Stray current corrosion

[berkshire]

I have gone back through the records on this, but cannot seem to find an exact question or solution.
I suspect it is a problem to which there is no final answer.

As some of you may already know, I am Maintenance chief to a sailing club (Volunteer position with 16 boats to look after) and just lately have been plagued with stray current corrosion.
The latest incident turned a propeller on an outboard motor into a Swiss cheese in a week. One of the members had left it in the water instead of lifting it out like he was supposed to.
I have Zinc "goldfish” bombs suspended around the dock wired back into the bonding systems on the boats with alligator clip leads,
I suspect that somewhere on the adjacent dock a boat owner has a ground fault, and that it is only active when the owner is on the boat.
Any clues of finding an intermittent problem of this type: i.e. volt meter in the water.
B.E.

 

[mshimko]

The only way you can get that type of corrosion from "stray currents" (assuming your boat/slip isn't a source for the stray current) is if there is a sufficient potential difference from location to location.

If you have acccess to a "dip cell", you can take a "hull survey" around the boat and dock area. The reading can be used to determine if stray current is likely.

Regarding shanging zinc anodes, I wonder if you have a real good electrical connection. I recommend a very tight nut-bolt-star washer connection. Also, how long do your anodes typically last? Ypu may want to keep a record of when they were installed, visual observation of wastage every quarter, etc. That way, if you start seeing a more rapid consumption of the anodes, something has probably changed.

 

[berkshire]

mshimko
Thank you for the reply it is good to hear from you again.
Is what you are calling a dip cell, a voltmeter with silver/ silvercloride electrodes, inserted into the water?
With the hanging electrodes I am seeing some erosion but not much yet. I am pulling them up once per week to inspect.
Based on what you are saying,with regard to the way I am doing this, I may have to re think this. At present I have the Zinc bomb insulated cables clamped to the dock with a pigtail on to the boats with an alligator clip on the end so that the people using the boats can leave the bomb behind.You are saying that my connections may not be good enough.
Since I have been raising a fuss about this, and now have the marina involved, I have not had another instance, but for a while I had bronze shafts going bright in the water.
B.E.