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Old 03-05-2012, 22:18   #1
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Rudder bearing material

What's the best (lower) rudder bearing material to use?

We have spade rudders. The upper bearings are fine but the lower bearings are really too small, so we're increasing the shaft diameter (sleeving the shaft) & replacing the old (very worn) bottom bearing. The old bearings were self aligning (spherical, with a big hole for the rudder shaft) but I see no point in that so we're going with a 4" high cylinder of bearing material around a 50mm dia shaft.

Primary Factors I'm looking at are: 1) Good wear resistance, & 2) Low moisture absorption.

Ultra-high Molecular Weight Polyethylene (UHMW-PE) has excellent (almost zero) water absorption & very good wear resistance, but low compressive strength & low PV-value (whatever that is - is it important?).

Polyethylene Terephatalate(?) and Polyacetate (+ glass fiber) both have minimal water absorption & much better compressive strength & PV but will glass wear my SS shaft?

Another option is Delrin (Acetol or POM) which I know to be very strong but has ~12x higher water absorption.

Surely CF has several experts here? Thanks!
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Old 03-05-2012, 22:46   #2
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Why not use good old fashion brass or bronze?
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Old 03-05-2012, 22:47   #3
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Re: Rudder bearing material

Im old but whats wrong with oil lite bronze for a bearing of this type ?? Just asking
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Old 03-05-2012, 22:48   #4
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Re: Rudder bearing material

From what I've been told, Vesconite is the miracle material of choice.
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Old 03-05-2012, 23:05   #5
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Re: Rudder bearing material

Thanks Mike. Vesconite sounds good (from the website it lasts 10x as long as bronze). But it's also a trade name & I wonder if it's available here in Thailand. Any idea what the generic is? I'd rather use something locally available, as it will have to be machined down to fit.
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Old 04-05-2012, 00:10   #6
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Quote:
Originally Posted by Jon Hacking
Thanks Mike. Vesconite sounds good (from the website it lasts 10x as long as bronze). But it's also a trade name & I wonder if it's available here in Thailand. Any idea what the generic is? I'd rather use something locally available, as it will have to be machined down to fit.
I have seen Vesconite is some of the light engineering shops in China Town, Bangkok - walk over from Central station and you will find them easily.
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Old 04-05-2012, 01:31   #7
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Re: Rudder bearing material

If you cannot find the Vesconite you should be able to get Delrin easily - it is supposed to have a swelling problem in water but we have used it for rudder bushings with several years of constant immersion without any problem. From memory I thonk we had approx 0.5 mm clearance on a 55 mm shaft.
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Old 04-05-2012, 02:06   #8
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Re: Rudder bearing material

I have used the same PTFE bottom bearing for 25 years. buy a square of suitable thickness, cut it and drill it to suit, ( had to go to an engineering workshop to use a pillar drill to cut a hole large enough to take the pintle of the rudder).
I cut two at the same time to have one as a spare as I use the boat at sea and in the canals and was worried about wear, the spare is still in the locker.
Good luck.
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Old 04-05-2012, 05:35   #9
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Re: Rudder bearing material

Hi Jon, Mike here, Vesconite is the best choice, try to get some. Just oversize the hole to the % of absorbtion plus 1%. You will not regret the effort in getting it.
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Old 04-05-2012, 07:46   #10
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Re: Rudder bearing material

PS
Entry to Design-a-bush calculators

Just put your email address into the field then use the calculator to design your own bearings. After that, you can just order it from them or have one made up.
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Old 04-05-2012, 14:33   #11
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Re: Rudder bearing material

There is some information on material choice here:
Material Selection Guide - Quadrant

Alain
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Old 04-05-2012, 17:54   #12
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Vesconite is the way to go, even saw it in Tahati. Any machine shop will be able to fabricate it if you get a hold of a peice.
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