Figure 11-5.--Paper cutter system.

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

roll.

CATHODIC PROTECTION

POWER DISTRIBUTION

Cathodic protection reduces the corrosion or dete-

SYSTEM

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

MAINTENANCE

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

ELECTROCHEMICAL ACTION

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.

11-6