Disappearing Zincs

[Harvey18667]

During the last year or so I have been searching for a cause that results in the erosion of the zinc I place on the shaft. I have checked the general culprits like poor grounds and have even checked the potintial between the dock and boat and the water at the dock. In addition I have measured voltages between an anode (special anode for this purpose placed in the water) and one on the shaft after switching each item on and off from the panel. Everything is within the recommended range. I have also checked the galvanic isolators; and they check out ok as well.
Anyone have any recommendations. Note Zincs disappear in about 6 weeks. My daughter's boat docked in the next slip changes her zincs annually even though they show little wear.
Any suggestions?

 

[KD3PC]

who or where are the zincs made??? Some are mystery metal, and may dissolve or corrode in short time....6 weeks is pretty quick, though...

I would change brands or makers of zincs to start or double up and see what they do. That fast should be apparent somewhere along the line.

 

[Don S/V ILLusion]

To state the obvious, there has to be a voltage between the water and anode(s) to cause this problem. That you measured nothing significant therefore cannot be correct. If you are completely confident in your measurements this far, the only possibility is some intermittent problem if that helps.

 

[Bill Roosa]

Your boat could be fine and is just participating in the next slip over great electron migration.
If the guy next to you has a messed up boat and is leaking current to ground your boat can be a participant also even if all your stuff is correct. This only occurs in fully bonded boats though. The current comes in through a thru-hull and out through the prop anode.
Are your thru-hulls bonded? Try unbonding them.

 

[Harvey18667]

The thru hulls are not bonded!

 

[Benny17441]

We had a similar situation with the h320 docked next to an h27. The anode on the h320 would last maybe 4 months and on the h27 a full year+. Other than scratching our heads we really did nothing. One day the battery charger died and It was replaced with a new unit. A few months latter we realized that the anode was lasting much longer. There is no doubt in my mind that the battery charger had something to do with it. Perhaps it could explain why you got no significant voltage when you measured as you may have measured at a time when the batteries were fully charged and the charger was not putting out, nor drawing much. To dispel any misconceptions just take a reading in the water the next time your battery charger may be operating on bulk charge.

 

[ms-card@cox.com]

Zincs

I was having a similar problem right after I bought my Hunter 38 in April.

After extensive searching and testing, we found that the shaft strut was not grounded and it looked like it never had been. We ran a ground to the strut bolt (very inaccessible) and the problem is solved.

I wish you success.

Mike

 

[Harvey18667]

Re: Zincs

Thank you all for responding. I took all of your suggestions, but none appears to have been the problem. I had hoped an ungrounded strut would be the solution, but it was grounded. I spoke with Zinc.com and their suggestion was that I was suffering from the small added electrolyis from many of the boats on the same dock. He recommended using Aluminum Anodes as well as an "aluminum guppy. I will try those beginning today.

 

[Crazy Dave Condon]

I found in many cases that electoylsis is caused from either faulty wiriing on a dock or from other boats. In any case, it is a safety issue should someone come into contact with the water. A friend's son died falling overboard due to someone using a defective shore power chord that was in the water.

Sacrifical zincs are a good way to find out. IF you are not plugged into shore power nor running the engine and the sacrifical anode is dissolving for better lack of terms, then it is probably an outside source and then the investigation needs to be done. If at a marina, I would have the shore power checked and if the marina fails to do this or simply reluctant, contact the authoirty is in charge of code violation. The marina will then check quickly. If it is not the shore power, then find the culprit boat.

 

[Harvey18667]

Thanks for the suggestion! It was one of the first thiings that was checked out. The marina wiring was checked by a professional and found to be in fine shape as were my pair of galvanic isolators.