Gyro Compass is a navigational equipment (bridge watchkeeping equipment). It is used for ship’s navigation and also for stability. Gyro stands for gyroscope and compass stands for the direction measuring equipment with respect to geographic directions.
It has an electrically driven gyroscope which has a heavy well balanced wheel spinning at a high rate (above 2200 rpm). Gyroscope is nothing but a device for measuring the angular velocity and position. Gyroscope (Gyro) is an instrument which contains spinning wheel or disc shape body and works on the principle of conservation of angular momentum.
Gyro does not depend upon the earth magnetism. It is free from variant and deviation of magnetic effect.
It has freedom of movement in three axis i.e. Spin axis, Horizontal axis & Vertical axis.
Gyro compass consists of master compass, repeater compass, course recorder, motor generator, voltage regulator and control panel etc.
Gyro is controlled by two steps i.e. Gravity & Damping. In gravity control, gyro compass spin axis is north seeking and in damping control, gyro compass spin axis is settling the north.
Gravity Control in Gyro
The rotation of earth gives us a free gyroscope, which can be controlled by precession and for that we need to use property of earth’s gravity and rotation to create the torque. And for that we will create a top heavy/bottom heavy effect.
Speed Error: When ship is moving, speed and course of ship affect gyro. Gyro error is maximum in N-S direction error is minimum in E-W direction because earth rotates from W to E and movement of ship in E-W direction only adds or subtracts from earth’s rotational speed.
Latitude Error or Damping Error: The error is proportional to the tangent of latitude. Therefore it increases with latitude. It also depend on the design and construction of individual compass. This error is calculated and applied as latitude correction.
Methods for finding the Gyro Compass Error
By taking Azimuth (Sun, Moon, Star, Planet)
By taking transit brg.
By taking amplitude (Sun)
By taking HAS
By taking VSA
By taking leading light
By taking at jetty
Note: We can’t take amplitude of moon because moon is very ear to earth and its reflection is very less.
There are 2 basic nature in Gyro compass i.e. Gyroscopic Inertia & Precession which make it perfect.
Once a free gyroscopic is set spinning it will maintain a fixed direction in space as long as there are no disturbing force. However due to the rotation of earth on its axis the axel of the gyroscope will be seen to drift (horizontal) and tilt (vertical).
The movement of the sin axis in direction of azimuth is called as drift. The angle of elevation or depression of the spin axis above or below the horizontal is called as tilt.
Starting of Gyro Compass
Make preparation 4 hours before the gyro put in service.
Check all supply switches are open.
Check the oil is sufficient.
Switch on alternator.
Adjust latitude and speed setting.
Switch on compass and azimuth switch.
After heading is stead, switch on repeater.
Test the alarm switch on the alarm panel.
Advantage of Gyro Compass
It always shows true north.
The gyro will have a number of repeaters.
Gyro input can feed to Radar/ARPA/Auto-pilot/Echo sounder.
It doesn’t use earth magnetic field as reference.
It has high reliability, compact size, small errors etc.
Disadvantage of Gyro Compass
It operates with electricity. So when the electricity fails the gyro also fails.
When gyro compass stop for any reason, it will take time to settle down 5 to 6 hours.
Care and Maintenance of Gyro Compass
Check repeater with master compass to ensure repeaters are functioning properly. If power fails, repeater may have to be reset.
Check compass error by azimuth.
Speed and Latitude correctors should be reset as necessary.
Inspect compass to guard against any abnormal condition of operation monthly.
Check alarm buzzer.
Clean and oil any part as indicated by manufacturer’s instruction.
General cleanliness should be checked.