Signs Your Zincs Need Changing

You don't need to be a diver to know when your zincs are done. Here's what to look for — or what to ask your diver to check.

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, swap it. Don't push it.

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 new set of zincs costs a fraction of what a new prop, shaft, or through-hull fitting costs. I've seen boats with thousands of dollars in corrosion damage because someone skipped a $200 zinc change. It's the cheapest insurance on your boat.