cathodic protection systems, and are listed with their
After the print is developed, it is fed through the
definitions in Apppendix I, Glossary.
paper cutter (fig. 11-5), where it is cut off from the paper
Cathodic protection reduces the corrosion or dete-
rioration of metal caused by a reaction with its environ-
ment (ship's hull and seawater). The chemical action
Most reader-printers operate on 115 volts 60 Hz.
that is created is similar to the electrochemical action of
The power distribution system supplies the power to
a battery or cell. Figure 11-6 shows a dry-cell battery
operate the system in the reader-printer to produce a
circuit. So that you may understand the electrochemical
print. There are numerous motors, switches, and relays
theory shown in figure 11-6, you need to use the con-
that operate the systems in the reader-printer. These are
ventional theory where current flows from positive to
supplied by the power distribution system.
negative. The positive current is indicated by a positive
deflection of the voltmeter needle when the positive
Most maintenance, regardless of the type of reader-
terminal of the meter is connected to the cathode (posi-
printer, is outlined on MRCs. The MRCs give detailed
tive terminal) of the cell. As the electrochemical action
step-by-step instructions in performing needed mainte-
continues, the process will eventually corrode, or con-
sume, the anode that is providing the current to light the
nance on reader-printers.
lamp. This process is called electrochemical action.
CATHODIC PROTECTION SYSTEM
In a marine environment, corrosion is an electro-
The next sections of this chapter will introduce you
chemical process caused when two dissimilar metals
to cathodic protection systems installed on naval ships.
are immersed in seawater, with the seawater acting as
There are two systems, the sacrificial anode and the
the electrolyte. This process is shown in the electro-
impressed current. The two systems are different in both
chemical corrosion cell (fig. 11-7). You must under-
construction and operation.
stand that in an electrochemical cell a metal that is more
Some technical terms used with this part of the
corrosion prone always has a higher driving voltage
chapter may be unfamiliar to you. These terms apply to
Figure 11-5.--Paper cutter system.