Ensure your bonding system is doing its job.
Immerse a bronze propeller and a stainless steel shaft in sea water (an electrolyte), and you’ve just created a battery. The same is true of any other combination of two or more dissimilar metals. Even if it’s just a quarter of a volt higher, the metal with the positive charge will erode. In the example above, the stainless steel will actually pit or maybe even crack.
By comparison with the basic metals used on boats, zinc acquires a more positive charge than anything else, thereby protecting all other underwater hardware. (Magnesium typically replaces zinc in fresh water.) But zinc only protects metal that is part of what’s called a bonding system—a network of wires that interconnects rudders, shafts, trim tabs, and struts, as well as interior components, to a transom zinc or zincs. But as we all know, wire connections can go bad. So how can you be sure your bonding system is really working? The following four tests will help:
See a video of how to test for continuity, resistance, voltage potential, and stray current flow in a boat’s bonding system here ➤
This article originally appeared in the June 2013 issue of Power & Motoryacht magazine.