With the ever-growing use of chart plotters, GPS and AIS it's easy to forget how important and effective RADAR can be. It's still an important part of the sailor’s armoury when performing his duties under maritime law, specifically maintaining a watch by all means available.
Nowadays, many yachts which have chartplotters are able to overlay a RADAR signal over an electronic chart or, at least, alongside it on the screen. This can be extremely reassuring when navigating busy shipping lanes or coastal waters when in poor visibility or fog. There is usually a RADAR standby mode which allows the operator to save power when it's not needed.
RADAR can be presented ‘North Up’ or ‘Heading Up’ and various electronic filters can be applied to better define targets. Many chartplotters will now also overlay AIS information which can be very useful when confusing data is being presented by radar or GPS.
RADAR is usually presented on screen by way of a central transmitting point (the boat) and then a 360 degree transmit / receive range measured in radial bands, the scale of which can be changed by pressing a button. The radar transmits in clockwise circular sweeps and targets ‘blip’ on the screen. The radar can be tuned using the gain control and anti clutter filters (for example, to try and reduce pollution from rain showers).
Once a specific target has been identified an EPL can be set (electronic position line). If the target remains on the line as it closes then it must be maintaining a constant bearing to the RADAR transmission source and is, therefore, a collision risk. The distance to target is taken from the radial rings which can be scaled up or down as required. Using distance covered over time and bearing to target, we can identify the position and speed of a target thus making VHF communication effective. Position lines can also be used to take a bearing and distance off definable landforms, like headlands, etc. Modern RADAR may have ARPA (automatic radar plotting aid) which makes using RADAR even easier.
It's worth remembering that RADAR works best when bouncing off three dimensional metal surfaces. This is why many fibreglass yachts also carry a radar reflector high on their mast to better aid their detection by other vessels.
Finally, when operating radar it's imperative that people do not have the opportunity to pass directly in front of the transmitter. This is a particular risk when someone is scaling the mast in front of the transmitter.