Screen Scene: A Case for 2D Sonar

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Welcome to Screen Scene, a new regular column in In-Fisherman magazine that focuses on electronics. Screen Scene will serve as a classroom whiteboard to illustrate basic understanding, advanced settings, and applications of electronics to help you find, identify, and catch more fish. In addition to appearing as a regular column, you might occasionally see elements of Screen Scene as a part of select feature articles where additional discussion of electronics applications support the topic at hand.

As we traverse through these sonar-related subjects, you’ll note that various brands have different terms for similar or same technologies. Humminbird’s Side Imaging, Lowrance’s SideScan, and Garmin’s Side-Vü, for example, all reference side-viewing sonar, but their applications and settings options inside those operating systems are generally the same. Part of our goal is to help clarify those seemingly muddled waters.

Sure, you catch fish without electronics on your boat or on the ice, but there’s little argument to be made that disqualifies how productive anglers can become after embracing and effectively utilizing modern electronics. It takes commitment and a desire to learn to remain current, but most of all it takes seat time—and who’s going to complain about that? So let’s jump right in.

Changing by the Day

By now, we’re several versions deep into live sonar and it seems to be a mainstay among the tournament ranks and recreational anglers alike. But with the changes to current live platforms within the Garmin, Humminbird, and Lowrance families, so has advanced the quality of 2D sonar. It’s better than ever.

Some say that the advancing of live technology has seemingly cast a shadow on “lesser” technologies—an erroneous assumption, indeed. Don’t be fooled—you need 2D to be as productive as possible.

Before we discuss a few specific applications, let’s talk about some important settings adjustments. Becoming knowledgeable with 2D or any modern technology includes how to navigate menu options and quickly adjust settings to fit your preferences and current fishing conditions.

Frequency: Hertz (Hz) is a unit of frequency equivalent to one cycle per second, and sonar frequency—the number of pulses sent out from the transducer per second—is generally measured in kilohertz (kHz) (1,000 Hz is one KHz). As sound pulses are emitted, echos are returned, and the unit processes this information to create a sounding—or image—on your unit’s screen. Sonar cone width is a part of this discussion, too. (Think of an upside-down ice cream cone beginning at the transducer and getting wider as it looks into the depths.) Lower frequency means a wider cone with greater bottom coverage, and a higher frequency means a narrower cone with higher detail and lesser bottom coverage. Most modern units offer multiple options from 50 kHz up to a 200 kHz beam.

For improved detail (target separation) and increased resolution, a higher-frequency selection is worth trying, but your field of view will be limited because the cone width is smaller—often the best option for deep water. In general, both for ice-fishing and open-water fishing, a lower frequency is likely best in shallow water, say 10 feet and under.

Sensitivity and Contrast: These are two settings adjustments you should regularly work with, especially from lake to lake. Also, when switching between frequencies, you may need to adjust the contrast and/or sensitivity to maximize the quality of your image—the two settings together can provide several viewing options. If you select a higher frequency in deeper water, increasing the contrast might return a crisper image. However, the images might indicate more debris in the water column, thus creating more clutter on your screen. Perhaps decreasing the sensitivity in this case, especially if you’re fishing in relatively dirty water, might generate the best image. But by default, these adjustments may also reduce resolution of actual fish and vegetation. It’s a give and take. Experiment to produce the highest level of information return.

Chart Speed: Chart speed adjustments are made to accommodate the speed at which the boat is moving. If you have a 2D transducer mounted on the back of the pad beneath the boat or in a through-hull position, you can effectively use 2D sonar while at speed. There is a point, however, where the boat may be moving too quickly—25 to 30 mph is about the maximum speed to run while relying on 2D sonar. If you plan to scout for schools of fish at speed, you’ll want the chart speed maxed out; just know image quality won’t be as high of resolution as it would be at a slower chart speed.

If using 2D sonar while ice fishing, or trolling at 1 to 2 mph, a slow chart speed makes the most sense. Just recognize that clarity and target separation will be more discernible at slower chart speeds. Adjusting sensitivity and contrast at different chart speeds may return the best image with the most information.

Direction and Motion

The more information you can garner, the more productive your time on the water will be—the very essence of utilizing modern electronics. Being able to determine which way the fish are facing or traveling can be accomplished by understanding the perspective your transducer is producing. If the fish is large enough, for example, such as sturgeon, paddlefish, muskies, and stripers, you can often determine which end is the head and which is the tail.

Years ago, I was on a paddlefish expedition and my guide clued me into a fascinating use of 2D sonar on his Lowrance HDS 12. Based on the formation of the mark returned by his transducer on his screen, he could tell if the fish was not only a paddlefish, but whether it was a female or male. In the case of a female fish, the brighter color near the belly of the fish was its roe. He proved it to me on several occasions.

When looking at your screen, the far right-hand side of it shows the most current information from directly below the boat (from the most recent sonar returns). Therefore, if a large fish’s head is facing to the right, you can assume the fish is swimming toward the front of, or generally in the same direction, as the boat. If the marks are angled upward to the right, you can assume the fish are rising in the water column, and conversely, if the marks are angled down and to the right, the fish are descending—likely in reaction to your approaching boat. All valuable information that should impact your next move.

Also consider adjusting the color palette to a preferred color combination based on the harshness of the ambient  light. There’s even a night mode that’s easy on the eyes once the sun sets. Users can also maintain or remove the depth lines, and adjust the primary readouts, including water depth, water temperature, boat speed, and local time.

2D On-The-Water

There are many fishing techniques where 2D sonar shines, but they require adjustments to maximize information output. Again, there’s no substitute for time on the water. If making minor adjustments to existing facets of the 2D technology is intermediate, incorporating the sonar into specific fishing techniques is certainly an advanced skill to hone.

Drop-Shot: Implementing 2D sonar into your drop-shotting routine will take an already effective presentation and make it deadly. Consider first, that your trolling motor either features a built-in 2D sonar transducer or has one strapped to the trolling-motor head. In your unit’s menu settings, select the 200-kHz setting, increase your contrast, and reduce sensitivity until you can see both the drop-shot weight and bait as it falls and reaches the bottom.

If you see a fish suspended above the bait, simply raise it to face-level with the suspended fish. The results will speak for themselves.

It’s critical to keep the bait directly beneath the transducer because recall that the cone at higher frequencies is not as wide as a lower frequency. A useful feature of 2D sonar in this situation is it shows a history, thus illustrating something of a pattern of how fish are responding to your rig. Adapt to those encounters. Learning how to master this application while ice fishing is a very effective method before putting it to work on open water with a drop-shot.

Marking At Speed: Whether searching for submerged timber in southern reservoirs, schools of baitfish, deep weededges in northern natural lakes, or schools of suspended feeding walleyes in the Great Lakes, being able to cover water quickly is key to making the most efficient use of your time. The position of the transducer is the most important part here; if it’s out of the water or covered in bubbles while the boat is on plane, it won’t produce accurate returns.

For our purpose, the transducer meant to provide 2D information needs to be in clean water at all times, and the best spot for this is at the rear of the pad. The other option is with a through-hull transducer, which only works on a fiberglass hull. The largest benefit here is the ability to cover a lot of water, looking for a target and eliminating unproductive water quickly.

Comparative Screening: While the proper use of 2D sonar is a critical skill to master, cross referencing that information with side- and down-viewing sonars only increases the amount of information you have at your fingertips. I keep 2D on my graphs almost always, but in a split-screen viewing platform to compare what I’m seeing in a couple other views.

Having an array of technologies available in a couple locations on your rig provides a tremendous amount of information that contributes to solving the puzzle. And it’s not exclusive to just bass fishing or just walleye fishing—it applies across the board. And that’s why you need 2D sonar.

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