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You believed the weather forecast and, for that matter, so did everyone on the water this evening. Big mistake. That system that was supposed to veer away and miss you had a change of heart. One minute it’s clear and still (too still really) , and the next minute the wind picks up and the clouds roll in to drop their payload. On top of all that, fog arrives driving what was poor visibility right down to no visibility.
You’re in the shipping lanes and the merchant vessels out there have propellers larger than your entire boat. One miss-step and you’re pride-and-joy becomes a new artificial reef - with you as fish feed - without the ship's deck officer noticing a thing. The only thing standing between you and a dinner date with the little mermaid is that miracle of modern science, radar.
With radar, you and that deck officer for that matter (assuming he’s looking at his radar plot and not using that fancy system he has to play solitaire) can avoid catastrophe. For those of us who are a little more than fair weather boaters, radar is an invaluable navigational aid that can keep us safe and on course at night and in adverse weather conditions.
(RA)dio (D)etecting (A)nd (R)anging
The way that radars work is akin to using a spotlight in the dark; only instead of putting out visible light to illuminate, it sends out radio waves, “seeing” anything it bounces off. The radar antenna constantly rotates to keep the image it produces updated, creating that circular sweep look that we’re all familiar with.
Radar units come in many shapes and sizes and can equip boats as small as 18 feet all the way to quarter mile-long supertankers. Small radomes are often in the neighborhood of twelve inches in diameter and weigh in at less than 10 pounds. Even these inexpensive units provide all the basic capabilities you really need (target range and bearing) while drawing very little power. 
As you would expect from the spotlight analogy, radar range is limited by line of sight. The listed maximum range of a unit is rarely important considering that targets relevant to you – other vessels, navigational aids, shoreline features – can only be detected at shorter ranges because of their limited height above the horizon. In a similar vein, radars should not be mounted more than 22 feet above the water on most vessels; any higher and the boat’s motion may disrupt radar coverage while providing very limited range increases in range.
Distance is calculated by timing how long it takes for radar energy to go out, reflect off the target and return to the emitter, while speed is determined by Doppler shift. The kind of radar image produced results from the reflectivity of the object being illuminated. Small and large objects will generally appear as such.
Reflecting on Absorbing & other Cooking Tips
Radar reflectivity is not just a matter of size though. Various materials have greater or lesser reflectivity. Wood and fiberglass tend to absorb more energy making smaller boats made of these materials difficult to detect. Metal objects, on the other hand, reflect very well. Rain and other forms of precipitation absorb radar energy, reducing range and sensitivity.
Oh, and by the way, people absorb radar waves very well too. That being said, remember that other useful device that uses radio waves to cook in the kitchen? That’s right, microwaves and radar waves aren’t too dissimilar. For this reason, mount your radar a few feet above and away from you and your crew’s heads to limit interference and slow roasting.
The more powerful the radar, the less problems exist in dealing with low signature targets and natural conditions that degrade performance. Power generally ranges from 2 kW for smaller units to 50 kW for larger ones. This doesn’t mean that you should go overboard though; more power means increased size, weight and cost. Most any unit will suffice for basic navigation and collision avoidance in all but the most extreme inclement conditions.
Aye Candy
These units pipe their output onto CRT or LCD screens. Some are color and some are monochromatic. Color LCD screens are rapidly becoming the popular choice among newer units. A multitude of display modes allow skilled users to glean extra information by adjusting how the radar returns are interpreted. Learning what your unit can do will greatly enhance your situational awareness on the water.
As good as these displays can be, their radar pictures are seldom as clear as they are sometimes depicted in movies or on television. It takes practice to decipher radar returns quickly and accurately. Practice tapes are a helpful training tool for new users that are widely available.
Radar Love
One last thing to remember is, as always, not to rely on any one kind of navigational technology. As with electronic conveniences like VHF and GPS, you should not be dependent on radar. Always maintain the maps and other non-electronic equipment necessary to get home in a jam and don’t forget how to use them or finally learn how to use them, whichever the case may be. That being said, radar is a great navigational aid that helps keep time on the water fun and safe under almost any conditions.
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