GPS is a satellite-based positioning system that determines a receiver’s exact location by calculating its distance from multiple GPS satellites simultaneously in view.
How It Works (Simplified)
Each GPS satellite continuously broadcasts its position and precise time. A ship’s GPS receiver picks up signals from several satellites at once and calculates its own position through triangulation based on the tiny differences in signal arrival time.
Role on a Ship
- Primary position-fixing method — has largely replaced older methods like celestial navigation and terrestrial position-fixing for routine navigation
- Feeds ECDIS — the vessel’s real-time position on electronic charts comes from GPS
- Feeds AIS — the position broadcast to other vessels and shore stations is GPS-derived
- Supports autopilot — course-keeping systems use GPS position data
DGPS (Differential GPS)
Some applications use DGPS, which corrects standard GPS signals using a nearby reference station for improved accuracy, particularly useful in port approaches and pilotage.
Backup Navigation Skills Still Matter
Despite GPS’s reliability, deck officers are still trained in traditional position-fixing methods (celestial navigation, terrestrial fixes) as a backup for the rare event of GPS failure or signal jamming/spoofing, which has become a more recognized real-world concern in certain regions.
Exam Relevance
GPS principles, its integration with ECDIS/AIS, and traditional backup navigation methods are core topics in the Navigation section of deck officer competency exams.