Odd anode damage. - Page 2

Nos4r2 · 02 October 2008, 14:21

Quote:

Originally Posted by Blackroady

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.

PeterM · 02 October 2008, 15:28

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 ! )

doggypaddle · 02 October 2008, 16:17

perhaps our anodes are made of cheese

jyasaki · 02 October 2008, 16:24

Quote:

Originally Posted by Blackroady

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

blinddog · 02 October 2008, 16:57

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

Poly · 02 October 2008, 17:43

Quote:

Originally Posted by blinddog

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?

blinddog · 02 October 2008, 17:59

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

Nos4r2 · 02 October 2008, 18:05

Quote:

Originally Posted by Polwart

Nos - are they getting worse or has it stabilised?

It seems to have stabilised now.

Nos4r2 · 02 October 2008, 18:06

Quote:

Originally Posted by blinddog

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.

Pete7 · 02 October 2008, 19:02

Quote:

Originally Posted by Nos4r2

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

Nos4r2 · 02 October 2008, 19:06

Quote:

Originally Posted by Pete7

Is the other side the same? because if it's not then how about cavitation?

Pete

It's not, and I hadn't thought of that. No cavitation damage to the the prop though. Would that be evident?

Pete7 · 02 October 2008, 21:57

Quote:

Originally Posted by Nos4r2

It's not, and I hadn't thought of that. No cavitation damage to the the prop though. Would that be evident?

Not sure, I have only had cavitation damage when we bushed a Suzi prop and put it on a Yam engine. Looked right and size was good but just didn't go. However what it did do was strip all the paint off in 10 miles of cruising and pitted the Ali prop quite badly.

If it's not cavitation but only on one side, like the side that the water coming off from the prop would drive towards the annode then perhaps there is something going on there. Afterall the total driving force to make the boat go is through that little shinney whisk thingy at the bottom of the engine.

Other possible thought, you're running a pre mix two stroke, are the exhaust fumes acidic? and the warm water off the prop again pushing against one side of the annode more than the other.

Pete

Poly · 02 October 2008, 22:05

Quote:

Originally Posted by Pete7

are the exhaust fumes acidic?

they will be.

Nos4r2 · 02 October 2008, 22:28

I think it's the wrong side of the anode though for exhaust gases? I wonder if it's connected that both areas of wormholing are right to the edge? I can see how that might tend to support Pete7's cavitation theory.

Martyn, any chance of a pic of yours?

Pete7 · 02 October 2008, 22:38

Quote:

Originally Posted by Nos4r2

I think it's the wrong side of the anode though

Well thats stuffed that theory then

Either way since you still have more than 50% it's not a problem for while yet.

You could always paint it to stop it corroding

Nos4r2 · 02 October 2008, 22:51

Quote:

Originally Posted by Pete7

You could always paint it to stop it corroding

Careful, Timw will do it

Bigmuz7 · 02 October 2008, 22:53

Quote:

Originally Posted by Pete7

Well thats stuff that theory then

Either way since you still have more than 50% it's not a problem for while yet.

You could always paint it to stop it corroding

Steady now,.. some peeps will believe you

.. If I had to throw a dart in the dart board of answers here .. I'd plump for Jw's answer.. it makes most reasonable sense

No other process can develop such a regular and deep corrosion pattern IMO wierd tho it is

Nos4r2 · 02 October 2008, 23:02

Quote:

Originally Posted by Bigmuz7

Steady now,.. some peeps will believe you

.. If I had to throw a dart in the dart board of answers here .. I'd plump for Jw's answer.. it makes most reasonable sense

No other process can develop such a regular and deep corrosion pattern IMO wierd tho it is

I'm leaning that way too.

However....just had a thought-I wonder if it IS caused by oil getting on the anode during flushing as the engine oils up sitting at tickover? It's on the correct side-the side that doesn't get the flushing water thrown onto it by the prop.

Doggypaddle, is your engine premix too?

K&S · 02 October 2008, 23:58

One of the boats i work with has a similar wear on it and i suspect it was caused by cavitation.

The boat was using the wrong sized propellor however thee was no sign of cavitaion burning on it.
The anode had not been adjusted for trim and so it had probably been creating its own cavitation which i believe had caused the same damage as you have on yours.

Is the trim tab offset or left in the centre position?

jwalker · 03 October 2008, 00:04

I can't say it isn't but the cavitation damage I've seen looks nothing like that. It's more a fine pitting errosion...kinda like deep sand blasting.