Stop 16: Gyrocompass


The master gyrocompass is located in the gyrocompass room. There are additional repeaters on the bridge for the helmsman, one in each wing of the bridge, one on the flying bridge and one at the emergency steering station aft and where ever else required. Through various cables from the master gyro compass, a uniform indication of true north can be obtained in several locations simultaneously.

It is interesting to note that the suspended mass of the gyrocompass, over a hundred pounds, is supported by a tortionless strand of steel cable. The strand of cable used for the purpose is about 3/32nds thick. This cable permits the ship to swing completely around the rotor which maintains the direction in which it was started, or to which precessed. As the ship turns around the rotor the compass card (fastened to the perimeter of the gyrocompass – the ship) indicates the direction of heading as the ship turns.

The gyrocompass has the following advantages over the magnetic compass: (1) Does not rely on earth’s magnetic field for directive force and is unaffected by the ship’s magnetic field; (2) Seeks the true meridian instead of the magnetic meridian; (3) Its directive force is greater than that of the magnetic compass however, as the ship moves away to the north from the equator, the directive force diminishes until, at the poles, it is zero; (4) The master unit can be located within a ship which would be impossible with a magnetic compass; (5) Bearings and Courses are true eliminating the need to convert back and forth from compass to true, and vice versa; and (6) Can be connected to fire control systems or automatic pilots.

There are certain disadvantages inherent in its design. (1) It is complicated and relatively delicate. (2) It requires a constant, and dependable, source of power. (3) It requires intelligent, if not expert care, and attention.

A caveat: The day always comes when a failure of power supply or a derrangement causes the gyrocompass to fail. Once that happens, the largest ship at sea is dependent, like all ships for hundreds of years back, on the magnetic compass, or today a GPS unit. For that reason, magnetic compass correction procedures are still taught at all government sea service academies and, at sea, information to keep the magnetic compass corrected is continually updated.

Bridge Gyrocompass Repeater

Just to the left of the steering wheel, you can see the gyro repeater which has a card like a magnetic compass. The gyro indicates (almost) true north and is, today, most often used to steer by. However, gyros have some inherent problems, i.e., they require a steady supply of electricity, constant attention and routine maintenance.

Bridge Deck Left Wing Gyrocompass Repeater
Bridge Deck Right Wing Gyrocompass Repeater