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Corrosion or Electrolysis

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Jontie999 View Drop Down
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    Posted: 22 December 2022 at 09:47
Hi
We are about to purchase a Hanse 400 and this issue cam up on the survey. We don't know if it is an electrolysis / bonding issue or poultice corossion on the rudder stock head and inside fittings.

Can anyone advice on what it might be and how to resolve? The rudder stuck is unaffected.

Please see pictures. 
see

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Ratbasher View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ratbasher Quote  Post ReplyReply Direct Link To This Post Posted: 22 December 2022 at 11:20
There's a few threads on this site (try 'advanced search') about bonding/not bonding rudders and model year/engine manufacturer are significant factors.  Some boats, like my 2008 model/Yanmar powered 400, suffered electrolytic corrosion but only on the external surface of the stock between the rudder and the hull, nothing on the unbonded steering quadrant.  What does your surveyor say about the structural integrity of the fitting as it is?  Of course, surveyors are generalists and it might be worth getting an opinion from a corrosion specialist.  I had one check my boat out and was surprised by the very reasonable fee which you could always haggle with the present owner about.  Hopefully, others with more direct experience will comment more usefully than I have.  

If the rest of the boat is in decent condition and the price is OK I wouldn't necessarily be put off by this.  I've seen far worse on some 'quality' boats and the Hanses tend to be strong where they need to be strong.
H400 (2008) 'Wight Leopard', Gosport UK
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H8jer View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote H8jer Quote  Post ReplyReply Direct Link To This Post Posted: 22 December 2022 at 11:38
Hi Jontie999

Jefa Marine that built your rudder + assembly don't recommend grounding/earthing the installation.
The green/yellow earthing wire on you second photo is most likely the culprit.

/h8jer
Hanse 370#487 30HP 3-cabin
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Jontie999 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jontie999 Quote  Post ReplyReply Direct Link To This Post Posted: 22 December 2022 at 15:03
Thank you all. I have since found out the earth wire is connected to the external anode, not the original bonding sites. The rudder was replaced and original bonding removed.




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Ian Coverdale View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ian Coverdale Quote  Post ReplyReply Direct Link To This Post Posted: 22 December 2022 at 16:45
Looked at many Hanse's over the last few years but not seen anything like that! Traditional Jefa electrolytic corrosion is caused by stray electrical currents below the waterline. This is clearly not that.

Is the corrosion just within 10mm or so of those stainless steel fasteners. Is it possible someone has reassembled these parts using an inappropriate anti-cease compound such as copper loaded grease? 
Ian & Andrea
SV Gabrielle (H445)
Liveaboards - currently Gosport UK for winter 2023/24.
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Jontie999 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jontie999 Quote  Post ReplyReply Direct Link To This Post Posted: 23 December 2022 at 10:49
@Ian & Andrea
I think this is the most logical explanation. We are going to have them dismantled and reinstalled. 

Thank you.
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Ian Coverdale View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ian Coverdale Quote  Post ReplyReply Direct Link To This Post Posted: 23 December 2022 at 12:50
Very good. If you're on the hard, takes only an hour or so to drop the rudder. Can take a far amount of thumping with a block of hard wood and heavy mallet to 'unstick' it. Wetting the lower bearing with water from a hose pipe helps. Good luck.
Ian & Andrea
SV Gabrielle (H445)
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H8jer View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote H8jer Quote  Post ReplyReply Direct Link To This Post Posted: 23 December 2022 at 13:17
If you are on the hard, there are some measurement you could do.

States the ohm value between the rudder stock and the propellershaft should be indefinite. 

But as mentioned above, it does not look water related. Looks like mixing Stainless+Aluminium+saltwater+air+time


Edited by H8jer - 23 December 2022 at 13:19
Hanse 370#487 30HP 3-cabin
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