RADAR part two: Start-up, setup, settings, inputs and troubleshooting
For collision avoidance and for navigation
Relevant documents and M-notices: MGN 379, Bridge Procedures Guide, MSC.192(79).
Starting the radar unit
At OOW level it is common for the examiner to ask how you start the radar on your vessel, or something to that effect. This may be asked as part of a more general question, for example ‘how do you prepare the vessel for departure’. They are looking for you to demonstrate that you know and follow best practice:
Check the antenna is clear. If you’re in port you’ll have had flags up; has a halyard parted and wrapped round the antenna?
Check that no permit to work is in force for work on the mast or monkey island.
Turn on the console, which goes into self-test mode. The antenna will turn a few times then stop as the radar warms up for a few minutes. There will be a countdown on the screen.
Re-check that the mast is clear
Switch the radar to standby to transmit. It is best practice to turn all settings down before doing this, then to bring them up one by one in a set order:
Brilliance. You need to be able to see the screen. Increase brilliance until you can see the sweeps.
Gain. This is the strength of the pulse that is sent out. Raise this until you achieve a light speckling.
Tuning. The frequency of transmission of the radar changes as it warms up and as the unit grows older. What you’re adjusting here is the frequency of the receiver, to get it as close to that of the transmitter as possible. Most radars have options for automatic tuning so it constantly adjusts to receive the strongest return signal.
Clutter. We’ll discuss sea and rain clutter in detail below.
Adjust the range scale so that it is appropriate. Consider whether to offset the radar display; this can give the benefits of a small scale display while still allowing early detection and acquisition of targets.
Radar standards are that a unit should take no more than four minutes to reach operational condition from cold, and should go from standby to operational within five seconds.
Sea clutter, rain clutter and automatic clutter suppression
When setting up the radar unit we adjust the sea clutter suppression and rain clutter suppression settings to achieve the best result. It’s worth delving into these features a bit to ensure that you have a good understanding of what they actually do.
Sea clutter is caused by radar pulses reflecting off the sea. This is most pronounced on the leading edges of waves (where they are steepest). Therefor sea clutter is normally worst on the windward aspect of the vessel and least bad on the lee aspect of the vessel.
Rain clutter is caused by radar pulses being reflected by rain, fog, sandstorms, snow etc.
Sea clutter is a sensitivity setting. Increasing this makes the radar less sensitive by increasing the number of subsequent returns needed for a target to show up. This only works on the first three to four miles of the radar display.
Rain clutter suppresses weak targets. It is a far less discriminating form of suppression and thus must be used with greater caution. It affects every returning pulse, getting rid of weak signals. It affects the whole radar display.