Recently one of my readers sent in the photo above with a question regarding the green wire connected to the steering quadrant. The question basically went like this: “Can you tell me what is electrical in my steering system? I do have autopilot, but that is connected to the steering system via a mechanical servo arm. What purpose does this green wire serve on my cruising sailboat?”
OK, it’s not particularly obvious what that wire’s purpose is. It is a part of an on board bonding system that ties all bits of metal that are also in contact with sea water together by a common conductor. This is done to help mitigate corrosion of under water metal.
There should also be an appropriately sized anode attached to this system, which will be the sacrificial part of the system, in this case vs. your rudder stock. The theory here is pretty simple. By connecting these metal components together by a common conductor, and then to an appropriately sized anode, an electro-chemical process known as “polarization” occurs.
Polarization effectively equalizes the electrical potential of all of these bits of metal and if the anode is sized correctly will ensure that the anode, which must be at least 200 mV more negative than the connected bits of metal, will be the part that gets sacrificed to corrosion over the course of the boating season.