Through hull anode bolts

[superheat6k]

The boat in question does not need a bonding circuit. It has a saildrive with its own anode which wastes slowly. If he removed all the existing bonding and the anode he would have nothing to create a circuit through the water.

I had 2 similar boats with saildrives and no other anodes moored right by a huge steel pile for over 10 years with no problems, even on shorepower. With the last boat only one anode change in 6 years in the water all year round.

See this thread forums.ybw.com/index.php?threads/galvanic-isolator.587219/

The poster was asking why his pear anode was dissolving so I suggested some things he could check. Dissolving a whole anode suggests something more than galvanic currents at play.

 

[bignick]

Well I found 6k’s reply useful and will be working my way through the list he provided later in the year.
Probably on a damp Saturday morning in November when I’m looking for something to do before the boat comes out.

 

[stuartwineberg]

Electrolytic corrosion is not just galvanic - i.e. the corrosion caused by dissimilar metals, but also stray current, which in many cases will be a lot more severe, especially AC high voltage leaks.

Here is a list of things to check.

1 Disconnect the +VE terminal at the battery/ies. Turn off all services that would be off when the boat is left idle. This normally just means the bilge pumps and battery charger are left on.

Measure for voltage between the loose terminal and battery post from whence it was just disconnected. The result should be 0.0v. If you can measure a voltage then you have a DC leakage, and this could easily be eating your anode.

2 So following on check any flapper style pump switches. Disconnect each in turn and repeat check at 1, then dod the same for the bilge pumps. If the reading drops to 0v you have found the culprit.

3 Do you have a live / neutral reversed polarity indicator for the shore supply ? If so is the indicator a neon or a diode - if the latter this could be bypassing your GI. However, disconnect the power reversal lamp and purchase a test plug and use it each time you plug in to shore power.

4 Do you have any steel piles or steel hulled boats nearby.

5 Do you have any rather dodgy looking boats nearby. Either of these can emit stray currents that hitch a ride along your bonding circuit, causing havoc to your anodes.

Thank you, will investigate. I certainly have lots of metal nearby being next to the marina walkway

 

[superheat6k]

Thank you, will investigate. I certainly have lots of metal nearby being next to the marina walkway

I would also collect a couple of old anodes and bolt these to a short stainless rigging wire, then connect this to a copper cable above the water surface (do not immerse the copper), then dangle this the side of the boat with the most metal work so it sits between your dissolving anode and the client metal work. Connect to a convenient position that is connected to the anode bonding circuit, which should be also connected to the battery negative.

This may take the hit instead of your installed anode, or worse fittings metals.

Then make a large notice to place next to the engine key "Retrieve anode before starting".