Both deep water and soft bottoms tend to return a weak signal. In deep water, the signal travels a long way on its round-trip from surface to lake bottom and back to the surface again. As it travels, it weakens and becomes harder to detect, translate, and display. On soft bottoms like muck and silt, much of the signal is absorbed by the substrate. To improve readings over such substrates, turn up the unit’s sensitivity in manual mode to a level higher than the default one the unit’s auto mode selected. In water shallower than 5 feet, the return signal can be too strong because of the short distance it travels. In this case, auto mode may not reduce the sensitivity enough to produce a clear picture. Instead, the whole screen may “gray out.” To adjust, turn down the sensitivity in shallow water or over a hard bottom, thereby providing a narrower cone angle. In deeper water or over softer bottom, increase sensitivity to provide a broader cone angle.

Vegetation provides another set of challenges for adjusting sensitivity. It’s common for fish to hold along edges of weedlines or above the tops of weedbeds. Locators set in auto mode have difficulty handling such situations. If you increase sensitivity to penetrate to the bottom in a weedbed, the screen will be saturated and lack detail. Remember that increasing sensitivity raises the unit’s listening ability, not the locator’s power. When you power up in auto mode in dense vegetation, you get a strong return signal because vegetation is a good reflector, sending back a strong signal that lacks detail because of the multiple surfaces of the plants’ leaves. Your unit is on overload. To reduce its sensitivity around vegetation, use the sonar in manual mode, experimenting with sensitivity settings to learn which works best.

The sensitivity control is the locator’s most important function. Learn how it affects what you see on screen, so the unit works for and not against you. Launch on a favorite body of water and check familiar locations. Position your boat in shallow water, deep water, over hard bottoms, soft bottoms, rockpiles, and around vegetation. See how the unit interprets each of these areas. Adjust its sensitivity settings to see how doing so affects the information displayed. Decide which work best in situations you’re familiar with. Doing so will give you more confidence in your sonar’s capabilities.

Fine-Tuning

Today’s sonars are highly sophisticated—some even include a computer-style hard drive. Faced with multiple buttons and arrows, which lead to layers of menu options, most anglers opt for the auto button. And given that this setting provides serviceable images on most good units, that’s as far as many go. But to achieve the best possible depiction of bottom, bait, and fish, given the computer-like capabilities of modern marine technology, adjustments are needed.

Split Screens

Before delving into sensitivity, colorline, and so forth, consider your fishing style. Are you structure-fishing or setting up a trolling spread for open water? For structure, try switching your unit to split-screen zoom mode. That way, the nuances of bottom are displayed on both sides of the screen. Moreover, the zoom window is powerful enough to pick out individual fish lying on bottom. Dropping a jig in the unit’s cone angle shows your presentation in relationship to the fish, perhaps even their approach toward it. You can mark crappies in zoom mode and watch them rise off bottom or out of a school to inspect and strike bait.

On the other hand, full-screen mode is preferable for the wide-screen view of what lies below. It’s possible to go into the “sonar setup” menu to create upper and lower depth limits to read specific bands—say, 20 to 40 feet—to zero in on bait and fish with greater accuracy. If you primarily troll, however, split-screen mode may not be for you—wide-screen view is better for this application.

Colorlines

Next up: The crucial setting of sensitivity. While it was once important to crank the sensitivity almost to 100 percent with black-and-white units, color screens operating with higher power levels no longer require full-tilt sensitivity. Rather, the best way to set it is to turn it up until clutter and distortion fill the screen to the point of unreadability. Then back off until the screen clears itself of all but a little sprinkling that looks like a dusting of pepper. Then back off one or two more clicks for good measure. You’ll need more sensitivity in deeper water, less in water shallower than 15 feet. Fish show in shades of red and orange, depending on their size and location in relation to the sonar’s cone angle.

That brings us to colorline, the modern version of grayline, once the standard way black-white units provided separation of targets from bottom. On a color screen with colorline, you’re better able to see fish on structure and even in weeds. For most applications, start with a colorline range of 75 to 90 percent, then adjust as needed.

To dial-in specific numbers, experiment with the colorline settings until the bottom shows a black, defining line with yellow underneath it. Then increase the colorline until the yellow has a hint of red in it; reduce the level from there until the red disappears, then increase by a click or two. At this setting, changes in the sonar return indicate both fish and differences in bottom content.

Selecting Speeds

Although cranking settings to maximum is no longer needed in modern sonars, a couple of parameters are best taken to the limit—that is, to a 100-percent setting. Ping speed and chart speed both affect how fast impulses are dispatched and returned to the sonar unit. Ping has to do with the rate at which the sonar’s signal is sent out, returned, and interpreted by the unit’s processors. Furthermore, keeping ping at max rather than frequently adjusting it is going to yield a semblance of consistency in what you’re seeing—all the better for your own interpretation.

Setting chart speed at max, which influences how fast the picture moves or scrolls across the screen, accomplishes something similar. At 100 percent, the readout shows what’s being displayed at the fastest rate possible for the best possible real-time viewing, with better fish arches in the shape of elongated, upside-down smiles rather than more compact, inverted V’s.

Side-Imaging Sonar

In 2005, Humminbird introduced a new type of sonar. Their high-end units have Side-Imaging (SI) sonar color imagery plus GPS map navigation features. At roughly $2,000, the Humminbird 987c SI is about the most expensive sonar and GPS unit available. But experienced anglers have found the SI to be a better searching tool than standard units.

Buyers gain a new search capability that simplifies the process of finding cover and structure likely to hold fish. SI allows an angler to make passes down a shoreline or around important structures and mark spots as waypoints. The angler can then return to fish each waypoint to see if the spots are productive. Users more rapidly learn new waters and gain knowledge about underwater features they already fish.

One drawback is that fish returns are smaller and more difficult to identify in SI imagery compared to standard vertical sonars. Schools of small baitfish appear as murky clouds rather than dark blobs. Fish the size of crappies or yellow bass may appear as small white dots, and individual gamefish like bass aren’t much different from the returns created by stumps on bottom; but this is a cover-location tool, and effective use always has a learning curve.

Although gamefish and baitfish show as separate returns in SI imagery close to the boat, fish echoes farther to the side are mixed in with returns from the bottom and are more difficult to see. The clue that an SI return is a fish rather than a bottom or cover echo is a matching fish shadow farther away. Side imaging can help an angler locate and relocate moving schools of predator fish in relatively open water, but this is a bonus feature, not a primary benefit.

Beds of underwater vegetation are visible as marbled or bumpy bottom, but the soft edges of many submerged weedbeds may be indefinite. The prime benefit of SI is in definition of hard elements. Rockpiles and the deep edges of riprap are clear. Bridge construction and cover near pilings are revealed. Laydowns and underwater brush seen as blobs on bottom with vertical sonars become distinct logs and trees with defined branches. The clarity of various images recorded with the SI can be seen on the Humminbird website (humminbird.com). The increased fishing capability created by such detail is much like having photographs of exposed cover in a reservoir or lake.

While the unit has many positive features, anglers should also be aware of its limitations. The SI unit’s transducer must be located externally on the stern of a boat. The system works best at speeds under 10 mph and on straight-line courses, as turns distort the imagery.

How the stern is shaped and the outboard motor mounted influence whether the unit can “see” well to either side. Nothing may be placed in the line of sight to the sides of the transducer, and external mounting exposes the transducer to possible damage. Yet reasonably careful operation avoids damage, even in reservoirs with abundant standing timber and stumps.

Beginners with the SI system learn to better identify echoes and use other features on every outing. If you’re a non-techie, you may find the complexity of menus and some options non-intuitive, but learning the details is rewarding. Users need to buy a map chip and may want another chip to record images for later review on a personal computer.