Electronics and navigation

Navigation electronics commonly include a multifunction display/chartplotter, GNSS/GPS antenna, depth/speed/wind instruments, magnetic heading sensor, radar, AIS transceiver, fixed VHF with DSC, handheld VHF and data network. AIS broadcasts vessel identity/position and receives equipped targets; Class B SOTDMA units typically transmit at higher power/update priority than older CSTDMA units. AIS does not show untransmitting boats, debris or land.

Modern solid-state pulse-compression radar can show rain, land and non-AIS targets; Doppler/moving-target coloring helps distinguish approaching from receding targets but does not identify everything automatically. NMEA 2000 is a shared instrument network; NMEA 0183 is older point-to-point serial data. Starlink is communications, not a navigation or collision-avoidance sensor, and service legality/coverage can change by country and plan.

Radar, AIS, depth and reliable charts reduce—but do not remove—collision and grounding risk. VHF/DSC carries distress and local traffic. A correct heading source is essential for radar overlay and autopilot performance. Integration faults can create confident but wrong displays. Offshore resilience requires independent position/chart and communications paths, not two screens fed by one failed GPS/network.

Start by cleaning power/network faults, updating software and calibrating heading, depth offsets, speed and wind. Replace corroded connectors/antennas or one failed display when compatible. A VHF antenna/coax problem may degrade AIS and radio together. Verify the AIS MMSI cannot require factory/dealer reset before ownership transfer.

Replace a whole ecosystem only when network incompatibility, support and desired sensor integration make partial work uneconomic. Choose one primary ecosystem for radar/chartplotter/autopilot compatibility, but preserve independent GPS/tablet/handheld VHF. Add Starlink with waterproof mounting, 12V conversion or inverter load and a current service plan; do not rely on it for distress.

• Covered by a standard survey — power-on/function of displays, depth/speed/wind, VHF basic radio check, radar/AIS presentation and visible installation. A surveyor may not verify AIS over an external receiver or calibrate sensors.
• Not covered — network packet/termination analysis, RF power/SWR, AIS programming, radar performance calibration, transducer extraction, subscription/coverage validation and software-support roadmap. An NMEA electronics technician ($700–$2,000) is valuable before purchase for an expensive claimed-integrated suite, intermittent faults, mixed brands/generations or failed radar/AIS.

• The broker or owner — “Send model/serial/software version and invoice for every display, sensor, radar, AIS, VHF and network component.” “Provide the NMEA diagram and MMSI/registration details.” “Which functions are intermittent or unsupported, and when were charts last updated?”
• The surveyor — “Verify sensor values against independent references, check AIS transmission on another receiver/service, test VHF/DSC and radar on known targets at short and medium range, inspect network power/terminators, and identify shared single points of failure.”

Cold-boot the entire suite and note errors. Compare heading with a hand compass, position with a phone/tablet, depth with chart/tide and wind direction with a masthead visual reference. Find your AIS target on another vessel or qualified receiver. Call a radio-check service at low then appropriate power. Run radar while tied up and identify docks, buoys, rain and moving boats; check bearing alignment. Wiggle—not disconnect—suspect plugs and watch for resets.