From The Forums: Sacrificial Anodes 101

November 2015

On our forum page, one member was wondering whether there’s a need for sacrificial anodes in fresh water. Find out more by reading the seasoned responses below:

Endurance: Other than the sacrificial anodes on my outboard motors, my aluminum pontoon houseboat has no zincs. It is in fresh water and the only salt water it will experience is in an ice cream maker in the galley. Is there any reason for me to have sacrificial anodes? 

OLD HOUSEBOATER: If you get into a situation where the shore power is "dirty" or dockmates have electrical problems, you'll wish you had them. 

easttnboater: What OHB said. I was in one of the cleanest lakes in the country—South Holston in NE Tennessee—and after three years, the anodes on my Bravo IIs were half gone.

GoVols: Zinc anodes do not work in fresh water. You MUST use magnesium. I bought new ones from and replaced mine last year.

easttnboater: Got mine at Anodes is the proper term— come in zinc, magnesium, and aluminum. But "zinc" is used as the generic term for anode. And, yes, I used magnesium. 

Endurance: Thanks, all. That's kind of what I thought. Like easttn, I use "zincs" in the generic sense as a shorthand for sacrificial anodes. Kind of ironic that for fresh water, a good portion of the recommended zincs for my aluminum hull will be made of aluminum. 
Even though my boat pretty much never plugs into shore power and I am on a buoy rather than a dock and the neighbors I would have on a dock, I think I'll add some anodes. After all, they're cheap. It looks like I'll be buying an alloy of magnesium and aluminum. I was thinking that having anodes could never hurt until I came across this tidbit: "It is not recommended to use magnesium anodes in salt or brackish water. The result may be an accelerated corrosion rate . . . ."
The wrong zincs can accelerate corrosion. Ouch!

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