Though the number and types of navigation equipment may differ from ship to ship, virtually all ships will carry the following:
- At least one gyro compass (the primary compass).
- A magnetic compass (the auxiliary back-up compass).
- At least one radar (operating in the 30 GHz frequency band). Ideally it should have two,
one operating in the 30GHz band and one in the 10 GHz band. Both should be equipped with ARPA (Automatic Radar Plotting Aid).
- An echo sounder (depth recorder).
- An electric/electronic log (ship’s speed through the water sensor ).
- A Global Positioning System (GPS – satellite based electronic navigation system). Ideally
it should have two independent units.
- An AIS (Automatic Identification System).
- An ECDIS (Electronic Chart Display and Information System). It is mandatory for all passenger vessels and cargo vessels, if foreign-going and above 300 gross tons.
- A radio direction finding system.
Gyro Compass. The gyro compass is usually contained in a compartment at the rear of the bridge. It is the primary compass consisting of a gyro which is lined up with true north. The gyro feeds a number of satellite gyro repeaters, the radar(s), the GPS, ECDIS and the radio direction finding unit. The repeaters are situated inside the bridge, on the bridge wings and at the emergency conning and steering positions.
Magnetic compass. The magnetic compass is usually situated either in the bridge or on the monkey island above the bridge. It works off the magnetic field of the earth and lines itself up with the magnetic north pole.
Radar. The radar equipment is usually fitted in a separate compartment whilst the video displays and controls are situated on the bridge. In a warship it would also have video displays and controls in the operations room which is usually situated under the bridge. Radar is used to locate, track and display graphically the positions of land, ships and any other objects that could pose a danger to the ship. It uses the transmission of electro-magnetic pulses to detect objects and, like a bat, it can see in the dark and restricted visibility. Since the speed at which electro-magnetic energy travels is known, it is merely a matter of timing the transmission of the pulses and the reception of the echo and multiplying the two (speed and time) to obtain the range of the object. Since the system is fitted with a rotating narrow band antenna, we can also determine where the objects are relative to the ship.
Echo sounder. The echo sounder uses the transmission of sound waves through the water to “bounce” a signal off the sea floor. Since the speed of sound through water is known, it is merely a matter of timing the sound waves, multiplying it with the speed and dividing the result by two. This will give the depth of water under the keel. The information is displayed graphically on the bridge.
Ship’s log. There are various types of log but all consist of a sensor in the bottom of the hull and the display of speed and distance on the bridge. Most logs only record the speed of the ship through the water and do not take into account the effect of sea currents. There is a log however, that uses the transmission of sound waves on the sea bottom and the Doppler effect of the returning echoes to determine the speed over the ground.
Global Positioning System (GPS). The GPS is an electronic navigation system which makes use of data transmitted by a system of satellites to determine the position of the vessel. The data display unit is situated above the chart table in the bridge.
Automatic Identification System (AIS). The AIS system comprises short range radio coupled with a transponder that is activated by other ships transmitting in the vicinity. Details of each ship complete with courses and speeds are transmitted automatically to one another. The data display is mounted on the bridge near the radar display.
Electronic Chart Display and Information System (ECDIS). This system replaces paper charts and is permanently connected to the GPS system. By converting existing charts to a digital format, it provides the navigator and the officers of the watch with a very advanced tool for navigating. The system provides up to date positions and plots it in real time on the digital chart, which is displayed on a special video display. The system can also superimpose the radar picture on the chart which will also give the positions of vessels and other objects in the vicinity. The display is mounted in the bridge.
Radio Direction Finder (RDF). The RDF is a system which comprises a MF radio receiver with a direction finder. It is used to determine the bearing of fixed (shore based) and mobile (ships) radio stations transmitting in the MF band.