Interpreting Sonar
The problem with both deep water and soft bottom is the weak signal they return. In deep water, the signal travels a long way on its round-trip from surface to lake bottom and back to the surface again. As it travels, it becomes weaker and therefore harder to detect, translate, and display. On soft bottoms like muck and silt, much of the signal is absorbed by the substrate. To improve readings over such substrates, turn up the unit’s sensitivity in manual mode to a level higher than the default one the unit’s auto mode selected. In water shallower than 5 feet, the return signal can be too strong because of the short distance it travels: In this case, auto mode may not reduce the sensitivity setting enough to produce a clear picture. Instead, the whole screen may “gray out.” To adjust, turn down the sensitivity in shallow water or over a hard bottom, thereby providing a narrower cone angle. In deeper water or over softer bottom, increase sensitivity to provide a broader cone angle.

Weeds provide another set of challenges for controlling sensitivity. Bass fishing along the edges of weedlines or over weedbeds is common. Locators that are set in auto mode have difficulty handling such locations. If you increase the sensitivity to penetrate to the bottom in a weedbed, the screen will be saturated and lacking in detail. Remember that increasing sensitivity raises the unit’s listening ability, not the locator’s power. When you power up in auto mode in dense vegetation, you get a strong return signal because vegetation is a good reflector, sending back a strong signal that lacks detail because of its multiple surfaces. Your unit is on overload. To reduce the unit’s sensitivity around weeds, use the sonar in manual mode, changing its sensitivity settings several times to learn which works best.

The sensitivity control is the locator’s most important function. Learn how it affects what you see on screen, so that the unit is working for and not against you. Head out to your favorite body of water and position your boat in shallow water, deep water, over hard bottom, soft bottom, over rockpiles and in front of weedlines. See how the unit reports back on each of these areas. Adjust its sensitivity settings to see how doing so affects the information displayed. Decide which work best in situations you’re familiar with. Doing so will give you more confidence in your sonar’s capabilities.