timeoff
Junior Member
Posts: 10
Jeanneau Model: Sun Odyssey 36i 2012 model
Yacht Name: Soirée
Home Port: Pittwater
Country: Australia
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Post by timeoff on Jun 18, 2019 8:11:07 GMT
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Post by zaphod on Jun 18, 2019 19:41:30 GMT
That is some pretty serious corrosion for such a young boat. It looks like electrolysis to me, although it seems strange that it is localized to the section of the shaft under the cutlass bearing.
The picture of the drip less seal section doesnt look like corrosion, it looks more like wear, and isnt too serious.
My guess is the propshaft was not protected with zincs in a marina full of electrical leaks at some point in it's life.
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Post by ForGrinsToo on Jun 18, 2019 20:20:47 GMT
I agree Zaphod on all points. Any place you have dissimilar metals in an electrolyte (even freshwater, though not as fast) you're going to get corrosion, and there is a sacrificial zinc on the 36i prop nut. I wonder if the skeg is electrically connected to something other than the engine block.
The dripless seal can be lubricated with grease (fill a plastic soda straw, push it under the seal along the shaft, then push the grease into the void) and should be burped frequently.
Geoff
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Post by zaphod on Jun 19, 2019 20:20:10 GMT
I am wondering if the reason only the cutlass bearing area of the shaft corroded is because the rest of the propshaft was covered with barnacles or other growth, creating a barrier from the electrolysis.
It's the only explanation I can think of!
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timeoff
Junior Member
Posts: 10
Jeanneau Model: Sun Odyssey 36i 2012 model
Yacht Name: Soirée
Home Port: Pittwater
Country: Australia
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Post by timeoff on Jun 20, 2019 7:20:55 GMT
Thank you for your further thoughts zaphod but in the words of one former slip operator "your boat looks better coming out of the water than most do going back in (after slipping ) ". As a matter of interest I use a Propspeed type product on the shaft and prop and use the boat at least once a week. The mystery continues...
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Post by ForGrinsToo on Jun 20, 2019 19:50:15 GMT
I suspect the damage was cleaned up a bit before the photos were taken. So maybe this is not electrochemical corrosion, but abrasion? It sure looks like corrosion, especially in the cutlass bearing region.
Do you use a galvanic isolator? Has someone connected the shorepower ground to the battery ground? Do you maybe have an invertor that is not correctly wired? The skeg should be electrically tied to the engine/battery negative (shown on page F11/1 of the 36i electrical schematics); have you checked that?
And I think, finally, nobody else (144 views and just a couple of comments) has seen something similar.
Geoff
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Post by vasko on Jun 20, 2019 20:16:57 GMT
The are with the lips seal is normal and no issues at all, but the part under the cutlass is VERY unusual/strange - what was the cutlass material ? Looks like it is not rubber , but rather something that conduct electricity or material stronger the SS but still metal.,,
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Post by rene460 on Jun 21, 2019 11:30:48 GMT
Hi Timeoff, I have been looking at your photos since you first posted them but have been a bit slow to reply. There are two areas of particular importance as I see it.
First the shaft seal area. Relatively normal to a greater or lesser extent I expect, though probably exacerbated by insufficient lubrication or ineffective burping of the seal when the boat is returned to the water after slipping. I would expect you might have a slightly leaking seal with that damage, but not necessarily. The solution is relatively simple when you decide to replace the seal. There is a device called a speed seal, or speed sleeve. Basically a metal sleeve over the shaft in the seal area, sealed to the shaft by an o-ring. The seal runs on the outside of the sleeve which is easily replaced if necessary. Buy the sleeve and the seal as a set. Make sure it is lubricated when first installed, and make sure you burp the seal each time the boat is returned to the water. The seal is lubricated and cooled by the sea water, and if there is an air bubble trapped there, you get poor cooling and no lubrication, sure recipes for such shaft damage.
The cutlass area is much more troubling. It definitely looks like galvanic corrosion to me. If it was abrasion, I would expect the grooves to be around the shaft rather than generally longways. Normally the shaft should be noble with respect to the cutlass bearing materials (some sort of bronze if a metal type) but in some circumstances all the stainless steels which are normally passive can become active; low oxygen, low flow and other environmental conditions that I don’t pretend to understand. Look up galvanic corrosion and galvanic series for more information. In this case I would suggest the rubber compound cutlass bearings as Vasko has suggested would be a good idea. It would be interesting to know what other boats in your area use, and if they also have problems. But what to do about that shaft? That is more difficult.
It is the highest stress area of the shaft, subject to both torsion and bending. The bending is due to the weight of the propellor, and as the shaft rotates, the bending becomes an alternating stress on the surface of the shaft, so contributes to fatigue. I don’t know if there is any satisfactory way to repair that shaft. Epoxy filling would not maintain the strength, welding would affect the metallurgy, and I don’t have the experience to know whether any such repair would be satisfactory. I think I would be talking to my propellor manufacturer about a replacement shaft. (I found that my propellor was actually manufactured in my home town. I had a good talk to them before buying, and have no doubt that they would be happy to make a shaft, and they had the material in stock. So I assume other manufacturers would also.) Also talk to your mechanic about local people who would make a shaft of the correct metallurgy. Unfortunately, you might have to remove the shaft to measure the overall length required.
You have not mentioned your anodes. Most of us have one on the propellor nut, and depending on your propellor, you may also have one on the shaft. If these are in perfect condition, they may not have good electrical contact with the metal they are supposed to protect. The paint has to be removed from the shaft and the seating surface of the propellor anode before they are installed. But surely your yard knows this. But if there is a corrosion cell where the shaft contacts the metal of the bearing, the anode may not be relevant. Such is the nature and mystery of this type of corrosion. I really wish one of our members was a corrosion engineer who could help us in this area.
I wish I could deliver better news. Please keep us all informed as you wrestle with the problem.
Rene460
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timeoff
Junior Member
Posts: 10
Jeanneau Model: Sun Odyssey 36i 2012 model
Yacht Name: Soirée
Home Port: Pittwater
Country: Australia
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Post by timeoff on Jun 22, 2019 6:32:03 GMT
Hi Timeoff, I have been looking at your photos since you first posted them but have been a bit slow to reply. There are two areas of particular importance as I see it. First the shaft seal area. Relatively normal to a greater or lesser extent I expect, though probably exacerbated by insufficient lubrication or ineffective burping of the seal when the boat is returned to the water after slipping. I would expect you might have a slightly leaking seal with that damage, but not necessarily. The solution is relatively simple when you decide to replace the seal. There is a device called a speed seal, or speed sleeve. Basically a metal sleeve over the shaft in the seal area, sealed to the shaft by an o-ring. The seal runs on the outside of the sleeve which is easily replaced if necessary. Buy the sleeve and the seal as a set. Make sure it is lubricated when first installed, and make sure you burp the seal each time the boat is returned to the water. The seal is lubricated and cooled by the sea water, and if there is an air bubble trapped there, you get poor cooling and no lubrication, sure recipes for such shaft damage. The cutlass area is much more troubling. It definitely looks like galvanic corrosion to me. If it was abrasion, I would expect the grooves to be around the shaft rather than generally longways. Normally the shaft should be noble with respect to the cutlass bearing materials (some sort of bronze if a metal type) but in some circumstances all the stainless steels which are normally passive can become active; low oxygen, low flow and other environmental conditions that I don’t pretend to understand. Look up galvanic corrosion and galvanic series for more information. In this case I would suggest the rubber compound cutlass bearings as Vasko has suggested would be a good idea. It would be interesting to know what other boats in your area use, and if they also have problems. But what to do about that shaft? That is more difficult. It is the highest stress area of the shaft, subject to both torsion and bending. The bending is due to the weight of the propellor, and as the shaft rotates, the bending becomes an alternating stress on the surface of the shaft, so contributes to fatigue. I don’t know if there is any satisfactory way to repair that shaft. Epoxy filling would not maintain the strength, welding would affect the metallurgy, and I don’t have the experience to know whether any such repair would be satisfactory. I think I would be talking to my propellor manufacturer about a replacement shaft. (I found that my propellor was actually manufactured in my home town. I had a good talk to them before buying, and have no doubt that they would be happy to make a shaft, and they had the material in stock. So I assume other manufacturers would also.) Also talk to your mechanic about local people who would make a shaft of the correct metallurgy. Unfortunately, you might have to remove the shaft to measure the overall length required. You have not mentioned your anodes. Most of us have one on the propellor nut, and depending on your propellor, you may also have one on the shaft. If these are in perfect condition, they may not have good electrical contact with the metal they are supposed to protect. The paint has to be removed from the shaft and the seating surface of the propellor anode before they are installed. But surely your yard knows this. But if there is a corrosion cell where the shaft contacts the metal of the bearing, the anode may not be relevant. Such is the nature and mystery of this type of corrosion. I really wish one of our members was a corrosion engineer who could help us in this area. I wish I could deliver better news. Please keep us all informed as you wrestle with the problem. Rene460
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timeoff
Junior Member
Posts: 10
Jeanneau Model: Sun Odyssey 36i 2012 model
Yacht Name: Soirée
Home Port: Pittwater
Country: Australia
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Post by timeoff on Jun 22, 2019 7:12:08 GMT
Thanks to zaphod, ForGrinsToo,vasko and rene460.Replies follow roughly in order. Zaphod;I cannot vouch for anode protection prior to my ownership but I have no reason to believe that the end of shaft anode wasn't in place and in good condition when the boat was in a marina as it was when I bought it 18 months ago.
. Also the boat has a 240 v electrolysis blocker/galvanic isolator fitted supplied by Marine Protection Systems p/l.The 3 bladed feathering prop is a ss one from Autostream and is top of the range.The skeg bearing was and is a rubberised backing type. ForGrinsToo.The damaged shaft was not cleaned up and is exactly as it came off the boat.As to an electrical connection between the skeg and the engine /battery negative I am wondering how this is done as there is no physical evidence inside the boat re such a connection. How is this physically done and / or can be checked? Vasko.As far as I am aware the bearing was a rubberised compound and has been replaced by a similar one. Rene460;Thank you for your extensive input. The speed seal idea sounds like a good one which I will discuss with my engineer as does the extra lubrication after slipping for the dripless seal. As for the damaged shaft a new one was machined up and fitted. If the same problem occurs then the notion of inferior stainless steel being utilised will not be a question mark.The boat is now on a swing mooring in salt water and I had no such problems with my previous 30 feet yacht of 22 years ownership. As I have mentioned elsewhere my very experienced engineer tells me that this isn't the first time he has seen ss corrosion problems on yachts out of the Beneteau/Jeanneau stable . So I suppose time will tell.I am not expecting any admissions of faulty/inferior materials being used in the construction of the boat and any subsequent compensation but a definitive answer to the problem would be nice.
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Post by MalcolmP on Jun 22, 2019 14:25:36 GMT
I tend to agree with the theory this is electrolysis and quite possibly stray current from another boat or pontoon. See my recent experience of this on my P bracket. jeanneau.proboards.com/thread/7459/stray-current-corrosion I do note my shaft was not affected only the P bracket but it seems the black art of electrical paths are difficult to replicate and I changed my shaft last year from the original to a duplex type as the original was worn at both cutless and lip seal areas.
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Post by Trevor on Jun 23, 2019 13:32:29 GMT
It looks like crevice corrosion to me. The thing that is baffling is the boat has been used regularly. Crevice corrosion seems to have a bad habit of attacking randomly and mercilessly. I had to replace a prop shaft once many years ago because of pitting and it was an expensive exercise. Reference to this is worth a read. highseasyachtservice.com/technical-articles/Select "Crevice Corrosion" and download the PDF. Regards, Trevor
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timeoff
Junior Member
Posts: 10
Jeanneau Model: Sun Odyssey 36i 2012 model
Yacht Name: Soirée
Home Port: Pittwater
Country: Australia
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Post by timeoff on Jun 24, 2019 1:18:38 GMT
Hi Trevor; That article is very interesting and there is every chance that the boat did in fact stay idle for extended periods of time prior to my ownership as it was very lightly used and in fact apparently was one of the main reasons I was told for its sale. It will not be idle while I own it. Cheers Tim
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Post by zaphod on Jun 25, 2019 16:04:54 GMT
Thank you for your further thoughts zaphod but in the words of one former slip operator "your boat looks better coming out of the water than most do going back in (after slipping ) ". As a matter of interest I use a Propspeed type product on the shaft and prop and use the boat at least once a week. The mystery continues...
The damage could have happened any time in the life of the boat. If you use an antifouling coating on your shaft and prop that may also explain the localized corrosion. It could be crevice corrosion. Perhaps the previous owner did not use the boat very much, so the prop shaft sat in one position for long periods of time. The lengthwise corrosion would be consistent with the channels between contact points on the cutlass bearing.
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