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In Reply to: I have read this someplace. Zinc is considered posted by demet 85'745 CT on April 30, 2002 at 08:59:18:
First of all you need to metals and a electrically conductive medium.
On a boat/ship/yacht you have the metal of the hull, usually steel or aluminium.
This is your least noble metal(Anode) in the equasion.
Than you have the metal of the propeller, usually bronze or brass(Cathode)?
This is your noble metal.
Then you have as electrically conductive medium the salt/sea water.
There is a flow of electrons from the less noble metal(hull=Anode) to the noble metal(propeller=Cathode) through the saltwater medium.
If left it would eat away the hull of the ship.
Were two metals are touching within an electrolyte you get the so called local element.
This is nothing else but an electrolical process like in your car battery. But here it is purposely and your metals get eaten away while producing electricity.
Something you do not want to happen outside a controlled enviroment.
Therefore an even less noble metal is used (zink) to replace the iron anode(hull).
Now the effect takes place between the zink anode and the propeller, thus preventing/protecting the ships hull from rusting.
Now this effect requires and electrolyte(in this case seawater)
Because of the Nitrates(salts)in it, it is a rather good conductive medium.
To what degree it makes sence when the medium is less conductive (sweet/drinking water or even air) has to be worked out using the appropriate physics formulars. And surely must depend on the mass of the metals.
Considering the size of the anodes used on a 45ft 10t steel yacht(quite small) the amount of zinc to be used on a car must be miniscule by comparisson.
So it sounds very feasonable that a zink coating would do the job satisfyingly.
More info about the role of zinc in paint if you follow the link
Best regards
Ralf
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