Understand Your LCR

Understand Your LCR


by Joel Tinker
Throughout the years I’ve had the pleasure of being in the boat with many knowledgeable fishing people. Hopefully, I was able to increase their know-how, I know that mine has benefited greatly. The one reoccurring thing that I find even with experienced, knowledgeable fishermen is their misunderstanding and confusion about their electronics. This ranges from trying to interpret the image on the screen, to understanding the actual electrical processes that are going on within the unit itself, to putting the two together to draw the whole picture of what their LCR is trying to tell them.

Many of the answers that I have found over the years have come from picking the brains of electronic reps and engineers. I have to say that although reps sell the units, their knowledge of the actual workings of the units will very greatly. Engineers have proven to be invaluable to me. Also, what one finds is that all displays DO NOT look the same for the same conditions. This can very greatly, even within different models of the same brand. This makes experience with YOUR unit important. Some things will always remain constant, but if you jump from one unit to the next you probably will never know any of them well.

One more thing before moving on. It has been my experience that once I can find the person with the answers to my questions they are usually accurate with their information. The only place that I have found there to be misinformation is in the area of using gray scale to determine bottom hardness. More about this later.

When fishermen know the general concept behind the workings of their locators they usually grasp the simple things that their unit is trying to tell them. First, lets do a simple test to see how much understanding you may have of the general workings of a LCR.



1) Which would be the correct interpretation of screen #1?

A) You are anchored on a drop off.

B) You are anchored on a flat.

C) Both A and B are accurate interpretations.

D) Neither A or B would be accurate interpretations.

2) Which would be the correct interpretation of screen #2 if you’re boat is motoring in a straight line?

A) You are motoring across a flat.

B) You are motoring along a straight drop off.

C) Both A and B are accurate interpretations.

D) Neither A or B would be accurate interpretations.

3) How about #3 if your boat is moving?

A) You are motoring over a series of midlake humps.

B) You are motoring along a drop off.

C) Both A and B are accurate interpretations.

D) Neither A or B would be accurate interpretations.

4) And #4?

A) You are anchored on a drop off.

B) You are motoring up on a drop off.

C) Both A and B are accurate interpretations.

D) Neither A or B are accurate interpretations.

5) Screen #5 is telling you what?

A) You have just motored over a hump.

B) You ran you’re boat over a point.

C) You are running a drop off.

D) None of the above are accurate interpretations.

E) All the above are accurate interpretations.


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Answers 1)C, 2)C, 3)C, 4)B, 5)E

If you got any of these questions wrong you probably could use further review of the basic concepts of locator operation. Read below.

To understand what you’re LCR is trying to tell you in regards to the shape of the bottom, you should view the picture as a graph of bottom readings. The pixels coming on the screen to the right are the newest readings, as you move left on the screen the readings get older. As the line representing the bottom changes up and down that is a reflection of the bottom depth changing. Too many people try to read their units as if they are watching a TV. The picture is not what the bottom looks like, it is a picture of how the depth changed. Once this is understood some of the above questions start to make sense. In question 1) the answer is C because when you’re boat is sitting still there is no change in depth so no matter what the bottom looks like you’re unit will show it as flat. The answer for 2) is C because motoring across a flat will show no change in depth and if you were to motor along a drop that was straight and you’re boat goes straight there would be no change in depth, so you’re unit shows a straight line. Do you now see how in 3) there is no way to know if we are going over midlake humps or bumping up against the edge of a drop off until we investigate further. So much of learning the layout of a lake is just that, putting in the time to figure out what you’re unit is telling you. Often times I’m in the boat to fish and I never wet a line. I figure if things are slow, I might as well learn something. Knowledge of you’re lakes bottom layout is something that no one can take away from you and it will put fish in your boat many times over for the amount of time invested. Make the investment!

If we look at the answer to question 5) we can see at least three possible interpretations of screen #5. Many people would look at the display of screen #5 and think that the picture shows a hump, but all the picture is telling us is that we were at one depth, we motored up onto shallower water and than continued on to drop back into deeper water. Only by running you’re boat at the same structure from different angles can you truly tell what type of structure you are on.

The signal that is sent into the water by you’re locator is a cone of sound, as the sound goes deeper in the water, the cone gets wider. Question: If you’re boat is sitting on a sharp drop off and the cone of you’re LCR is covering the drop, what depth does you’re unit think it is in? (See figure #1 below, are you in 25ft or 37ft?)



The answer would be 25ft. Although you’re unit is going to try and tell you that it is reading depths ranging from 25ft to 37ft, it will take a fairly skilled person to pick up on it. What most people would read is the top of the bottom reading and the digital read out for depth and figure they are in 25ft of water. It would be possible to have fish in your cone that would not show up because they would be part of the bottom reading.

One of the more confusing things that I have found in trying to use my electronics is telling bottom hardness. All reps and engineers that I have talked to tell me that the thicker the greyscale shows the harder the bottom is. I have not found this to be true in all instances. In fact, in some places I have found just the opposite to be true. Much of my fishing in the fall is done with someone using a large jig or blade bait over the side of the boat. This is a great way to keep in contact with the bottom and is a very accurate way to judge bottom hardness. During the rest of the fishing year there is always a jig in my boat in case I need to check the bottom. One thing to be careful of using this method is that from time to time you will find a bottom that feels hard, but if you probe carefully, you find that you are actually sinking the jig through several inches of very soft silt before it is coming into contact with the harder bottom. This soft silt will sometimes show up on your LCR as a thicker dark line at the very top of your bottom reading.

I do not know why this grayscale thing is not consistent, but if you use the same locator all the time it does not matter. The same spot will read the same each time you pull your locator over it. Once you use the jig to find out what your unit is saying, you can trust those signals for that spot from there after.

I have places that are packed sand and gravel and you would never know it by the thin or at times none existent greyline. Yet, I have other places that show an extremely thick greyline and are nothing but three feet of silt. There just is not the constancy in readings that one is lead to expect. I have had this same thing happen with several brands of locators. Some are better at allowing you to see when you have had a change in greyscale and this is a plus, but the ones that I have experience with are hit or miss as to what is actually under you from what the reading is saying.

The most important thing in using bottom hardness for catching muskies is to know when you are in a transition from one type of bottom to another. It is the change in the reading on your locator that will tip you off to this, not the greyscale. In most instances the change in bottom content is very abrupt, usually just a foot or two separates hard from soft. It is this line of change that fall muskies relate to and if you can stay near it you will come into contact with fish. Lets look at some examples of readings which may be typical of a bottom change.

Screen #6 is showing a change in bottom hardness. By the book this should be a move from hard to soft bottom. My experience has not always shown this to be the case. What is important is to know that in this spot this is what the change looks like, be it from hard to soft or from soft to hard. Put the jig down and know for sure which you are being shown, than remember it for future reference.


While units are not a fast and true method of knowing bottom content, the jig is. If you use the two in conjunction with each other you will be amazed at how well you know your lake. Not only do you know the depth layout, but you also know the content layout as well. To start to have knowledge of this magnitude is what starts putting fish in the boat consistently.

The next area on the horizon for me is the use of the new video camera technology that is now available. It should help me to determine what my locator is trying to show me with some of its finer details. The new cameras should be great at letting one see what those detailed bottom signals might be. Are they small fish, weeds, rocks, old roots, etc.? Also, they should come in handy for checking out schools of baitfish. Wouldn’t it be great to know exactly what type of bait is under you at any point in time. If these questions can be answered with this new technology, I will have the answers soon. Stay tuned.

Joel is the owner of Top Tackle Guide Service
http://www.toptackle.com