What to check on a GPS/GNSS Receiver.
A GNSS receiver only fixes position; it tells the bridge nothing about heading. That job belongs to the gyrocompass and magnetic compass sitting alongside it in this category. Unlike a handheld consumer unit, a SOLAS-fitted receiver tracks several satellite constellations at once - GPS, GLONASS, Galileo, BeiDou - and applies satellite-based augmentation (SBAS, e.g. EGNOS or WAAS) or differential corrections to bring horizontal accuracy from the 5-10 m of standalone GPS down to 1-3 m. Two independent receivers, wired to separate antennas and power feeds, are standard on SOLAS vessels…
What sets a GNSS receiver apart
A GNSS receiver only fixes position; it tells the bridge nothing about heading. That job belongs to the gyrocompass and magnetic compass sitting alongside it in this category. Unlike a handheld consumer unit, a SOLAS-fitted receiver tracks several satellite constellations at once - GPS, GLONASS, Galileo, BeiDou - and applies satellite-based augmentation (SBAS, e.g. EGNOS or WAAS) or differential corrections to bring horizontal accuracy from the 5-10 m of standalone GPS down to 1-3 m. Two independent receivers, wired to separate antennas and power feeds, are standard on SOLAS vessels so a single antenna cable fault or jamming event does not blind the ship.
Main components
Antenna
An active antenna with a built-in low-noise amplifier, mounted with clear sky view away from radar scanners and funnel exhaust. Cable length and quality matter: a long, degraded coax run is the most common cause of intermittent fix loss.
Receiver/processor unit
Tracks the visible satellites on multiple channels (typically 20-70+ channels across constellations), computes position, course over ground, speed over ground and UTC time, and runs receiver autonomous integrity monitoring (RAIM) to flag an unreliable fix.
Output interfaces
Feeds position and time to ECDIS, AIS, VDR, autopilot and the alarm system over NMEA 0183 or NMEA 2000 (IEC 61162 series). Loss of this output silently degrades several other systems at once, which is why the receiver sits on an uninterruptible supply.
Backup power
A small UPS or battery buffer keeps the receiver's clock and almanac alive through a brief mains interruption, avoiding the several-minute cold-start delay needed to reacquire a full satellite almanac from nothing.
Selection criteria
| Criterion | Why it matters |
|---|---|
| Constellations tracked | More constellations mean more satellites in view and faster recovery after signal loss in port or under superstructure shadow |
| Augmentation support | SBAS or DGNSS input tightens accuracy for pilotage and dynamic positioning work |
| Update rate | 1 Hz is enough for passage navigation; DP and survey work want 5-10 Hz |
| Interface protocol | Must match the ship's existing NMEA 0183 or 2000 bus and IEC 61162 wiring |
| Type approval | Wheelmark certification confirms compliance with IMO performance standards |
Regulations and class
SOLAS Chapter V, Regulation 19 lists a GNSS receiver among the mandatory navigation equipment for ships on international voyages, sized by gross tonnage. IMO resolution A.915(22) and the receiver standard IEC 61108-1 set the performance requirements a type-approved unit must meet. Class societies check the fitted receiver during annual and renewal surveys of navigation equipment, mainly confirming it is operational, correctly interfaced and carries a valid wheelmark; there is no separate periodic calibration for the receiver itself since it self-corrects against the satellite signal.
Typical faults
- Degraded antenna cable - corroded connector or chafed coax causes intermittent signal loss, often blamed on the receiver when the fault is really upstream.
- Jamming or spoofing - increasingly reported in conflict areas and some straits; the receiver may report a confident but wrong position rather than losing the fix outright.
- Flat backup battery - a dead buffer battery forces a cold start after every power interruption, delaying the fix by several minutes at the worst possible time.
- Multipath near quay walls - reflected signals off steel structures in port cause position jitter that can trip autopilot or DP alarms.
- Firmware/almanac mismatch after long lay-up - an old almanac slows first fix acquisition until the receiver downloads current ephemeris data.
What to look for in a supplier
- Current wheelmark/type approval certificate matching the installed software version, not just the model line
- Genuine multi-constellation tracking rather than GPS-only with constellation names added to the spec sheet
- Documented compatibility with the ship's existing NMEA bus and alarm system wiring
- Antenna and cable kits available as matched spares, not just the receiver unit
- Clear guidance on jamming/spoofing detection features, if fitted, and how alarms are presented to the bridge team
Keep a log of position jumps and RAIM alarms as they happen - a spoofed fix looks entirely plausible to the autopilot, and the only way to catch it is by comparing it against radar, visual fixes or the second independent receiver.