Using a Fishfinder for Walleye Fishing – Sonar Basics

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I always tell my son that people really did locate and catch fish back in the old days before depth-finders, trolling motors, ultra-lightweight rods and every other newfangled, must-have fishing gizmo was invented. Fishing really is a very simple activity if you master some of the basics. I remember back in my teenage days spending an evening with a friend who had a basic aluminum boat, and a rope and concrete block for a boat anchor. We used that anchor to figure out how deep we were on the lake, and to locate the edge of a drop-off. Crude, but it worked.

Despite our ability to improvise, knowing what I know now about fishing with decent equipment I can tell you that fishing is much more fun, and much easier with the right tools. You really need to have some sort of electronics to tell you how far the bottom of the lake is beneath your boat. Anybody who does a great deal of fishing should really invest in some sort of sonar. The word “sonar” is an abbreviation for “SOund, NAvigation and Ranging.” It was developed during World War II to track enemy submarines. A sonar consists of a transmitter, transducer, receiver and display.

Fishing sonar units transmit an electrical impulse that is converted into a sound wave by the transducer and sent into the water. This wave strikes an object and rebounds, the echo hit the transducer, which converts it back into an electric signal, which is interpreted by the receiver and sent to the display. Sound travels in water at a constant speed of 4800 feet per second. Knowing this, the time between the transmitted signal and the received echo can be measured and the distance to the object determined. This process repeats several times each second.

In practical terms, the display of most fishing sonar will consist of a liquid crystal display something like the following:

On most units the screen scrolls by to give you a series of readings as the signals bounce off the lake bottom. This is from the Lowrance 334c. Even the least expensive units will have a similar display, although most at the lower-end will be black and white. The scale on the side gives you the depth reading. The solid line at 50 is the lake bottom. The little “hooks” you see above that line represent fish. Sonar gives you an instantaneous reading so you have a constant stream of information flowing to the unit. If you are cruising along the shoreline or along a point, you can watch your sonar to locate sharp drops or humps below the surface. In addition, most fisherman will use the sonar to determine whether or not there are any fish hanging around. If they don’t see those tell-tale hooks, they generally won’t waste any time tossing a bait in the water. Pretty tough to catch what isn’t there!

As if this innovation weren’t enough, we are now in the era of the combined technologies of sonar and GPS. Many of you have a Garmin or some other such navigation device in your car. Well, imagine how nice it would be if you had a detailed contour map of the lake you were fishing right on your depth-finder. Well, I’m pleased to tell you that this technology has been available for quite some time now. The image to the left is a typical image produced on modern fishing electronics. Units that include GPS features typically have a slot to accept an SD memory card produced by companies like LakeMaster or Navionics. These companies spend hours mapping popular lakes and then produce high quality maps like the one to the left. The best of these maps include very detailed countours as fine a three feet. Combined with global positioning, your boat’s position is overlayed on this map (which you can zoom in or our for more or less precision) allowing you to have a visual representation of your position on the lake relative to the physical features you see on the map. It used to take me a good 10 minutes buzzing back and forth to locate a mid-lake rock pile on my favorite local lake. And even then I might not have been exactly sure which end I was at. With the LakeMaster chip in my Lowrance I just leave the landing and head right to the rockpile. Guesswork gone. As with all things electronic, prices range from reasonable to ridiculous. You can expect to shell out $600-$700 for a color sonar/gps unit with a 5″ screen. Way more if you go for the bigger screen.

The bottom line is that the walleye fisherman’s arsenal really needs to include some form of sonar. A basic unit that gives you depth and fish marking will suffice for most anglers. A unit that can give you the depth and will mark fish below the boat accomplishes two very basic principles of successful fishing… locating structure, and locating fish. If there are no fish below your boat, there isn’t much point in dropping a line down there!

Ready to paddle out with your fishfinder? Learn how to use a fishfinder in a canoe or kayak. Or if you’re not ready to take the plunge, check out our recommendations for finding fish without a fish finder.

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