised pintles and gudgeons that have worked for decades.

I can vouch that Delrin is easy enough to machine. I turned new rollers for a broken and discontinued shower door with no difficulty on my wood lathe.
 
macd said:
If I've understood Robert correctly, I very much doubt seizure could be an issue: he seems to be talking about what is effectively just a shim under the rudder shaft. It will though, need to be very durable. And, as I've banged on before, if there's any drain hole in the shoe, the shim should not interfere with it (which is perhaps why he describes it as a washer).
Click to expand...

You understand me correctly, sir - even if I didn't make myself abundantly clear!!
 
Amulet said:
Who gave you the "apparently" as a matter of interest?

I got a recommendation like this from a surveyor years ago on a bearing with no space for Delrin. On questioning, he imagined the gudgeons being rebored to make it all work. Took no notice and all is well. My boat has galvanised pintles and gudgeons that have worked for decades.

I can vouch that Delrin is easy enough to machine. I turned new rollers for a broken and discontinued shower door with no difficulty on my wood lathe.
Click to expand...

No-one in particular, but in my earlier thread (the lonnnng one!) about my skeg problem various folk made the suggestion.

I think I shall try to find a bit of Delrin to use as a "washer" under the end of the stock, but there appears so little wear on the sides and bottom of the shoe, and none at all on the stock, I may be worrying in-necessarily.

Thanks one and all, as usual.

R
 
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