Having radar can be a double-edged sword: Under the gaze of an experienced operator, it can provide eyes where there is no visibility, but with an inexperienced captain, it can provide confidence where there should be none.
Case in point: 24 miles off the coast of Ocean City, Maryland, during the summer of 2004, a 22-foot center console was nearly mowed down by a 36-foot convertible running at 22 knots through a fog so thick that the outrigger tips were leaving wakes. I happened to be standing on the deck of the smaller boat, and we had the convertible on radar long before its bow suddenly broke out of the mist. Moments before the targets merged onscreen, with the rhythmic sound of twin diesels roaring closer by the second, we nailed the throttles. Our boat jolted forward as the convertible materialized, then ran through our wake no more than 20 feet astern. In the few seconds the other boat was visible, I looked at the bridge and made eye contact with the captain. He was someone I knew from the docks, whose boat was just five or six slips down from ours. From his bugged-out eyes and slack jaw, I knew he realized just how close a call it had been; then within seconds, he faded back out of sight.
LENNY RUDOWOn days with low visibility, you'll need that radar for safe navigation.That evening as we washed down the boat, he approached us to apologize. "I just don't get it," he said. "I was watching the radar, but never saw your boat at all." We walked down to his boat and turned on his unit. Immediately, I saw what had happened. In an effort to clean up the on-screen view, he'd upped his anti – anti-clutter, that is – and lowered the gain. But he forgot that small fiberglass boats provide poor radar returns, which can sometimes be eliminated entirely by over-tuning the radar. If he'd had a better understanding of how radar works, he would have learned how to peer through some clutter and recognize solid returns from the false ones.
Do you know how to use your radar to its fullest abilities? If not, start now.
THE BASICS
Picture yourself standing in a dark field, holding a powerful spotlight. Shining it into the abyss, you see nothing. As you turn in a circle with the spotlight parallel to the ground, halfway around it briefly illuminates a tree 50 feet away. That brief moment of illumination is similar to the way radar picks out targets, except it uses a microwave pulse to illuminate solid items.
As the radar antenna – used for both transmitting and receiving – rotates, shooting out those rapid pulses of energy, it notes the reflection from a solid target, then alerts the radar's "brain" to its existence. A mathematical calculation involving the amount of time the pulse took to be reflected is then performed, which gives the unit an exact distance to the target. The radar then paints a blip on screen in the corresponding location. Large pulse reflections are painted with big blips, and weak ones are represented with small blips.
GARMINA smaller antenna (usually enclosed in a dome) has a wider beam width.In the grand scheme of things, size differences on screen are a poor indicator of reality, as a 300-foot tanker may appear just a little larger than a 40-foot sailboat. But there's a bigger problem: Fiberglass and wood don't reflect microwave pulses well. Worse yet, they're designed with smooth, rounded, sleek lines, which deflect radar beams. In fact, unless a fiberglass boat is really large and has lots of metal on it, chances are it'll provide a weak return – weak enough to dial out, if you set your radar wrong.
Won't a more powerful radar provide better returns from farther away, and pick up that fiberglass boat? Not necessarily. In fact, power is just one factor. First, consider a radar's ability to pick out weak targets. Contrary to popular belief, the amount of power your radar zaps a target with isn't the best lone determination of how good a return it will get. Beam width is a key factor.
Think of that flashlight again. Set the beam to a tight spotlight, and it'll penetrate the darkness. But widen it to floodlight setting, and it can't shine nearly as far. Radar beams work the same way. A wide beam width – say, six degrees – paints a pretty weak picture. But a tight, two-degree beam width penetrates the darkness and picks up smaller, farther returns far better. That's why anglers, who may use a radar to search for birds (which indicate feeding fish below), often choose units with beam widths as low as 1.2 degrees.
GARMINA larger, more expensive antenna has a tighter beam and can see better at a distance.Wattage is, of course, still an important factor. Just like that flashlight, more power will illuminate farther into the distance. Low-end units putting out a mere 2 kilowatts can't be expected to "see" much farther than 16 to 20 miles, and weak returns like a small fiberglass boat aren't likely to show up from more than a mile or two away. Four-kilowatt units usually fall into the 32-mile range, and will see weak returns a bit farther, while more powerful units can see farther still.
So power and beam width work together to determine how weak a target your radar will be able to detect. But, when it comes to how far that radar can see returns from, there's still one more factor: the curvature of the Earth. Because we can't bend the horizon or the microwave beams we send out to it, the combination of the height of your radar antennae and the height of the target you're looking for will determine just how far your radar's eyes can see. The formula that expresses the relationship between the height of the target and height of the radar antenna is 1.22NM x square root Height of radar + 1.2NM x square root Height of target. Thus, if your radome is mounted on a hardtop that's nine feet above sea level, and you're looking for a target that's nine feet off the water, your range to that target is 1.22 x 3 + 1.22 x 3 = 3.66 + 3.66 = 7.32. No mater how powerful your radar may be, no matter how narrow its beam width, it won't see that nine-foot-tall marker in the inlet until your boat is 7.32 nautical miles or less away.
TUNING IN
Of course, your radar's ability to see must be translated into your own ability to see them, on screen – and how your unit displays targets is another key feature to consider. The first step to proper radar operation is making sure your unit is tuned correctly. Don't trust the manufacturer to have tuned it for you; each installation is different, so this is essentially impossible. Although most modern units have fairly competent auto-tuning functions, they aren't perfect, and if you've never manually tuned your unit, you must assume it's not functioning at its best.
