Construction of a Gyroscope
A gyroscope consists of a thick wheel known as the gyro wheel, which is designed to rotate at high speed. It is mounted on a circular ring by its axle. To allow the disc to rotate in every direction, three rings are used, as shown in the animated image above. These three discs are connected at 90-degree angles, providing a full 360-degree movement in any direction. This design allows the gyroscope to have three degrees of freedom:
1) Spin on its axis: The gyro wheel can rotate around its own axis.
2) Tilt about its horizontal plane: The gyroscope can tilt up and down from the horizontal plane.
3) Turn about its vertical axis: The gyroscope can turn around its vertical axis.
Properties of a Free Gyroscope:
1) Rigidity in space: When the disc is set in motion to spin on its axis, it continuously maintains a fixed direction regardless of the movement or tilt of its supporting base. This unique property is known as the rigidity of space.
2) Gyroscopic precession: The axis of rotation has a tendency to turn at a right angle to the direction of an applied force.
Terms and Definitions:
1) Tilt: This refers to the angle by which the spin axis of the gyroscope appears to have moved up and down from the horizontal plane.
2) Tilting: This refers to the apparent motion of the gyroscope’s axle on the vertical plane, which can be upward or downward depending on the factors causing it.
3) Drift: This is the angle by which the gyroscope’s axle has deviated or moved away from its original direction in the horizontal plane.
4) Drifting: This refers to the apparent motion of the gyroscope’s axle on the horizontal plane.
Operational Errors of a Gyrocompass:
1) Latitude error (Damping error or setting error): This error occurs when the gyroscope fails to align with the true north due to incorrect latitude settings or damping.
2) Course, Latitude & speed error (Steaming error): This error is caused by a combination of the Earth’s rotation and the ship’s movement. It leads to errors in course and latitude readings, which can be corrected by adjusting the latitude and speed correctors on the gyroscope.
3) Ballistic deflection: This error occurs when the ship’s speed and course are rapidly changed, resulting in a surge of mercury from one part of the gyroscope to another. It can be compensated for by employing damping mechanisms.
How a Gyrocompass System Becomes North Seeking:
To achieve damping in tilt and damp unwanted oscillations, the gyrocompass system is offset slightly to the east of vertical. This offset creates a torque that counters the tilting motion. By pre-calculating the magnitude and direction of this force, the system achieves the required damping oscillation. As each oscillation occurs, its amplitude is reduced to one-third of the previous oscillation, ultimately allowing the spin axis to reach equilibrium and settle in a position that counteracts drifting and tilting, thus becoming north-seeking.
Various Types of Gyrocompasses Used on Merchant Ships:
1) Admiralty Sperry type
3) Arma Brown compass
Procedure for Starting and Stopping a Gyrocompass and Routine Maintenance:
Starting a Gyrocompass:
1) Follow the manufacturer’s manual and procedure.
2) Allow for a preparation time of at least four hours before the compass is needed for service.
3) Check that all supply switches are open.
4) Adjust the latitude and speed settings accordingly.
5) Switch on the alternator and wait for it to reach full speed (approximately 10 seconds).
6) Test the alarm switch on the alarm panel.
Stopping a Gyrocompass:
1) Open the repeater switch.
2) Open the azimuth motor switch.
3) Switch off the alternator and lock the rotor.
During each watch:
1) Check the repeater with a master compass to ensure proper functionality.
2) Verify the compass error using azimuth.
3) Reset the speed and latitude settings as necessary.
4) Inspect the compass for any abnormal conditions of operation.
a) Check the alarm buzzer.
b) Clean and lubricate any parts as indicated in the manufacturer’s manual.
c) Ensure the general cleanliness of the compass.
Repair and maintenance should only be carried out by a professional, and any abnormalities should be addressed promptly.