AC Circuit on a Steel Hull Vessel

[dlochner]

I've become involved in the restoration of a steel hull sailboat. The boat has a history of corrosion issues causing the hull to need replating a few years ago. The corrosion is back. This is a freshwater boat. Anodes (probably zinc) look almost as good as the day they were made.

As I was going through the electrical system today, I noted that the AC ground (green wire) and DC Negative are both bonded to the hull. No resistance between the stud for the AC ground and the DC negative, a nice solid electrical connection. Also the AC system does not have a galvanic isolator.

My suspicion is that the main culprit in the corrosion is the AC ground connected to the steel hull, followed by a lack of a galvanic isolator, and then the wrong and inadequate number of anodes (should be magnesium or aluminum).

Am I on the right track?

There are other electrical issues that need to be addressed, like unfused circuits, cheap battery charger, and probably many more. We'll get to those later.

Thanks for your insights.

 

[Benny17441]

Both grounds need to be bonded to the hull for safety reasons. It will protect both persons inside and outside the hull. To prevent galvanic corrosion you need to install a galvanic isolator. Verify the composition of the anodes, for fresh water I would recommend magnesium but aluminum will also work and have the added advantage of providing adequate protection in salt water also.

 

[captcoho]

The anodes need to be magnesium , not zinc if the boat is in freshwater.
Magnesium Alloy Anodes = Fresh water only
◦Not recommended for use in salt or brackish water
◦The only alloy proven to protect your boat in fresh water

 

[Maine Sail]

I've become involved in the restoration of a steel hull sailboat. The boat has a history of corrosion issues causing the hull to need replating a few years ago. The corrosion is back. This is a freshwater boat. Anodes (probably zinc) look almost as good as the day they were made.

As I was going through the electrical system today, I noted that the AC ground (green wire) and DC Negative are both bonded to the hull. No resistance between the stud for the AC ground and the DC negative, a nice solid electrical connection. Also the AC system does not have a galvanic isolator.

My suspicion is that the main culprit in the corrosion is the AC ground connected to the steel hull, followed by a lack of a galvanic isolator, and then the wrong and inadequate number of anodes (should be magnesium or aluminum).

Am I on the right track?

There are other electrical issues that need to be addressed, like unfused circuits, cheap battery charger, and probably many more. We'll get to those later.

Thanks for your insights.

You really need to bring in an ABYC corrosion specialist.

You could not pay me to own a steel hull boat without at least an isolation transformer and a built in hull potential meter. Unless welded in all seacocks need to be isolated from the hull. This only scratches the surface on a metal boat and corrosion so do get someone in board who understands them..

 

[dlochner]

Maine,

Thanks for the advice. Suggestions on finding an ABYC Corrosion Specialist?

Dave