The Devil is in the Details

“Great floods have flown from simple sources,” said William Shakespeare, which is a fitting opening for the subject of the potential negative effects of corrosion aboard your boat and the possibility of big troubles because of it. How big? Great floods, indeed.

Here are a few facts. Steering clear of any chemistry lesson, electrolysis involves only one metal and a major change occurring in an electrolyte with chemical properties that make it capable of conducting an electrical current. A good example is when a lead-acid battery discharges and produces a significant alteration in the concentration of the battery acid. So when one of my dock mates called me on the VHF asking for a tow, he was wrong when he stated, “Electrolysis caused that blade on my prop to weaken and finally break off.” No, shipmates, his problem was most likely brought about by galvanic corrosion or, in part and sometimes in collusion with, its equally evil relative, stray current.

With galvanic corrosion the deterioration occurs between the dissimilar metals as they react while immersed in salt water. This is caused by the current—the movement of an electric charge—that flows between the two, each acting as anode or cathode, depending on its place on the galvanic chart of metals in sea water, and as a result of either being physically or electrically connected.