Signs Your Zincs Need Changing

Three visual signs tell you a zinc is spent. You can check for the first two yourself from the dock if the boat sits high enough; a diver confirms the third.

1. More than half gone

A new zinc has a defined shape. As it sacrifices itself, it gets smaller, rough, and pitted. Once it's about 50% of its original size, that's our usual recommendation to swap it - but the call is yours. On every dive we flag what we see and tell you what we'd do; some owners replace on a fixed schedule, others push a cycle longer. Either is fine as long as you know where you stand.

2. White crusty buildup instead of clean erosion

Good zincs corrode with a relatively clean, grey surface. If you see thick white or chalky buildup, the zinc might not be making good electrical contact with the hull. It's corroding on the surface but not actually protecting anything. This is worse than a missing zinc because it looks like it's working when it isn't.

3. Your other metals look rough

If your prop is getting pitted, your shaft is turning pink (a sign of dezincification in bronze), or your through-hulls look corroded — your zincs aren't doing their job. Either they're spent or there's an electrical issue.

What happens if you wait too long

A zinc change is a few hundred dollars. A new prop is a few thousand. I've seen both happen to the same boat because someone skipped the zincs.