Fish Finders: Real time readings

Fish finders, Depth finders or Sonar’s, no matter what you want to call them they are all the same in what they do by helping the angler determine the best place to throw some baits. but in this post I’m going to refer to them as a depth finder

How Depthfinders Works

Depth finders work by sending out an electronic impulse from the unit to the transducer. The transducer converts the impulse into a sound wave that is beamed through the water column. The sound wave will travel downward until it reaches the bottom structure, after which it will bounce back to the transducer. The sound wave will also travel through any objects found between the lake bottom and the surface of the water (fish or baitfish). When the signal is received, the unit will then make its interpretations, finally showcasing the results on the screen. These results will include depth of bottom, any vegetation or structure found and any fish or baitfish that were located under the boat at the time of the reading.

Technology has advances in the last five years that gives us more choices and options like the side view and the GPS mapping, just more tools to help us in our search for our targeted species. The GPS is the coolest thing though for the way I fish, because I like to fish natural structure and I can mark a mapping path of a deep ledge by making way points every 30-50 foot and then connect the dots with my boat keeping the baits in the strike zone and you can get right back on that ledge the next time your fishing the area. This saves a lot of searching time.
The new side view is cool because you can see structure up to 150 ft out each side of the boat, making it easier to find structure and potential spots, mark that spot on your GPS and you will be able to set up on it quickly.

There are many different brands and horsepower’s along with prices that will reflect on the amount of gadgets and task they perform. It just depends on where you fish and what you want it to do when choosing a depth finder.

The power of a sonar unit is described in Watts. The term “peak to peak” is used to describe the overall output power of the transmitter. When dealing with depth finders, the higher the wattage, the more efficient and powerful the overall unit will be. The bare minimum peak-to-peak power would be 800 Watts Low wattage will ultimately bring you slow readouts, meaning a delayed reaction for a reading of a spot you have already traveled over, but accurate at keeping you in touch with the bottom.

These low-wattage units will run anywhere from 99.00 to 300.00 and will keep you in touch with the bottom structure and maybe give you a temp reading.
One key point to remember: before you purchase a unit, the shallower the water you fish, the less power you will need.

For those that fish deeper water (such as the big rivers and reservoirs) I would recommend the higher wattage units 3000 plus Watts. these units can run from 499.00 to 2200.00 it’s best to choose the most powerful unit that will do what you want it to do, for what your wallet will allow.

I personally use two depth finders on my rig. One on my dash for locating structure and GPS mapping spots when I first pull up on them and the another one on my trolling motor to pin point my bait delivery and staying on the structure or path. And both are in the mid priced range and these units will perform right out of the box with just one push of a button.

Al though these units have lots of functions and settings I use them with their factory defaults. I see a lot of guys that mess with the settings a lot because there not seeing what they think they should see and get totally frustrated pushing buttons and getting the fish finder all out of whack in the process. I’ve found that the auto adjust setting works best for me right from the get-go.

I personally don’t use my depth finder to locate fish. I use it in a process to locate spots that have all the elements that the catfish are attracted to.

Knowing how to use the depth finder is easy if you don’t expect it to solely rely on it for locating cat fish, it’s kind of like a puzzle and you have to put the pieces together. What I mean by that is, take the information from the depth finders, add that with your basic knowledge of the prey that you’re fishing for and then combine that with your (gut feeling). You know that feeling you get when you’re on the water? Cruising down the bank and see a spot and say yea! That’s the place?

Depth finder readings
Basic fishing knowledge
Gut feelings

The trick here is to use these three pieces of the puzzle to place your baits in most productive area.
My fish finding process
I’m going to start the blue catfish finding process as soon as my depth finder is turned on, first ill check the general water temperature which gives me my first clue to process, OK, 69 degree the middle of October so fish could be anywhere, because that temperature is in there comfortable zone but it also tells me that there a lot more places I can look in shallower water, so on the next piece of the puzzle, I’ll be using my gut feeling and looking for a likely spot that looks good.
Alright I’ve picked a bank with my gut that has a transition on it which goes from a mud bank to rock bank just down from a channel bend. Now I’m going to cruise the area to gather more information. as I cruise the area I will zigzag heading towards the bank and then back out towards open water determining the general water depths and looking for depth changes , drop offs, hard or soft bottoms, just gathering all the info about the area that I can start to understand what’s happening in the wet unknown.
Now also while I am checking the area I also have an eye out for fish and bait fish but take note! I don’t put as much faith in seeing the fish as I do locating the natural structure, ledges, and drop offs, points, and flats. Places catfish travel and feed. Seeing fish just reassures me that I’ve picked a spot where fish in general are holding and catfish are sure to be there too.
Ok now I’ve got to evaluate what I’ve learned from searching this area and decide where to start fishing.
Here’s what I’ve got so far! I’m at the end of a channel bend where the transition of mud turns to chunk rock. The water depth goes from 10 ft at the bank, descending slowly creating a flat with an average depth of 28 ft flat, dropping to 35 ft on a natural break and dropping off and flatting out and then dropping into the 45 ft channel. The bottom is hard rock and gravel, I didn’t see any bait as I was searching but this spot has all the other elements that I think the blue cat inhabits so I’m going to continue piecing the puzzle.

So now I’m going to bring back the factor of the water temperature of 69 degrees. I know that’s pretty much a comfort zone for most fish, so the catfish do not have to be deep as they were in the summer, and I can look shallower. Also I’m going to add some cat fishing basic knowledge to the mix and that is, catfish use breaks and drops to navigate the area. Adding this Intel to the process of the fish finding puzzle.

OK here we go the final decision on where to start cat fishing is based on all my resources. #1 gut feeling #2 basic cat fishing knowledge and #3 information obtained from the depth finder.
So here’s my conclusion, I’ve decided to fish the shallower break line, just because the water temperature is cooler, and im thinking the fish don’t need to be deep, but they still have quick access to the deep water and I know that the catfish use an area like this as a road so to say for traveling, feeding and resting. So I’m going to start on the break in 28 ft of water that drops into 35ft to see what’s up.

Try this fish finding process yourself the next  time your on the water to see if it works for you.

Heres a cool little video I shot this summer of some real-time readings on my depth finder, I was able to see and call the bite. And this was on my basic 400.00 trolling motor unit, set up on the factory defaults and auto sensitivity by pushing the on button only..


  1. blackhorse says:

    Very good information as always Steve.

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