Losing antifoul from metal hull fittings

[goboatingnow]

Originally Posted by Andina Marie

HUH? Reading across the galvanic isolator will reveal considerable information.
If it reads ZERO voltage the isolator is shorted or bypassed somewhere.
If it reads more than about 1 volt DC it indicates that DC current is flowing that is not being blocked by the isolator and causing electrolytic corrosion.
If it reads more than 1.2 volts it indicates that the diodes in the isolator are burned out.
If the AC voltage is greater than about 0.5 volts it indicates that DC current can be flowing on top of the AC cycles and reducing the isolator efficiency up to 50%.
It is not an ultimate test but certainly the easiest test to make.

a galvanic isolator is purely connected to the earth wire. Hence it should have no Voltage across it.

The presence of approx 2xdiode drops indicates that sone current is flowing in the earth lines, this not atypical , however what can't be deduced is what is happening , such current may or may not be causing the problem , furthermore AC current will not cause too much corrosion , but there may be DC currents on top of the AC and yiu will not see this in any meaningful way on a voltmeter.

Dave