The controls
| Control | What it does |
|---|---|
| Range | How far out the display shows. Use a short range for close-quarters work and a longer one for early warning. |
| Gain | The overall sensitivity. Too low and you miss weak targets; too high and the screen fills with speckle. |
| Sea clutter (STC) | Reduces echoes from waves near the boat. Set it too high and it removes small real targets too. |
| Rain clutter (FTC) | Reduces echoes from rain and showers, which can otherwise hide targets inside them. |
| EBL | Electronic bearing line: measures the bearing of a target. |
| VRM | Variable range marker: measures the range of a target. |
| Guard zone | An alarm that sounds when a target enters an area you set around the boat. |
Display orientation
- Head-up: the top of the screen is the way the boat is pointing. Easy to relate to what you see, but the picture swings every time you alter course.
- North-up: the top is north, like a chart. Stable and easy to compare with the chart, but needs a heading sensor.
- Course-up: the top is your chosen course, steady until you reset it.
Spotting a collision course
Put the EBL and VRM on a target and watch it. If it stays on the EBL while its range closes, it's on a collision course, the radar version of a steady compass bearing. A single glance isn't enough: the COLREGS require radar plotting or equivalent systematic observation, and warn against assumptions based on scanty radar information. See risk of collision.
Some sets can track targets automatically and show their closest point of approach (CPA). Overlaying AIS helps identify ships, but remember that not every vessel transmits AIS.
What radar can miss
- Small or low targets: yachts, especially GRP or wooden ones without a good radar reflector, small fishing boats, kayaks and debris.
- Targets in clutter: anything hidden in sea clutter close to the boat or inside a rain shower.
- Shadow sectors: areas the scanner can't see, behind the mast, a headland or a large ship.
That's also why your own yacht should carry a good radar reflector: other vessels' radar can miss you too.