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Old 03-10-2016, 12:25   #1
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Rudder bearings when to replace?

There is a small amount of play in my rudder bearings but I don't know if its enough to necessitate hauling and replacement. We will be heading across the Pacific early next year I thought of just replacing them as a safety precaution, but it might be a bit unnecessary.

Is there a practical way to determine if the bearings need to be replaced? Have others replaced theirs when did they decide they needed replacement?

Our rudder + shaft is 1.85m the bearings are about 0.5m apart, so the blade extends about 1.35m below the bottom bearing. The bearings are bronze sleeves with nylon thrust washer above and below to support the rudder which I guess must weigh around 50kgs!

The play at the quadrant is probally under 1mm, but it's VERY difficult to measure, i cannot use my calipers or feeler gauges, there's a slight knocking noise if I haul as hard as I can shaking from side to side and about the same fore,aft at the very the top of the rudder shaft.

From the bottom of the rudder there is a lot more play, there always was, but at the bearings it's probally under 1mm, again very difficult to measure as the boat is in the water. When I haul side to side and fore, aft like I'm trying to break off the rudder there is a audible noise so some play.

Thanks for any suggestions.
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Old 03-10-2016, 12:46   #2
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Re: Rudder bearings when to replace?

If the play is small and not annoying, I would replace next time in the boatyard.

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Old 10-10-2016, 14:02   #3
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Re: Rudder bearings when to replace?

Hi sail abroad, I've been watching this thread hoping for some good advice as I have had the same question. Our boat is an Allures 44 with twin short rudders and I would say there's quite a bit more play than you describe. If I pull the rudder tips from side to side there is a significant knocking noise. This doesn't really have any negative effect on the steering capability.
I think the main concern is whether the movement can translate to additional shock loads on the shaft which could cause damage. With the short rudders, and given that the Allures is designed to be able to sit on the rudders when beached so they would be quite over-engineered, I am happy to leave the bearings for now. My gut feel from what you describe on your boat is that you could delay replacement for quite some time before it's a significant mechanical problem. Having said that, I am no engineer, the best thing to do would be to ask Beneteau or an experienced shipwright. In asking Beneteau there is always the risk that they will suggest replacement regardless to cover their xxxs
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Old 11-10-2016, 11:08   #4
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Re: Rudder bearings when to replace?

Reporting in with more nformation:��

(1) I talked to a marine engineer he had some VERY interesting bits of information about rudders.

He told me there should be NO play in the bearings any AT ALL, any is out of spec.

He fixed a loose bearing on one boat, underway, by inserting a plastic Coke bottle, it has lasted several thousand miles and is still OK!

He suggested the [lower] autohelm arm's through shaft bolt is critical and should be replaced or a clamp added, a fail is catastrophic from the leverage if the rudder drops onto the top quadrant.

A very recent beneteau rudder failure was caused by resonance from the propeller amplified buy loose steering cables that destroyed the bottom bearing housing causing a slowish leak.

In a thousand miles the shaft might go through 80,000 cycles, but bearing failure isn't normally unpredictable, so the play will slowly increase to the point there is a mechanical failure - replace early or check regularly.

(2) I talked to Beneteau tech support:

12mm is the maximum play allowable on a NEW beneteau at the bottom rudder tip. Old boats: "If you can feel any movement of the rudder shaft IN the shaft log then it's time to sort out the problem"

Perhaps it's the bearings, could also be the shaft is warn thinner, the shaft log itself has been ovaled or one of many other factors.

"The quadrant and autohelm arms don't have published torque settings for the through and clamping bolts". I forgot to ask about cable tension.

Scary! It is obvious that the torque is critical as both arms clamp the rudder shaft, to much torque crushes or weakenes the (hollow) rudder tube to little and the rudder is only held by the through bolts.

(3) Measurements I made when the boat was 5 years old are very! surprising - in light of the spec beneteau provided of 12mm! Perhaps my figures were contaminated by the force I used (blade flex?)or the way I did the measurements?! Hmm not sure..

Rudder dimensions:
shaft = 500mm (between top and bottom bearings)
blade = 1600mm (below bottom bearing to tip)
Total length = 2100mm

Fore-aft play: = 51.15mm(bottom tip)
When pulled really hard and held under tension. calipers used.

Side-to-side play: = 42.21mm
Pulled as hard as possible, loverly assistant using calipers.
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Old 11-10-2016, 13:26   #5
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Re: Rudder bearings when to replace?

To me it sounds somewhat surprising that a 1 mm play at the bearings (spaced 500 mm apart) could translate into 50 mm movement at the tip.

Some of it is the shaft is bendy, OK. But then we are talking two things at once.

If you have 2 inches of FREE PLAY at the tip, I would very carefully investigate the matter next time in the boatyard. And I would consider consulting other owners on this prior to any bigger trips.

Good news is some free play at the bearing is unlikely to cause much trouble while you avoid pushing the boat hard.

All the above my opinions, not facts.

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Old 11-10-2016, 14:16   #6
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Re: Rudder bearings when to replace?

Quote:
Originally Posted by barnakiel View Post
To me it sounds somewhat surprising that a 1 mm play at the bearings (spaced 500 mm apart) could translate into 50 mm movement at the tip.

Some of it is the shaft is bendy, OK. But then we are talking two things at once.
Yeah, by my math 1mm play in bearings 500 mm apart should result in ~15mm play at the tip (1350mm away.)
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Old 11-10-2016, 18:45   #7
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Re: Rudder bearings when to replace?

Measuring the play at the bearing is very difficult, I guessed it around 1mm..that still seems right.
I might ask around and borrow a dial indicator, but as I'm on anchor in Panama I don't have access to resources I would otherwise have.

The play at the tip doesn't seem to be coming from the bearing play. Its not free movement of 50mm it feels like a gradual increase in tension, like flex in the rudder system. The rudder is heavy but not stiff like a full skeg or Hallberg-Rassy, I am pulling hard to get it to 50mm.

Two possibilities: I believe the bottom bronze bearing is glued into the shaft log with 3M 5200 to stop it turning in the stainless shaft log, so there is some play there, there should be also be a 1mm gap in the bronze sleeve bearing at the front, more flex? Possibly.

The play was a slow incremental increase, there wasn't any issue, noises or worrying movement,. The bearings have only done about 15k miles and the boat is 8 years old. So currently investigating.
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Old 12-10-2016, 11:21   #8
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Re: Rudder bearings when to replace?

I'm also noticing play in my port rudder. I will certainly address it on my next haul out but I have to cross the pacific too. Short video of the problem : https://youtu.be/j2eHL8d7I6w
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Old 26-10-2016, 21:18   #9
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Re: Rudder bearings when to replace?

Ok further information: if anyone is still interested?

Today with the help my engineering mate we tested the bearings.

First of all beneteau insist that all rudder strengthening modifications for my boat have been done at the factory: There is a thorough bolted cross beam that looks like it replaces the metal bolt on bracket that was retrofited for problem boats( the metal bracket that fits between the quadrants) I tried to obtain the metal bracket from Beneteau but they wouldn't sell me it repeating that all necessary modifications have been done.

OK first test: Insert emergency tiller, I pulled on rudder shaft while the engineer watched from inside the boat.
Results: No obvious signs of any bearing wear, no movement at all in relation to support structures.However!! The rudder support structures flex and move a lot, my engineering mate had never seen anything like it before, and he has a considerable amount of experience over many years, across many different boats.

Second test: I dived and really hauled on the rudder at the tip and he watched and filmed:
Results: No signs of bearing problems, however again a serious amount of flex and movement from the steering support structures. When I watched the video it was disturbing, worrying.

We couldn't transfer the video to my tablet but will I do the test again and get my girlfriend to video, if possible I post here or link to the video.

The engineer checked for any detachment or lamination problems with the support structures, and there is none, all looks in excellent condition, nothing broken, separated or cracked all is well.

He also suggested that although there is a lot of movement it looks to be doing what is is supposed to, just that it flexes A LOT. We discussed possible modifications to stiffen it up, and decided on a slight modification to easily monitor the loading while underway, if the steering structures are getting a hammering then perhaps we should change trim or engine rpm etc.

One concern for me is the bottom bearing, where the steering tube joins the hull, it's glassed in, as this is a rigid connection the fiberglass must get cycled millions of times weakening it? each time the support structures flexes?!

Hmm I will look at that bit again in the next few days.
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Old 26-10-2016, 22:50   #10
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Re: Rudder bearings when to replace?

Throw up some pics. Sadly, beefing up rudder post & bearing installations is a common necessity. And has been for decades.
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Old 26-10-2016, 22:51   #11
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Re: Rudder bearings when to replace?

I'm not a dyed in the wool Bennie Basher, but in light of the Blue Pearl rudder failure, I would not go to sea without stiffening that whole structure up to where it did not have perceptible flexion when tested as you describe. Sounds scary to me.

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Old 27-10-2016, 08:18   #12
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Re: Rudder bearings when to replace?

Yes.

Now the whole picture makes plenty of sense: the bearings seem fine but the whole thing moves about a lot.

Follow your engineering friend's intuition. If you have a boat on dry, talk to a well established surveyor.

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Old 27-10-2016, 08:27   #13
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Re: Rudder bearings when to replace?

I am standing by listening to the developments.

I feel like the other guys that this must be sorted out prior to any offshore adventure.

I see some flex in some areas is a 100% norm BUT I would not extend my rule to the the structure supporting the rudder post. My so far experience is that if any flex there is built-in then the supporting structure is built rigid and flex is calculated into the rudder post/blade. (I am not an engineer, just a heavy user.)

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Old 27-10-2016, 13:14   #14
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Re: Rudder bearings when to replace?

Hi Jim, the modifications that beneteau did to my boat were the fixup for the problem that the blue perl suffered from: I believe with the blue perl the rudder support structures separated from the rear bulkhead.

Oh I forgot to say if anyone else wants to test their beneteau the easiest way is to insert the emergency tiller and hammer the engine, forward, reverse and through different rpms, the turbulence on the rudder will give you the same effect as hauling, Which incidently may have been the cause for a recent beneteau sinking.

Its hard to gauge how big a problem this really is, i dont want to be a danger mastabator, and there are literally thousands of beneteaus out there, in every port we have been we have seen at least one , from Pohaia to Auckland and they all sailed there! so failure rate is exceptional low.

It would take some exceptional engineering to stiffen up the support structures without creating point loads: My engineer mate suggested the engineering seems to be working well to distribute the forces - so does not contain them like more traditional? engineering.

But I have to get the video to Beneteau engineering for further comment.
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Old 27-10-2016, 14:24   #15
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Re: Rudder bearings when to replace?

In my experience, once structures (that aren't supposed to move) start moving they start fatiguing. After that, they start breaking.

That's a glib oversimplification coming from someone who isn't a mechanical engineer, but I think it's fair to be concerned about this.

I also suspect Beneteau's engineering staff looks less like NASA, more like a handful of overworked folks trying to strike a balance between safety and cost. I'd certainly want their opinion about your video, but wouldn't consider it the final word on the matter.
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