Learning To Love Your Boat Radar Part 1
Here"s article by Lenny Rudow worth reading.
Radar can seem daunting to a newcomer.
Here's a brief introduction on all you need to know to get you started.
Whether there's a pea-soup fog or night has fallen, there's no substitute for radar when it comes to operating a boat in reduced visibility. Even on clear, sunny days, radar can be a huge advantage, letting you "see" for miles into the distance.
But radar is expensive and complex, right? These days, no, not so much. Today's units are light-years ahead of those found aboard recreational vessels just a decade or so ago. They're easier to use, more sensitive, and less expensive. Yet still, many mariners who haven't used radar are a bit apprehensive about looking at all those blips and blobs and decoding exactly what they mean.
Here's How Radar Works
Before we delve into using radar, let's make sure you have a solid understanding of the basics. In a nutshell, radar sends out a transmission in the form of a high-frequency radio wave and "listens" for it to be bounced back by a solid object. Most traditional radar units send out this transmission in a burst of power, then calculate the time delay of any returned signals to calculate distance to the target. As a general rule, this type of radar provides the best long-range abilities. Unfortunately, that big burst of power creates something called a "main bang" 360 degrees around your boat. This is a visionless dead-zone that can cover 100 feet or more. So while long-range performance is excellent, very short ranges are hampered.
Instead of using strong bursts of power, some newer solid-state radar units instead calculate the difference between transmitted and received frequencies. The advantage is better target discrimination at short range; there's no big burst, so there's no main bang. Their range, however, is often more limited than that of traditional radar.
The latest and greatest units may combine these two technologies, and some also apply Doppler enhancements. Remember learning about the Doppler effect in high school? As an ambulance gets closer and closer, the frequency of its siren sounds higher and higher, and as it gets farther away, the frequency sounds lower and lower. Many of the latest marine radar use this same principle to help determine the speed and hazard-level of moving targets.
The strength of a radar's return depends on a number of variables, including the target's material, shape, and size. That's why some items (such as channel markers, which are designed to maximize radar returns) may appear to be bigger on radar than a boat 10 times their size. This is also why small fiberglass boats may not show up on some radar at all, or may show up only at very close range. Your radar's beam width also has a big impact on how it sees things. The narrower the beam, the more gain (intensity) it has, and the more range it will have at a given power level. Beam width is determined by antenna size, which is why larger, open-array units generally have much narrower beam widths, and hence more maximum range, than small, enclosed-dome antennas.
What's most important to recognize about radar range, however, is that beam width, power, and every other factor gets trumped by the curvature of the Earth. Radar is "line-of-sight," so the height of your antenna and the height of the target are most often the limiting factors that determine range. Ready for a little math? Here's the equation:
1.2NM x (square root of antenna height in feet) + 1.2NM x (square root of target height in feet) = Range
An example (don't worry, we'll keep the math simple for now): Your radar sits 16 feet above the water on your boat's hard-top, and the vessel you're looking for stands 16 feet above the water's surface. That's 1.2 x 4 + 1.2 x 4, or 4.8 + 4.8. No matter how expensive and powerful your radar may be, it will never see this other boat until it's within 9.6 nautical miles. Period.