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How the Next Generation of Radar and Sonar Will Impact Boaters

The latest generation of marine sonar and radar lets you see both above and below the water like never before.

September 6, 2012
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With Google Maps I can switch to street-level view and take a virtual walk down your block and see what flowers you planted in the front yard or even the color of your trash cans on the curb. If someone’s looking hard enough, there’s almost no such thing as privacy in the modern world. On land, that is.

The ocean depths are now considered the last great unexplored and mysterious places on Earth. Even above the water, a boat has always been a way to disappear for a while. But now, electronics companies are pushing the envelope on what we can see both above and below the waterline. You don’t need to be a NOAA scientist or the captain of a Navy sub to see it; any recreational boater can, provided he has space at the helm for the latest in compressed high-intensity radar pulse (CHIRP), side-view sonar and solid-state radar.

Companies like Garmin, Raymarine, Humminbird and others offer (or will offer) similar products, but we tested three from Simrad Yachting off the coast of Florida. And we found that, with these technologies, there’s almost nothing that can’t be found.

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HD Undersea (StructureScan HD)
“Here we go,” I thought, as Stuart Wood scrolled through photos on his iPad like a proud parent. But then Wood — a manager with Navico Americas — stopped on one that blew me away: an incredibly detailed image of a sunken oil rig, taken from a fish finder equipped with Simrad’s StructureScan HD.

Paired with one of three Simrad multifunction displays, the black-box StructureScan HD unit returns incredibly crisp images, left and right to 300 feet with side-scan sonar as well as to 300-foot depths with ­­down-scan. In split screen, you can see them simultaneously.

To test it, we positioned ourselves over a shipwreck and set the display to view the down scan, split with a traditional sonar return. In 120 to 125 feet of water, we saw the precise outline of a vessel listing on the seafloor. We could clearly make out its bow, stern and tower. In the traditional view, it looked like a large lump on the bottom.

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“High frequency accounts for the detail of image,” Wood said.

Thanks in part to a larger, more refined transducer (see our Web Exclusive at boatingmag.com/transducers), StructureScan HD gets better resolution than previous models at 455 kHz (twice the normal “high” frequency). The higher the frequency, the sharper the bounce-back (but the less the range too). Side imaging also uses a narrow 180-degree beam compared with the more conelike beam of traditional sonar.

What’s the benefit to boaters? For divers, you can get a precise view of wrecks and reefs. For cruisers, you can get accurate pictures of mooring fields, and of potential hazards. For anglers, it should be fairly obvious.

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Going Deep (CHIRP Technology)
The captain who piloted us around is well known for his swordfishing and general bottomfishing prowess. He told us what any captain would tell you: Knowledge of location is paramount. (Ironically, we are keeping his name and his boat’s name secret so you don’t follow him.) To show us the value of CHIRP technology, he ran and set up on six fishing spots in the span of three hours.

Then it dawned on me: We ran and set up on six wrecks in three hours. And, en route to these spots, our captain passed over new “undiscovered” structure and marked it with his MOB button. One of the key facets of CHIRP sonar is that it holds ground deep, and at speed.

“At 25 knots I can mark a fish at 1,000 feet,” said our amazed captain. (A Garmin unit recently held bottom at below 17,600 feet.)

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CHIRP is one of the biggest game changers to filter down from the military to date. Here’s why.

Traditional sonar operates at a single frequency, though you’ll likely get a choice of two, like a short, fast, high pulse (or ping) of 200 kHz for shallow returns or the long, slower pulse of 50 kHz for deep readouts. Some fish finders even let you run two frequencies at once, but the limitations are documented: lost returns on intermediary marks, lost bottom at high speeds and so forth. One of the main problems with deepwater returns at 50 kHz is that the long waves required to probe the depths do not pick up detail. So structure readouts come back as flat bottom, slight contour changes or lumps.

The Simrad BSM-2 box, paired with the proper Airmar transducer (see boatingmag​.com/transducers), solves those problems. Instead of a single-frequency “ping,” CHIRP sends a modulated pulse — a chirp — that sweeps through a range of frequencies: 130 to 210 kHz for the high band and 25 to 45 kHz for the low. The BSM-2 module translates the best frequency based on the best return and constantly adjusts it in motion to show detailed reads from the depths.

What does this mean? Our captain could run to a designated spot and quickly scan the structure to see if fish were holding, and exactly where they were holding. So he’d know where to set his anchor or his drift and the depth to set his lines to get a bite. Oh, yeah, he marked a large, free-swimming pelagic fish at 700 feet while we were at cruise.

What does this mean for nonanglers? The price of Simrad’s BSM-2 is steep ($2,495, plus a four-figure sticker for the transducer), so unless you’re a wreck fisherman or a swordfisherman, you may not yet have a justification for it. Or maybe you do.

As our captain noted, “On our last trip to Bimini we marked a big ol’ mountain range at 2,500 feet.” He went on, “I’ve made that crossing hundreds of times and never knew it was there.”

Free and Clear (Broadband Radar)
Heading back to the inlet, we turned on Simrad’s 4G Broadband Radar. Navico, which owns Simrad, Lowrance and B&G, is so far the only maker of solid-state marine radar. Broadband is significant because it eschews the high-voltage magnetron technology of conventional radar, opting instead for a solid-state frequency-modulated continuous wave (FMCW) transmitter, a low-power frequency swept signal.

Approaching the breakwater of the inlet, we immediately experienced 4G radar’s most important benefit: Every boat, marker and crab pot buoy in close range was visible on our MFD screen. With solid-state radar, there is no “main bang,” a blind spot in magnet-based radar that typically covers a radius of 80 feet.

This is why I believe solid-state radar is the most significant of the new “see everything” technologies for recreational boaters, because most of them spend most of their time in close-quarters cruising situations. As we approached the inlet, two personal watercraft blasted by, and on screen we watched them in our wake, driving the point home.

Inside the inlet, Wood played with the unit’s split-screen function to show the true worth of this radar. On the left side of the screen, he turned the new “beam sharpening” function off and adjusted it to create a return similar to that of traditional radar. On the right side, he turned on the beam sharpening, which improves the system’s “azimuth resolution,” or the horizontal beam width of the broadcast signal. Without it, a dock jutting into the water looked like a solid blob. With it, we could distinguish each separate piling and even deadheads — remnants of an old dock — barely jutting out of the water. It made for a remarkably detailed image of everything within a half-mile of the boat.

With a Simrad NSE or NSO multifunction display you can set the radar to dual range mode, setting one window to close-quarters and another for long range out to 36 nautical miles — more than enough coverage for the majority of recreational boaters.

But what’s great about 4G is that it’s an excellent option for operators of small boats. Firstly, the 4G dome is a mere 19 inches in diameter, so it won’t dwarf a small hardtop. Secondly, 4G draws 30 percent less power than magnet-based radar. And it has significantly fewer emissions, so it’s safer in close quarters.

As we neared the dock, Wood called to my attention the function that made my decision to keep the captain’s name out of print an easy one: MARPA. The acronym stands for mini automatic radar plotting aid; the function allows you to track other boats. Select one with the cursor and it will automatically provide its bearing, speed and closest point of approach. While MARPA is for collision avoidance, if you have it, no boat within range can hide. It’s great for cruisers traveling in tandem but scary for charter captains. So we’ll give ours a break. Because with these technologies, nothing else on the water will remain a secret.

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