Aluminum or zinc anodes

ericcarr2000

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I will be replacing the drive anodes this spring. I've come across aluminum and zinc anodes. Which one is better?
 

tpenfield

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Neither, aluminum for salt water, zinc for fresh water.



EDIT: my bad . . . was thinking of Magnesium for the fresh water.
 
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alldodge

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Here is a good read but comes down to aluminum is best all around for stern drives
http://www.performancemetals.com/anodes/AnodeFAQs.shtml

Tables from the link
ABYCrec.jpg


WhichAnodes.jpg
 

ericcarr2000

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So with me being the greatlakes, should I use the Zinc instead of the aluminum ones then?
 

Bondo

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So with me being the greatlakes, should I use the Zinc instead of the aluminum ones then?

Ayuh,.... The Great Lakes are the largest bodies of Freshwater, in the World,.....

Look at the chart above again,....
 

alldodge

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So if Im reading it correctly then Ill need the Magnesium anodes then right?

You can use Mag or Aluminum for fresh water. If you read the entire document in my post above it basically leans to Aluminum.
 

eastont

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How would aluminum anodes protect from corrosion while attached to aluminum outdrives ?

I don't understand how that would work.
 

alldodge

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How would aluminum anodes protect from corrosion while attached to aluminum outdrives ?

I don't understand how that would work.

Go to post 4 and select the link, there is a lot of info there explaining it. In short, the aluminum drive is painted, the anodes are not. There are also cheap aluminum anodes which are not made in accordance with MIL-A-24779(SH).
 

lg260ss

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If you have a Merc Bravo drive or a VP Duoprop drive I would suggest you use magnesium anodes in clean fresh water. They are more active in clean fresh water than aluminum and that is what you want, they are sacrificial for a reason. If the water is polluted or impure, magnesium may be too active and wear too quickly. I get 1 season out of my magnesium anodes with the boat in the water for around 6 months. Both Volvo and Merc recommend them in fresh water. Merc Bravo 3 corrosion issues in fresh water are well documented from the mid 2000's.
 
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