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Zincs vs. Magnesiums

 
 
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Old 04-01-2012, 07:16 AM   #1 (permalink)
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Zincs vs. Magnesiums

I was working on my boat yesterday getting it ready for Spring launch. A mechanic stopped by to chat and told me that i should have magnesum blocks in place of my zincs. He said that the zincs don't really do anything as I am in fresh water, that they should be replaced with magnesums?

Does this make sense? or he just trying to sell me?
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Old 04-01-2012, 09:09 AM   #2 (permalink)
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He's right.
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Old 04-01-2012, 01:41 PM   #3 (permalink)
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On the galvanic chart series, magnesium is least nobble from Zinc which means the magnesium will then sacrifice itself to protect any zinc installed on the vessel making the zinc a more noble metal in that situation.
Fresh water does carry less TDS to carry electric currents and atoms to flow through but I would be interested to know why or how magnesium could sacrifice itself better than zinc to preserve the more noble metals just because it is in fresh water oppose to salt water.
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Old 04-01-2012, 01:50 PM   #4 (permalink)
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It was covered in a previous thread: http://www.yachtforums.com/forums/te...um-anodes.html
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Old 04-01-2012, 01:53 PM   #5 (permalink)
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Quote:
Originally Posted by C4ENG View Post
On the galvanic chart series, magnesium is least nobble from Zinc which means the magnesium will then sacrifice itself to protect any zinc installed on the vessel making the zinc a more noble metal in that situation.
Fresh water does carry less TDS to carry electric currents and atoms to flow through but I would be interested to know why or how magnesium could sacrifice itself better than zinc to preserve the more noble metals just because it is in fresh water oppose to salt water.
Hi,

If you can overcome the sales pitch there is some good info to be found here.

Cathodic Protection - Marine Cathodic Protection - MGDUFF
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Old 04-01-2012, 05:31 PM   #6 (permalink)
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I found the answer as to why mag would be better than zinc in fresh water in the link you sent. I cut and pasted for others to see......

Not all anodes are suitable for every environment, for example the surface of a zinc or aluminium anode will if left in fresh water for some time become covered with an off white crust of oxide which effectively seals the anode and stops it working even when returned to salt water.
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Old 04-01-2012, 05:35 PM   #7 (permalink)
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Originally Posted by NYCAP123 View Post
It was covered in a previous thread: http://www.yachtforums.com/forums/te...um-anodes.html
I read the post but did not feel they explained exactly why mag was better than zinc in fresh water, but it is clear now.
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