I tend to get caught up in semantics, so please pardon my pedantry.
Galvanic & Electrolytic (Stray Current) corrosion are two similar, yet different ,types of corrosion.
results when two dissimilar metals, of sufficiently different potentials (about 0.1 V on the galvanic series) (a galvanic couple can also occur within regions of a single
alloy), are electrically connected (bonded; deliberately or not), and immersed in a common electrolyte (water). The same electro-chemical reaction creates the current flow in a storage battery
(or Electrolytic) corrosion
results when an applied current flows
through immersed conductive materials, other than an intended electrical
Stray currents can come from an outside source either internal or external to your boat
. Internal sources involve a short in your boat’s wiring
system, such as a poorly insulated wire in the bilge
, an electrical
accessory that may be improperly wired, or a wire with a weak or broken insulation
that is intermittently wet.
External sources are most often related to shore power
connections, or other boats on the dock
To generate electrolytic corrosion
, the stray current must flow onto the metal at one location and then flow off the metal at another location.
When an applied current passes in and out of a metal part, an electrolytic cell is set up, resulting in a localized anodic site, where the positive current exits the metal part. This causes the local oxidation (corrosion reaction) of the metal piece, which may lead to a very rapid metal loss, which is limited only by the amount of current available.