John Green of Kemah, Texas, asks:
"Many sailboats in my marina have “grouper” or “guppy” anodes that dangle in the water on a wire clamped to a shroud or backstay. I’ve asked a number of owners why they are doing this, and their answers range from grounding the standing rigging, to preventing galvanic corrosion of the rigging, to helping lightning find a route to the water in the event of a strike. Have you seen grouper anodes being used in this way?"
Don Casey replies:
Considering the gauge of the wires I’ve seen attached to the ever-popular grouper anode, I am doubtful that the arrangement will be able to provide much of a path to ground for a lightning strike. And I don’t think that galvanic corrosion of the rigging is a legitimate concern either. Sacrificial anodes are always installed on a boat to protect underwater metal from corrosion. Because it is less noble the anode metal will corrode first and that action protects any adjacent, nobler, metal. An anode that becomes reduced in size does provide an early warning that there is corrosion somewhere.
However an anode has to be connected to the metal it is protecting and the better the electrical connection the more effective that protection will be. That’s why an anode bolted to an underwater metal component is a better choice than one that’s connected by a wire and hung over the side.
Grouper anodes are often deployed in marinas because they do give a boat owner a warning that there is stray current corrosion that needs to be explored further. However, it’s my view that unless an anode is actually connected to the boat’s underwater metal it won’t be very successful at this.
And just clipping a wire lead from the grouper to the standing rigging will not provide much protection against a strike unless the rigging is also bonded or otherwise connected to the boat’s underwater metal components.