How Long?

[PhilF]

Should anodes last?
I worked out how to open the hatch yesterday and took out the engine anodes.
Merc 3.6DL 180's
The anodes were completely gone.
There were allegedley replaced in April of this year.
Could they have worn by now?
Please personal experience only, no "how longs a piece of string" type anwers!!
Saw a big big sail boat being towed into Ocean Village, anyone know why?
Have a nice weekend

Phil F

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[BrendanS]

Click on 'Mirabella V launched' in bar on top of page for story about yacht. Biggest sailing boat ever launched. That you one you saw?

<hr width=100% size=1>Any sufficiently advanced technology is indistinguishable from a rigged demo

 

[PhilF]

ergh - no

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[oldharry]

If they have gone that quickly then you have a major electrolysis problem - and now the anode metal is gone its eating away at your expensive engine.

The simple answer is to get an experienced engineer in - and soon, as there are no other simple solutions to rampant electrolysis.

Electrolysis occurs when 2 dissimilar metals (dissimilar in the galvanic scale) are placed in an electrolyte - which is what salt water is. They produce an electric current which flows from the anode to the other metal (acting as a cathode). This has the effect of transferring metal from one to the other, which is why your anode has disappeared. The trouble now is that the next available metal in your engine has taken over as anode and is also rapidly dissolving! It is stopped by bonding the dissimilar metals electrically to effectively short circuit the electrical cell effect.

It can also be caused by stray currents from the batteries. On many marine installations the starter and alternator negative return independently of the engines metalwork. If the block is not properly bonded to the negative pole, or there is no bond to 'true earth' (i.e. the sea) an electrical potential can be set up with the same results.

Without examining your installation, there is no way to tell what has gone wrong. You could try using a digital volt meter between the anode and various other metal parts that should be at zero voltage. If not - there is potentially a problem, and it should be shorted out. There are various books which can explain causes and remedies more fully if you want to find out more.

As an example, I have seen an electrical fault in which electrolysis at full battery voltage burnt through a steel sump case in less than 24 hours - with the obvious disasterous result!

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[PhilF]

Thanks for that.
I suspect that the anodes were not changed at the last service, as previously they have lasted 2 years with moderate wear.
I will moniter the new anodes over the course or the next month and get some expert assistance.
The out drive anodes seem to be wearing evenly

PhilF

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[gonfishing]

There can be loads of reasons for quick dissolving anodes it could be if you are using shore power thet there is a poor earth connection or poor bonding on the engine or a poor earth within the Marina or it could be a lot of metal in the Marina /pontoons or you are berthed next to a steel boat, all these will have a direct effect on how long your anodes last, there are a couple of options
keep checking anodes and replace as req bit of a pain and expensive
or get a large block anode and hang over the side when in the Marine easy option
or have alook at <A target="_blank" HREF=http://adverc.co.uk>http://adverc.co.uk</A> for an in depth explanation of galvanic isolation[found on their technical page]

Julian

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[PhilF]

Thanks for that, what would I connect the block anode to, an earth point on the engine?

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[davedpc]

I have the 220hp version of your engine and mine only last one season.

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