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MAINTENANCE
ELECTROLYSIS AND GALVANIC PROTECTION
Salt water allows electric current to flow from anodic to
cathodic material. Anytwo metals fromtwo components,
and their relative positions in the galvanic rating table,
will determine which loses material (the anode) and which
remains largely undisturbed (the cathode). The rate of
wear is determined by the distance apart on the galvanic
table oftwo metals. Thus a sacrificial zinc anode is often
fitted to the underwater area ofa boat to attract any de-
structive currents away from bronze or steel propeller
shafts, for example.
It is not enough to know that your boat does not suffer
from electrolysis: a newcomer in the adjacent marina berth
may start a too-friendly association with metal compo-
nents on it. An easy place to fit an anode is on the pro-
peller shaft, or covering the propeller nut. The anode
should not be painted because this will only defeat the
purpose.
To prevent electrolysis in sea water, the difference be-
tween the voltage of two adjacent metals should not ex-
ceed 0.20V. Znc and carbon steel, for example, used
together, risk corrosion, while lead and active stainless
steel are compatible. Metals with a high voltage corrode
faster and need a larger area to difrrse the electrochemi-
cal reaction.
PAGE 30
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