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December 1965 Popular Electronics
 Table of Contents
Wax nostalgic about and learn from the history of early electronics. See articles
from
Popular Electronics,
published October 1954 - April 1985. All copyrights are hereby acknowledged.
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A news story with a
title about a boat and reverse current is more likely to be referring to water flow
in a river or stream than about electrical current in a conductor. Having
grown up in a neighborhood next to a tributary of the
Chesapeake
Bay, I spent quite a bit of time around boats, both large and small. Salt water
is particularly destructive to metal hulls due to
cathodic
corrosion, exacerbated by the salt water's conductivity. While working as an
electrician in the 1970s, I installed electrical supplies for a few dockside cathodic
protection systems that probably functioned like the one described in this 1965
issue of Popular Electronics magazine. The principle is fairly simple whereby
anodes are placed in the water around the hull and a counter-current is induced
to cancel the natural current flow. Evidently the systems needed to be fine tuned
so as to not harm the hull's paint.
Reverse Current Keeps Ferry Afloat
Converted ferry was stripped of machinery and engines, and connected
to city water, gas, electricity, etc. Problem was to prevent the hull from rusting
away without yearly dry-docking.
By William P. Brothers
When the San Francisco firm of J. Walter Landor ran out of space, it simply bought
one of the last of the Bay ferryboats. The company tied the boat up to a dock and
converted the topside into offices. Keeping the steel hull of the 40-year-old ferry
from scuttling the studios and staff was a problem.
Electrical potential of steel hull is measured every month. Brass
studs brazed to hull give solid electrical contact, accurate reading. Amount of
d.c. current required depends on exposed hull area.
A permanently moored ferryboat is corroded by the electrolytic action of sea
water. One ampere of d.c. will wear away 20 pounds of steel each year. To overcome
this action, designer Alexis Tellis dropped four carbon anodes overside and fed
them d.c.-reversed to the corrosive action of the hull. A solid-state rectifier
supplies 0.85-0.95 volt to the rods. More voltage damages the paint; less voltage
corrodes the hull.
Designer Alexis Tellis examines one of four carbon anodes dropped
around steel hull. Anodes, charged with d.c. equal to that ferry would ordinarily
lose by electrolytic action, counteract current flow.
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