RADAR stands for Radio Detection And Ranging and is mainly used as a ‘ship finder’ to avoid collisions in poor visibility.
What does it do?
Radar can also be used for navigation, but with the advent of GPS has taken a back seat in this respect. It detects objects, determines their distance (range) and maps them on a screen. It consists of an antenna (scanner), that houses a transmitter/receiver and a display to give you a bird’s eye view of what’s around you.
How it works
Radio waves are transmitted from a rotating antenna, so any reflective object in the way will bounce back a small part of the signal as an echo. This reflected signal is analysed by the receiver to show the target’s range and bearing on the display.
What to look out for
Radar’s horizontal beam width is determined by the antenna: the longer the antenna, the narrower the beam. If a 2° beam hits a metal post it will paint a 2° mark on the screen, but a 6° beam will paint a 6° mark – so the thin post now looks like a boat. Narrow beams give better detailed images of targets but the size of the antenna is controlled by space and power constraints.
There are two types: radomes and open arrays. The radome has the spinning antenna inside it, so it is less likely to snag halyards, and is compact, lightweight, and has relatively low energy consumption. Open array antennas are more efficient and the larger ones offer narrower beam widths – but they also have increased power demands which makes them more suitable for motorboats.
If you just want radar to spot big ships then many people are satisfied with a small mono screen and a wide beam width. But colour screens are getting cheaper and are being combined with things like chart plotters so that both can be displayed on a split screen, or with a radar overlay. For the amateur, radar pictures are hard to interpret so having it combined with a chart plotter picture lets you see that if a blob isn’t on the chart it’s probably a ship. The down side is that splitting the screen gives you a smaller radar picture, though some manufacturers no longer sell a dedicated radar display.
Ease of use
Radar displays usually show relative motion. In other words if a vessel was doing the same speed as us, on the same heading, he would be represented by a stationary blob at a fixed distance from us. If we stopped, the blob would move away up the screen as it would be showing true motion.
Relative motion can be hard to understand, but it is good for collision avoidance because any blob heading for us in the centre of the screen is likely to hit us. Knowing which way to turn to avoid this collision means you must understand relative motion and be able to do a radar plot.
Some radars have automatic tracking aids such as Mini Automatic Radar Plotting Aid (MARPA), target tracking, Automatic Tracking Aid (ATA) and Electronic Plotting Aid (EPA). These will do the radar plot for you and display the other ship’s movement in vector form –
but the display must also be stabilised with some form of heading sensor. The Col Regs (IRPCS) say that ‘proper use shall be made of radar equipment if fitted and operational,’ so you must be able to use it correctly and that ‘every vessel shall at all times maintain
a proper look-out by sight and hearing’. But in poor visibility there is no stand-on vessel so
Col Regs Rule 19 takes over.
HD and Super HD Digital Radars
Raymarine’s new Super HD and HD Digital radar technology – is truly revolutionary. HD Digital technology improves target detection by eliminating virtually all noise and extracting more information from the radar echo return than has ever been generally available to the leisure navigator before. HD Digital radar extracts more information, targets that merge with standard radar displays can be identified more clearly with HD Digital. For example, vessels at low tide close to mud banks would merge with standard radar, whereas HD Digital can separate them for a clearer picture – targets with different frequencies are ‘tagged’ with different colour for clarity. Super HD Digital adds another level of digital signal processing to further enhance the performance and improve the resolution, providing stunning multi-level colour target displays with extra clarity and detail.
Finding the right radar for you
HD and Super HD Digital Radar:
The Super HD Digital secret is Digital Signal Processing, delivering performance and target recovery in a 4kW package to rival that produced by conventional 25kW radar.
HD Digital Radome Radar Antennas:
HD Digital technology is now available in new full colour Raymarine radome systems; bringing colour target distinction, clarity and resolution capabilities to the space-saving 18″ 4kW radome and the larger 24″ 4kW superior resolution radome.
Click here for the full range of Raymarine radar systems.