Zinc Anodes: The 2-Minute Explanation

Your boat has different metals underwater — bronze props, stainless steel shafts, aluminum outdrives. When different metals sit in saltwater, they create a battery effect. The less "noble" metal corrodes to protect the more noble one. This is called galvanic corrosion.

Zinc anodes are sacrificial. They corrode instead of your expensive stuff. That's the whole idea. The zinc gets eaten away so your prop, shaft, and through-hulls don't.

There's another side to it too — when your metals start corroding because zincs are missing or spent, that rough corroded surface attracts marine growth faster. Barnacles love to latch onto pitted, rough metal. So good zinc protection also helps keep your running gear cleaner and your boat performing better.

Where they go

Prop shaft, prop itself, rudder, trim tabs, hull (for sailboat keels), and on the engine (internal zincs). Every piece of underwater metal needs protection.

When to replace them

General rule: when a zinc is about half gone, it's time to change it. Don't wait until it's a tiny nub — by then your other metals may already be corroding.

In Victoria's saltwater, check your zincs every 3-4 months. Most boats need new ones every 6-12 months. Boats plugged into shore power at a marina can chew through zincs faster because of stray electrical currents.

If your zincs are lasting less than 3 months, something else is going on — could be a wiring issue or a bonding problem. Worth investigating.

Zinc vs magnesium vs aluminum anodes

Zinc for saltwater. Magnesium for freshwater. Aluminum works in both but is most popular for brackish water. In Victoria, zinc is what you want.