Earthing problems and anode corrosion

[esheridan1]

Hi, I have a steel hull boat and when I took her out of the water I discovered that the anodes had almost disappeared. My initial thought was that I have a bad earth and potentially a faulty piece of 240v kit on board causing the anode corrosion, but after inspection to my surprise that doesn't appear to be the case. The 240v mains earth appears to be totally isolated from both the battery negative and the steel hull. Therefore my logic cannot understand why the anodes are being used as a path to earth. I am very tempted to bond the mains earth together with the hull and battery negative. Any ideas?
As a side issue which may or may not be related, I get through a battery almost every year with very little usage made of them. This could be because my charger is not very intelligent and is cooking them, but I do wonder if it is related to the earthing issue.
Any help would be much appreciated.

 

[ostell]

Could be your charger is providing the earth path, ie the output is connected to earth for safety reasons. Look for the double insulated symbol (square within a square) on your charger.

 

[noelex]

DC faults will result in a high anode wastage on a metal boat. Look for problems like multiple dc ground connections. I suspect your problem is DC not AC related.

 

[VicS]

Some wastage of the anodes will occur in protecting the hull.

The mains earth should be bonded to the hull of a steel boat unless the mains power supply is via an isolating transformer.
If there is a transformer there should be no connection between hull and shoreside earth but one side of the transformer secondary should be bonded to the hull create an on board "earth"

If there is no transformer then a Galvanic isolator should be fitted in the incoming earth to protect the boat and in particular the anodes from excessive galvanic corrosion while the shorepower is connected.

You should read ISO 13297 for all the details regarding the installation of main electricity. http://www.earlhill.de/files/ISO_13...Systems_Alternating_current_installations.pdf
But be aware that there is a new edition on the way even if not already published.


Your DC system may or may not be bonded to the hull and earth. If the engine is designed to be fully isolated then the DC system need not, perhaps should not, be earthed.

If the DC system is bonded to the hull it should be at one point only and the hull should not be used as a negative return in the way that car bodies are.