How freshwater anglers are capitalizing on new sonar technology.
Two-dimensional views at right show a “bump;” three-dimensional sonar, left, reveals a ladder that may have been blown off the dock.
It’s doubtful there’s a bass angler anywhere who, at some point in time, hasn’t wished he was in a glass
bottom boat.

Once you leave the comfortable world of visible shallow water cover, knowing exactly what’s below is a key to catching bass. Traditional two-dimensional sonar depthfinders can be your underwater eyes, but they’re sometimes a bit myopic. They will show “bumps” and “things” and “stuff,” but unless an angler is extremely skilled at interpreting that 2D display, that’s about all they will see.

A new generation of high definition sonar is changing that.

Introduced in 2004 with Humminbird’s Side Imaging, and followed quickly by Lowrance with StructureScan, this advanced technology uses a combination of cutting edge transducers and intelligent software to process the signals. The transducers shoot an extremely thin, but wide-shaped, signal from either side of a moving boat. Different portions of the beam strike targets with a miniscule time delay that—unlike the 2D depthfinder signals— produces a shadow-like effect on the target and results in a three-dimensional

What before was an interesting lump on a depthfinder now becomes a fallen tree, complete with branches, limbs and twigs. It may not be quite as good as a glass bottom boat, but it’s close.

The popularity of this high definition side scanning sonar prompted Humminbird (Down Imaging) and Lowrance (DownScan) to turn their transducers downward, in combination with their side scanning systems. This produced a three-dimensional image that completely surrounded the boat.

The amount of detailed information provided was remarkable. And, for some, a bit overwhelming. For that reason, these high tech units offer split screen displays combining the side scanning screen with the down scanning screen, and the traditional 2D depthfinder display that anglers have become comfortable with. Anglers can compare one screen with another to define, confirm, and determine exactly what they are passing over. Short of donning a mask and going over the side, it’s the most detailed look you’ll get. And, while saltwater anglers have been the biggest fan of this new technology, serious bass anglers are also embracing it.

“For a professional bass angler that makes his living by the bass he catches, these machines are mandatory and you’ll see them on just about every tournament pro’s boat,” says Shaw Grigsby, who may well have won more money in bass tournaments than any other Florida angler. “For the weekend or club angler, what these machines do is elevate them from just being an angler who pounds the banks to one who now has the whole lake opened to them, and doesn’t just have to cast to visible cover.”

As effective as these units are, they do have limitations and there are some things they won’t do. One is differentiate the size of fish. Don’t expect to idle along a grass line or docks and pick out where the 2-pounders and the 5-pounders are. Fish show as small white dots, unless they are tarpon-sized. Another limitation is shallow water. The side scanning system is largely ineffective until water depths exceed five or six feet, so anglers should not plan on cruising shallow cover edges looking for “white dots.” While the side scans suffer in shallow water, the down scan reads just fine and some of the things it will show (that the 2D display will not) are worth knowing.

“Many depthfinders will not show short bottom grass, like shrimp grass,” Grigsby says, “But that stuff holds a lot of fish offshore, and the down scan finds it easily. It looks like fuzz on the screen. And, if you have new growth short hydrilla, you can even see the individual stalks.”

Another advantage is finding thermoclines. When lakes stratify during the summer, there is insufficient oxygen below the thermocline to support fish, so there is no point in fishing below that.

During a recent trip to Lake Santa Fe with Grigsby and his Lowrance HDS 10, we pulled into Melrose Bay. The 2D screen showed baitfish pods at nine feet. The DownScan screen right above it showed them also, and told us why they were there. It showed a distinct thermocline at 11 feet. The 2D unit didn’t show the thermocline. Moving into the main lake, the thermocline was at 15 feet. That basic data eliminated half the lake from our search for bass.

Combine that with the three-dimensional bottom object display and bass anglers have a whole new way to look at their lakes. FS

First published Florida Sportsman November 2012

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