GPS (Global Positioning System)

In maritime navigation, GPS (Global Positioning System) refers to the space-based radionavigation system operated by the United States Space Force. Outside nautical terminology, the acronym GPS may denote non-maritime organizations such as the Great Public Schools Association of Queensland, but for mariners, it is the primary electronic positioning standard.

The system calculates a vessel's position by measuring the time delay of radio signals transmitted from a constellation of Earth-orbiting satellites. A minimum of 4 satellite signals is required to compute latitude, longitude, and precise clock bias. Standard marine receivers offer a horizontal accuracy of 2 to 5 meters, which can be improved to sub-meter precision (<1 meter) using Satellite-Based Augmentation Systems (SBAS) or Differential GPS (DGPS).

Integrated into modern marine networks via NMEA protocols, the receiver continuously calculates Course Over Ground (COG, measured in true degrees from 000° to 359°) and Speed Over Ground (SOG, expressed in knots, where 1 knot equals 1.852 km/h). Understanding how GPS functions in electronic navigation is essential for skipper decision-making, as COG and SOG represent the true movement across the seabed including current and leeway effects. However, electronic positioning should never fully replace traditional seamanship. Relying solely on satellites exposes the vessel to risks like signal jamming or power failures, making the proper use of the marine compass an indispensable backup for safe navigation.