Saildrive disappeared...

Hallo

Rolf, do you have any more pictures? It would be interesting with a close-up, if you have one.

Did you get any leaks?

Johan

Hi all,

In respect to the previous posts here an article on Electrolysis.

http://www.jefa.com/install/electro.htm

Regards, Willem

Edited by copain - 04 December 2008 at 17:49

Hi Folks,

This case is not as odd as it seems. Yes, the consequences are extreme, but the problems regarding elecrolytic corrossion are everyday problems for the average boat owner.

So what can cause this extreme corrosion? The magic words are known as "shore power"

Saltwater.  Your boat floats in it.  Another name for it is electrolyte. Your saildrive? It can be an anode or it can be a cathode. In cases regarding galvanic corrossion the most noble metal is the cathode. In the world of electrolytic corrossion, you actually do not now. It all depends what way the electrons will move and that all depends what is the positive and what is the negative part of the circuit - and of course that we do hav a closed circuit. Well, you can call it by its real name. It is called a battery. And in your case your saildrive is the anode in the circuit. You can call it a sacrificial anode. The thing that gets eaten that is.


So how does the saildrive get eaten up in the first place? Well, normally it would not. That is of course only the case if your boat, every elses boat and the shore power all are without any fault. The chance for this to happen is of course much smaller than winning the the lottery and become a billionare.

Given the fact that there is always  some kind of a fault somewhere, your boats underwate rpart is about to get electrolytically corroded and eventually disappear. Well at least those part that has some kind of connection to battery minus. And what parts would  that be? Well, if your boat has an engine that is not electrically isolated, then battery minus is connected to the engine block. And guess what? The engine block is elecricalle connected to your saildrive, propeller, maybe a rudder, some seacoocks.... most underwater metal parts actually.

And guess what again? Hanse do connect shore power ground with battery minus, and so do most boat builders. Is this plain stupidity? No, not at all. This is according to the given safety regulations. These regulations takes care of the personell safety, not the safety of your zincs or other metal parts.

Given these circumstances, we are now ready for the corrosion devil to do his job. Fortunately this job is still a tuff one to acomplish.  A ground fault interceptor on shore will cut the circuit off in case of a ground fault. But then again, your boats health depends on wheather this interceptor works or not. And, if it works, it would still not cut off these small currents in the range of 5-10-20 and up to 30 mA or whatever the trigging current may be. And these currents will definately harm your boat. But then again - only if your boat become the anode in the circuit. Do you feel lucky? Perhaps not, but there was a chance that your boat could have been the protecting cathode in the circuit. A 50% chance acutually.

Five monts with shore power connected. Five monts with at large ground fault.  Sorry mac. This is not the boat buiolders problem. This is not the engine manufacturers problem. This is your problem and yours only. sh*t happends. 

And for all the rest of us? There is only one safe solution to the problem. Do get rid of the shore power ground cable. The problem is that this cable is there to save your life in case of a fault. If you cut it, you have to have a better  - and a legal - alternative. The altarnative is called an isolation transformer. Another alternativ is to disconnect the ground wire from the battery minus and then only use double isolated electrical equipment. A third alternative is to enable a local earth plane on board. An excellent alternative like how it is done in most homes and legal to do on boats in many countries. Local earth plane is as simple as an underwater metal part of a given size which do make an excellent job in transporting the ground falt current safely back to its source without causing harm to your boat, the other boats or to any swimmers nearby. The salt water is an excellent conductor - much more safe than a questionable shore ground wire and even more important a far better conductor than the human body.