Zinc Anodes Disapearing quickly on one shaft and rudder only

[chiropaul]

Hi everyone,
Just got a call from my diver that the anodes on the port shaft and rudder will need changing by next month, while the starboard look fine. All were replaced this past November 3 months ago). They had lasted approximately 9 months. Only thing new, is a new boat in the slip adjacent to me since around Dec.


I have a single 50A, 125/250 power cord going to a 50-2-30A splitter to the boat.


all bonding wires that I can see are connected. About 2 weeks ago I did reconnect one wire that had come off the port rudder post.


Any ideas?
Thanks,

 

[tiltrider1]

Do you have galvanic isolators? Do you also have a diver dream zinc attached to the bonding system? Is the new boat a sailboat that replaced a dual engine power boat? Have you replaced any electrical appliances on board? Do you have an ELCI breaker installed or at least tested to see if you are suffering any current leakage.

These problems usually have a lot more questions before a problem can be found.

 

[Larry M]

I’d get a corrosion analysis by an ABYC certified corrosion tech. He’ll check your boat and the shore power looking at the bonding system, stray current, grounds, etc. We had one done a few years ago. It took him about an hour with me helping. Here’s a link that should help you find one for your area.

https://abycinc.org/mpage/findatech

 

[psneeld]

I would recheck all the connections...but if the bonding was lost on the Port side rudder post...maybe that's all it was and replace the zincs and keep an eye on it.


A corrosion survey is never a bad idea...

 

[chiropaul]

Thanks everyone,
Tiltrider1, Yes I have all underwater fittings tied to a divers dream plate. Just so happens a sailing Cat moved into that slip, which was empty. Have not replaced any electrical equipment or appliances since Sept, when a new A/C was installed (thanks for the reminder, as the ground had separated and I had to reinstall it a couple of weeks after initial installation...will check it now). No ELCI here at this marina.


Will definitely be adding galvanic isolators (2-50A, 125V services on boat, only using one now, so will probably need 2 isolators).

 

[chiropaul]

Thanks Larry for the link. Will do that if can't rectify this situation, that is new.

 

[JohnEasley]

I would recheck all the connections...but if the bonding was lost on the Port side rudder post...maybe that's all it was and replace the zincs and keep an eye on it.

That's the direction I was leaning, too.

 

[Island Cessna]

Also be sure your anodes are all the same metal. It is easy to mix up zinc, aluminum, and magnesium. The shelves are filled with a bewildering selection, often poorly marked, or even mixed up. The least noble will go first in a bonded system.

 

[chiropaul]

So, just got back from the boat. Diver was still there and talking to a couple of other guys with boats on the dock. Diver said several other boats have been having similar problem recently. One owner has spoken to the marina personnel and is trying to have an electrician check out the dock wiring.


As regarding that catamaran next to me...he was bottom painted and had new zincs installed in December. Diver said bottom was in poor shape and zincs almost gone. Could be the culprit. He will report his findings to the owner.


As far as I could tell, all bonding wires are well connected. That A/C ground wire is also fine. So as of now, I will install galvanic isollators and it's a wait and see what shows up when the marina has the electrical system checked.


Thanks for everyone's quick responses.

 

[catalinajack]

Woul

So, just got back from the boat. Diver was still there and talking to a couple of other guys with boats on the dock. Diver said several other boats have been having similar problem recently. One owner has spoken to the marina personnel and is trying to have an electrician check out the dock wiring.


As regarding that catamaran next to me...he was bottom painted and had new zincs installed in December. Diver said bottom was in poor shape and zincs almost gone. Could be the culprit. He will report his findings to the owner.


As far as I could tell, all bonding wires are well connected. That A/C ground wire is also fine. So as of now, I will install galvanic isollators and it's a wait and see what shows up when the marina has the electrical system checked.


Thanks for everyone's quick responses.

A galvanic isolator would protect your boat from other faulty boats. A 30-amp Promariner can be had for about $220, a 60-amp for about $320.

 

[CharlieJ]

@ catalinajack #10 A bit of clarification is in order.

A galvanic isolator will protect against cathodic protection current from leaving or entering your boat via the safety ground wire. Cathodic protection current is simply galvanic current working in our favor and is produced by the difference in galvanic potential between different metals, electrically connected and immersed in the same electrolyte; e.g., the shaft anode and the shaft. The potential produced by sacrificial anodes are < 1.7VDC. Therefore galvanic isolators are designed to block voltage of about 1.7VDC.

Here is the punchline: A galvanic isolator will do nothing to protect against stray DC current being produced by another boat since the stray current is being produced by battery voltage, typically 12 or 24VDC, which far exceeds the blocking capacity of the galvanic isolator.

On the surface, the catamaran with the failed freshly painted bottom and anodes certainly appears to be inducing stray current into the water column.

 

[catalinajack]

@ catalinajack #10 A bit of clarification is in order.

A galvanic isolator will protect against cathodic protection current from leaving or entering your boat via the safety ground wire. Cathodic protection current is simply galvanic current working in our favor and is produced by the difference in galvanic potential between different metals, electrically connected and immersed in the same electrolyte; e.g., the shaft anode and the shaft. The potential produced by sacrificial anodes are < 1.7VDC. Therefore galvanic isolators are designed to block voltage of about 1.7VDC.

Here is the punchline: A galvanic isolator will do nothing to protect against stray DC current being produced by another boat since the stray current is being produced by battery voltage, typically 12 or 24VDC, which far exceeds the blocking capacity of the galvanic isolator.

On the surface, the catamaran with the failed freshly painted bottom and anodes certainly appears to be inducing stray current into the water column.

Thank you for the correction. This stuff really is a black art.

 

[Benthic2]

I would not be swimming from those docks when the weather warms up!

 

[OldDan1943]

My thoughts, just because the bonding connections appear or even feel tight... disconnect each one to see if there is corrosion.
Start at the connection furtherest away.... why, you may ask? Because maybe someone started checking the connections, getting the easy ones first and never got around to doing the difficult to reach connections.

 

[SteveK]

@ catalinajack #10 A bit of clarification is in order.

A galvanic isolator will protect against cathodic protection current from leaving or entering your boat via the safety ground wire. Cathodic protection current is simply galvanic current working in our favor and is produced by the difference in galvanic potential between different metals, electrically connected and immersed in the same electrolyte; e.g., the shaft anode and the shaft. The potential produced by sacrificial anodes are < 1.7VDC. Therefore galvanic isolators are designed to block voltage of about 1.7VDC.

Here is the punchline: A galvanic isolator will do nothing to protect against stray DC current being produced by another boat since the stray current is being produced by battery voltage, typically 12 or 24VDC, which far exceeds the blocking capacity of the galvanic isolator.

On the surface, the catamaran with the failed freshly painted bottom and anodes certainly appears to be inducing stray current into the water column.

Charlie, the bolded.
Did you mean to say AC or care to elaborate on a DC leak. DC is within a boat and has no reason to seek a return circuit to the boat.

 

[CharlieJ]

@Soo-Valley #15
No, I didn't mis-speak but I do need to clarify a bit more. Thanks or the question.

A boat built to be compliant to ABYC Standards has the AC and DC grounding and bonding systems interconnected. Thus, when boats plug into shore power they are interconnected by the safety ground (green) wire and to any other metal components tied into the safety ground system ashore. The galvanic isolator is designed to stop the cathodic protection current from Boat A, with well maintained sacrificial anodes, leaving Boat A via the safety ground wire and protecting other underwater metal components connected to the safety ground system; e.g., Boat B with poorly maintained sacrificial anodes, metal sheet piling in the marina, metal docks and underwater metal dock components, etc.

If there is true DC stray current being produced by a boat, that current will attempt to return to the source of the current, usually the stray current producing boat's battery B- via the positive ion flow in the electrolyte. IF, and it is a big IF, a properly bonded boat is in the ionic path, a complicated cathode/anode path will develop culminating in the stray current returning to the errant boat's battery B- via the safety ground wire. Since this current will be > 1.7VDC, a galvanic isolator will not block it.