"Help! My Anodes Are Missing!"

As the Halloween season descends upon us like the foam of so many pumpkin spice lattes, we'd like to take the opportunity to offer a spooky story of our own.

It was a perfectly normal day at the marina, when your good diving buddy went below the water line to swap out your anodes.  Sure, there had been many more bats in the air than usual and sure, folks had been certain they'd seen lights and heard ominous sounds coming from that abandoned Victorian mansion at the top of the hill, but otherwise?  An uneventful, mundane, easy sort of day with nothing noteworthy or out of the ordinary to it whatsoever.  Yep.  Everything's fine.  Boring, even.

Well, except for when your diver comes up out of the water and tells you that there were no anodes on your boat!

(HOW LONG WAS YOUR BOAT UNPROTECTED?!  JUMPSCARE!)

Maybe it's just us, your friendly neighborhood marine corrosion experts, but stories like this tend to stop us in our tracks.  Now that our heartrates have come down somewhat... let's talk about what might have happened here.

Your sacrificial anodes should, ideally, make it through a season before they need to be replaced.  That timeline tends to be longer for freshwater boaters and can be shorter for boats running in really warm, salty waters.  When our hypothetical diver went under, they would have been expecting to see an anode at or near 50% of its original mass.  That's the line for an anode having run its course, one that would then be weak enough that it needs replacing.

An anode that isn't there at all is definitely worth thinking about.  For prop shaft zincs, the most likely scenario is that they just fell off.  That may have been because it wasn't installed properly initially (to install a shaft anode, it's important to tighten down the anode as much as you can and then to whack its center on both halves with a hammer to get a few more turns of the wrench in).  Or it may be that the anode corroded enough around its mounting holes to come loose and, over time, to come off (which would be a good indicator that you need a bit more material on your prop shaft - consider adding another one or using a Heavy anode).  If your anode's gone and you see damage to the prop or shaft, too, you should consider the possibility of stray current corrosion.

The same logic would apply to prop hub anodes.  They may have vibrated off, in which case you may want to consider using a mild threadlocker on your next anode's mounting bolt.  Or it could be that the anode as-is is being taxed by the chemistry of its environment.  "Heavy" prop anode variations don't really exist, but you may need to consider adding a hanging anode to your system for a boost of protection potential.

Most hull anodes have inserts cast-in to keep them on until they're ready to be replaced.  If yours wear all the way down to that insert (or are getting very close within one season), you should consider using a larger zinc.

A missing anode isn't necessarily indicative of a serious problem, but in any case, it would be pointing to something that needs to be addressed.