All fish finders include a feature that allows to sonar unit to automatically set the sensitivity (gain). The effectiveness of the feature varies widely based on the manufacturer, water conditions (temperature, salinity, etc.), speed, other manual settings, and the type/placement/quality of the transducer. To ensure the best results the angler needs to learn how to manually adjust sonar sensitivity.
The following steps will ensure the best fish finder performance:
- Bring your boat to a depth you commonly fish (preferably more than 20ft). Do not attempt to do this in shallow water. The cone of bottom coverage from even the best transducers in shallow water is so small that the sonar unit is only good for showing the depth.
- Turn off the auto-sensitivity (gain) feature and turn off the auto-range feature (you can turn that back on later). Be sure that both auto-features are off! If your fish-finder is equipped with a fish ID feature, turn it off and NEVER turn it on again (see How to Understand Your Sonar).
- Manually adjust the range to more than twice the depth. If you are in 20ft of water you need to adjust your range to 50ft (40ft will not work). You can even set the range to three times the depth and get the same results.
- Adjust the sensitivity (gain) so that you can just see a faint second bottom echo. If your depth is approximately 20ft, you will see this echo at 40ft. The second echo occurs because your sonar signal is hitting the bottom and being reflected back up to the transducer. Some of that signal reflects off the surface of the water back to the bottom and up to the transducer again. The presence of the second echo ensures that the full signal is being picked up at the transducer. If your sensitivity (gain) is too high then the signal will be distorted and you will have trouble distinguishing bait from fish.
- Re-adjust the range to your desired depth or turn on your auto-range feature. Leave the auto-sensitivity and fish ID features off (indefinitely).
Periodically re-adjust the sensitivity of your sonar unit especially when moving the boat to an area when one or more environmental factors have changed. The optimal sensitivity (gain) depends on the following factors:
- Water depth
- Water temperature/density
- Water clarity
- Salinity (critical around outflows and river mouths)
Boat speed can also change the optimal desired setting. Less gain is required when a boat is drifting slowly in calm water than when the boat is trolling or cruising. The signal loss can be so significant that at higher speeds, full gain is required just to get a consistent bottom reading. In those situations the auto gain feature is probably the best bet (you are not going to mark any fish anyway).
When you are confident that you can properly adjust your fish finder, then you need to learn how to understand what you are seeing on your sonar.
The following video demonstrates the concepts for manually adjusting fish finder sensitivity.
Click to view on YouTube or share this link http://youtu.be/O9YTM5PTumU
Frequently Asked Questions
Turning off the auto-sensitivity (gain) and fish ID features allows you to manually adjust the sonar settings for the most accurate and reliable readings. These auto features can often distort signals or provide misleading information, especially under varying water conditions and depths. Manual adjustment helps distinguish bait from fish more effectively.
First, turn off the auto-sensitivity and auto-range features. Then, set the range to more than twice the water depth to ensure appropriate signal coverage. Adjust the sensitivity so that you just see a faint second bottom echo, which confirms your sonar is correctly picking up the full signal. Re-adjust sensitivity as needed when environmental conditions or boat speed change.
Fishing at depths over 20 feet provides a larger cone of bottom coverage for your transducer, making sonar echoes more distinct and meaningful. In shallow water, the limited bottom coverage reduces the fish finder's effectiveness mainly to depth display, limiting its ability to detect fish accurately.
Water conditions such as temperature, density, clarity, and salinity influence how sonar signals travel and reflect. These factors affect the optimal sensitivity setting, requiring anglers to periodically readjust gain when moving to areas with different environmental characteristics to ensure clear and accurate sonar readings.
Auto-gain may be beneficial during situations where the boat is moving at higher speeds, such as trolling or cruising. At these speeds, signal loss increases and full gain is often required for consistent bottom readings. However, using auto-gain in calmer conditions is not recommended if you want to distinguish fish accurately.
The faint second bottom echo appears when a sonar signal bounces between the bottom and water surface before returning to the transducer. This echo confirms that your sonar is receiving the full signal and is properly set to detect fish and bait accurately. If the echo is too strong or absent, sensitivity may need adjustment.
Boat speed affects the sonar signal's consistency and strength. When drifting slowly in calm waters, less gain is needed because signal loss is minimal. When trolling or moving faster, increased speed causes greater signal loss, requiring higher gain settings or auto-gain to maintain good sonar performance.
