Operation, Maintenance and Repair of Ship Radar Stations
Regulatory setting
Radar is required under SOLAS V/19 for ships of 300 GT and above, with two sets (including a 3 GHz unit) for 3,000 GT and above; 9 GHz X-band is the baseline. Equipment must meet IMO performance standards and be type-approved for the service. Keeping the installation operational is the master's responsibility; a defective set must be reported and, where the rules require, recorded.
Routine operation
Before starting: confirm the antenna area is clear, the scanner turns freely, nobody is working aloft, and power is available. Then power up, allow warm-up, adjust tune for maximum echo or performance-monitor indication, raise gain only until noise speckle is just visible, use sea and rain controls sparingly, select the range, and check the heading marker against a known object. Measure range with the VRM and bearing with the EBL at the leading edge of the echo, then apply gyro error.
Maintenance
Clean the display and antenna; check the dehydrator; log magnetron hours; inspect waveguide joints; check scanner motor, gearbox and slip rings or brushes; run the performance monitor; and compare displayed ranges of fixed charted objects. Keep sensible spares: magnetron, TR cell, fuses.
Repair
Internal repair and adjustment belong to holders of the ship radar endorsement; crew may operate and do user-level care only. After any repair, prove performance: performance-monitor pattern, receiver noise, range accuracy against a charted object, heading-marker alignment, and the ARPA/AIS interface.
Worked example
On the 6 nm scale, a charted breakwater light reads 5.70 nm on the VRM but lies 5.82 nm from the antenna position. Error is 0.12 nm (about 120 m); tolerance is 1 percent of 6 nm = 0.06 nm, so the reading fails. Before adjusting anything, confirm the antenna position used and check the same object on the 3 nm and 12 nm scales; a consistent offset points to range calibration or trigger delay.
Traps
- Leaving FTC (rain) on at long range, which erases weak echoes.
- Excess gain that fills the screen with noise and hides small targets.
- Treating a lit picture as proof the radar is operating correctly.
- Carrying out internal repairs without the radar endorsement.
Interference, Safety and Troubleshooting
Interference and false echoes
- Mutual radar interference: other sets on the same frequency appear as dotted radial lines, spirals or a sunflower pattern. Use interference rejection, a different PRF, reduced gain or a shorter range.
- Second-trace echoes: a target appears at a fraction of its true range because its echo returns after the next pulse. Change PRF or range scale to confirm and remove.
- Side-lobe echoes: arcs either side of a strong close target; reduce gain or use a narrower beam.
- Multiple echoes: repeated equally spaced echoes between own ship and a large reflecting target.
- Indirect (ghost) echoes: reflections from masts, funnels or cranes giving a false bearing near the real echo. Shadow sectors are genuine blind arcs and should be noted on the chart or in standing orders.
- Sea and rain clutter: STC and FTC respectively; X-band degrades more in rain than S-band.
RF and electrical safety
Peak powers at the antenna flange are hazardous. Never look into an open waveguide or flange, never stand in the main beam, and respect the manufacturer's exclusion zone ahead of the scanner. Before servicing, switch off, lock out and discharge the pulse-forming network and high-voltage capacitors; the magnetron is a strong permanent magnet and can be damaged by ferrous tools. Work aloft only with the radar secured and tagged.
Troubleshooting logic
No picture: power, fuse, breaker, display. No rotation: scanner motor, belt, drive. Picture but no echoes: transmitter (magnetron current, performance monitor), duplexer or TR cell, receiver, tune. Weak echoes and short range: ageing magnetron, moisture or arcing in the waveguide, detuned receiver, low gain. Ozone or a burnt smell: pressurization failure or a damaged flange. A bright arc close aboard is usually sea clutter, not a target.
Interference with other systems
Radar pulses can disturb GPS, VHF and AIS reception; separate antennas, use shielded cable, and recheck for blanking or interference after any installation change.
Worked example
A large ship is plotted at 4.5 nm while AIS and visual bearing put it at 9 nm; a faint echo also sits at 9 nm. Lowering the PRF makes the 4.5 nm echo vanish. Diagnosis: second-trace echo, not a close target. Action: keep a PRF or range scale whose unambiguous range exceeds 9 nm and prevent ARPA from acquiring the false echo.
Traps
- Tracking an interference pattern as if it were a target.
- Using FTC at long range and losing real echoes.
- Assuming a blank sector means a failed receiver.
- Opening the waveguide with the transmitter energized.