Rudder bearings.....material?

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dukes4monny

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I am planning on replacing my Jaguar 27 rudder bearings this winter. What material do the learned forumites suggest as the best for manufacturing the new bearings?
I am considering using Delrin (Acetal) for the top and bottom bearings........one is obviously submersed and the other not, would Delrin be ok for both?

Thanks in advance for any pointers.
 
I was recommended to use PTFE rod from http://www.directplasticsonline.co.uk/. Make sure whatever you use will not be affected in any way by long term immersion. Many people have used stock nylon bearing material, only to find their rudders jammed solid after six months in the water. DPO give information on immersion durability in their material specs.

I would have thought Acetal would be equally good, with possibly slightly more wear resistance than the PTFE I used. the only real difference is that my bearings will still work at -250 C! As if.... :)
 
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The best material currently available for rudders would be Maritex Aquarius, this has a surface finish that resists marine growth on the shaft and a surface chemistry that also resists marine growth on the bearing surface, as well as having dry running lubricants giving low friction properties, it is also mechanicaly very strong being able to withstand high compression loads without deforming.

Having said that, for your boat Delrin would work perfectly well.

Be aware that it does swell with water absorption and also temperature, so check with the supplier what clearances you should use, giving him the water temperature range you expect to sail in, and also whether you plan to fit it as a clearance or interference fit in the bearing carrier.

PTFE is mechanically soft, so not that great under high loads. We use an MoS2 impregnated composite for dry high load bearings.
 
Rudder bearings..materials

Yes the Delrin would be fine for both bearings,an alternative would also be Tufnol,that is also used for cutless bearings fir some yachts;this material also absorbs some water and needs the correct tolerance when boring the finished dimension,but very long-lasting too.

ianat182
 
Neil_Y said:
The best material currently available for rudders would be Maritex Aquarius...
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That Maritex sounds fantastic! (Please PM me with the details) Over here we usually use stuff called Vesconite- rather like Delrin, except that it doesn't swell any sensible amount. I thing non-elastic deformation would be a problem with PTFE, because it seems to "flow" under static load.
 
Don't underestimate the problems of getting it wrong. Mine were renewed 2007 half way throuh 2008 the boat was only steerable sitting down, and using two hands.
 
Thanks to all for your replies, they are all useful.
KREW2, do you know what material was used to for the bearings which caused your problems?
The Maritex Aquarius does sound interesting......I might consider using it if it isn't much more expensive than Delrin /Acetal. Neil_Y, do you know if the Maritex is easy to machine using a standard lathe / tools?
 
I use Delrin from DirectPlasticsOnline. Very easy to machine with ordinary lathe tools, as is nylon (but no good in this case). Only prob (for me)is they do not ship overseas.
Don't think Tufnol is suitable, water absorbtion is a problem. Makes nice old looking deck fittings though.
A
 
DownWest said:
Don't think Tufnol is suitable, water absorbtion is a problem. Makes nice old looking deck fittings though.
A
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Tufnol has very low water absorbtion according to the suppliers, and was specified for rudder bearings on a number of boats in the 70s, proving highly stable and wear resistant. The bearings I removed from my boat were original 1972 - and made of it! The play proved to be a corroded rudder shaft, but we damaged the tufnol getting it out which was a PITA as it would still have been serviceable.

PTFE has to my certain knowledge been recommended and used for rudder bearing replacement for a number of years and appears to be trouble free in this application. Not necesarily saying its best - but it 'does what it says on the tin', and goes on doing it!
 
Check out UHMWPE. I read on here a while ago that it was recommended by Nigel Calder. I bought some and had it machined locally. It seems perfect but the bearings have only been in for a year.
 
dukes4monny said:
Thanks to all for your replies, they are all useful.
KREW2, do you know what material was used to for the bearings which caused your problems?
The Maritex Aquarius does sound interesting......I might consider using it if it isn't much more expensive than Delrin /Acetal. Neil_Y, do you know if the Maritex is easy to machine using a standard lathe / tools?
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Afraid not, I was assuming it was ordinary nylon.
Mind you, having read some of the other replies maybe it was delrin, and not given enough tolerance. Next time I see the boat builder who refixed it I will ask him.
 
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Hi Dukes,

Yes easy to machine with normal lathe tools, produces a swarf similar to aluminium, not toxic or acrid dust, and swarf is non flammable.

There is a sizeing calculator on our website that gives machining tolerances for a range of carrier and shaft sizes.
 
Swelling's a killer, Krew- I sell a range of high-end bearings which use rollers and all sorts of other high-tech stuff, and we had a unit with a self-aligning component "lock up" because the acetyl sphere swelled from immersion in seawater, and wasn't allowed the requisite clearances. I guess the exotics like Maritex and Vesconite are the way forward because the accuracies you can achieve are so much higher where the swelling/distortion is minimised.
 
It's a mine field for those without experience or knowledge, but one thing to look closely at is what happens at higher temperatures. Heat can induce the changes that lead to siezure and complete failure.

It might be warm water that starts the problem but it will be friction induced heat that probably starts the failure. Fibre wound materials can delaminate at this point as the fabric/fibre filaments are concentric with the shaft. Many composites are made from a type of polymer that softens or is maliable with heat which leads to material transfer, some even quote that they will deform and this is a benefit to reduce edge loadings?

The secret is to know what you are going to subject the bearing material to at its limits, whether that is tropical sun or particularly warm waters.
 
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