Module 10 - Chartwork
Waypoints and GPS Navigation
GNSS receivers, often described as GPS, can provide position, course over ground and speed over ground. A plotter can then show bearing and distance to a waypoint and cross-track error from a route leg. These are powerful aids, but a route line between two safe-looking points is not itself a checked safe route: inspect the whole leg at a suitable scale for hazards, depth, chart notes and chart currency.
A plausible display can still be wrong because of an incorrect waypoint, wrong chart datum, outdated or unsuitable chart data, user settings, loss of integrity, jamming, spoofing, power failure or damaged equipment. Cross-check position and trend against available visual information, depth, radar, expected tidal effect and the vessel's recent DR or EP rather than waiting for an obvious alarm.
The safe backup depends on the vessel and passage. RIN guidance favours a means of navigation independent of the primary system and power supply. A current paper chart kept in use can be one solution; an independently powered second electronic system may be another when its data and positioning vulnerabilities are understood. Two apps on one device, using the same GNSS and battery, are not independent.
- A waypoint coordinate does not prove the route leg is safe
- Inspect the route at a scale that reveals relevant hazards
- Cross-track error measures displacement from the active route leg
- Cross-check electronic position before a discrepancy becomes critical
- Backup should not share the primary system's single points of failure
Optional quick check
Section 6 of 7
Which arrangement is the strongest independent backup to a tablet used as the primary plotter?
Continue studying Chartwork
This public lesson is part of Revision Module 10. Full revision access adds the guided Learn, Practise and Test flow, flashcards and revision progress.