hUMMINBIRD flasher

Basic Operation

Your flasher is only as good as your ability to read and interpret the information it’s giving you. The best way to learn what you see on your display is to go over your favorite spot, where you know there is a tree stand, stump field, submerged grass etc., and see how it appears on your flasher unit. Approach it from several angles, put your rod down and just observe. Maybe you fish a spot where you’ve come up with the shell of a muscle clinging to your hook. Chances are this is a shell bed, which are bass hangouts during certain times of the year. You need to scope the area out by going over it and watching your flasher for a stronger bottom signal or a second echo.

Reading the Dial

A lake bottom is seldom level or uniform, and objects both suspended and on the bottom will also vary in depth. The dial readings on your flasher will indicate these varying conditions accordingly. To distinguish between the dial indications of structure and fish, anchor the boat and watch for signals that change. A changing signal will usually indicate a moving fish.

“O” Line

Depth finder flasher

The “O” line is your reference point. It means exactly that, zero depth or surface line. When you turn the “off/sensitivity” knob to the on position, the zero line will appear. Even if the boat is out of the water you’ll get a zero depth indication on the flasher dial. It is also telling you the unit is turned on. If for some reason you turn the unit on and the zero light does not appear, you either have an open in your power line or low voltage.


  1. Check to make sure your power cord is properly connected to the back of the unit.
  2. Check to make sure you have a good connection at the power source.
  3. Check your fuses.
  4. Look for a break in the power cord.
  5. If everything checks out physically, then you’ll need to use a meter and check to see if you have at least 10 volts at the power connector.
Even if the transducer cable is disconnected, the zero line will still be present.

If the zero line is not on zero or another words it’s at minus or plus 4 or 5 feet, again check to see that you have proper voltage at the connector. If this checks out you might need to have your unit repaired. When you first power the unit up you’ll see the zero line come from the negative side of the zero until it aligns with the zero and then locks in. This is normal since it takes the motor a couple of seconds to reach maximum rpm. It’s after the flasher has been on for a while and still will not align with zero that you need to be concerned.

Bottom Reading

Depth finder bottom reading

To set your depth finder's bottom reading, move the boat out from the bank until you think you’re in about 10 feet of water. With the noise reject knob turned to its lowest setting, turn the sensitivity knob up until the bottom reading appears. Now continue turning it up until you barely see a second line at exactly twice the depth you’re in…more on that in the next section on second echo. Now you have a depth reading to start with but will need to be adjusted when moving through different depths and changing bottom density.

A flasher unit does not have automatic sensitivity mode like a LCD unit that monitors changing signal strength. You have to watch the dial to see that you’re receiving a strong bottom signal to determine if the sensitivity is set at an adequate level.

Second Echo

The second echo is what you’ll use to determine adequate sensitivity level to give you strong bottom returns, structure and fish as discussed in the previous section on “bottom reading”.

Flasher unit second echo By setting your sensitivity high enough you’ll get a second bottom reading referred to as a second echo. It’s called a second echo because your bottom reading is the first echo. The second echo helps you determine whether you’re over a hard or soft bottom. While moving your boat over a consistent bottom depth, watch the second echo. If the second echo starts to fade or completely disappears this indicates the bottom is softer and absorbing the sound put out by your transducer. If a second echo or even a third appears, when your flasher was set low enough not to show a second return, you’re now passing over a harder bottom. Another indicator, without using the second echo method, is to watch your bottom line closely. If the bottom line narrows it means your moving over a softer bottom. The reverse occurs when passing over hard bottom. A hard bottom gives a stronger signal return causing the bottom line to widen. Passing over an old road bed or foundation with your flasher is an extreme example producing a second or even third echo to appear. Just remember these examples are based on your boat moving over a consistent depth. Keep in mind that depth change, although not as drastic, will also cause the width of the bottom line (signal strength) to change.

Noise Reject

Depth finder flasher interference Except for the Humminbird In Dash 60, a flasher is designed with an adjustable noise reject system. The noise reject knob should always be turned to the full counterclockwise position unless you experience noise interference. Noise will appear on the flasher dial, as seen in the illustration, as a flashing, moving pattern that cover the circumference of the dial. If the noise reject is needed, the amount of reflected signal may be slightly reduced. This is why you need to keep it turned to the full counterclockwise position unless needed.

I remember one particular problem we had with the Mariner outboards 40HP and below. The solution was simply to replace the spark plugs with a resistor plug made by NGK.

From time to time we would run into an occasional problem where we would need to work with another electronics maker of trolling motors, radios, livewell pumps, radar etc. to find a solution.

To eliminate engine noise you may need to reposition your transducer and cable away from the outboard. In the case of electronic noise from other accessories, relocating your flasher control head away from other electronics on your console may be the solution. The simplest way to determine if the interference is coming from another electronic accessory is to first turn each component on one at a time to determine which one is causing the problem. Then put some slack in the power and transducer cable and move the control head around until the interference disappears.

Bottom Density
Fishfinder flasher rocky bottom

Fish finder flasher muddy bottom

These two examples show the difference between your flasher bottom readings when passing over soft vs. hard bottom. The soft bottom, like the “FLAT MUDDY BOTTOM” illustration, will absorb a lot of the sound and not reflect it back to the transducer resulting in a narrow bottom line. Almost all of the sound will bounce back from a hard bottom, like the “ROCKY BOTTOM” example, sending a much stronger signal giving you a wide bottom line reading.

Reading Structure

Following are more examples of different bottom structures and how they would appear on a fish finder unit.
Flasher underwater cliff

Flasher brushpile

Notice the void area between 36 and 45 feet on the “underwater cliff” example. This could be confused with fish, from 15 to 36 feet, over a hard bottom since you have a wide bottom reading. Again, flasher units give you more information than a LCD type unit but can be more difficult to interpret. The old timers that learned to read a flasher first, swear by them and will always have at least one rigged on their boat. An important point to make here is the width of the bottom line. Since the average cone angle is approximately 18 to 20 degrees and the bottom coverage is about 1/3rd the depth, you would be seeing roughly a 15’ circle of the bottom in 45’ of water. However with the cliff interrupting the path of the transducers sound output, it can only show a portion of the bottom. If you know the bottom is rock then you would be able to determine something is blocking the sounds path giving a smaller bottom line. With this known, you can then realize you’re looking at a cliff and not a school of fish. If it was a school of fish, then you would see the entire 15’ circle.
Flasher depth finder steep rocky ledge The “brush pile” illustrates how a flasher would display limbs of a brush pile or tree over a soft bottom. The soft bottom is indicated by the narrow bottom line as compared to the wider reading on the “underwater cliff” example. It is possible to see fish in the limbs under the right conditions. If the boat is setting perfectly still you have the best chance of separating limbs from fish. If the readings on the dial appear and disappear or move up and down, while setting over the brush pile, chances are this is fish moving in and out of the cone or changing depth. The rougher the water surface is the tougher this becomes. Branches on the outer limits of the cone will look like fish as they continually disappear and reappear within the circle of the cone.

The “steep rocky ledge” shows what the reading would look like from several echoes coming back at different depth readings. Reading rocky ledges and bluffs can be difficult but it tells you that this is probably an area that is best fished parallel to keep your bait in contact with the bottom.Grass resembles the same reading you receive from a brush pile. However, since the returns received from the fish’ bladder is stronger than that of grass, by reducing the sensitivity you can actually separate the fish from the grass. The limbs and branches from a tree or brush pile are too dense to get the same separation as you would in grass. This is a technique I often use on Florida waters. Thick matted hydrilla is a little more difficult for this to work on but in the sparser patches it will.

Turbulence can come from your outboard prop, current or heavy winds. This usually will occur in the first couple of feet but if you’re fishing below a dam, the turbines can create turbulence several feet deep making it nearly impossible to determine between fish and air bubbles.

Surface clutter can be caused by wind or boat traffic. Surface clutter is not much of a problem with flasher’s as it is with LCD units. Some of the earlier model LCD’s would have a problem with the signal being blocked right at the surface and not allowing the sound to travel past the air bubbles at the surface eliminating any kind of bottom reading.

Thermocline is that level of sudden temperature change in the water. This usually occurs in the larger reservoirs during the warmer months. The sudden change in temperature also causes a change in water density at that level and sends a return back. This is more obvious on LCD and paper graphs than it is a flasher displaying a line across the LCD or paper graph at one pronounced depth. What it is telling you is to concentrate your fishing efforts from this depth up since the oxygen level below the thermocline is depleted and the fish will stay above it.

Fish Finder Flasher + LCD

Although a flasher is more difficult to read, I still have one mounted on my boat. I rely on it mostly for running from place to place. I keep one eye on the dial to catch a glimpse of any sudden depth change or that isolated structure that no one else knows about. A LCD type unit will not display information as fast as a flasher and cannot keep up with rapid bottom changes. Once I reach the spot I’m going to fish, I’ll turn my LCR on and the flasher off. Leaving both units on could cause interference to the LCR, especially when you move into deeper water where the transducers transmitted signals can overlap each other. Most boat packages still come rigged with at least an in-dash flasher for high speed use.

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