Electrolysis or is it Galvanic corrosion?

[Bill1565]

My diver recently moved on. I got a new diver to scrub my boat bottom. He braggs unmercifully about his zincs. Since I started using his, my zincs only last a month. My old zincs from Ace and WM lasted a full year. New diver insists that there is electrical leakage in my canal. Certainly possible, but???

Do I need to spend $125 to get a silver probe for my VOM to check this?

 

[alexco38]

Put in a galvanic isolator instead. If you are handy you can make one yourself with rectifier diodes for just a few dollars.

 

[kloudie1]

And check to see if he is using magnesium instead of zinc in the electrodes.

 

[Ken13559]

Between the 2, I'll trust your diver's zinc then search for leakage current. I had one zinc that last a year, lost the prop!

 

[alexco38]

My zinc has been there for 4 years now since I put in the galvanic isolator. Most new boat come with it. That's where I got the idea after seeing them in new boat shows. Some boat (e.g. new Hunters) use isolation transformer. But it's heavy.

It creates a 1.4 volt difference between your shore power ground and the metal part under water

As long as you can isolate or differentiate the ground voltage, that would stop the galvanic reaction. It's like electrical plating. Less noble (lower atomic weight) migrates to more noble (higher atomic weight) metal if there is electrical current.

Just google "galvanic isolator"

 

[Bill1565]

And check to see if he is using magnesium instead of zinc in the electrodes.

Easy for you to say. How can I tell?

 

[Bill1565]

Put in a galvanic isolator instead. If you are handy you can make one yourself with rectifier diodes for just a few dollars.

I can do that with guidance. Problem may be somebody else's boat or boat lift. I don't live alone on my canal. Might be good idea anyway

 

[Don S/V ILLusion]

Losing zincs quickly isn't always a bad thing. It's doing it's job. An anode which lasts 4 years either isn't working or you are very lucky. The issue is not how quickly it gets eroded but what is the cause.

 

[wetass]

Could be leakage, but could be magnesium anodes. You can test this. Get yourself a silver/silver chloride half cell (I got mine for <$75) and you can determine the voltage potential difference between your zinc and the silver/silver chloride. (Since I can't see my zincs from the doc, I use it in the winter just as peace of mind to check if they are still there or not).

A zinc anode should show a difference of -1000mv. A magnesium anode would be around -1600mv. Basically you just plug the lead from the half cell into the neg side of your volt meter (DVM) and then attach the pos side to your grounding system (or just the prop short). The voltage it reads is going to be the difference between the silv/silv chloride and the most anodic metal in the water, which is going to be your zinc. Should take all of about 2 minutes to test.

 

[alexco38]

That's precisely the root cause of the leakage problem. It may not be your boat. so long as you can eliminate the -1600mv or so from the circuit, anode will not go to cathode.

The galvanic isolator injects 2 x voltage drop of a diode into the circuit. There is not enough for the anode and cathode to form a cell.

Fix the root cause not just the remedy.

Test this as suggested by WetAss. Now unplug your shore power cord and see if you still have any voltage. Poof, it's gone!!

 

[seadaddler]

How About

Let him put his zinc and tell him also put yours on too,2 zincs can't hurt and see what happens.
Nick

 

[Bill1565]

Could be leakage, but could be magnesium anodes. You can test this. Get yourself a silver/silver chloride half cell (I got mine for <$75) .

Where? when? best Google could do was $125. Also $220 and $348.

 

[RichH]

Let him put his zinc and tell him also put yours on too,2 zincs can't hurt and see what happens.
Nick

That wont make any difference as the 'least noble' in chemical composition anode will do most of the 'work'.
You can 'over-zinc' a boat leading to 'reverse' problems; you really nead a 'reference cell' to do this 'correctly'.

 

[alexco38]

Galvanic Isolator

Here's the circuit to build one yourself. It's rated 120A 450V AC. Way more than your shore power can pass.

 

[wetass]

Bill,

Should have read your post more carefully - I see you were already heading down this path and the silver reference was part of your questions - Sorry about that.

I bought mine a few years ago so not 100% sure where from.

I did a quick search and mine looks similar to the one that boatzincs.com sells. Theirs is now 125, and mine wasn't anywhere near that much. I also found one (while not identical to mine) for $99:

http://www.reliabilitydirectstore.c.../rdi-cre.htm?gclid=CPjmsaCcsasCFYYZQgodVxTmcA

 

[wetass]

Alex,
I had no idea that galvanic isolators were that simple - Its almost a crime the prices they charge for those things.

 

[bobtigar]

A simple solution is to drop a fish zinc over the side and attach the clamp to the prop shaft, coupler or transmission case. I was going thru 4 -6 shaft zincs per year. The fish zincs weigh about 6 lbs and last years. My prop zinc now lasts over a year. Just remember to take the fish zinc off before you leave the dock. Bob

 

[Bill Roosa]

commercial isolators HAVE to have a monitoring system that indicated if they are still working. This is what costs the bucks

If you put a zinc and a magniesum on a steel shaft in salt water will not zinc and mag act as a cell and corrode the mag. Kinda dumb to put a zinc next to a mag don't you think?

 

[Bill1565]

Thanks for all the suggestions, computer will be shop few days, so can't respond.

 

[zeehag]

some divers do the zinc thing to make money, i have learned and there is actually a decent zinc on the boat when he removes it-i would ask for the old part returned to see for yourself if that is the case before buying hundreds of dollars worth of items to correct a problem you may NOT have.