Does a zinc made of any other material
still work as well? Or perhaps even better?
By Roger McAfee
henever a boater
new zincs on my
of the times we used
to say go for a even though
almost nobody in the group drank beer.
Scotch or rum were preferred! It was
merely an expression. Unfortunately for
boaters, when many of them have sacrificial anodes installed they are, in fact,
made of zinc, even though there are sacrificial anodes made of a material that
might well do a better job.
Sacrificial anodes are necessary to
combat galvanic corrosion in metal
structures. As boaters we most often
think of galvanic corrosion, and the
problems it causes, in relationship to
boats only. In fact, pipelines and most
other metal infrastructure projects also
have problems with galvanic corrosion.
Galvanic corrosion comes about when
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two dissimilar metals are immersed in
an electrolyte. Sea water is a great electrolyte. Fresh and brackish water also
act as electrolytes, but not with the same
vigour as salt water. When the two dissimilar metals are immersed in salt water, a flow of electrons moves from one to
the other. Without getting into the eyeglazing electro-chemical details, this
flow causes the corrosion.
The constant push by environmentalists has created a mindset among many
that the metallic zinc, when dissolving
in water, is not environmentally friendly.
Zinc, in large amounts, has, in fact, been
found to be harmful to marine life and
that has led to pressure in some jurisdictions to ban the use of sacrificial zinc.
Some zinc anodes also contain cadmium, a heavy metal that can be a serious
The U.S. Environmental Protection
Agency has a regulation in place that
requires sacrificial anodes on all commercial vessels shorter than 80 feet to
be environmentally friendly to the
extent technologically feasible and economically practical and
While the wording of the regulation is,
legally, nothing more than a it does indicate the likely direction
the matter of sacrificial anodes is heading. This regulation does not yet apply to
The EPA also notes is
less toxic than aluminum and aluminum
is less toxic than
Generally speaking sacrificial anodes
made of zinc work well in salt water,
magnesium anodes work best in fresh
water and aluminum anodes work well
in salt, brackish and fresh water. It appears the use of aluminum sacrificial anodes satisfies both the environmentalists and boat operators, something one
rarely sees. The aluminum anodes are
This article has been limited to sacrificial anodes. For boaters wanting a more detailed marine and technical
electro-chemical corrosion discussion there are a number of books on the market, two of which are most
useful. One is published by McGraw Hill and carries the title The Guide To Corrosion and is
written by Everett Collier. The other is authored by a well-respected naval architect and marine writer Nigel
Warren and carries the title Metal Corrosion In Boats. published by Adlard Cole Nautical.