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Old 09-05-2015, 17:09   #1
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torlon balls under rudder post

I have a skeg-hung rudder with a 1 1/4" stainless rudder shaft. The weight of the rudder is supported by a 1/4" thick sheet of torlon under the bottom lowest rudder bearing. I was thinking of replacing the sheet with 1/4" torlon balls to make the rudder a bit lighter to turn.

Any opinions?

Thank you,
Jim
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Old 09-05-2015, 17:27   #2
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Re: torlon balls under rudder post

Personally I don't think it would make much difference. If it heavy now, I suspect the problem (if any) would be somewhere else. If it is already light, then not much can be gained.

What is the rudder construction or perhaps better question, does it float or almost so when submerged? If so, there isn't much load on the bottom bearing surface anyway.
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Old 09-05-2015, 17:40   #3
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Re: torlon balls under rudder post

Thanks Wotname, I hadn't thought of it that way. Steel boat, steel rudder. I guess it weighs about 25 kg, no idea how much water it displaces, but I think it would still be heavy even when floating.
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Old 09-05-2015, 17:45   #4
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Re: torlon balls under rudder post

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Originally Posted by jimthom View Post
Thanks Wotname, I hadn't thought of it that way. Steel boat, steel rudder. I guess it weighs about 25 kg, no idea how much water it displaces, but I think it would still be heavy even when floating.
Hollow section or big flate plate? My latrge hollow section steel rudder on a 30 ft boat was bludi heavy on the hard but pretty light when in the water.

Tiller or wheel?
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Old 09-05-2015, 18:14   #5
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Re: torlon balls under rudder post

My rudder is tiller hollow section, but pretty thin foil shape, so it doesn't displace much water. But when I read you're original post my immediate thought was "you're right, it probably won't do much good" But I've got the boat on the hard at the moment so a relatively simple modification.

Curious how you know your rudder is light in the water? Mine is like a big barn door so water resistance alone make it feel heavy.

Cheers, Jim
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Old 09-05-2015, 18:36   #6
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Re: torlon balls under rudder post

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Originally Posted by jimthom View Post
My rudder is tiller hollow section, but pretty thin foil shape, so it doesn't displace much water. But when I read you're original post my immediate thought was "you're right, it probably won't do much good" But I've got the boat on the hard at the moment so a relatively simple modification.

Curious how you know your rudder is light in the water? Mine is like a big barn door so water resistance alone make it feel heavy.

Cheers, Jim
By light in the water I meant light as in weight, not resistance to turning

It had a small vertical movement in the support and when in the water, it didnt take much effort to lift it up a bit but on the hard it took a lot of effort to lift it.
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Old 10-05-2015, 23:54   #7
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Re: torlon balls under rudder post

The total contact area of the balls would be minute compared to the full contact area of your current setup, which would mean a much higher contact stress on the surfaces, especially during a shock loaded situation. I would be very reluctant to make that switch.
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Old 11-05-2015, 00:27   #8
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Re: torlon balls under rudder post

Years ago when building larger steel fishing boats with a similar powered rudder, we put stainless balls under the shaft (usually 3" shaft or more) and never had problems. The rudder might get pulled every 10-20 years for maintenance. No idea on the weight but beyond several humans lifting ability. The rudders were balanced - some blade in front of the shaft.
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Old 11-05-2015, 00:56   #9
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Re: torlon balls under rudder post

Obviously, I don't know the configuration of your rudder. But I can't help but to think, that with one solid bump on it, & you'd just have donated all of your ball bearings to Neptune.
It would depend on the setup, although even were you to go with well captured bearings, rudders see a LOT of load. Just in normal use, let alone should she get into a mild "real estate argument".

If the steering's stiff, odds are it'd pay to look at the other connective points/hinges & bearings on the rudder. And check to make sure that they're both; in line with one another, & have reasonable free play tolerances.

Also, there are other choices for bearings besides Torlon. Such might bear looking into. Ditto on bearing configurations, as it sounds as if you've got one flat plat atop another. With both made out of the same material. Which, from an engineering standpoint, isn't the ideal way to go.
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Old 11-05-2015, 09:29   #10
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Re: torlon balls under rudder post

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Originally Posted by UNCIVILIZED View Post
...If the steering's stiff, odds are it'd pay to look at the other connective points/hinges & bearings on the rudder. And check to make sure that they're both; in line with one another, & have reasonable free play tolerances...
This. Forget about ball bearing complications.
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Old 11-05-2015, 16:31   #11
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Re: torlon balls under rudder post

Thanks for your responses. I take your point about loads. I found an on-line calculator which calculates the number of small circles that can fit into a larger circle. In my case, I can fit only twelve 1/4" balls under my rudder shaft. Not much, considering the bearing surface of shaft on sheet is 1.23 square inches. They cannot escape, but they could collapse.

Thanks, Jim
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Old 11-05-2015, 17:11   #12
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Re: torlon balls under rudder post

I have done one installation converting the rudder bearings to roller bearings, custom made for the 43' boat. Even in that installation there were only solid thrust bearings (custom made) and not rollers or balls.

By far the greatest friction will be in the axial shaft bearings, not the thrust bearings.
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Old 12-05-2015, 05:57   #13
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Re: torlon balls under rudder post

Good information Terra Nova.

Thanks to everyone for their ideas.

Cheers, Jim
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