Discolored hull paint, bonded thru hulls with no anode

[LifesBetterWhenYoureBeating]

Originally Posted by boatpoker

Altho' theoretically possible, after hundreds of corrosion surveys I have yet to see another vessel be the issue. I have always found the corroding boat to be the master of it's own disaster. It seems that owners prefer to blame someone else rather than look at their own boat.

So no need for a galvanic isolator?

[boatpoker]

Originally Posted by LifesBetterWhenYoureBeating

So no need for a galvanic isolator?

They are a cheap bet. I have one.

[s/v Jedi]

Originally Posted by LifesBetterWhenYoureBeating

I don't usually need shore power so this had been low on my todo list. I'm now going to leave the boat on a slip and so want to get this right.

All my underwater metals are now isolated.

My AC ground and DC negative are not connected

My DC negative is connected to my engine and that provides a path to earth via the prop shaft

As I understand it, this configuration will stop galvanic corrosion from current generated by other boats but won't provide safety against AC faults on my boat?

If I connect my AC ground to my DC negative and install a galvanic isolator, will that provide safety from AC faults with no risk of galvanic corrosion?

Sent from my SM-A225F using Cruisers Sailing Forum mobile app

You can install a battery switch in the negative connector to the engine block and isolate from the water. Something I would do for sure.

For safety aboard, do you mean with shore power?

[LifesBetterWhenYoureBeating]

Originally Posted by s/v Jedi

You can install a battery switch in the negative connector to the engine block and isolate from the water. Something I would do for sure.

And that switch would be ON only when I start the engine? If so, that'd mean no o more path to earth from my DC negative. I thought that was necessary, or is it only when there's a bonding circuit connecting underwater metals?

For safety aboard, do you mean with shore power?

Yes, I thought that was clear as I said safety from AC faults, but maybe they could come from an inverter (which I don't have) as well?

[s/v Jedi]

Originally Posted by LifesBetterWhenYoureBeating

And that switch would be ON only when I start the engine? If so, that'd mean no o more path to earth from my DC negative. I thought that was necessary, or is it only when there's a bonding circuit connecting underwater metals?

Yes, I thought that was clear as I said safety from AC faults, but maybe they could come from an inverter (which I don't have) as well?

You keep the switch on while using the engine, or you turn it off when not using the engine for a while

For AC grounding, see my attached diagram. An isolation transformer is the best protection for people as well as for the boat. It will completely eliminate the issue. Look at every detail of the diagram, especially every grounding wire. A very important point is that the ground from shore terminates at the transformer and does NOT connect to the transformer ground wire that connects to the rest of the boat.

Also, for bonding metals: when you have underwater metals and they need cathodic protection, they usually have zincs. This is mostly for parts made out of several different metals, like propshaft and propeller etc.
I am not a fan of connecting everything to a central zinc. Most metals, like bronze thru-hull fittings, don’t need anything.

Then there’s also bonding for lightning protection. This concerns the mast, stays and shroud chainplates and connecting these either to underwater bonding plates or special discharge fittings just above the waterline. Searching on this forum will find threads on the subject.