The Vestas Wind debacle raises points about maximizing your radar picture.
I firmly believe that a good pair of eyes is the most indispensable navigational device currently available, so long as you can see, and there is something to be seen. But sometimes we turn to radar because it can see things that we can’t, such as breaking seas on a reef at night a couple of miles ahead. Salt water, it turns out, provides a very good radar echo so that even if there is no large land mass, radar can pick up surf. That Vestas Wind grounded on a reef with breaking seas makes one wonder just how closely the radar was being monitored, and if the picture was properly adjusted to give warning of the danger ahead.
Gain and tune are your two most important radar picture controls. Back in the day, we were taught to think of gain much like the volume knob on a transistor radio. If the volume is too high, the song is loud but distorted. If the volume is too low, you can’t hear the song. Likewise, when gain is too high, echoes are blotchy and distorted but if it is too low, targets may not show up. Similarly, tuning a radar is like tuning a radio: If you are too far to the right or the left on the dial, the station won’t come in. With radar, we move the tune adjustment back and forth until the echoes are strongest. With both gain and tune, the operator uses his or her eyes to determine when the picture is ideal for the situation.
Nowadays, most radars offer “automatic” adjustments: auto-tune, auto-gain and auto suppressions (sea clutter and rain clutter). I have used these features to good effect but here’s what you need to remember about all auto-adjustments: they are automatic. They adjust themselves. They do not ask for your involvement or your opinion. Most importantly, they cannot intuit your priorities on a given day or night. Auto adjustments provide a nicely balanced picture that a manufacturer in a distant place has determined is good for most situations. But there is no such thing as a single optimal picture for all situations. There are times when the operator needs to take control and customize the picture.
Top, a short pulse nicely defines docks to port, but not targets well ahead.
Bottom, a longer pulse better displays targets but distorts docks.
For example, offshore at night your highest priority is the early detection of land and/or ships; you want to know what is out there. Therefore, you may elect to use more gain, even if it produces more clutter close to your vessel. You don’t care about the clutter nearby because it is a lower priority under the circumstances. In close quarters where detection is less of a challenge, you might want better resolution nearby so you can match the radar outline of the shore to that on the chart. Backing off the gain can help with this. Remember though, the choices are situational, not necessarily automatic. Though the crew of Vestas Wind had no inkling that they should even be looking for a reef, more aggressive use of gain may have shown the ribbon of breaking surf out ahead, and thereby gotten their attention.
But there’s more to it. Changes to the range scale also require readjustment of tune and gain. For instance a radar that is properly adjusted for the 12-mile range scale will probably have too much gain on the 6-mile scale, and certainly at the 3-mile scale. What is optimal at one range will not be at another. Auto-adjustments may or may not handle these kinds of range-related changes, therefore the operator needs to know at least this much about what’s going on inside the box.
The big thing most operators overlook is pulse length. If this sounds like it’s about to get technical, it isn’t. Basically, on long ranges (usually 12 miles or more) radars send out a long pulse length to make up for the fact that some of the transmitted energy gets lost on the journey out and back. A long pulse for long ranges insures that enough energy makes it back to paint an echo on your screen. Short ranges (1.5 miles or less) use a short pulse length that gives a cleaner picture when detail and picture resolution are a priority. Medium ranges use a medium pulse for everything in between. Pulse length, therefore, is automatically linked to range scale.
However, all radars make it possible to override the default pulse length and pick one more suitable for the situation. For instance, under some circumstances you may be ranged down in the fog to, say, a mile and a half but because of the presence of small recreational craft, kayakers, or other weak targets you might still select a medium or long pulse. The extra energy coming back will distort the picture, creating large blobs out of relatively small targets, but you will know who is there and that may be more important than a pretty radar picture. Conversely, a medium pulse on a medium scale may not give you the detail that you want under the circumstances. And selecting the short pulse may cause weaker targets to become intermittent, but if it gives you a clearer picture of your priority targets, it may be worth it for a short time.
Like all of our tools, radar, has its limitations and it too can fool the operator. But the premise of using echoes to detect targets is so fundamentally incorruptible that, as long as your radar is adjusted properly for a given situation, it is unlikely to deceive. But getting the most out of your radar requires constant engagement, not passive acceptance of prescribed auto-data. Indeed, engaging more deeply with your radar set will make you a much better navigator, even if you do use auto features much of the time.
This article originally appeared in the April 2015 issue of Power & Motoryacht magazine.