Can you put too much zinc on your prop?

[Hermit Scott]

I have gotten some definitive answers to this question. Unfortunately they were opposing.
This came up in another thread. Please present your theories and evidence.
I think there are different schools of thought on this like bonding through hulls or not bonding through hulls.
Maybe in some situations you can "over zinc" your boat? Please present what you think or know or what you think you know. I would like to hear it all.

 

[txtowman]

is a galvanized trailer over zinced? "zinced" looks wrong how do you spell it?

 

[jviss]

No.

 

[Don S/V ILLusion]

I too have noticed a few disparate comments and each has some merit. The problem is in the context - there can be such a thing as too much zinc depending on the circumstance in that the real answer depends on what is happening in a particular situation. As an example, if you have an existing electrolysis problem or galvanic problem, adding zinc can under certain conditions can and usually does exacerbate the situation.

If such problems exist, they are always fixable and one should always choose to fix the cause rather than depend on zinc(s) to mitigate them.

If you have a problem, identifying the cause is fundamental to your question. If you don't have a problem, the question is moot.

 

[RichH]

Yes ... you will start to electrically nullify your bottom paint, etc. and you will soon wind up with a lot of attached barnacles, etc. especially in close proximity to the 'zincs'. And, you can damage any underwater aluminum componets (outdrives, etc.).

http://www.boatzincs.com/corrosion-quiz.html

 

[Ross]

As I read that link I was impressed with the risk of using the wrong type of anode not the wrong size. If physical size of a zinc was a factor then a "D" cell would produce more voltage than a "AAA" cell.

 

[Mike Holibar]

Ross has clarified my thinking on this. it's a long time since I owned a steel boat but the one I had had all kinds of problems with stray currents and over zincing which totally destroyed the paint system, blew it off in sheets. As I recall the important factors were getting the right type of anode for the job and fitting the right number in the right places. The size of the anode was only important in respect of the time it would last. i believe having too many anodes will create problems. The practice of using "stripping" anodes illustrates this point. Basically, a bundle of anodes is hung through the inspection hatch of a ballast tank, the tank being full of sea water. The effect is to blow all the loose scale and paint off the steel. The tank is then pumped out and cleaned. If these anodes were left any length of time the corrosion in the tank would be severe. So I think Ross's analogy with the batteries is a good one, more anodes = more voltage, bigger anodes = more amp hours.

 

[Don12364]

Galvanic Potentials

Galvanic Potential of zinc is -1.01V.
Bronzes are all approx -0.3V.
So the difference is -0.7V.
It can be no more!
Fibreglass and antifouling paint are essentially insulators (even when wet) so I do not see how the potential difference between anode and prop etc is involved.
IMHO the advice given in Boatzincs.com cannot be correct.