Galvanic Corrosion/Stray Current - Regal LS4 Owner's Manual

Galvanic Corrosion/Stray Current

Metal parts underwater can be subjected to two
basic styles of electrolysis: galvanic corrosion
and stray current corrosion. Both can damage the
outboard drive, propeller, underwater parts, boat
and motor if not correctly monitored (testing at 2
week intervals) and avoided.
Galvanic corrosion is an electrochemical reaction
between two or more metals. Drive systems consist
of several different metals. Some are more active
than others.
Galvanic corrosion of the more chemically active
metals can occur whenever two or more dissimilar
metals that are "grounded" (connected by actually
touching each other, or through a wire or metal
part) are immersed in a conductive solution (any
material that can conduct electricity). Anything but
pure water is conductive. Saltwater, fresh water
with a high mineral content and polluted freshwater
are highly conductive. Conductivity increases with
temperature. That is why Florida boats experience
more corrosion than boats in Maine.
Specifi cally look at a typical marine drive unit with a
stainless steel propeller. The aluminum is the more
chemically active metal (called the anode) and the
stainless steel propeller is the less chemically active
metal (called the cathode).
CORROSION TABLE
Gold
Stainless Steel
Bronze
Copper
Brass
Steel
Aluminum
Zinc
Magnesium
Least Active
Most Active
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