Other boats leaking current

[brak]

So, I'll take this out of another "current" thread. How can I test a slip (in a prospective marina, for example) for current leakage from other boats? I.e. - what do I connect my multimeter to?

[SteveInMD]

Stray current from other boats arrives onboard your boat via the ground wire in your shore power cord. So,theoretically you would test for the voltage between the ground terminal at your dock power connection box by at your slip and the water below. The only problem is that you can't just stick one probe in the outlet and drop one in the water. You need a silver/silver chloride (reference) electrode which replaces one of the meter leads and is lowered down to the water. I think WM sells them for about $100.

Note: If you get a big spark when shoving your multimeter probe into the outlet and dropping the other probe down the water, you've selected the wrong terminal!

Or, you can install a galvanic isolator which disconnects the ground unless the voltage goes over approximately 2 volts. Just make sure you get one that warns you if the it fails, otherwise you can create a dangerous situation where you have no ground connection for your shore power.

[GBurton]

What if you measured between your boat's shore cable ground pin (obviously with the cable not plugged in to shore power but plugged into the boat) and the dock ground (on the pedestal)?

[brak]

my boat has galvanic isolator, so that's not the path for stray current to get there (I am also virtually never on shore power).

The thing is - I am planning to move to a different marina next season and would like to test slips before I move in. So there won't be a boat in the slip - just piles and water.

[SteveInMD]

The only path for stray current is through the ground wire of the shore cord. If you are not plugged into shore power for long periods you have no need to worry about the conditions at the marina. You will not be affected by stray currents. You have nothing to worry about.

Since you have a GI you wont have a problem even if you decide to plug in.

There is no such thing as current flowing through the water and attacking your boat.

[brak]

Originally Posted by SteveInMD

There is no such thing as current flowing through the water and attacking your boat.

Well, something certainly was attacking my boat - zincs were gone in a matter of 3 months, with boat standing in a slip, power turned off, shore cord not connected.

So, there must be another way for it to get to the boat. If not - what happens to zincs and what causes galvanic corrosion on my boat?

[artbyjody]

Link: Electrolysis

On my Catalina, I had to replace the zincs every 6 months. The new boat it looks like that maintenance will be each year. Link above may explain why yours are going at 3 months?

Also, if you are a DIY zinc anode type, one has to be careful about selection of the proper zinc. Fresh water and salt water zincs are not the same and use of one in the other enviroment will lead to rapid failure. Check out also the types that you can clip to your rails and drop in the water. I carry one on mine that I brought over from my Catalina since winter sailing was not an option on that boat. They will act as a barrier to your prop zincs.

[SteveInMD]

Your boat may have a problem with the electrical system. If you had a corrosion problem (zincs gone in 3 months) and you were not plugged in to shore power, the problem is not with the marina or the other boats. I believe sailingdog posted a rather complete explanation of how to track down a current leak on a boat. Maybe he'll chime in here or you could search for it.

[SteveInMD]

I found it.

http://www.sailnet.com/forums/gear-m...t-mystery.html

Post #8 is what I was referring to.

[SteveInMD]

You can actually use current to protect your boat...

Electro-Guard, corrosion and cathodic protection specialists for boats, yachts and small ships.