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Old 02 October 2008, 09:21   #21
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Has it been chipped by stones when its being towed ??????? OK not really a sensible suggestion , but the first one that came to me ! It COULD be , but probably not......

Not sure how this would affect an anode.
It's one of the things I wondered to start with actually.

What's really puzzling is there's no fur on it at all though.
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Old 02 October 2008, 10:28   #22
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If its on the trailer and not in the water much would it go furry at all ? The anodes on my Yam are 2 years old - the longest it has been in the water is 2 weeks ( at any one go) and they still look like new & are solid with only one or two very very minor marks.

Given the almost perfect looking shape of them ( the 'holes') I think it must be some reaction -almost as if a wire has touched it & fromed the near perfect sphere - God only knows how though.

I woudl expecct he only things that could do this on such a localised basis is either somekind of current at those points, some kind of chameical acting as a catalyst, or the chemical already inbedded in the anode speeding things up. All of these have been suggested.

I will spend some time at 'work' searching for pics of sacrificial anodes to see there are any like this on the net !

OR someone with a drill who has a dislike of anodes ( clearly likes you otherwise they would drill into the boat inteslf ! )
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Old 02 October 2008, 11:17   #23
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perhaps our anodes are made of cheese
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Old 02 October 2008, 11:24   #24
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Has it been chipped by stones when its being towed ???????
Not sure how this would affect an anode.
Shouldn't affect it at all, except for the stone chip itself. An anode is a piece of zinc (or magnesium for fresh water folks), unpainted, untreated. Zinc is fairly soft, so you aren't going to chip out a crater as shown in the pic; the exposed metal will be the same as everything around it, so it shouldn't erode any differently.

Dunno what's causing it.


jky
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Old 02 October 2008, 11:57   #25
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Noblilty of steels gives normal corrosion of the zinc as it is suppost too, but looks like localised deep attacks' i've seen this kind of attack before from bacteria on our Subsea systems which have been down for a while the bacteria is called (desulfovibris desulfuricans) think this is the right spelling this is not uncomman.


gaZ
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Old 02 October 2008, 12:43   #26
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Noblilty of steels gives normal corrosion of the zinc as it is suppost too, but looks like localised deep attacks' i've seen this kind of attack before from bacteria on our Subsea systems which have been down for a while the bacteria is called (desulfovibris desulfuricans) think this is the right spelling this is not uncomman.


gaZ
Desulfovibrio desulfuricans is an anaerobic bacteria so won't grow when its out the water, and I doubt would be active enough even with near surface levels of disolved oxygen, to cause that much damage in relatively short periods of time. Much more common if equipment is submersed in deep water where low levels of oxygen are present. If D. desulfuricans (or other sulfate reducing bacteria) were causing problems at near surface levels I would expect to see visible signs of the bacteria - i.e. some sort of slime/biofilm deposit which protects them from the environment, sunlight and oxygen.

Nos - are they getting worse or has it stabilised?
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Old 02 October 2008, 12:59   #27
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If the other anode is ok why not just go and put a new one on to replace the damaged one ?
Its not an expensive item.

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Old 02 October 2008, 13:05   #28
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Nos - are they getting worse or has it stabilised?
It seems to have stabilised now.
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Old 02 October 2008, 13:06   #29
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If the other anode is ok why not just go and put a new one on to replace the damaged one ?
Its not an expensive item.

gaZ
I will do-but I'm curious about what could give such an odd pattern of corrosion.
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Old 02 October 2008, 14:02   #30
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I will do-but I'm curious about what could give such an odd pattern of corrosion.
Is the other side the same? because if it's not then how about cavitation?

Pete
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