One of the most common questions I get asked at my electronics seminars is "Why can’t I see more on my depthfinder?" A simple answer isn’t available but after a few questions of my own, a solution can usually be found. Below are outlined the most common mistakes sonar users make and how to fix them.

The first step is simple-turn the unit from automatic to manual mode. The biggest mistake most fishermen make is using their sonar unit in automatic mode. This may be the easiest way, but it is also the quickest way to guarantee most of the information you want and need to be seeing won’t be showing up on your screen! Automatic mode sets the depth ranges, sensitivity level, grayline and chart speed of the unit based on factors such as depth, speed, bottom composition etc. The problem with these automatic settings is that they are never high enough for seeing the targets fishermen want to see.

With the automatic mode off we need to set up our sonar which brings us to our second step-using the proper depth ranges. Sonar units have a limited amount of resolution, which is measured by the number of vertical pixels. To get the best possible picture we need to use as many of those vertical pixels as possible. Top quality sonar units allow the user to set the top and bottom depth as long as they are at least 5 feet apart.

Here’s an example-suppose we are in 42 feet of water. On automatic the depth range will be 0-60 feet, which means that 18 feet of what we are seeing is below the bottom of the lake (60-foot scale minus 42 feet depth). That’s almost 1/3 of our total pixels wasted! Now on manual mode we can set the bottom depth at 46 feet-we want a few feet under the lake bottom so we can tell how hard the bottom is-and set the top range at 6 feet. When we talk later about sensitivity you’ll see why to never use 0 as a top range. With our manual settings we now are looking at a 40-foot section of the lake (6 feet to 46 feet) which means on a quality unit with 200 vertical pixels there is one pixel for every 2" of water. Any targets separated by 2"or more will show up as different signals. Now we can tell if what we see is a couple suspended walleye or a school of bait.

As a general rule of thumb my sonar units use a setting of 4-6 feet on the top and 6 feet deeper then the lake bottom for the deep setting.

Now that our depth ranges are set properly we need to jump to step 3- using the proper sensitivity setting. Sensitivity, also called gain, determines how much power is used to get a sonar return and is probably the most important setting. Too little power and you’ll swear there is nothing in the lake, too much power and all targets are drowned out and the screen "blacks out". The sensitivity will need to be changed constantly during a fishing trip. Increase the setting as the water gets deeper; decrease as the water gets shallower or when in heavy weed or wood cover.

A good baseline setting can be gotten by taking the boat to about 10-12 feet of clean sand bottom (no cover) and turning the sensitivity all the way down. Now start increasing sensitivity until you start to see thin vertical marks on the screen, when this occurs turn the sensitivity down until the marks disappear. Now the sensitivity is set right. You will also notice that the top of the screen from 0 down to about 3-6 feet is solid black. This is okay and is called surface clutter. Setting your top depth range just below this mark eliminates it and maximizes pixel use.

So far so good. Now that depth and sensitivity are properly set we can get into something that most fishermen don’t really understand-grayline or whiteline. Step 4 should clear up any confusion. Grayline is a feature that does 3 things, First grayline shows how hard the bottom is and visually shows areas of bottom composition changes, Secondly grayline helps determine the hardness of an object in contact with the bottom, Lastly grayline helps separate bottom hugging fish from the bottom.

The first function of grayline is determining bottom composition and hardness and this directly relates to the setting of the grayline feature. To properly set grayline return to our sensitivity setting spot, 10-12 feet of clean sand. After getting the proper sensitivity setting make sure the grayline is turned all the way off. Now set the bottom depth range to be 6 feet lower than the lake bottom. Begin turning grayline up until you see grayline (it looks like a light colored checkerboard) under the lake bottom. Keep increasing grayline until you have 3 feet of gray under the lake bottom. That’s it. Throughout the day if the bottom gets harder then sand the grayline will get further below the lake bottom, if the bottom gets softer then sand grayline will get closer to the lake bottom. Pretty simple with some practice.

With the proper grayline setting the other 2 functions of grayline can be used. The grayline feature will effect any object that contacts the bottom. If an object in contact with the bottom is as hard or harder then the bottom the object will have grayline under or inside it. Any objects softer then the bottom will have no grayline and will look like black bumps on the bottom. Fish lying on the bottom can be detected with the grayline feature. When we use the proper depth ranges and sensitivity settings fish close to the bottom will usually have a little bit of room between their bellies and the bottom. With the grayline feature on this space will show between the lake bottom and the fish.

We still have 3 more steps left for another article but so far there is a lot of stuff to practice. The best way to understand your sonar unit is to use it! Try different settings of sensitivity, depth and grayline. Keep a notebook with your notes and findings. Pretty soon you’ll be an expert and begin finding fish faster, and finding fish faster means one thing-catching more!