How to Understand Sonar Fish Finders

How to Understand Sonar Fish Finders
Back in the day, fishing was performed with a stick, some line and a hook. Now, fish-finding sonar systems make it possible to essentially see beneath the surface of the water, making them viable tools for anglers seeking the ultimate catch. That being said, a fish-finding sonar, like many other high-tech gizmos, can be confusing. How does it work, after all? Understand sonar fish finders by understanding how sound travels in water and what happens when something gets in its way.


Difficulty: Moderate

Step 1
Understand sonar. This is the foundational tool that sonar fish finders use to locate large schools of fish. Sonar is sound--sound waves, that is. These sound waves are beamed out into the water, causing the water molecules to oscillate. Of course, if the sound waves are not obstructed, they simply continue to travel away from you.
Step 2
Understand reflection. If the sound waves beamed out by your sonar hit something--like a large school of fish--they bounce back. The resulting rebound is translated graphically onto the sonar's screen.
Step 3
Understand obstruction. Many factors--obstructions--can hamper the fish-finding sonar process. The first is simply the nature of large bodies of water, affected as they are by waves, wind and currents. Water is also filled with sediment--dirt, salt, plankton and algae, to name a few. These and other similar factors may cause a sonar's readings to be inaccurate.
Step 4
Understand the sonar's limits. A sonar cannot identify a certain type of fish, or even a specific underwater form. Rather than help you find a white marlin, for example, a sonar can be especially useful in locating drop-offs or gullies (where your hoped-for catch is likely to be) or large schools of fish pressed together (possibly pursued by a larger fish).
Step 5
Understand frequencies. Typically, low frequencies are used to penetrate deep water (exceeding 300 feet). Low frequencies also allow for wider beams--meaning the sonar covers more area. High frequencies are reserved for shallow waters (300 feet or less). A general rule of thumb is that the shallower the water is above 300 feet, the less you'll be able to see.
Step 6
Read your individual sonar system's manual cover to cover. Sonar systems operate differently depending on brand and model. It is therefore imperative that you become intimately familiar with your system's operation. To start, that means reading the manual--then getting out there and testing the system on the water. As your system beams back reflections of what's underwater, these images will be projected onto your sonar's LCD screen as distinct shapes. The resolution (in pixels) depends on your particular brand and model. Over time you'll improve your ability to read the shapes on the screen.

Tips & Warnings

Consider sonar with GPS. You'll be able to locate fish and underwater forms--and make a note of the best fishing spots via GPS coordinates.

Article Written By William Jackson

William Jackson has written, reported and edited professionally for more than 10 years. His work has been published in newspapers, magazines, scholarly journals, high-level government reports, books and online. He holds a master's degree in humanities from Pennsylvania State University.

Don't Miss a Thing!

All our latest outdoor content delivered to your inbox once a week.



We promise to keep your email address safe and secure.