Most mid-range and virtually all high-end fish finders are now equipped with side-scanning sonar, high-quality down-scanning tech, and standard 2D downward-facing sonar.
As a result, it’s almost never a question of which one you want, but rather which one is better at this time and in this place.
And while plenty of anglers understand how to use and fish that 2D sonar, few really understand how the more technologically advanced side- and down-imaging options work or how to make the most of them.
Humminbird’s Saltwater Field Staff Manager, Bill Carson, says, “I see it every day… 90% of the anglers utilize 10% of their fishfinder. One of the most powerful capabilities is Down Imaging and this is by far the least used of the sonar technologies.”
Are you one of the 90% not getting all the performance you paid for? Or are you one of the savvy 10% that wring every dollar out of your fish finder?
If you’re not sure about the differences, advantages, and disadvantages of side-scanning versus down-scanning sonar, we’ll cover everything you need to know.
So keep reading!
Table of Contents (clickable)
What is Down-Scanning?
Down-scanning sonar provides an exquisitely detailed view of what’s directly beneath your hull.
To provide that detail, down-scanning sonar uses very high frequencies, typically in the 455kHz to 1.2MHz range, as they carry more information. Of course, the flip side of this coin is that high frequencies can’t penetrate the water column as well as lower frequencies can.
Charter captains and tournament pros use DI sonar more than you do.
That’s a simple fact.
And the reason is clear – literally.
You can run side-scanning sonar while moving, spotting fish you’d miss on standard 2D mode.
That makes it incredibly effective in open water or while trolling, and you can home in on schools you’d pass and never see in the old days. Just keep in mind that the faster you’re moving, the more lag you’ll generate, meaning that images you see will be seconds old, showing what’s behind you.
It’s also an awesome option in shallow water.
2D sonar’s low frequencies really punch through the water column, but as you’ve no doubt already experienced, in shallow water, the sonar cone is too small to be really useful, and interference with the bottom can cause the sonar to run amok.
As a shallow-water tool, SI sonar is unbeatable, and unlike DI, many anglers take the time to really learn the ins and outs of this tech because its advantages are immediately obvious.
But keep a few things in mind.
First, SI is completely blind to what’s beneath your hull. Once you find the spot you’ve been looking for, you’ll want to switch to 2D and DI to really get on the fish.
Second, it can’t penetrate the water column as well as 2D sonar, especially CHIRP.
And third, the images can be confusing or just plain hard to read on small screens. To get the most from side-imaging sonar, you really want the biggest screen you can afford.
Advantages
- Extremely detailed images
- Spots fish that 2D sonar would miss out to each side
- Identifies species of both bait and predator, allowing you to make informed choices
- Great for searching for fish while moving
Disadvantages
- Limited depth when compared with 2D sonar
- Blind to what’s directly beneath your hull
- Images can be hard to read on smaller screens
How the Pros Use their Fish Finders
As you can see, there’s a time and a place for 2D, DI, and SI. Fish finders are definitely not a “set it and forget it” tool!
In deep water, charter captains and tournament pros will run 2D sonar looking for fish, typically in conjunction with GPS positions and predetermined hot spots like wrecks, humps, submerged islands, drop offs, weed beds, etc. – the stuff we all look for to find fish.
The more cluttered the bottom is, that is, the more variance it offers the sonar, the more likely it is that they’ll pause and switch to down imaging to look for fish that 2D sonar misses. That’s also true if they found fish with the standard sonar: they’ll switch to DI to get more detail, spot more big fish, and get a really good read on exactly what’s happening down there.
Are tuna slamming mackerel or squid? Are the bass holding tight to a submerged tree, or are they scattered nearby?