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Hello sleuths - Can you tell me why my rudder broke off at sea?

7K views 72 replies 22 participants last post by  Zanshin 
#1 ·
I finally got my 2003 43" Jeanneau hauled today to replace the rudder. The solid metal stock broke off right at the through-hull and after dropping it and doing a quick bit of cleaning this is what the remnant looked like:



There are no sharp edges, but I have been in a marina for the past 4 weeks waiting for the replacement part to arrive. I was surprised at the copper buildup and my first thoughts are that I might have an AC power issue and that the copper has been plated from the surrounding bottom ablative coat.
 
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#55 ·
Since you mentioned earlier that your shaft zinc was fine that sends me away from the galvanic issue - But..... do you have an electrically operated auto pilot that may have an electrical connection to the rudder it shouldn't have or a lack of one it should have. In the same vain is your rudder grounded to the rest of the boat ? ... should it/was it designed to be ? Just some wild guesses :rolleyes:
 
#56 ·
christyleigh said:
Since you mentioned earlier that your shaft zinc was fine that sends me away from the galvanic issue
Can i ask a dumb question? Isn't it possible that the shaft zinc being ok COULD imply that something else was doing it's job for it? (i.e. a rudder shaft?) I'm not an electrician, nor do i play one on tv, but just playing 'devils advocate'.
 
#57 ·
Zanshin-
Failure Analysis
Found by googling "photos of metal failure modes". There are some good references on that page, good photo or a torsion failure in rod stock--very different from what you have--a basic book reference, and email contacts for the professor who wrote it.
It's a shame there are no libraries for sailors, i.e. where you can take a book out and post it back from the next port.
 
#58 · (Edited)
christyleigh said:
Since you mentioned earlier that your shaft zinc was fine that sends me away from the galvanic issue...
That was a good point. The rudder is attached to the quadrant which is attached to the 2 pulley wires and to the hydraulic ram of the autopilot. I shall measure conductivity when the sun gets lower on the horizon (I need to crawl into the rear of the boat and it is quite hot in there).
I decided to replace the shaft zinc yesterday and when I started to remove the 4 hex screws holding the zinc in place I noticed that the zinc rotated very freely about the shaft, there was enough play so that I could actually "rattle" the zinc a bit. So perhaps it wasn't functioning correctly as it wasn't fully attached all the time. :eek: It did show that it was eaten-away on the outside to about 2/3 of its original weight (assuming the new one I put in was the same model) and the 4 bolts were tight.

After the boat was put back in the water this morning I went back to the yard to get a pail full of cleaning materials and the rudder stock. The pail was still there, but the stock was gone! There went my plans for asking the yard to cut away the top couple of inches and to use the rest! All I have now are the rest of the pictures.
 
#59 ·
ReverendMike said:
Can i ask a dumb question? Isn't it possible that the shaft zinc being ok COULD imply that something else was doing it's job for it? (i.e. a rudder shaft?) I'm not an electrician, nor do i play one on tv, but just playing 'devils advocate'.
Rev - That's what I was getting at in a round-about way with a bunch of open ended questions with the purpose of getting Zen to think about any possible electrical issues with the rudder itself. To me it's one of 2 things - The rudder was cast as junk to begin with or it corroded off because there is no way it should have failed without some extreme shock involved - heck it's not that old.
 
#60 ·
Zan-

They shouldn't be throwing out your stuff without your permission, regardless of whether the part was junk or not.
 
#61 ·
I checked the dumpster and it wasn't there so I assume someone "appropriated" it; perhaps thinking I'd left it for junk. I did want to give it a fitting burial in 100 fathoms or more but perhaps it has found a better home.

I've posted some pictures and queries on 2 online metallurgical forums and engineering forums and if I get and interesting information I'll cross-post.
 
#62 ·
Zanshin-
I haven't seen a shaft zinc loosen up that way yet, but I have found that I need two mallets (actually, one dumdum hammer and one maul) to put a shaft zinc on properly. I'll hand tighten the bolts, then clap it between the two mallets, and it inevitably tightens up on the shaft. Even if you hold the heavier one against the zinc, and slap with the other one. Then tighten a bit, tap a bit, retighten, it is amazing how much tighter they get.

Maybe this is one of those "all brands aren't the same" deals, or maybe it is a metric/inch thing...Dunno, I just find two war hammers make a happier zinc installation.<G>
 
#63 ·
I think the wording on the little piece of paper stuck in the new zinc used the term "tap with a hammer before and once again after tightening". Lol - I prefer your mallet method! All I did was use a hesitant little taplet! Next time I dive on the boat I'll see if it has already come loose.

I just realized that this thread spans several pages of very interesting observations and comments and hasn't drifted off topic yet. That in itself is a pretty good track record!
 
#64 ·
Zanshin, make sure to use properly sized shaft zink for your boat. French boats have metric zincs (as does mine, for example) and you probably won't be able to fit imperial zinc on it properly.

Properly fitted zinc really wouldn't get off of the shaft unless you pry it or bang on it a bit.

One thing you could do in the future is install a zinc on the rudder, perhaps. I've done that for my (iron) keel and it really helped avoid the rust even though rust protection was not the best. I tapped into keel wing and bolted one of those tear-shaped zincs on it flat. On the rudder you might be able to install either a small teardrop shape or a flat round one - i'd just tap into the rudder stock somwhere down below and bolt it on. The bolt would provide electrical connection. Arguably, this might admit water into the rudder - so this is something to consider, but since water gets into rudders anyway sooner or later, this may not make much difference.
 
#65 ·
There are just a couple of centimeters of rudder shaft exposed, so a zinc on the rudder isn't going to be practicable. The end of the prop shaft is threaded for a zinc, but they had no appropriate zincs here, so I just bolted one onto the prop shaft. But I will check out the zincs in St. Maartin when I get there and also measure electrical conductivity on the rudder to make sure that it is grounded to the rest of boat.

My original surveyor has responded to the pictures with "...There does not seem to be signs of corrosion or pitting. Looking at my book on corrosion, ‘Corrosion Fatigue’ might be the factor here. The copper discoloration is odd. It would be interesting to send the photos to a metallurgist."
 
#66 ·
Hmmm I think this could be starting to get there...
Idiens said:
Another 2cents. If it were a straight fracture break in solid unwelded metal, then at least part of the area (the bit that finally failed under stress) would show the characteristic metal crystal structure. The fact that there appears to no sign of crystaline fracture suggests something else happened. Corrosion could be responsible for most of the weakening, but the last bit has to break. Or it was a weld and those bits of copper are the last remains of the "habit" that was holding it on.
If that copper were left over from a welding rod, then it would adhere poorly to SS.
The only sure way to tell whether the fracture was down to chloride stress corrosion, galvanic action or fatigue is to section what remains of the old stock longitudinally. ie: take slices up the vertical axis of the shaft, polish them, and then carefully examine the change in grain structure (if any) near the break versus further up the shaft.
**Chloride stress corrosion requires absence of oxygen, so if the break occured outside the thru-hull, that ain't the answer.
**Fatigue will show up as increasing crystalline sizes in the metal towards the break point. In pure fatigue you might also expect to see some "necking" (stretching and thinning) of the shaft at the break point.
**With Galvanic corrosion, I would expect to see more material removed from the surface of the shaft - ie shaft thinning - prior to failure, and a quick review of Galvanic Series reveals that the zinc (as we all rely on) should have corroded long before the stainless.

My money would be on a combination of chloride stress corrosion, fatigue, and faulty materials.

(which is why I have a keel-hung rudder, he says smugly ;) )
 
#67 ·
Zanshin said:
There are just a couple of centimeters of rudder shaft exposed, so a zinc on the rudder isn't going to be practicable.
I didn't mean bolting the zinc onto that part. Rather, I meant installing it over the actual rudder somwhere. The shaft goes all the way down the rudder (or at least half-way) and from it there may be some internal webbing in the rudder too, but that may be harder to find.

In fact, I recall seeing installations just like these - essentially a hole is drilled through the rudder into the shaft, tapped and then a zinc can be bolted on. The zinc will be on the surface of the rudder (so it has to be not too large and have proper shape not to disrupt water flow much), and the bolt will create electrical connection to the shaft.

Having a zinc on a prop may not be all that helpful for the rudder, it is pretty far and unless you have a bonding system connecting all those metal fittings together - it probably has quite a bit of resistance on the path of electricity from rudder shaft to prop shaft.
 
#68 ·
I wouldn't expect chloride (crevice) corrosion, even inside the entry to the rudder tube. Consider if you will, that crevice corrosion occurs when there is oxygen depletion and stagnant water. But where the hull is hobbyhorsing (as all do, to some extent, all the time) or squatting and rising as speed changes, the rudder and rudder tube are getting "pumped" in the seawater so there would appear to be a regular flushing/oxygenation there.

Not an expert--just someone trying to examine the issue.

I'd also be loathe to make any holes in a rudder to bolt on anything. Some of them actually are not leaking and saturated, and if one is--it is time to overhaul it or replace it BEFORE the armature fails, not time to make more holes in it. If one wanted to install a zinc closer to the rudder stock, one could drill a hole in the hull and simply through-bolt a metal plate connected to the bonding system, then bolt the zinc to the outside of it.

More holes in the hull, yeah.<G> I wonder if the insurers or anyone else are accumulating data and pictures on rudder failures, and if not, perhaps it would be worthwhile (to those of us who prefer boats that don't fall apart) to make that some kind of formal project/appeal, to the insurers and the boaters, to try and find out why rudders are being lost.

I think it was Beneteau who reported/claimed some 13 rudders lost per year in the 30-40 foot range were "normal"....I wonder if they also tracked just where/why those rudders failed. It shouldn't be so hard to create such a primitive machine (a rod and lever) and do a reliable job of it.
 
#70 ·
There was an interesting article in the English Practical Boater magazine about how many rescues were performed last year around England for disabled vessels and what caused the disablement? If I remember correctly the majority of rescues were for deruddering(sic) and that leads to the question as to why the appendage wants to fall apart. One item that I found interesting was their questioning of Otto's or autopilots. They have a tendency to react and not to anticipate as a helmsman could and would consequently otto throws everything into reaction and spends a good time hunting about for the proper angle much more then a good helmsman would need to. This causes more stress on the rudder. Also the spade rudder was mentioned as the weakest rudder design. If I remember right the one boat that was pictured in the article in the water rudderless was a Beteneau?
 
#72 ·
bestfriend said:
If I stick my finger really far up my nose, can I scratch my brain?
Nah, it's too small, you'd miss it... ;)
 
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