New prop zincs are pitted after 2 weeks

[JV II]

After 2 weeks in the water my shiny new prop cone zincs are both heavily pitted with craters and flaking corrosion. I couldn't see the other zincs. The port cone is very uniformly rough all around with none of the original surface left. The starboard cone looks quite different with craters that are in patches with some of the original surface left. I assume this is not normal. What could be causing this? Mercathode problem, stray current?

I'm having the dealer check it out. They asked if there were any old boats within 100 feet of mine that could be dumping current into the water. How the heck do you answer that one?

If it is a problem with the marina, will keeping myself disconnected from shore power prevent the problem?

 

[NoWakey]

Mike,

Sounds like your on track.
Quick question first. I see you are in the Boston area. What type of water are you in? You mentioned that new zinc anodes where just installed. With this I assume that you are in salt, or at least brackish water. Is it possible that a mistake was made and Magnesium prop anodes were installed? They would get ripped up pretty fast in salt water.
Meanwhile back at the problem;
Yes, I would get off of shore power until more diagnosis can be accomplished. Top of the list would be to make sure the Mercathode System, Galvanic Isolator, and bonding system on your boat are all working as they should be. Next, have the marina test if there is any potential on the shore power ground circuit on your specific dock section.
A very good device to have in diagnosing this type of issue is a reference electrode.

http://boatzincs.com/corrosion-reference-electrode.html

Good luck, I'm sure others will join in with more ideas.

Cheers,

Jim

 

[JV II]

Jim,
That is all very helpful. I'm in salt. I imagine that the dealer would not make the mistake on using Magnesium, but it is in the realm of possibility.
The dealer will check out the Mercathode, isolator, and bonding system. I'll reply with the results. It is strange how the two cones are corroding very differently.
I'm also going to talk to the marina and have the slip tested as you recommended. I'll let you know the results of that.
I'm off the shore power for now.

 

[NoWakey]

It is strange how the two cones are corroding very differently.

That is very strange indeed....
You never know Mike, you may well have more than one thing going on here. You could have a Mercathode out on one engine and not the other. Or, the anode manufaturer may have mixed up some stock and you ended up with two different nobility value anodes. But no matter what, it sounds like you have accelerated corrosion going on.
I will be interested in hearing what you find out.

Cheers,

Jim

 

[JV II]

THe Sea Ray tech did a visual inspection today and did not think there was anything wrong with the way the boat was wired or the Mercathode system, but he did not use any electrical testing equipment. He did agree that the amount of corrosion on the zincs was excessive, especially the deep pitting. We walked the docks and did not see any older boats in close proximity with obvious problems. What we did see were many shore power and coaxial cables in the water. One shore power cord had 15' in the water. We did notice another Sea Ray close by with new zincs and the same pitting. The dockmaster said there have been no complaints and they do not test. The dealer will be sending someone over to test the docks. The visit today was more or less to confirm there was a problem with the zincs before they went to the next step.

 

[Half Off]

Interesting thread, keep us updated.

 

[NoWakey]

Mike,

That sounded like a bit of cursory check over, but I guess it has to start somewhere.....
I promise not to beat this to death, but I would really take a strong look at picking up a reference electrode so that you can see for yourself exactly whats going on. As an example: You can take a measurement off the stern of your boat in the marina, then move to another dock somewhere without shore power and repeat the procedure. If you have a low reading in the marina, and normal at the other dock, you know the issue is something in the marina. If you have low and similar readings in both areas it would point to something amiss with your boat. etc.
You also can verify that your Mercathodes are working with the following test: Turn all electrical equipment off. Take a reading and note it. Then do something like turn your air conditioning on. You will see the reading value drop, and then climb back up to normal as the Mercathode compensates for that electrical activity. In all test scenarios the boat should be in still water, and at rest for at least 15 minutes before readings are taken.
O.K., I'm done harping.
I really do look forward to hearing what you find out. It's an interesting case.

Cheers,

Jim