Aluminum or Zinc anodes?

[sharffj]

Need opinions. Have always used zinc anodes on shafts, rudders, hull and trim tabs as was in salt year round. However last two year have been in fresh water from October to May and salt from May to October. Have a galvinic isolator on boat. Have read that zinc oxidizes in fresh water and the coating prevents the zinc from working in salt.
Any thoughts?

[catalina_mike]

My understanding is Zinc in salt water and Aluminum in fresh. Brackish would need to be monitored and use what is being eaten. This is a pretty good article where they recommend Aluminum for brackish water and Magnesium for fresh. http://www.defender.com/html/zincs_info.html

[Jeremyvmd]

Magnesium is best for fresh iirc. I use aluminum in the salt as they are supposed to last longer. I thought zinc was ok for both but aluminum never for fresh...

[Tree]

It seems many people are moving over to aluminium, especially since they cost a lot less.

Magnesium in salt water will work really well, but won't last very long, hence why its best for fresh water.

Zinc is probably the most common as with the mix of metals in a boat, especially 316 stainless and NAB for your propeller etc, you really want a material with a good anodic reaction and as you can see by the attached, zinc is more anodic than aluminium.