How to Read Side Imaging Sonar — The Complete Guide
By the ChargedAnchor Team
What Side Imaging Actually Does
Your standard 2D sonar shoots a cone straight down and shows you what’s directly beneath the boat. That’s useful, but it’s like looking at the road through a paper towel roll — you only see a tiny slice of what’s around you.
Side imaging sonar uses a razor-thin beam to take a sonar snapshot of the area up to 400 feet to the left and right of your location, then adds each return image to the images taken immediately before and after to build an incredibly detailed view of the lake bottom.
Think about what that means in practical terms. With down scan alone you’d have to drive your boat up and down an entire area 20 to 30 times to get a sonar picture of it. With side imaging, you only have to drive past once. That’s the difference between spending your morning searching and spending your morning fishing.
How to Orient Yourself on the Screen
This is where most beginners get confused — side imaging looks nothing like regular sonar. Here’s how to make sense of it immediately.
The center line on your side imaging screen is the path of your boat as it moves forward. The most recent data is at the top of the screen, so the image is read from top to bottom. Everything above is more recent, everything below is history.
On either side of that center line you’ll see:
The Water Column — The dark center portion of the screen represents the column of water directly below your boat. This is essentially dead space on a side imaging screen — you need your 2D or down imaging running simultaneously to cover what’s directly underneath.
The Bottom — The lighter areas spreading out from the center to the left and right show you the lake floor extending away from the boat. The further from center, the further from your boat.
Structure and Objects — Anything rising up from the bottom — trees, rocks, brush piles, stumps, docks — appears as a bright return coming up from that bottom line.
Shadows — This is the key to reading side imaging like a pro and we’re going to spend real time on it below.
The Shadow — The Most Important Thing on Your Screen
If you take nothing else from this guide, take this. Objects reflect sound and show up bright, but they also block sound from hitting the bottom behind them. This creates a dark sonar shadow. The length of that shadow directly correlates to the height of the object — a long shadow means a tall tree or piling, a short shadow means a low rock.
Think of it like sunlight. When the sun shines across a flat field and hits a telephone pole, the shadow behind it tells you how tall the pole is. Side imaging sonar works exactly the same way — except with sound instead of light.
Here’s where it gets really useful for fishing: if a bright dot — a fish — has a shadow detached from it, that fish is suspended off the bottom. The distance between the dot and its shadow tells you exactly how high off the bottom the fish is holding.
That suspended crappie sitting four feet off a brush pile? You can see that. The bass hovering two feet off a ledge? You can see that too. The shadow doesn’t lie.
What Different Things Look Like on Side Imaging
Hard Bottom vs. Soft Bottom
Hard bottom — rock, gravel, shell — returns a bright, sharp signal. Soft bottom — mud, silt, sand — returns a softer, less defined image. You can get a clear understanding of your bottom type by locating rocks and crevices, and clearly identify weed beds with detailed definition. Bottom transitions from soft to hard are almost always worth a cast or two.
Submerged Trees and Timber
Timber is one of the most recognizable things on side imaging once you’ve seen it. The trunk shows as a bright vertical return coming up from the bottom, with branches spreading out above and the shadow stretching away behind it. You can see trees and even identify old building foundations and steps with remarkable detail. The taller and denser the structure, the longer and darker the shadow.
Brush Piles
Brush shows up as a cluster of irregular bright returns with a ragged shadow behind it. The denser the brush, the brighter the return. Once you’ve identified a brush pile on side imaging, drop a waypoint immediately and come back with your 2D or LiveScope to work it properly.
Fish
When a fish appears on your screen it shows up as a white line and sometimes with a shadow too. If you ever see a small white line, assume it’s a fish regardless of what else is around it. Schools of fish show up as clusters of white lines or a bright mass. You can see the light spots where sonar is reflecting off fish as well as the dark shadow cast below them — and you can watch a school appear on screen as you approach them.
Weed Beds
Vegetation shows as irregular, fuzzy returns spreading across the bottom. The edges of weed beds — where weeds meet open bottom — are almost always more productive than the middle. Side imaging lets you trace those edges precisely so you can work them efficiently.
Docks and Pilings
Dock posts show as individual bright dots in a row with shadows extending behind them. You can count the pilings and see exactly what’s holding around the base of each one before you ever make a cast.
Speed — The Setting That Controls Everything
The optimum boat speed for side imaging is between 2 and 6 knots. Too fast and data from some image slices will be missed, resulting in a distorted picture. For optimal results your boat should be moving in a straight line — a turning boat causes sonar pulse returns to overlap and distort the image.
In practical terms, idle speed to searching speed is your sweet spot. When you’re running at full throttle, side imaging is essentially useless. When you slow down and run a straight line over promising water, the picture becomes remarkably detailed.
Side imaging also works best in calm conditions. When your boat pitches up and down in rough water, it causes bubbles and disturbs the sonar readings — there’s often so much clutter and noise that it’s not worth using in a heavy chop. Save it for the calm days and flat early mornings.
Frequency Settings — 455kHz vs. 800kHz
Most side imaging units give you a choice between two frequencies. Here’s how to choose:
455kHz — Wider coverage area, scans further out to the sides. Best for searching large areas of open water or deep structure. Use this when you’re covering water and looking for something to investigate.
800kHz — Narrower but much sharper image. Better target separation and detail. When you want to hone in on fish, setting your range tighter and running 800kHz gives you crystal clear images with significantly more detail. Use this when you’ve found something worth studying closely.
The smart move is to search at 455kHz, then when you find something interesting, switch to 800kHz and make another pass to get a sharper look before you fish it.
Range Settings
Range controls how far out to each side your unit is scanning. More is not always better.
Setting your range to 75 feet in combination with higher frequency gives you far more detail than scanning out to 200 feet. When you’re in a known productive area and want to see exactly what’s around you — individual fish, specific structure — tighten your range. When you’re searching unfamiliar water, open it up.
A good starting workflow: start at 100–150 feet of range to find areas of interest, then tighten to 50–75 feet to study what you found before making your cast.
How to Use Side Imaging to Catch More Fish — The Workflow
Here’s the exact process serious anglers use:
Step 1 — Search Mode. Run at idle to searching speed in a straight line across your target area. Side imaging at 455kHz, range set wide. You’re looking for structure, bottom transitions, and fish.
Step 2 — Mark Everything Interesting. The second you see a brush pile, a stump, a school of fish, or a hard bottom transition — hit the waypoint button. Don’t slow down, don’t stop. Keep moving and marking.
Step 3 — Study What You Found. Make a second pass at 800kHz with tighter range over your waypoints. Get a detailed look at the structure before committing to fishing it.
Step 4 — Fish It. Now switch to 2D or down imaging and work your waypoints thoroughly. Side imaging shows you which side of the boat most of the fish are on — use that to position your boat so you’re casting toward the fish rather than away from them.
Step 5 — Learn What You’re Seeing. One great way to accelerate your learning is to idle over places where you already know what’s underneath — an old roadbed, a bridge piling, a dock you can see from the surface — and study how those known objects appear on screen. That knowledge transfers everywhere you fish.
Common Mistakes to Avoid
Going too fast. The number one side imaging mistake. Slow down and your picture improves dramatically.
Ignoring the shadow. Most beginners focus on the bright returns and ignore the shadows entirely. The shadow tells you height, depth off bottom, and whether fish are suspended. It’s half the information on your screen.
Fishing while searching. Side imaging is a search tool, not a fishing tool. Resist the urge to stop and fish every mark you see. Search the whole area first, mark everything, then go back and fish methodically.
Wrong range for the situation. Too much range in shallow water spreads your signal too thin. Match your range to your depth and target distance.
Expecting it to work in rough water. It won’t. On a rough day run 2D sonar and wait for calm water to put side imaging to use.
Quick Reference
| Setting | When to Use It |
|---|---|
| 455kHz | Searching, deep water, wide coverage |
| 800kHz | Studying detail, identifying fish |
| Wide range (150–200ft) | Open water searching |
| Tight range (50–75ft) | Studying specific structure |
| 2–6 knots boat speed | Optimal image quality |
| Straight line travel | Best image, no distortion |
Final Thought
Side imaging is the fastest way to learn a new body of water ever invented. Anglers who use it correctly can cover in one morning what used to take an entire season to figure out by feel. The technology is not magic — it still takes time on the water to truly learn what you’re seeing — but the learning curve is shorter than you think.
Slow down, run straight, watch the shadows, and mark everything. The fish are there. Now you can find them.
Have a question about your specific unit’s side imaging? Leave it in the comments — we read every one.
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