Marine Radar
by Captain Tom Martin
 Radar is the most important collision avoidance tool a boat can have.
Radar used with skill allows you to navigate at night, in fog and beyond the visual horizon.
Radar used with a chart plotter or as a plotter/radar overlay offers a thoroughly comprehensive all weather navigational system.
Raytheon Radar/Plotter
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In days of old, and for a lot of folks currently, keeping an eye on the horizon or posting a lookout for other vessels has been the only method of collision avoidance. Most recreational boating enthusiasts don't go out at night or in the fog. However, commercial vessels do not have the luxury of only moving on sunny days so the development of ships radar was a natural and needed development. From there, a technology advanced, radar devices moved quickly to pleasure boats.
When you look at a radar screen in either monochrome (green), or in color what you're seeing is a series of blips representing the radar signal reflected off of objects and land masses. The way a "blip," appears on the screen is determined by a number of variables including what material the signal is reflecting off of, the angle the signal is reflected at and the size of the object, to name a few of the possibilities.
Learning to discern what each blip is and whether it's moving is an acquired skill. The simplest way to learn is practice. Practicing in full day light allows you to make accurate comparisons between radar screen and your visual observations. There are also differences in brands of radar equipment, and software. It is best to learn on whatever equipment you have on your boat. Once you have gained some skill reading your displays, learning others will be easier.
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As you practice in daylight your use of the basic range and bearing controls will develop. Reading the operators' manual's description of the functional dials and switches will give you a straight forward understanding of your radar equipment.
Navigation and collision avoidance are the primary uses of radar. In normal collision avoidance situations with another vessel that is also underway; constant bearing and range mean a collision is immanent. Originally grease pencils were used to mark range and bearing on a plastic overlay now it is done by software integral to the equipment. Radar uses a combination of electronic bearing line (EBL) and variable range marker (VRM) to help determine if a collision is immanent. Ultimately any object's relative position to yours, at the center of the screen, must be watched and used for navigation and/or collision avoidance. Some radar units offer a "wake" function that shows the motion of an object by simulating a wake behind any moving object.
Other controls on your radar are; sea clutter, rain clutter, gain and interference control and sensitivity controls. Some radar has automatic guard zones that alert the operator of movement in a targeted area. By law, that alarm zone function does not replace someone acting as a proper lookout.
Radar is important for power boats and sailboats. You might think a high speed boat would need radar more than a slower vessel. The size of boat and how fast it can go do not diminish the need to find your way home when visibility is limited in some way. There are low power limited range models to accommodate smaller vessels. Most manufacturers offer weather resistant day light viewing models for cockpit installation.
If you plan to leave the dock you must be able to find your way back no matter the weather or lack of light. Aside from spotting land at a distance by increasing the range the longer ranges allow you to pick up storms beyond the visual horizon and avoid them.
As your skill and competence at using radar increases you'll not only be able to find your way home, you'll also be able to track storms, find land, locate marked channels, and inlets, avoid collision and eventually even spot birds circling over bait fish getting hit by predators.
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