Start hereRules checked 20 October 2026
Radar is the instrument officers trust most when visibility closes in, and it is easy to trust it too much. A heading line a couple of degrees out, a magnetron that has lost half its power, or a gyro input that has silently frozen will all still give a clean-looking picture. The targets are simply in the wrong place, or missing.
The IMO performance standard for radar, resolution MSC.192(79), sets measurable limits for accuracy, tracking and alarms, and SOLAS requires radar installed from 1 July 2008 to meet it. This lesson turns those limits into checks you can do on the bridge and that a service engineer or surveyor will do with test equipment.
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In this lesson
- Pre-departure check of the radars on a 12,000 GT bulk carrier
- In plain words
- In detail
- What the rules say
- Flag and class notes
- Key numbers
- What inspectors find
- Quiz: 6 questions
Try it
Pre-departure check of the radars on a 12,000 GT bulk carrier
In plain words
A ship’s radar sends out short pulses of microwave energy from a rotating antenna and listens for echoes. From the time each echo takes to come back it measures range, and from the antenna’s direction it measures bearing. The display paints these echoes around the ship and, with heading from the gyro and speed from the log or GNSS, can show the picture north-up and calculate how other ships are moving.
Every ship of 300 GT and above carries an X-band radar (around 9 GHz, good detail and needed to see search and rescue transponders). Ships of 3,000 GT and above add a second radar, usually S-band (around 3 GHz), which sees better through rain and sea clutter. The tracking function, still often called ARPA, follows selected targets and works out their course, speed, closest point of approach (CPA) and time to it (TCPA).
The radar is only as good as three things: the radar itself (transmitter power, receiver sensitivity, antenna), its alignment (the heading line must point exactly where the bow points), and its inputs (gyro heading, speed, position). Each can fail in ways that leave a convincing but wrong picture. Good officers check all three before departure and whenever something looks odd.
In detail
What the standard requires
Resolution MSC.192(79), adopted in December 2004, applies to radar installed on or after 1 July 2008. Its Table 1 scales the requirement with ship size:
| Ship size | Minimum operational display diameter | Acquired radar targets | Activated AIS targets | Sleeping AIS targets | Auto acquisition | Trial manoeuvre |
|---|---|---|---|---|---|---|
| Under 500 GT | 180 mm | 20 | 20 | 100 | No | No |
| 500 to under 10,000 GT (and HSC under 10,000 GT) | 250 mm | 30 | 30 | 150 | No | No |
| 10,000 GT and over | 320 mm | 40 | 40 | 200 | Yes | Yes |
Key performance figures:
- Range accuracy: within 30 m or 1% of the range scale in use, whichever is greater (5.2). Fixed range rings must meet the same limit (5.11.2).
- Bearing accuracy: within 1 degree (5.2).
- Heading line: electronic means to align it to within 0.1 degree; with more than one antenna, each antenna’s heading skew is stored and applied automatically (5.14.2).
- Consistent common reference point (CCRP): all measurements from own ship are made from one reference point, usually the conning position, with offsets for each antenna entered at installation (5.9.1).
- Range scales: 0.25, 0.5, 0.75, 1.5, 3, 6, 12 and 24 NM must be provided (5.10.1).
- Performance monitoring: a means, automatic or manual, to detect “a significant drop in system performance relative to a calibrated standard established at the time of installation” (5.7.3).
- Target tracking: trend within 1 minute and prediction within 3 minutes after acquisition (5.25.4.1); tracking continues for targets clearly visible on 5 of 10 consecutive scans (5.25.4.3).
- Sensor failure: failure of the gyro, log, azimuth, video, sync or heading marker should be alarmed (5.34.2). If heading stabilisation is lost, the radar must switch automatically to unstabilised head-up within 1 minute and indicate that only relative bearings can be used (9.1).
- SART detection: the X-band radar must be able to detect SARTs and radar beacons (5.3.4.2).
On-board checks you can do
These are routine checks for the bridge team. They do not replace the manufacturer’s maintenance schedule.
- Heading line. Alongside or at anchor, take a visual bearing of a distant, well-defined object right ahead (or at a known relative bearing) and compare with the radar. Any consistent offset of more than a fraction of a degree means the heading line needs re-alignment by a technician.
- Range. Compare radar ranges of charted, radar-conspicuous objects with charted distances, allowing for the CCRP. Use the formula: limit = the greater of 30 m and 1% of the scale in use.
- Performance monitor. Read it at regular intervals and log the value. A downward trend shows magnetron ageing or waveguide problems long before the picture looks poor.
- Inputs. Check the gyro heading on the radar against the master gyro and the magnetic compass, and speed against the log and GNSS. Note the source shown for each input.
- Tracking. Acquire a known target and watch that the trend and vector appear in the required time and look sensible.
- Alarms. Use the manufacturer’s test functions where provided. Do not disconnect sensors to test alarms unless the manual says so.
- SART. When the SARTs are tested, check that the response appears on the X-band radar.
What the surveyor and technician check
At the initial survey the surveyor examines the radar, “including examining the waveguide and cable runs for routeing and protection and the display unit confirming lighting, correct operation of all controls, and functions”, and checks the plotting or tracking aids “using the appropriate test facilities”. At every annual survey they confirm the radar and tracking aids are in working order and that the shadow sector diagram is displayed. A service engineer goes further: magnetron current and hours, transmitted power, receiver noise figure and tuning, antenna motor and bearings, and the alignment and offsets set at installation.
SOLAS regulation V/18 sets an annual third-party test for the VDR and the AIS only. For radar, keeping it in working order is the owner’s and master’s duty under regulation V/16, supported by the manufacturer’s maintenance programme and the survey checks.
What the rules say
- SOLAS regulation V/19.2.3.2 requires ships of 300 GT and upwards and all passenger ships to carry a 9 GHz radar, and V/19.2.7.1 requires a second radar, 3 GHz or a second 9 GHz, from 3,000 GT.2
- Resolution MSC.192(79), operative paragraph 2, recommends that radar installed on or after 1 July 2008 meets the revised performance standards.1
- MSC.192(79), paragraph 5.2, requires range accuracy within 30 m or 1% of the range scale in use, whichever is greater, and bearing accuracy within 1 degree.1
- MSC.192(79), paragraph 5.14.2, requires electronic means to align the heading line to within 0.1 degree.1
- MSC.192(79), paragraph 5.7.3, requires a means to determine “a significant drop in system performance relative to a calibrated standard established at the time of installation”.1
- MSC.192(79), paragraph 5.34.2, requires failure of any signal or sensor in use, including gyro, log, azimuth, video, sync and heading marker, to be alarmed.1
- MSC.192(79), Table 1, requires automatic acquisition and trial manoeuvre on ships of 10,000 GT and upwards and sets the minimum number of tracked radar targets at 20, 30 or 40 by ship size.1
- The HSSC Survey Guidelines, 2025, paragraphs (EI) 1.1.4.33.9 and 1.1.4.33.10, require the surveyor to examine the radar and its plotting or tracking aids, and (EA) 1.2.1.20 to confirm the radar shadow sector diagram is displayed.3
- SOLAS regulation V/16.2 allows a ship with malfunctioning navigation equipment to proceed to a port where repairs can be made, if the master takes the failure into account in planning a safe voyage.4
Flag and class notes
- United Kingdom. MGN 610 stresses that radar performance depends critically on antenna siting and on accurate harmonisation with other equipment using the consistent common reference point, as set out in the IMO and IEC standards.6
- Annual servicing. Neither SOLAS nor the IMO survey guidelines set a fixed annual radar service. Some owners and flags require periodic manufacturer servicing; check your flag circulars, your class’s survey checklist and the manufacturer’s maintenance schedule.3
- Replacing a radar. Replacement radar must be type-approved and meet the performance standards in force at installation, under SOLAS regulation V/18. Update the Record of Equipment, the CCRP and antenna offsets, the shadow sector diagram and the VDR interface.6
Key numbers
| What | Value |
|---|---|
| Radar range accuracy | 30 m or 1% of range scale in use, whichever is greater1 |
| Radar bearing accuracy | within 1 degree1 |
| Heading line electronic alignment | to within 0.1 degree1 |
| Tracked target trend shown within | 1 minute1 |
| Tracked target prediction shown within | 3 minutes1 |
| Fallback to unstabilised head-up after heading loss | within 1 minute1 |
| Minimum acquired radar targets (under 500 / 500–10,000 / over 10,000 GT) | 20 / 30 / 401 |
| X-band and S-band frequency ranges | 9.2–9.5 GHz and 2.9–3.1 GHz1 |
| MSC.192(79) applies to radar installed from | 1 July 20081 |
What inspectors find
- Navigation equipment not working. “Absence or failure of the proper operation of navigation equipment, taking the relevant provisions of SOLAS 1974 regulation V/16.2 into account” is a ground for detention in the IMO Procedures for port State control, 2025.5
- Officers who cannot use the equipment. The same procedures list deck officers unable to demonstrate the operation of essential navigation equipment, and lack of awareness of how to test it, as operational deficiencies.5
- Missing shadow sector diagram. A specific annual survey item that is easy to lose when a bridge is refitted.3
- Safety of navigation overall. The Tokyo MOU named safety of navigation as one of the four major deficiency categories in 2024, with 8,066 deficiencies.7
FAQ
How often should the heading line be checked?
The standard does not set an interval. Good practice is to check it whenever there is a chance, such as alongside with a clear object ahead, after any work on the antenna or gyro, and if radar bearings and visual bearings disagree. Record the result.
Why does my S-band radar not show the SART?
Radar SARTs transmit on 9 GHz, so only the X-band radar can show them. MSC.192(79) requires the X-band radar to be able to detect SARTs; the operating manual should explain any special settings, such as switching off certain clutter processing.
Is ARPA still the right term?
SOLAS V/19 still uses “automatic radar plotting aid” for ships of 10,000 GT and upwards. MSC.192(79) uses “target tracking” for the function inside the radar. In practice they mean the same capability on a modern radar.
Our radar was replaced. Does the VDR need attention?
Yes. The radar picture is a VDR data item. Make sure the new radar is connected to the VDR and the change is entered in the VDR maintenance records; it will be checked at the next VDR annual test.
Quiz6 questions
Sources
- 1
IMO Resolution MSC.192(79), Adoption of the revised performance standards for radar equipment (adopted 6 December 2004), operative paragraph 2 and annex paragraphs 2 (Table 1), 5.1.2, 5.2, 5.3.4, 5.7, 5.9, 5.10, 5.11, 5.14, 5.25, 5.31, 5.34 and 9.1. https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/MSCResolutions/MSC.192(79).pdf
- 2
SOLAS 1974, as amended, chapter V, regulation 19, paragraphs 2.3.2 and 2.7.1. IMO consolidated edition (sales publication). https://www.imo.org/en/About/Conventions/Pages/International-Convention-for-the-Safety-of-Life-at-Sea-(SOLAS),-1974.aspx
- 3
IMO Resolution A.1207(34), Survey Guidelines under the Harmonized System of Survey and Certification (HSSC), 2025, annex, paragraphs (EI) 1.1.4.33.9, 1.1.4.33.10, (EA) 1.2.1.20 and 1.2.2.35. https://wwwcdn.imo.org/localresources/en/OurWork/IIIS/Documents/A%2034-Res.1207%20-%20SURVEY%20GUIDELINES%20UNDER%20THE%20HARMONIZED%20SYSTEMOF%20SURVEY%20AND%20CERTIFICATION%20(HSSC),%202025%20(Secretariat).pdf
- 4
SOLAS 1974, as amended, regulation V/16.2, as reproduced in MCA MGN 610 (M+F), page 14. https://assets.publishing.service.gov.uk/media/5f2140d3e90e071a603d33b3/MGN_610_2020.pdf
- 5
IMO Resolution A.1206(34), Procedures for port State control, 2025 (adopted 3 December 2025), appendix 2, section 5, item 10, and appendix 7, paragraphs 5.1.2 and 5.1.3. https://wwwcdn.imo.org/localresources/en/KnowledgeCentre/IndexofIMOResolutions/AssemblyDocuments/A.1206(34).pdf
- 6
Maritime and Coastguard Agency, MGN 610 (M+F), SOLAS Chapter V guidance, guidance on regulations 18 and 19. https://assets.publishing.service.gov.uk/media/5f2140d3e90e071a603d33b3/MGN_610_2020.pdf
- 7
Tokyo MOU, Annual Report on Port State Control in the Asia-Pacific Region 2024, Table 7. https://www.tokyo-mou.org/wp/wp-content/uploads/ANN24-1.pdf
Rules checked 20 October 2026. VSL Safety is not an approved training provider and doesn't issue certificates. These lessons don't replace STCW training, or the manufacturer's training and certification that service technicians need.
