Beneteau keel fins (a very common brand of sailboat) are made of carbon steel, which rusts in the salt water when it is not protected by epoxy. Naturally, any older Beneteau has spots where the epoxy is missing, causing rust and heavy growth in the rust spots.

There is something you can do to prevent this from getting worse: hanging an anode from the keel bolts to the water with a long cable. Be sure to stow the hanging anode when taking the boat out.

These do have one drawback: The submerged cable and anode will get fouled by seaweed and algae. When you take the boat out, you have a hanging garden that must be stowed somewhere. This can be combated by using a jacketed cable which can be scrubbed clean easier than a raw stainless cable. The cable and hanging anode should be cleaned with a scrubby or wire brush every month to keep it reasonably clean.

This hanging anode neutralizes the keel’s tendency to act as an anode by introducing a sacrificial anode, which takes up all the anodic activity that would normally be done by the keel of the boat. This works on other boats with the same issue: J/111 boats, Cal 20, Santana 22, are a few.

If the anode is working, you will see a noticeable degradation or “wasting” of the anode within a few months. Pitting and oxidized powder will show on the surface of the anode. If the anode still looks brand new after a few months, it means A) There is poor conductivity between the anode and the keel bolt or connection point, or B) The naturally-occuring corrosion on the boat is extremely low-level, barely enough to see. The anode should be replaced when it is over 50% wasted, or whenever you suspect it is wasted enough to lose conductivity between the internal steel contact rod and the external anode. Over time, even if there is material left on the anode, there could be enough corrosion inside between the steel rod and the sacrificial material that there is no longer a viable contact between the sacrificial material and the keel.

Keywords: beneteau keel fins, carbon steel, epoxy, rust, sailboat, sacrificial anode, hanging anode, seaweed, algae, jacketed cable, corrosion, rust prevention, keel bolts, conductivity, anodic activity, corrosion prevention