Corrosion

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nielsen1

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As anyone experienced rapid corrosion of zinc anodes/ Keels? 8 weeks for a large M.G.Duff pearl type anode to waste away.
Its happening on the upper reaches of Portsmouth Harbour, Half tide mud berths, most boats at the Marina have succumbed, so its not a internal bonding problem. None of the boats are connected to the pontoons other by mooring lines, so its not electrical problems. Could it be something in the mud?
Any ideas?
 
This question is posed in a marina context, yes? Then it may be an external bonding problem. If your boat bonding is connected to the earth of the marina, as it will be if you have a mains charger with no special isolation, then a big battery can be formed between your anode (and everything else on the boat earth) and some nasty great pilings, or someone else's boat with a leakage. I am not expert enough to make such a complex subject easily understood, but you may need to look to getting a galvanic isolator (or get the shore-side problem sorted!).

Try this link and then click on galvanic isolators

Can't think of anything else which would eat anodes as fast as you say, and all the boats around suffer the same. :-)
 
I would agree, but.....
There is no connection to the Pontoon other than ropes, niether are there connection between boats. We have lights along the pontoon, but I believe you need a link from the boat to create a circuit!
This is a strange conundrum, /forums/images/graemlins/confused.gif
Thanks for replying.
 
It happens to our boat in Haslar. I was shocked to see the rate of corrosion and this was with a "Zinc protector" (diodes in the earth lead where it comes onto the boat).

The one at the end of the prop is the one that seems to be most affected in spite of the shaft anode
 
I'll give you a clue - What do St. Elmo and Michael Faraday have in common. /forums/images/graemlins/confused.gif
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"Artificial intelligence is no match for natural stupidity"
 
Something Brendan said about a strange composition of mud: I have a recollection of strange corrosion problems in a London dock, some time ago, that was eventually traced to coal on the sea bed. Can't remember any more about it and Google wasn't any help. Does anyone else remember this?
 
[ QUOTE ]
and would have to have an interesting composition mud to corrode zinc at that rate

[/ QUOTE ]Not really, more physical composition than chemical although the chemical composition could assist the accelerated corrosion rate.
A little research on LOP corrosion (low oxygen potential) and a bit of reverse logic might help explain one possible scenario. Think of where the electrons go when the zinc converts to the ionic form!.
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"Artificial intelligence is no match for natural stupidity"
 
Thanks for all the responses, one clue has come up....
Fareham had a coal quay close by (years ago), maybe there is a link with the properties of coal, but this problem seems to be cyclic, two years ago we didn't have the problem, five years ago a group of other boats at the same Marina had the problem.
As anyone heard of a bacteria that's in the mud, who's bi-product is a sulphide???? mix sulphur and water???
 
Nowt to do with coal in the mud. See my previous post.
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hammer.thumb.gif
"Artificial intelligence is no match for natural stupidity"
 
Although zinc anodes have been disolving before our eyes, the galvanised studding that holds the anodes also dissolved leaving 2 boats stinking. Stainless steel, bronze fittings, cast steel keels are also showing major corrosion in a very short time, therefore I don't think zinc corrosion is the only thing happening. Maybe because Zinc is lower down of the scale, its the first to go.
Has anyone experienced calling in a University or Organisation?
 
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