Alloy Selection - Zinc

What kind of anodes do I need?”

For new boaters, or for boaters who have never changed their own anodes before, that’s an extremely common question. And it’s one that, we’ve noticed, the internet seems to have a hard time answering directly. Do a search, and you’re tasked with wading through bad advice, old wisdom, dissenting opinions, and marketing.

So here in our series on the basics of corrosion and corrosion control, we’d like to take the opportunity to clear things up. Boaters have the option of zinc, aluminum, or magnesium. And the best alloy for you will depend on a few factors.

ZINC
saltwater only.

For the longest time, zinc was the only alloy boaters were likely to see on the market. OEMs supplied zinc anodes for their products and when the time came to them, zinc was the only option people would find on the shelves. Over time, “zinc” even became a shorthand for all anodes, as in, “I just put some magnesium zincs on my boat.”

That whole time, boats running in fresh or brackish water were underserved and underprotected. Zinc cannot be counted on to protect outside of saltwater. The problem is that, in the absence of salinity, zinc develops a hard, white, oxide coating. This, in a short time, will render the anode completely ineffective. These passivated zincs will last forever, offering no protection at all.  Luckily, for boaters in fresh or brackish water, magnesium and aluminum are widely available options nowadays.  More on those soon.

Zinc protects very well in saltwater. And if there's no chance of running in anything but saltwater, it's a terrific choice.  But there is a choice to be made there, between zinc and aluminum. We field a ton of questions related to that decision.  Check back for our next post where we'll be diving into the aluminum alloy, working to clear up some common misconceptions along the way.