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Side-Imaging Basics
Barry Featheringill


After the introduction of  ‘Side Imaging’ technology back in 2004 by Humminbird  that made the available to consumers technology that maps the lake bottom in picture like detail. It is as if your boat is an airplane looking down on the lake bottom and taking pictures. The screen presentation is more like a monochrome photograph than what the conventional screen presentation of conventional fish finders.

The first units that Humminbird came out with this new innovative technology uses technology derived from military and commercial products to present the picture like detail. This technology prior to Humminbird’s development of the 981c SI and the 987c SI Combo was extremely expensive to use. Humminbird coupled this technology with high performance and popular features to make available to consumers.

The concept caught on and with the 900 series ‘Fishing Systems’ in addition to be rather pricey the 900 Series unit are a lot larger in physical size to what we are accustom to seeing in a conventional fish finder. The price of almost two thousand dollars made it tough to be able to say that it would be a good investment.

In July of 2006 Humminbird after seeing the success of the 997 c SI series Side Imaging units and seeing the number of anglers who wanted the Side Imaging technology but did not have the space for the large unit announced a new compact unit. This unit, the 797 c2 SI Combo would meet the desire for Side Imaging with a compact unit.

The 797 c2 SI Combo unit made it to the shelves of retailers in December 2006. The fact that this unit in addition to being smaller in physical size cost about half as much has made it a very poplar unit. The 797 c2 SI unit omits a single beam 86 degree beam at a frequency of 455 kHz giving 180 degrees of bottom coverage out to a range from six feet to three-hundred-sixty feet to either one side of the boat or both side.

How It Works

The transducer for the Side Imaging units sends out a two-bladed signal at eighty degrees to both sides, two other signals at different frequencies are also sent out to cover the down looking center area directly under the boat. One of these two beams looks at a twenty degree cone area for precision viewing and the other is a seventy-four degree cone for broader viewing looking for fish, bait or structure under the boat. The signals’ beams are oriented so that it starts at the surface and extends to below the boat giving a 180 degree coverage.

At the top of the image above at the center you see  icon that represents the boat position at time the “snapshot” (term for image recorded) is taken . The returns from the sonar coming from either side are represented on the corresponding sides. The most current information is at the top and the oldest data is at the bottom. When the sonar ping is first sent out it travels down the water column represented by the dark area in the middle of the screen. If there is structure, fish or other objects in the area below the boat and slightly either side they will appear in this area. The width of the “:water column” will vary with changes in depth very much like traditional sonar expect turned 90 degrees. After profiling the bottom contour below the boat Side Imaging looks out to both side to define the bottom contours out to 360 feet either side of the boat. The changes in depth are defined by shading.  Lighter shades refer to rises in contour and dark shades represent descending terrain. Objects that are suspended off the bottom like fish will not have a shadow adjacent to it, but there maybe a shadow will away from the object.

Using Side-imaging

Side imaging offers the tournament angler and the recreational angler by saving time in finding fish attracting cover and structure in a shorter time than with traditional sonar or the use of search bait to learn where the rocks and stumps are located. Once the angler finds fish you can with the use of side-imaging and find a stump here and another stump there and tie it to the bottom contour.

With having to spend less time searching for cover and structure anglers with the help of side-imaging will have more time to experiment with lure choices and presentations. Side-imaging takes the guess work out of offshore structure fishing.

Fish show up as white spots on the screen of side-imaging and will become clearer images at a closer distance with sensitivity increase.  Side-imaging does not define fish with as much definition as it does a log.  The technology will show the position of fish along cover and structure making it easier to determine lure selection.

Side-imaging with it’s wide coverage makes finding schooling fish easier and it will assist in determining the exact location of the schooled fish.

Another advantage to side-imaging is the ability to find structure without having to run over the top of it and spook any fish present.

All of the side-imaging units are equipped with GPS which allows angler to place cursor on the exact spot off to either side of the boat and create (Mark) a waypoint. With a

traditional sonar unit to find structure you have to run over the top of it. The structure must be directly under the boat with the traditional sonar. Side-imaging allows angler to be away from the structure and still mark a waypoint on the exact spot. This technology works regardless of the weather to see the tops of stumps or other structure that normally would not be visible because of light conditions.

The new side-imaging units also have the traditional sonar view, chart view (navigation), real time sonar view, circular flasher view and birds-eye view as well as several combination views that make them a complete fishing system.

This new technology now reveals structure that holds fish in a matter of minutes that with traditional sonar takes some times hours. This giving more time to the fun part of fishing…CATCHING.