Regal 2000 ES Owner's Manual page 271

Chapter 7
Typically electrons ow from the anode (the aluminum drive
unit),via the external conducting path to the cathode (stainless steel
propeller). If there is a very large anode connected to a small cath-
ode, the anode will corrode very slowly. If a very large cathode is
connected to a small anode, the anode will corrode very quickly.
Obviously, if you do not control galvanic corrosion, over time the
aluminum will corrode away.
e rst sign of galvanic corrosion is paint blistering (starting on
sharp edges) below the water line- a white powdery substance forms
on the exposed metal areas. As the corrosion advances, the exposed
metal will become deeply pitted as the metal is actually eaten away.
Another condition which will increase galvanic corrosion is the re-
moval or reduction in surface area of the sacri cial anodes. Never
add a ermarket products that are connected to the engine ground
such as stainless steel steering aids and trim planes.
Zinc connected to aluminum will form a corrosion cell but the alu-
minum (drive) becomes the cathode and the zinc (anode) corrodes.
Even though your boat may not have shore power aboard current
from nearby vessels with shore power can produce stray current
galvanic corrosion. Stray current corrosion occurs when metal with
an electrical current owing into it is immersed in water that is
grounded (lake, ocean, pond). e current can leave the metal and
ow through the water to ground. is will cause rapid corrosion of
the metal at the point where the current leaves.
When a vessel nearby is plugged into shore power, they can po-
tentially tie your aluminum drive unit to their boat via the green
grounding shore power lead. Your aluminum drive unit could be
the receiving end of a large galvanic cell (a battery) interconnected
with nearby vessels or even through the marina's metal structures
via their electrical system.
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