Radar and Automatic Radar Plotting Aids (ARPA)

The master should ensure that at least one radar is available for use by the officer of the watch:

— as an instrument for fixing and monitoring positions;

— as an aid for assessing the risk of collision;

— for practising plotting, parallel indexing, etc.

The radar should be switched on in sufficient time before it is required in order to establish that it is operating correctly and to adjust it to obtain optimum performance.

If weather conditions are such that visibility may deteriorate, the ship’s radar should be operating or at standby. In reduced visibility the radar should be operating continuously and the display should be observed as frequently as the prevailing circumstances require.

The life and operating efficiency of radar sets are affected less by continuous operation than by frequent switching on and off. Therefore in periods of reduced visibility it is better to keep the radar operating or at standby. It two sets are fitted, one should be operating at all times.

The performance of the radar equipment should be checked before sailing and at least once every four hours while radar watch is being maintained. Where fitted, a performance monitor should be used for this purpose.

Whenever the ship’s radar is switched on and at the commencement of each watch if the radar is in operation, the trace should be checked — and if necessary adjusted — to ensure that it is rotating about the centre of the display. At the same time the alignment of the heading marker should be checked as shown in the operating manual.

When using radar for fixing or monitoring the ship’s position the following should be checked:

— the radar’s overall performance;

— the identity of the fixed objects observed;

— gyro error and the accuracy of the heading marker;

— the accuracy of the variable range marker, bearing cursor and fixed range rings;

— on true motion, that the display is correctly ground stabilised.

When operating ARPA, the use of audible operational warning signals to denote that a target has closed to a particular range, or that it is transiting a selected guard zone, does not relieve the master or the officer of the watch of the duty to maintain a proper lookout by all available means. When the ARPA is operating in an automatic acquisition mode, such warning devices should be used with caution, especially when in the vicinity of inconspicuous radar targets. Users should familiarise themselves with the effect of errors on the automatic tracking of targets as described in the ARPA operating manual.

When reduced visibility is encountered or expected, a radar plot should be promptly established. A reduction of speed may allow more time for plotting. The high standard of proficiency necessary for the use of radar in reduced visibility will not be achieved unless regular anti-collision and plotting practice is carried out. The master should ensure that all officers of the watch practice radar plotting regularly in clear weather, particularly when approaching coastal waters after a long ocean passage.