Using Depth Sounders

Part 1: Getting Started

These days, very few boat fishers venture out in search of angling action without a depth sounder, sonar unit or “fish finder” fitted to their vessels. Even kayak and canoe enthusiasts are increasingly relying on sonar technology to help find fish. But if you’re one of those folks still struggling to interpret what you’re seeing on your sounder’s screen, this series of Inner Circle blogs should definitely help!

There's no doubt that the intelligent use of modern depth sounders can boost your fishing success rate.
Modern sounders are so good that in many cases all the operator needs to do to get started is turn them on and set them on "auto"!
Modern combo units allow users to operate a GPS plotter (left) and sonar readout (right) simultaneously, via a split screen. Believe it or not, the target above the bottom here is a humpback whale!
Here, a split screen is being used to display standard sonar on the left and a StructureScan "downscan" image on the right. The targets are bass and golden perch schooling under a layer of baitfish (most likely bony bream). If you look carefully on the left image you can even see a lure being jigged up and down, creating a zig-zag pattern.
Here the split screen is displaying sonar on the left and StructureScan "sidescan" on the right.
Modern recreational depth sounders evolved from the SONAR (Sound Navigation and Ranging) equipment developed during the First and Second World Wars to help surface ships detect and locate enemy submarines. These technologies have come a long way in a century, and the calibre of entry level sounder available to recreational anglers nowadays would’ve completely amazed those wartime destroyer captains!

Today, very few boat fishers head offshore, or even onto our estuaries, lakes and rivers, without having some sort of sounder unit on board. These tools are now viewed as an almost essential piece of kit, with base units priced keenly enough to fit almost any budget. Yet I constantly encounter anglers who struggle to make sense of what their sounders are telling them. Hopefully, this series of blogs will help those people.

Many sounder users are best served by simply turning the unit on, setting it to auto and letting it do its own thing!

Without going into all the technical details, sonar works by transmitting sound pulses into the water, then listening for their return as they bounce off objects such as the sea bed, rocks or fish. By measuring the elapsed time between the transmission of the sound pulse and the return of any reflected echoes, a depth sounder can very precisely measure how far away those objects are. Most modern sounders then use this information to illuminate pixels on a screen, providing a graphic interpretation of what lies below.

Modern sounders are incredibly sophisticated and well-developed pieces of equipment. Rather like state-of-the-art cameras and computers, most casual users will only ever explore (or need) about a quarter of the potential power, functions and capabilities of their sounders! In fact, just as with modern point-and-shoot cameras, in the vast majority of cases, these casual users are best served by simply turning the sounder unit on, setting it to auto and letting it do its own thing! So long as it has been installed correctly in the first place and you’ve remembered to switch off the showroom “simulator” mode (a trap for new players!), the sounder should do a perfectly adequate job of telling you how deep the water is under your hull, showing you the basic contour of the bottom, and alerting you to any significant objects in the water column under the boat, all without you ever needing to push another button (except the ‘off’ switch when you get back to the boat ramp).

Remember to switch off the showroom “simulator” mode! This can be a real trap for new players.

At the most basic level, that’s what most of us want our sounders to do most of the time: tell us the depth, show us the bottom and give some kind of indication of the presence of any “targets” (which may or may not be fish) between our boat and the seabed. That’s really about it! So, don’t get carried away or confused by all of the other stuff you read about and see on line or in DVDs. Start with those basics, study the images in this blog and throughout the rest of the series, carefully read their captions… and you’ll already be well on the road to better understanding your sonar or depth sounder! In part two we’ll move on to some slightly more advanced stuff…

Any questions about this tutorial?