What to check on a Marine Radar.
Marine radar is the one sensor on the bridge that builds its own picture of the world instead of trusting a satellite or a shore station — it transmits a pulse, times the echo, and paints range and bearing to every solid object nearby, in fog, rain or full darkness. The type splits by frequency: X-band (9 GHz, roughly 3 cm wavelength) gives sharp detail and good small-target and coastline definition but is more affected by rain clutter; S-band (3 GHz, roughly 10 cm wavelength) sees through heavy rain and…
What defines this type
Marine radar is the one sensor on the bridge that builds its own picture of the world instead of trusting a satellite or a shore station — it transmits a pulse, times the echo, and paints range and bearing to every solid object nearby, in fog, rain or full darkness. The type splits by frequency: X-band (9 GHz, roughly 3 cm wavelength) gives sharp detail and good small-target and coastline definition but is more affected by rain clutter; S-band (3 GHz, roughly 10 cm wavelength) sees through heavy rain and sea clutter better but with coarser resolution. SOLAS ties the requirement directly to gross tonnage rather than ship type, which is why the same radar package appears on a bulk carrier and a cruise ship of comparable size.
Main components
Scanner (antenna) unit
The rotating slotted waveguide array that transmits the pulse and receives the echo; its length sets horizontal beam width, and beam width sets how finely two close targets can be told apart.
Transceiver
Generates the transmit pulse — either a magnetron (pulsed, cheaper, ages and needs periodic replacement) or solid-state transmit/receive modules (pulse compression, longer service life, faster warm-up, no magnetron replacement cycle).
Waveguide or coaxial run
Carries the RF energy between transceiver and antenna; on mast-mounted transceiver-integrated antennas this run is short, which cuts signal loss versus a below-decks transceiver feeding a long waveguide run up the mast.
Display / processor with ARPA
Automatic Radar Plotting Aid processes successive echoes into tracked targets with course, speed and closest point of approach, and is the layer that actually supports collision-avoidance decisions rather than raw echo painting.
Selection / Sizing
| Parameter | What it drives |
|---|---|
| Band (X or S) | Target definition vs. penetration through rain/sea clutter |
| Antenna length | Horizontal beam width and bearing discrimination |
| Peak transmit power | Maximum usable range and small-target detection |
| Number of ARPA tracked targets | Usable in dense traffic (VTS areas, straits) |
| Transceiver type | Magnetron replacement cycle vs. solid-state service intervals |
Tonnage sets the legal minimum, but traffic density on the intended trade is the practical driver — a vessel working the English Channel or Singapore Strait benefits from the higher ARPA target count and dual-radar redundancy well beyond what SOLAS mandates for its size.
Regulations / Class
SOLAS Chapter V, Regulation 19 sets the carriage requirement: every ship of 300 GT and above must carry a 9 GHz (X-band) radar; ships of 3000 GT and above must carry a second radar operating on a different frequency (S-band), giving redundancy if one band is degraded by weather or fails outright. IMO resolution MSC.192(79) sets the performance standard — minimum range scales, target discrimination, and ARPA tracking capacity that a type-approved set must meet. ARPA itself is mandatory on ships of 10,000 GT and above under the same SOLAS chapter. Class and flag surveys check the radar against its type approval certificate and confirm the required annual performance test has been logged.
Typical faults
- Magnetron ageing — output power drops gradually, shrinking effective range long before the set fails outright; often only caught by a proper performance monitor test, not by eye.
- Waveguide moisture ingress — a cracked or poorly sealed waveguide run lets in water, arcing the RF path and cutting transmit power sharply.
- Antenna motor or bearing failure — scanner stops rotating or rotates unevenly, corrupting the displayed picture without an obvious alarm.
- Poor clutter tuning — sea and rain clutter controls left on a fixed setting mask small targets such as fishing boats or debris, a repeat factor in collision investigations.
- ARPA tracking loss in clutter — dense small-target environments (fishing fleets, archipelagos) exceed the tracker's ability to hold locks, and targets silently drop off track.
What to look for in a supplier
- Current IMO/SOLAS type approval certificate for the specific model and software revision, not just the product family.
- Solid-state vs. magnetron transceiver, and for magnetron sets, confirmed availability of replacement magnetrons for the vessel's remaining service life.
- Integration compatibility with the ship's existing ECDIS and AIS so target data and overlays share a common display rather than sitting on a separate isolated screen.
- A service network that can reach the vessel's actual trading routes, not just the flag state's home port.
Run the performance monitor check at the start of every watch handover in poor visibility, not just at the scheduled interval — a magnetron losing power shows up as a shrinking range ring long before it shows up as an alarm.