Early yacht radar sets were cumbersome beasts with difficult-to-interpret screens that had to be peered at down a tube. Since those days it is not just the screens that have got better, although full-colour, sunlight-viewable screens have made things a great deal easier.
What has also improved (thanks to ever greater and cheaper processor power) is the ability of radar sets to tune themselves, making interpretation of what appears on the screen vastly simpler than it used to be.
To get the most from your radar you still need to understand the various adjustments which can make the display even more helpful, although most of the time you will probably not need to alter the automatic settings.
Navigational echoes may be large, small, bright or faint - and it is important to remember that this does not necessarily relate to the size of the object. Surface characteristics, material and aspect will also affect the quality of the echo - a vertical cliff will show up better than a sloping sandbank, a small metal buoy may show up better than a large GRP yacht, and so on.
Objects close to the water, such as buoys and small boats, which bob about on the waves, do not give a consistent reflection: their echoes tend to fade and brighten and may momentarily disappear.
It's also important to understand that not all radar echoes are produced by solid objects. Some echoes may come back from the water, particularly if there are steep waves - this is called sea clutter. Rain or snow, either around the vessel or in the distance, can also produce echoes (which can be extremely useful, or a nuisance, depending on what you are looking for!)
And then there are false echoes - ghost images, indirect echoes or multiple echoes - which can be minimised by tuning: adjusting gain, sea clutter and rain clutter controls.
Tuning can be automatic or manual. Most modern yacht radar sets will do a good job if left permanently on automatic, but it is worth experimenting with the manual controls when there is good visibility, to see what effect each has on the display - and how the display corresponds with what you can actually see.
Other controls adjust the way targets appear on the display. For example, interference rejection allows you to minimise the interference - which can appear on the screen as spidery lines - caused when two or more radar equipped vessels are operating within range of each other. Target expansion allows you to make targets easier to see by making them appear bigger on the display - but at the expense of range resolution.
Another useful control is wakes which can be switched on or off, according to preference. When switched on, it gives a useful indication of the direction and speed with which targets are moving, by showing previous positions at progressively fainter levels on the screen.
Perhaps the most useful manual controls are VRM (variable range marker) and EBL (electronic bearing line) which allow the operator quickly to measure the range and bearing of any target on the display, which can be useful for both pilotage and collision avoidance.
They can also be “floated” to measure range and bearing between two targets. It is definitely worth familiarising yourself with these features by working through them with the manual in hand, practising with radar in good visibility.
Radar sets also allow the setting of guard zones and alarms which theoretically enable the radar to keep watch automatically - a feature much used by single-handed sailors crossing oceans, as it allows them to get some sleep with reasonable confidence that they will not be run down.
However, even manufacturers like Raymarine stress that radar is not intended to be a substitute for keeping a proper lookout by conventional means.
“This unit is only an aid to navigation,” it says on the first page of the owner's handbook of the set I use. “It's accuracy can be affected by many factors, including equipment failure or defects, environmental conditions, and improper handling or use. It is the user's responsibility to exercise common prudence and navigational judgements. This radar unit should not be relied upon as a substitute for such prudence and judgement.”
