GPS / GNSS Navigator

What sets a GNSS navigator apart

Where the echo sounder reports depth under the keel and the speed log reports motion through the water, the GNSS receiver reports where the ship actually is, continuously and independently of local water conditions. It is the electronic position fixing system SOLAS requires as standard bridge equipment, and its output feeds almost every other navigation and safety system aboard: ECDIS chart position, AIS transmitted position, autopilot course reference, VDR recording, and often the ship's own timekeeping through the GNSS time signal.

Main components

Antenna

Mounted with a clear view of sky, free of obstruction from masts, funnels or radar scanners that could cause signal shadowing or multipath reflection.

Receiver unit

Processes signals from one or more satellite constellations (GPS, GLONASS, Galileo, BeiDou) simultaneously, computing position, course over ground and speed over ground from the combined solution.

Augmentation and correction

Differential correction via satellite-based augmentation systems (SBAS) or, in some regions, ground-based DGPS improves accuracy beyond standalone GNSS, useful for close-quarters manoeuvring and pilotage.

Interfaces

Output over NMEA 0183 or NMEA 2000 to ECDIS, AIS, radar, VDR and autopilot; loss of this interface, not just loss of satellite lock, is a common cause of position failure elsewhere on the bridge.

Selection and sizing

Multi-constellation reception improves availability and resilience, particularly in areas with known interference. Update rate (commonly one update per second) and the number of channels affect how quickly the receiver reacquires after a signal loss. SOLAS vessels are required to carry a means of determining position that does not depend on a single system, which in practice means two independent GNSS receivers or a second independent method, since GNSS as a technology is a single point of failure if only one unit is fitted.

Regulations and class requirements

SOLAS Chapter V regulation 19 sets the carriage requirement for an electronic position fixing system on vessels of the relevant size and trade. Equipment must carry wheelmark type approval confirming it meets the IMO performance standard for shipborne GNSS receivers. Periodic checks against known reference positions and interface verification during survey confirm the system remains within tolerance.

Typical faults

• Antenna cable degradation from UV and weathering, causing intermittent signal loss that is hard to diagnose from the bridge alone.
• Jamming or spoofing in certain sea areas, producing a plausible but incorrect position that downstream systems accept without warning.
• Signal shadowing from superstructure or scanners during certain headings, causing position gaps at predictable times rather than random ones.
• Receiver lock-up requiring a power cycle, sometimes triggered by a corrupted almanac after extended power-off periods.
• Interface faults on the NMEA bus that stop position data reaching ECDIS or autopilot even though the receiver itself is working correctly.

What to look for in a supplier

• Current wheelmark type approval valid for the flag and trade the ship operates under.
• Genuine multi-constellation support rather than GPS-only with other constellations listed but unused.
• Confirmed interface compatibility with the specific ECDIS, AIS and autopilot models already fitted.
• Firmware update path and technical support that does not require removing the unit from the ship.

A single GNSS receiver satisfies nobody's redundancy requirement; treat the second independent position source as mandatory, not optional, however reliable the primary unit has been.