Capt. Ken Henry, AMS, IIMS, IAAI
Marine Surveyor and Consultant
Servicing Maryland, Delaware, Pennsylvania, and New Jersey
Stray voltage is defined as "the occurrence of electrical potential between two objects that ideally should not have any voltage difference between them. Small voltages often exist between two grounded objects in separate locations, due to normal current flow in the power system. Large voltages can appear on the enclosures of electrical equipment due to a fault in the electrical power system, such as a failure of insulation."
To protect of the underwater metal parts of a boat or outdrive from corrosive electrolytic action, zincs are installed, an sacrificial anode which attracts the corrosive action to itself and away from the parts of the boat you want to protect.
If the metal parts of a boat located below the waterline is showing corrosion, it is "galvanic corrosion." The scientific term "galvanic" corrosion describes the type of corrosion that anodes are intended to absorb. This corrosion is normally caused by different metals being near each other. Galvanic corrosion, an electromechanical action, causes metal parts to decompose.
If the boat is showing an accelerated corrosion on the metal parts of the boat located below the waterline, it is "electrolytic corrosion". The scientific term "electrolytic" corrosion describes an accelerated type of corrosion that occurs when an electric current is added to the water surrounding the boat. The source could be the dock, a neighboring boat, or the boat itself. This corrosion is typically caused by faulty wiring that permits an electric current to enter the water. This corrosion, combined with galvanic corrosion, is also an electromechanical action which causes metal parts to decompose, but at a very accelerated level. This destructive process can be much more damaging in
a very short time.
If you are experiencing galvanic or electrolytic corrosion, I can perform four tests to detect the cause of this expensive problem and create a plan to correct or prevent further damage.
TEST 1 - MEASURING THE BOAT'S HULL POTENTIAL: analyze if the boat is properly protected, over protected, or under protected.
TEST 2 - VERFYING THE BOAT'S BONDING SYSTEM: analyze if the zincs mounted on a fiberglass hull is providing the corrosion protection to the shafts, struts, rudder posts, thru-hull fittings, and seacocks.
TEST 3 - CHECKING THE BOAT'S GALVANIC ISOLATION: analyze the boat when the shore power system is connected.
TEST 4 - FINDING STRAY CURRENT ON THE BOAT: analyze the boat's 12 volt system.
I will use several testing methods and readings to verify my findings.