Galvanic Corrosion; Corrosion Control - Yanmar SD25 Operation Manual

12/05

GALVANIC CORROSION

Galvanic corrosion results whenever two
or more dissimilar metals (like those found
on the sail-drive) are submerged in a
conductive solution, such as saltwater,
polluted water or water with a high mineral
content because a chemical reaction takes
place causing electrical current to flow
between the metals. The electrical current
flow causes the metal that is most
chemically active, or anodic, to erode. If
not controlled, galvanic corrosion may
corrode Sail-Drive components.
* "The Boatowner's Guide to Corrosion", by Everett Collier.
SD25 Operation Manual
PRODUCT OVERVIEW

CORROSION CONTROL

It is the boat designer's responsibility
and/or the re-powering engineer's
responsibility to design the proper systems
and equipment to control and reduce the
possibility of galvanic corrosion.
However, it is essential that the
owner/operator frequently monitor the
anodes for wear, inspect the sail-drive for
corrosion and replace the anodes often
enough to provide a sacrificial surface for
the electrical current to attack. Galvanic
isolators and isolation transformers are
also available from the aftermarket (not
supplied by Yanmar). The Galvanic
isolator is a device that is installed in series
with the (AC) grounding (GREEN)
conductor of the shore-power cable to
effectively block low-voltage DC galvanic
current flow but permit the passage of
alternating current (AC)*.
The rate of corrosion depends on
numerous factors, such as:
• the number, size and location of
sacrificial anodes on the sail-drive and
vessel;
• the marina environment, such as stray
current in the water, fresh or salt water
and use and isolation of shore power;
• improper application of marine paint or
antifouling paint;
• failure to repaint damaged areas; and
• how the vessel is bonded.
Please check with the boat builder, dealer
or other professional to determine if your
vessel and/or Sail-Drive is adequately
protected from galvanic corrosion.
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