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.

Start off by warming up the radar for at least 10 or 15 minutes. Radar frequencies can vary by tiny amounts as your unit changes temperature, so you want it to be constant when you're tuning up. You also need a calm, clear day, because you'll need to shut off the rain- and sea-clutter functions. Then run at least five or six miles from land, and pick out a target that's weak but consistent; small fixed channel markers or a large fiberglass boat with little metal often work well. Set the unit's gain high enough that some single-pixel dots just begin to appear on screen, then adjust the tuning setting up and down until you get the cleanest, sharpest picture.

Now that you're all tuned up, you need to set the gain. Again, make sure all clutter functions are turned off. Now turn up the gain until those tiny specks start appearing on screen again. Leave the gain high enough that there are a few of these specks, but not enough to be bothersome. When you're looking for more distant, weaker targets, you'll need to increase gain and watch that screen closely to differentiate between the single speckles and the multi-pixel returns. Radar with chart overlays, however, make tuning in easy – all you have to do is make the pictures match. Yes, you'll have to tweak the tuning in different conditions, but now you have a solid baseline to start from, and the practice you get while tuning in makes you more familiar with how your unit paints its picture.

LENNY RUDOWInterpreting a radar screen requires practice.ON-SCREEN INTERPRETATION

Okay: You know how your radar works, what your unit's capabilities are, and how to tune it. Those are the easy parts of becoming a competent radar operator. What comes next is learning to interpret what you see on screen, and in this case, there's no substitute for experience.

Even though targets appear different on individual units, we can make some generalizations. For starters, objects meant to be clearly visible to radar make clean, crisp, well-defined targets. Large buoys marking shipping lanes are a perfect example. Poor targets, on the other hand, show up as different-sized and -shaped blobs with every sweep of the antenna. Barely perceptible targets in motion, such as birds or small buoys in a large sea, pop on and off screen. These are usually the hardest targets for amateur radar users to nail down, because they appear quite similar to clutter as it appears and disappears. To differentiate between them, pay close attention for several minutes, and identify which smudges and dots appear, disappear, and reappear again in the same location. Of course, you're probably moving, so that means taking your own course and speed into account – or the target's, if it's also moving. Since it's really difficult to do this while operating a moving boat, have someone else take the wheel or watch the radar screen; don't try to do two jobs at once.

Note that radar re-paints its picture after every sweep of the antenna, which usually takes two or three seconds. So "hard" targets that are good radar reflectors keep their size and shape, while "soft" targets seem to morph every few seconds. How will you differentiate between buoys and boats with lots of metal and abrupt angles, which also provide hard targets? Motion. Not necessarily the object's motion on screen, since fixed objects appear to be in motion as your boat moves, but by their relationship with the other hard targets. If, for example, you see three good targets, and two of them remain parallel while a third constantly changes position, you can bet that the third is a moving boat running by a pair of buoys.

Luckily, most modern units allow you to "tag" moving targets, and some (expensive) ones even give you their speed and direction of travel if equipped with ARPA (automatic radar plotting aid). But if you have an older or a less-expensive radar, you'll have to figure this out the old-fashioned way. Watch the target for five minutes, and plot its progress. Let's say it moved one mile. Divide this distance by five minutes, and you get 0.2. That's the boat's speed in miles per minutes. Now multiply by 60, and you'll have miles per hour: 12. The boat's course has to be determined relative to your own. There are plenty of complex and more accurate ways to do this, but let's stick with the KISS method: Put your boat on as close to a 90-degree angle from the target as you can, look at your course line, and add 90 degrees (approaching from port) or subtract 90 degrees (approaching from starboard) to get its course over ground (COG).

Now let's throw a real wrench into these works: Should you use a heads-up display or north up? In heads-up mode, your boat stays pointing up as the screen revolves around it, reflecting course changes. In north-up mode, the screen is oriented in the north-up position, and a heading-indicator line represents your boat's heading. Since the decision is really a matter of personal preference, try it both ways, until you discover which works better for you. One detail to note: Multiple quick course changes in the heads-up mode can make it difficult to interpret target quality. The moving screen may cause some pixelization for a few moments, as it tries to keep up with the boat's motion.

CONFUSION SOLUTION

Like most electronics, radar causes a few crossed wires in your brain at first. So let's make sure you'll be ready to un-cross "˜em, while you're getting used to your radar.

PROBLEM: A target seems to bend around a range ring and grow blurry and smudge as it gets closer.

SOLUTION: Turn down your gain. The target probably looked perfect a few miles out, but as you grew close and didn't damp the gain, you're experiencing a phenomenon called side-lobe interference.

PROBLEM: Small pockets of returns appear and disappear all over your screen, mostly to the windward side of the boat.

SOLUTION: These are waves, so it's time to adjust your sea-clutter setting. Note that the windward side shows more clutter because the faces of waves offer better targets than the backs.

PROBLEM: Large sections of the screen illuminate, as though there's a huge landmass where you know there is none.

SOLUTION: Identify the track of this large mass, and head the other way; this is a rainstorm! You need to see through the storm? Raise the rain-clutter setting and lower the gain.

PROBLEM: Your unit works fine while your boat is at rest, but when you're running, it seems to miss a lot of targets.

SOLUTION: You'll have to re-mount your antenna; this common problem results from boats that have a lot of bowrise, which points the radar into the sky. Measure the angle your boat runs at with an inclinometer, then buy a mounting bracket that can match the degree of incline.

PROBLEM: Lines of dots form streaks across your radar's screen.

SOLUTION: You're getting interference from someone else's radar; don't worry, it shouldn't last long, and it doesn't usually clutter the screen too much. If you find it really annoying, you can squelch it out if your radar has an interference-rejection setting.

The bottom line: When it comes to being proficient with radar, practice is key. You can't jump on your boat and expect to immediately understand what that radar screen is trying to tell you. Instead, plan on spending hours at a time looking at targets from a distance, then running close enough to slap an eyeball on them for verification. Try sitting five or six miles from an inlet one morning, and see if you can guess the size of the boats on screen as they run offshore. Track them as they grow closer, then when you can see whether they're big sportfishermen, sailboats, or small cruisers. Practice differentiating boats from buoys, which often present much firmer, crisper targets, and buoys from fixed channel markers.

Getting the hang of it? Great – now do it in the rain, with clutter control added. And yes, you'll need to practice in the fog, too. But it's well worth the effort. One day it might just keep you from running down a small center console that never appeared on screen – or it might allow you to see the other boat bearing down on you, long before your eyes can.

Lenny Rudow was senior technical editor for Boating Magazine for more than 10 years, and is currently the electronics editor for Marlin magazine.