Radar is one of the most important parts of your boat’s electronics suite—and it’s also the one that’s least understood by most boat owners. Sure, you know it lets you see through the fog and out into the distance, and eliminates a lot of the stress associated with boating in restricted visibility. But many people over-spend on radar, outfitting their boats with expensive units that they’ll never be able to use to their full potential. And others under-spend, buying barely-functional units that don’t extend your vision much farther than a good pair of binoculars. So, which one’s right for you? Let’s find out.

Foggy Day on the Water

Radar can take a lot of the stress – and the danger – out of limited visibility conditions.


Forget about power, bandwidth, and antenna quality—the single most important factor in determining how far any radar unit will be able to see is the height of its antenna. Here’s where many buyers become over-ambitious. Radar range is limited by the curvature of the Earth. The height of your radar antenna and the height of the target you’re looking for is what will determine whether or not your radar can see over that curve. Here’s the key formula to remember: 1.22NM x square root height of radar + 1.2NM x square root height of target. In plain English, that means that if you have a boat with an antenna on a hard top that’s nine feet off the water, and you’re looking on-screen for a boat of the same size, you won’t see it until you’re within 7.3 nautical miles (1.22 x 3 + 1.22 x 3 = 7.32). And that’s the best-case scenario. Since fiberglass makes for a relatively poor radar reflection, you might not see it until you’re a whole lot closer.

Tower helps visibility

You can see farther from an elevated position, and so can your radar.

Since height is your biggest limiting factor, if your boat doesn’t have a tall tower or mast it doesn’t make a whole lot of sense to spend big bucks on a long-distance radar. You need to remind yourself that you won’t see even the best targets, like beachfront buildings and cargo ships, from distances extending beyond the horizon’s limit—so dropping all that dough on a 72-mile radar is a waste of money, pure and simple.

Weight and Size

Simple physical size and strength limitations may also affect your radar-buying decisions. Make sure the radar of your choice will fit on your boat before you break the bank—not afterwards. Enclosed domes will fit into some areas where big open-arrays won’t. And in some cases, the weight of a large radar antenna may be too much for a particular mast or mounting surface to bear, while a smaller one can be mounted in the same spot without causing problems. Now, think back to the range limitations we talked about a moment ago. If you have the choice between mounting a light 36-mile range dome on the Bimini top that shades your upper station controls, or mounting a larger, heavier open-array with a 64-mile range on the hard top below it, you may actually see farther by going with the lighter, smaller unit.

When choosing a mounting location also consider whether there’s a way to run the relatively thick antenna cable to and from the spot, without leaving it exposed. If you’re adding radar to an existing MFD system, you’ll also need to make sure you have a good mounting area available for the unit’s black-box brain. It needs to be well-ventilated, watertight, and spacious enough to access in case you need to have the unit worked on. And to state the obvious, you’ll also need to ensure adequate dash space if mounting a display is necessary.

Simrad BR24 Radome

Navico’s Broadband is a unique system, available on Simrad, Lowrance, and Northstar units.


The next factor to consider is what electronics you already have on the dash. Yes, with NMEA0183 or NMEA2000 you can get most units to talk to each other these days, but integrating mix-and-match systems can be both complex and troublesome. You’re usually much better off either matching the brand with what you already have onboard, or taking advantage of the opportunity to chuck those old electronics and invest in a whole new system, with plug-and-play functionality.

And yes, you will want the radar to be able to communicate with the rest of the boat. It enables numerous functions (like displaying the AIS data of targets, or overlaying the radar on your chartplotter), that are more than nice; they’re significant safety features.

Sell-By Date

Are some of the radars you are considering already dated? In the past five years, we’ve seen a lot of advancements in radar. In fact, many “new” radar units sitting in the stores at this very moment are thoroughly out of date. High definition digital signal processing and algorithms, high-speed data processing, and broadband have eclipsed the performance of older units, and although some new systems were plagued by bugs in recent years, at this point, the reputable manufacturers have overcome them.

HD radar brings much better target separation, clearer on-screen images, and reduces clutter. This is more due to software and programming than hardware, but the difference is notable. Particularly in foggy conditions, where a boat might bleed into an inlet jetty, these performance advancements give you a big confidence boost at the helm.

Broad Band Piles

Broadband’s real strength is in close-quarters target discrimination. Those dots inside the box are individual pilings.

Broadband will be of particular interest to small boat owners and as a second radar for large boat owners who want a back-up unit with advanced close-range sensitivity. Although its range is limited to 24 miles, the enhanced sensitivity and target discrimination is second to none. You can see individual pilings, small markers, and even birds, because there’s no bang suppression (which forms that close-range blind spot other radar suffers from), with Broadband. Instead of radiating microwave pulses with a magnetron (which necessitates suppressing the returns from 50’ to 100’ away, to eliminate clutter), Broadband sends out a continuous transmission wave. This wave increases in frequency as it moves away from the dome, hits a target, and is reflected back to the dome. The difference between frequency in the transmitted and returned waves is how the unit determines target distance. Not only does it allow for views of targets amazingly close to the boat, the process requires a mere 1/2000th as much power as traditional radar (about a tenth the power of a common cell phone), so it can also be mounted close to passenger-occupied areas without risk.


All other things being equal, as radars become more powerful, naturally, they can see farther out into the distance. Relatively weak radars usually have around two kilowatts of power, mid-range units have between four and 12 kilowatts, and the most potent may put out as much as 25 kilowatts.

Putting Broadband aside since it works on an entirely different principal, units with less than four kilowatts of power may be better than nothing, but users are rarely satisfied with their performance. Mid-range units work fine if you’re not expecting to see weak targets at long distances or if your range will be limited by other factors. If you want to be able to pick up very weak targets, such as a cluster of birds feeding on baitfish, or if you want to see for many miles into the distance and you have the mounting height that’s necessary, more power is more better.

Beam Width

Garmin GMR xHd Radar

New high-definition units utilize advanced software, which makes a huge difference on-screen.

Hand in hand with power, also consider beam width. Radar pulses may be broadcast at anywhere between about six degrees and one degree. The narrower the beam width, the more focused the radar’s pulses are. This translates into better differentiation between targets and more accurate bearings. Generally speaking, the larger and more powerful your radar is, the narrower the beam width is likely to be.

There is a down-side; very narrow beam widths can also limit close-quarters radar visibility, because minimum target width is dictated by minimum beam width. That means a small channel marker that’s just a mile away may look like a blob on a weak radar with a six-degree beam width, while it appears as a sharp, concise dot on a more powerful radar that has a narrower beam width. (That’s why many large vessels that need to use radar in close quarters often have a secondary, weaker radar onboard).

Take all of these factors into consideration before you go shopping for a new radar, and unlike most of the boaters out there, you’ll quickly figure out just which units fit your boat and your needs. You won’t over-spend, you won’t under-gun, and you won’t over-reach. Most importantly, the next time that fog rolls in, you won’t be over-stressed, either.

Lenny RudowLenny Rudow has been a writer and editor in the marine field for over two decades and has authored five books. He runs his own web site at HookedOnFishingBoats.com and his syndicated blog appears at Boats.com in the BoaterMouth blog section.