Other electronic navigation systems employed in the past include Consol, Loran and Omega (similar to Decca) and the forerunner to GPS, the American Transit system. The latter consisted of 5ive low orbit (1100 kms) satellites orbiting the earth in approximately one and three quarter hours. The system made use of the Doppler effect, ie changes in frequency of the satellite’s transmissions as they passed within range of the receiver was measured and compared. This was compared with a computed position obtained by DR in the receiver’s computer and a fairly accurate position obtained. In order for the computer to produce a DRIt can track targets position, it required inputs of start position and regular updates of courses and speeds. The chief shortcoming of this system was the limited number of satellites and their low altitude orbits. The orbits had to be between 10° and 70° above the receiver’s horizon to provide usable data. Because ofthis, fixes were erratic, during a watch of four hours one might only obtain one fix and at other times there were a number in one hour.

There are a number of other satellite navigation systems such as the Russian GLONASS (GLObal Navigation Satellite System) and the planned European “Galileo” positioning system, Chinese “Compass” navigation system and the Indian regional navigational satellite system. Glonass has also been made available for private/commercial use.

Technology is advancing at a tremendous rate and it is essential that the maritime industry keep pace with the latest developments in electronic navigational equipment. However, no matter how advanced the technology becomes, it is only as good as the people who use it. The human element is still the core to safety at sea and will remain so for the foreseeable future.