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Side-Imaging Sonar

Side-Imaging Sonar

During the span of human history, events that altered the face of fishing came along, on average, once in 10 lifetimes. If you're as old as I am, you've been around to see dozens of them occur in a single lifetime. That's how exponential the advance of knowledge has been in all fields—not just fishing.

Fishing electronics trickled down from other endeavors, for the most part. Sonar was developed by the military. When using standard sonar, you scan downward with blinders that limit the scope of vision to a relatively narrow beam that covers 5 to 15 feet of bottom at a time. Side-imaging sonar, in contrast, displays vistas 150 feet or more in diameter. Hills and valleys on "flats" that required a grid to visualize in the past now require one pass. Imagine removing bandages from your eyes and seeing for the first time in your life. That's side-imaging sonar.

Best Describes Best

"To me, it's the greatest advance I've seen in my career for fish-finding," says Kevin VanDam, current and four-time Bassmaster Classic champion. "Side-imaging and GPS mapping together comprise the biggest advance by far. When you use them in conjunction you find things in familiar waters you never knew were there. You can then mark them from a remote position using the cursor on the GPS. To be able to find and mark an isolated log or rockpile is invaluable.

"When I won the Classic at Lay Lake (Alabama), I was in the back of a creek arm on a shallow flat only six feet deep," he continues. "The entire bay had small depressions and a creek channel. In three passes back-and-forth, I saw every ditch, depression, rise, and other feature in it, including isolated stumps and brushpiles. Within half an hour, I knew everything I needed to know about that bay and how to approach it."

Some anglers fish only in natural lakes, others only in reservoirs, and some fish both. What about dense weed walls? Is side-imaging useful when working walls of hydrilla, coontail, or milfoil? "I've learned it takes a while to interpret the proportions of what you're seeing on the screen," VanDam notes.

"When scanning man-made features like bridge pilings or road beds, you can immediately translate the proportions involved and comprehend its true size. With weedlines, it takes time on the water to interpret features like height and density of weed stalks. It's hard to pick out individual fish, and it's still impossible to see bass buried in grass. But groups of bass holding along outside edges can be readily detected. Schools of hundreds of bass are easy to see, so now they're easier to find.

Author Matt Straw enjoys side-imaging slab smallies.

"Anglers don't understand how important side-imaging is in shallow cover," VanDam adds. "You can't compete without it on waters like Lake St. Clair. The key difference is you're looking at 150 feet of bottom instead of 5 feet with standard sonar. It greatly improves efficiency."

Big-Water Advantages

How do you tame big waters? With bigger views. Lake Erie is the Mecca for bass anglers. If you haven't been there, chances are good you have plans to go. The angler who's won more money there than anybody else, Joe Balog, suggests you bring side-imaging capability along.

"I had a Humminbird 997 the year before it was introduced to the public," Balog says. "I was first to use modern side-imaging on Lake Erie. I say modern because divers and salvage companies used other forms of side-imaging available to ocean vessels and commercial interests for years. I have old side-imaging pictures of wrecks on Erie from the 1980s.

Lowrance's HDS Gen2 units process information twice as fast as HDS and have twice the memory. They also include StructureMap view, an innovative tool that allows users to overlay and save StructureScan images on a chart for review.

"The bulk of my side-imaging on the Great Lakes is to determine bottom type. I'm looking for rock. Most rises on Erie's bottom are sand or clay. Smallmouths don't use those much. It's important to find rock and bottom transitions from sand to rock in deep water. One glance at a side image allows me to determine bottom type.


"Rocks, with their hard, irregular edges, are easy to distinguish and important because they hold the treasure—gobies. The key to locating dense concentrations of bottom-hugging gobies is finding bottom transitions and ridgelines. Side-imaging picks those out at distance and displays them in a way that's instantly recognizable.

"On Lake St. Clair, which is shallow with a lot of vegetation and subtle structure, it's hard to find a depth change by looking down," he continues. "Side-imaging helps a lot there, showing tiny ridges, isolated weed clumps, shallow wrecks, and subtle humps. It finds them much quicker than down-viewing sonar."

Both VanDam and Balog set their units to view the 75- to 100-foot range most of the time. "You can go out hundreds of feet to look for big, isolated objects like a wreck," Balog says. "But a shorter range provides the detail you need to find bass. I use a big unit for that reason—to see detail. I like the Humminbird 1198 best, but I use the smaller 998 on the bow. I keep raising the sensitivity until the picture begins to bleach out, then I back it down one number. I scan at boat speeds from 4 to 6 mph. I run the scanner on both sides so I don't miss anything."

Humminbird's 1198 SI Combo is their Cadillac unit, with 10.4-inch display with LED backlight, Side Imaging and Dual Beam Plus sonar, and GPS chartplotter with built-in Contour XD maps. Retail $2,799.99.

Stealth Finder

Kevin Short of Arkansas, winner of the Bassmaster Central Open on Table Rock Lake, Missouri, last fall, says he relies on Lowrance StructureScan units with the LSS-1 transducer everywhere he goes. "I use StructureScan almost every day, even when I'm fishing the same spots for a week," Short says. "Structure- Scan is a great asset because it covers 10 times more water than I could with traditional sonar. It's the biggest game changer since LCD sonar first appeared. Whether I'm ledge fishing, roaming flats with grass clumps, or searching for isolated rockpiles, with StructureScan I make a couple of quick passes through an area and see almost everything within 200 feet to either side of the boat.

"I network Lowrance Structure- Scan units on the bow and dash, using the transducer mounted on the transom for both. This gives a much clearer image than mounting the transducer on the trolling motor. I can't begin to tell you how much I've discovered, even in familiar waters, by splitting the screen on my bow unit and keeping an eye on the Side View as I fish along."

One of the most helpful features of his Side View, Short says, is the ability to place waypoints on spots and fish without driving over them. "When I find some distant object I want to investigate, I move the cursor to save a waypoint on top of it," he says. "After positioning the boat a cast length from the waypoint, I can usually hit that target within a few casts."

VanDam says that capability—using the cursor to mark waypoints on spots from afar—makes side-finding invaluable. "In some waters, you can pass over bass without spooking them, but not in nine feet of clear water. On Lake Erie, for instance, the boat affects them. But if you idle by 50 feet away, you're not disturbing them. Use the pointer on your GPS that tells you distance and it automatically puts a coordinate on it. When I drop my trolling motor I know exactly where that object is."


Setup And Process

Long-time Kentucky pro Mark Menendez sets his Lowrance HDS 10 on a "four-screen grid," he says. "The top left corner of my screen is the side-imaging box. On the top right is a standard sonar view. Bottom right is DownScan imaging, and on the bottom left I have my GPS map. There's a lot going on with this setup, but it leaves no doubt about what's on the lake floor.

"I'm as impressed with DownScan as SideScan," Menendez adds. "I learn more every time I use it. It clarified all those blobs and rocks my color sonar threw at me for years. Now, I get a clear X-ray-type image below the boat while SideScan provides clear images of the surrounding area on both sides.

"When looking for cover on top of flats adjacent to a drop, I scan from the top of the flat out to the edge of the drop. This gives me a real image of the top of the structure without much shadowing of the deep water. But this may spook bass on top of the drop. They may leave the area for a short time, but I find the best available cover that way—where big fish want to live."

Determining what's a fish and what isn't is part of the learning curve. "On SideScan, fish look like ghosts," Menendez says. "I call them 'fluffies.' Taking years of experience into consideration, fluffies aggregate in formations that usually indicate fish species. When fluffies are loosely grouped around a piece of cover, they're usually bass and the game's usually on as soon as a crankbait is ripped past that spot."

Menendez describes how fast SideScan finds fish compared to standard sonar. "The Elite Series had an event at Guntersville in 2010," he reports. "I had to go to a sponsor workshop on the third day of practice and couldn't get on the water until noon. I finally got out and drove around to look at offshore structure. I found five schools of bass in less than two hours. I never made a cast to those spots until the first morning of the tournament, but weighed over 24 pounds from 15 feet of water on day-one. Side-imaging makes me a much more efficient angler."

VanDam uses a similar setup with his Humminbird. "I use a 4-box split screen, so I can see down-imaging, side-imaging on both sides, GPS, and standard sonar without having to look all over the dash," he says.

Balog says the split-screen setup is the most efficient way to gather information. He also claims side-imaging helps him determine species on the Great Lakes. "When I mark fish relating to a drop, high spot, or break with side-imaging, I can trust they're most likely bass or drum," he says. "Walleyes typically suspend but don't sit right on rockpiles, although they do on occasion. White bass mark as tight schools, like baitfish. If I see fish on side-image mode on a breakline, it's bass or drum. Those two species mark very similarly. The only way to distinguish them is to catch one. At times, though, drum create too many marks to be bass. Erie is infested with them, so I look for two to four marks on the side-image out on the breaks, over a high spot on a reef, ridge, or wreck. I can distinguish those out past 100 feet."

Success of specific techniques can be amplified with down-imaging, too, according to Menendez. "When drop-shotting, my HDS 10 shows details of the of the lure and sinker, even in 70 feet of water," he says. "I've never been a video-game fan, but that's what it's like. I've become more efficient at making fish bite that I see beneath the boat because I can watch them react. Studying the screen of my Lowrance, I can impart different actions until I make that fish aggressive toward the offering. Sometimes it takes more than a minute to stimulate a fish. It can be tedious, but, when you hook it, what a rush."

Sounds like ice fishing to a lot of us up North. The ability to watch fish react to our presentations with sonar can be invaluable. But the true value of side-imaging sonar is the enhanced ability to find fish-holding structure and schools of bass in one tenth the time we spent in the past. When the bandages finally come off, weekend frustrations fit in a much smaller box.

Dissecting Side-Imaging

Side-imaging is not quite the same as side-finding. The key is the ability of that box in your boat to translate data. The transducer sends out a narrow, fan-shaped pulse of electronically-generated acoustics perpendicular to the direction of travel. Acoustics or "pings" are about the same as traditional sonar uses, but the equipment translating those pings separates them by measuring time intervals much faster and with much more detail, creating rich pictures of submerged landscapes instead of stick-people sketches.


Engineers call it "target definition," and it keeps improving as electronics deliver and interpret at ever-faster "refresh rates." Man-made objects, like walls and shipwrecks, yield detailed images, as do hard surfaces like boulders. "Softer" returns from vegetation and creatures require more interpretation. Just as you found with your first sonar unit, nothing tops time on the water viewing and double-checking with an underwater camera. The immediate advantage is an extended view of the lay of the land below the waves, cluing you to objects, breaks or unobtrusive rises and depressions that concentrate fish.

*Matt Straw, Brainerd, Minnesota, is an In-Fisherman field editor, avid multi-species angler, and long-time contributor to In-Fisherman publications.

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