Operating the Mk 19 Mod 3A Gyrocompass

which is identified as the normal mode while the ship

a true level position and the meridian gyro to settle on

sails in latitudes (north or south) between the equator

the true meridian.

and 75.

This system is actuated by placing the mode selector

switch, located on the front of the compass control panel

Auxiliary operating modes are described later for

(fig. 4-22) to the FAST-SETTLE position. This switch

compass (chiefly submarine) uses between latitudes 75

completes the energizing circuit to the fast-settle relay,

and 90 near the poles. Operation in the normal mode is

located in the computer control assembly.

generally undesirable in these latitudes because

horizontal earth rate (proportional to the cosine of the

When the fast-settle switch is closed, it energizes

the 4-pole, double-throw, fast-settle relay. The

latitudes) results in the compass period becoming very

operated fast-settle relay alters the resistance

high, causing slow settling and consequent poor azimuth

connections in the meridian gyro gravity reference

accuracy.

system, which increases the damping signal output. It

EMERGENCY OPERATION.-- If the ship's ac

also allows the primary voltage of the meridian

control step-up transformer to be taken directly

power line fails or drops below 105 volts, undervoltage

from the cathode follower instead of from a

relays open their normal contacts and switch to

potentiometer, thereby increasing the meridian

battery power that is applied to the dc generator so it

control output signal. When operated, the relay's

serves as a motor. Speed of this dc temporary motor is

contacts short a potentiometer in the slave gyro gravity

controlled by a centrifugally operated speed regulating

reference system, increasing the slave gyro leveling

device. The ac section then operates as a synchronous

signal.

generator (driven by the dc section) and, for a period of

The fast-settle switch also disconnects the alarm

15 minutes produces 0.75 kW, without excessive

circuit from the delay relay, rendering the compass

temperature rise.

failure alarms inoperative when the fast-settling system

is in operation. A fast-settle lamp is lighted when the

When the ship's power line is restored above 112

switch is closed, giving visual indication of fast-settle

volts ac, the relay automatically returns both units

operation.

(motor and generator) to their normal functions. The dc

section is then generating current and charging the

Operating the Mk 19 Mod 3A

storage batteries.

Gyrocompass

AUXILIARY OPERATING MODES.-- The fast

The Mk 19 Mod 3A gyro system maybe started by

settle mode is auxiliary to the normal mode. It is used

setting the fast-settle switch to either the OFF or the ON

on all Mk 19 compass models for starting.

position. The settling time is much longer when the

Two additional auxiliary modes are available on the

system is started in the OFF position. Therefore, it is

recommended to always start it in the FAST-SETTLE

Mod 3B, identified as high latitude mode and directional

position.

mode. Some converted Mod 3A gyros also have them.

These two modes of operation will be explained later in

Because the alarm system is NOT in operation while

this chapter when we discuss the starting procedures for

it is in the FAST-SETTLE position, the switch should

the Mod 3B compass.

be reset to ON as soon as practical. The amount of time

to settle is least when a ship is sailing at the equator and

is greatest at the poles (90 latitude).

Securing the Gyrocompass

Two hours (120 minutes) is the normal period

of oscillation at 40 latitude. With the fast-settle

When your ship returns to port after an underway

switch in the ON position, the period of oscillation

period, you must obtain permission before securing the

is reduced to 50 minutes. These approximate periods

compass. Permission to secure the compass is normally

are characteristic of all mods of the Mk 19 com-

granted by the engineer officer.

pass.

To secure the gyrocompass, turn the master switch

NORMAL OPERATION.-- Normal operation of

(fig. 4-22) to the OFF position. After the compass is

the Mk 19 Mod 3A compass is obtained after the

secured, notify the engineer officer.

fast-settle switch is moved to the OFF position,

4-36