General
It is important that watchkeeping officers are completely familiar with all the navigational and communications equipment, charts and publications on board.
Bridge watch keeping officers should acquaint themselves with the contents of operating manuals for equipment, particularly with regard to the setting up of controls and the procedures to be followed in the event of equipment failure.
Periodic checks on the equipment should be carried out. Equipment found to have operational defects should be brought to the attention of the master and recorded in the logbook and on the Pilot Card.
Regular preventive maintenance of all equipment should be carried out according to instructions set out in the shipboard maintenance procedures manual and manufacturers' manuals.
A full set of charts and publications appropriate for the intended voyage should be available on board and kept up to date.
Radar
The OOW should be familiar with the differences between X and S-band radars, and be aware that the X-band radar will be capable of operating in the 9 GHz frequency band for the detection of search and rescue transponder (SART) devices.
On ships fitted with a radar installation that includes an inter-switching unit to allow radar displays to change transceivers, the OOW should be familiar with arrangements to by-pass the unit should it fail.
Good radar practice
It is recommended that a radar is kept running and fully operational at all times. When using radar the OOW should bear in mind the following:
• the quality of performance of the radar needs to be continuously monitored: a performance monitor, if fitted, should be used for this purpose;
• an incorrectly aligned heading marker can give rise to misleading interpretations of potential collision situations: heading marker alignment needs periodically checking against both the compass heading and the fore and aft line of the ship;
· small vessels, ice and other floating objects such as containers may not be detected by the radar;
· video processing techniques should be used with care;
· echoes may be obscured by sea or rain clutter: the careful use of clutter controls will assist;
· masts or other structural features may cause shadow or blind sectors on the display: the OOW should be aware of these sectors.
Clear weather practice
Operating the radar at sea in clear weather will provide an incentive for
watch keepers to practise their radar collision avoidance and navigation skills; for example, radar observations and target vectors can be checked visually, and in safe waters parallel index techniques can be perfected.
Range scales
The choice of range scales will depend upon factors such as traffic density, speed of own ship and how often the radar is being observed.
Detection of targets, particularly small targets, is generally better at short ranges. However, if the radar is to be used for plotting it is not advisable to use a scale that is too short.
Advance warning of approaching vessels and land is an important factor in deciding upon a safe speed and requires the monitoring of longer range scales.
Radar and collision avoidance
Accuracy of own ship speed and heading inputs
In radar plotting, measurement of the course, speed and aspect of a target is used to determine the closest point of approach of that target and to indicate whether or not there is a risk of collision.
The accuracy of the target plot will depend upon an accurate input of own ship's course and speed during the plotting interval; a yawing ship or inaccurate speed and heading inputs into the radar will reduce the accuracy of calculated target vectors.
Plot inaccuracies will be most apparent in head-on situations and may make a target appear to be passing clear when in fact it is crossing ahead or nearly ahead.
The plotting period
A single observation of the range and bearing of a target cannot give any indication of target course and speed. Multiple observations are required, and the longer the plotting period, the greater will be the accuracy.
Accuracy in the plot will however be lost if either own ship or the target changes course or speed during the plotting period. A change in the course or speed of the target may not be immediately detected.
The estimation of the course and speed of the target and risk of collision is only valid up to the time of the last observation. The situation must therefore be kept closely under review.
Changing target bearing
It should not be assumed that because the relative bearing of a target is changing, there is no risk of collision. An alteration of course and/or speed of own ship may alter the relative bearing, and at close quarters, risk of collision can exist even with a changing compass bearing.
