2D, DownScan and SideScan

A fish finder with a Triple Shot style transducer can show three kinds of picture. Standard sonar, often called 2D, uses the cone and is the best at showing fish and how deep things are. DownScan uses a thin slice straight down and draws the bottom and anything standing on it in much sharper detail. SideScan sends two thin fans out to the left and right of the boat and shows what lies beside the boat, out to a distance you choose.

Think of them as three different cameras. 2D tells you what is under you and how deep. DownScan tells you what the bottom and structure under you look like. SideScan tells you what is out to the sides so you can find structure you could not see by driving over it.

Tap the tabs below. Each one shows the shape of the beam and a real screen from a Lowrance Eagle 7 in demo mode.

The screen photos on this page are demo mode (the unit running its built-in simulator), not a real lake, so the fish, bottom and temperature are made up by the unit. They are here to show where things are on the screen. The drawings are TexCast diagrams of how sonar works.

An interactive drawing goes here in the app.

On the water

• Start with 2D to learn the depth and find the bottom. Switch to DownScan or run a split screen when you want to see what is on that bottom.
• Use SideScan to scan along a bank, a point or a drop-off before you fish it. Drive a pass with the boat in the middle of the area, then fish the things you saw.
• On a split screen, keep the same range on both sides so the picture lines up.

Easy mistakes

• Expecting SideScan to show fish clearly. It is much better at structure and bottom changes than at single fish.
• Running SideScan over a range that is too far for the water. The image gets stretched, the detail disappears and the edges blur.
• Judging distance on a SideScan screen by eye. Use the scale along the edge, and remember the black band down the middle is the water under the boat, not empty lake.

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