Bad anode connection….or is it more.

[Chimo]

2017 R25SC gent in the water. After 8 years I generally change anodes (zincs) every 6 months. Doing so I have had no issues with galvanic corrosion until this week. When I hauled out I found that the starboard trim tab had marked signs of being eaten away. The anode attached to that tab showed little signs of being eaten away, unlike the ones on the rudder and the other tab. See photos.

I’m assuming I had a bad connection and didn’t clean the area under the anode well enough. The damage to the tab doesn’t seem catastrophic at the moment so I am going to really clean in the anode locations, change anodes and relaunch. I won’t know if I have a fix for 6 months or until a tab falls off.

Can anyone think of another cause for this issue? I don’t believe the trim tabs are in the bonding system but I may be wrong. Am I? If they are, advice on finding the connection location would be helpful.

 

[Martin610]

Any changes in the marina? New different boats, electrical issues?

 

[venajeff]

I would try testing the galvanic isolator, make sure it's still functioning. Also inspect your bonding wires, some times those will corrode at the crimps and break off.

 

[Chimo]

I would try testing the galvanic isolator, make sure it's still functioning. Also inspect your bonding wires, some times those will corrode at the crimps and break off.

Thanks for responding.
I test the GI annually. The only erosion is on the one tab so I too thought about the bonding system connection. Hence my question about the connection location.

 

[venajeff]

Thanks for responding.
I test the GI annually. The only erosion is on the one tab so I too thought about the bonding system connection. Hence my question about the connection location.

On our boat there was only bonding from the engine, drain plug, and the raw water thru-hull in the aft of the boat. I have not investigated much forward, perhaps more items are bonded up front.
When we first got our boat we had very fast corrosion happening on the zincs. Over 50% gone in 2 months. So I went ahead and bonded the trim tabs. It made a big difference. Now 2 months in the water shows only about 10% loss.
But I don't think that has anything to do with your problem as it just all of a sudden got bad. Maybe it is a new neighbor boat that is messing with yours.