Zincs on my boat are degrading faster than I anticipated.
How long did you anticipate? How much underwater metal are they protecting? With no GI you are probably protecting your neighbors boats with your anodes.
If my boat is the one leaking AC (or DC) current to the water, will installing a galvanic isolator on my own boat be of value?
Because our boats AC grounding wire (green) is
supposed to be bonded to the DC grounding system, for human safety, this means that when you plug into shore power your underwater metals are connected to your neighbors underwater metals via the green AC grounding wire.
A galvanic isolator is a device that is inserted, in series, into the green grounding wire (safety ground) of your shore power feed to help minimize or reduce the effects of
galvanic current from flowing between your vessel & your neighbors. While blocking
galvanic level current it also has to allow for the passage of AC fault current. This is why any galvanic isolator should be of the "fail safe" type or have idiot lights that tell you you still have an AC grounding connection.
This
blockage of low voltage galvanic current is achieved by using two diodes in-series in each direction. Each diode drops approximately .6V or
requires more than .6V to open and "
Flow". Two of them in series results in approximately a 1.0V - 1.2V threshold for blocking DC galvanic level voltage & current.
GI's normally have two diodes in each direction so the AC green wire is not "check valved" and acts just like a wire normally would. The only difference is it acts as one that won't pass voltages below 1.0V - 1.2V. Simple and pretty effective at blocking
galvanic level current. GI's do not however block
stray current that exceeds 1.2V...
Think of a diode as an electrical
check valve. It allows current to flow in only one direction but not in the other direction. One of the inherent traits of diodes is the voltage drop associated with them, which is usually around 0.6V. In a galvanic isolator application they have used this
often assumed bad trait of a diode to an
advantage. By wiring two diodes in series you now have a device that can block any galvanic level voltages below 1.0V - 1.2V from flowing into or out of your vessel.
If we understand the voltage potential spreads, between underwater metals, which is usually below a 1.0V differential, it becomes easy to see how a GI works.
Because the dissimilar metals connected together in the electrolyte can't really create more than 1.2V the GI stops your vessels anodes from protecting your neighbors underwater metals.
If plugging in at a marina a GI is the
absolute bare minimum level of protection that every boater should have. On personal level you'd never catch me plugged into any marina without an isolation transformer (IT). A simple GI won't cut it for me. Of course the conversation of
true isolation versus
galvanic isolation only takes on another life and is a whole other discussion & topic.
At a bare minimum you should have a fail safe galvanic isolator. If anode life does not improve after that then you will need to start with corrosion testing..