In addition to Bob's advice ... It is sometimes beneficial to set the 2d "Lower Range" setting under the Sonar xpress menu to a value just below actual water depth ...

This puts the display in manual where the 2d bottom contour is not automatically jumping up and down on the 2d image to keep the bottom detail in the middle of the display ...

Setting the "Lower Range" setting to a value just below water depth also stretches the echoes out vertically on the 2d image to make structure and fish look larger ...

Rickie