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NZFW's guide to buying or upgrading your echo-sounder/fish-finder

09 July 2015
NZFW's guide to buying or upgrading your echo-sounder/fish-finder

Ed note to start. John Adams is an ex commercial fisherman with a vast amount of expertise using echo sounder. He is the author of How to use an Echo Sounder/Fish Finder, and a keen recreational fisherman.

The Scottish author John Buchan (1875 -1940) wrote “The charm of fishing is that it is the pursuit of what is elusive but attainable, a perpetual series of occasions for hope”. It is the hope part we try to mitigate when investing in technology, like a quality echo sounder.

John Buchan was obviously a seasoned angler, to have such insight into fishing as quote above alludes to. For those anglers new to echo-sounder fishing, there is an expectation that once a sounder is fitted to a boat it will catch fish immediately and consistently. Unfortunately, this is a misconception - echo sounders find fish, they don’t catch them.  

Interpreting the information recorded on the display is, for many fishers, a mystery. I totally understand and sympathise with anyone new to echo fishing and struggling to interpret the images scrolling across the screen.

There are no mysteries or secrets attached to echo fishing, only facts. Once these facts and principles are understood, they can be applied to any colour sounder and in any waters.

Considerations when researching new echo sounders

I have listed some points you may wish to consider when purchasing a new or upgraded sounder.

Firstly, what is the sounder’s intended use? If it is primarily for navigation purposes and an accurate measure of water depth, then a depth sounder with a digital read-out and without all the fish-finding functions will do the job.

If its intended use is for fishing, a sounder specifically designed for that purpose would be needed.

Generally, when first starting out, fishers start with a basic entry-level sounder, and in most cases that is all they will ever need. Those who venture out to deeper water will require a higher performance transducer, low frequency output, and functions such as TVG (Time Variable Gain).

Because today’s echo sounders and transducers are manufactured to the highest technological standards, it is difficult to make comparisons between the different models within the same price range. This is because they generally use similar technology and have similar screen view presentations, operating functions, frequencies and settings. The only real difference is in the menu systems.

Transducer performance can range from low, medium to high, which affects the depth at which underwater objects can be detected. Therefore, the depth range the sounder will be to be operated must be within the transducer’s performance range.

Screen view options

Full screen view showing the complete water column from the bottom to the surface.

Split screen view with each side showing a different section of the water column, using a bottom follower.

Full screen View Bottom Lock.

It is always handy to have a large display screen. For many small boat owners this is not an option due to the cost, and in many cases there is no room to fit one.

Often this is no major issue because echo sounders specifically designed for fishing usually feature a range of screen view options that allow the operator to enlarge, expand or zoom any section of the water column within the display screen.

When targeting demersal fish (those near the bottom), I set the display screen on full-screen view to start with. Then, when I detect fish targets or a bottom structure I want to have a closer look at, I switch over to picture zoom, bottom zoom, marker zoom, or bottom lock to closer investigate the section of the water column in question.

When I want to view fish targets, such as pelagics, in the middle levels of the water column, I switch from a full-screen view to upper and lower depth ranges, where I can view any section of the water column - for example from 30-60 meters.

Some examples of the situations described above are shown in screen captures hereabouts, which are acoustic images of fish and bottom structure, using different screen view presentations commonly found in echo sounders designed for fishing.

During rough weather conditions the recording of the seabed can become very ambiguous, caused by the boat heaving and pitching, rising and falling over the swell and waves. In this situation I always switch over to bottom-lock, where fish targets can be seen much clearer above the seabed bottom-lock line.

Some fishers prefer to use the seabed bottom-lock function even in calm conditions; I am also one of them. I commonly use the bottom lock display when fishing rivers, to obtain information about the nature of the bottom; this can be achieved by closely observing the changes in the bottom echo signal below the bottom lock line. An amazing range of information about the nature of the bottom can be obtained from this function.

Viewing a section of the water column using depth range function. The column to right is the A Scope.

Transducer power output and frequency selection

The performance level of the connected transducer determines a sounder’s operating range.

Sounding in water depths of 0-60 meters only requires a low performance transducer. Operating depths of 0-200 meters will, at the very least, require a medium performance transducer.  

Sounding in water-depths of 200 - 600 meters will only be achieved with a high performance transducer.

High frequency (200 kHz) is selected in shallow water, and will produce highly resolved screen pictures in shallow water depths. The depth-range at which this frequency can be operated is restricted, due to its high acoustic absorption loss through the water during transmission.

Lower frequencies (83/50/28 kHz) should be selected in deep water, and will produce less resolved screen pictures. Due to their low acoustic absorption loss through the water during transmission the depth-range at which these frequencies can be operated is less restricted.

Beam angles

It is also important to understand your transducer’s beam angle as this allows you to estimate the size of the detection area under the boat in the depth-range you are fishing.

For example, if you are fishing in a depth of 200 meters and your beam angle is 45 degrees, the transducer’s detection area, directly under the boat, will cover an area of approximately 157 metres in diameter.

Time Variable Gain (TVG)

For fishing in water depths of 100 to 450 metres, I would recommend a sounder that has a TVG (Time Variable Gain) function. When turned on, TVG will ensure fish located in deeper water depths will not go undetected. For example, a school of fish located in 20 metres of water will produce a stronger echo signal on the display screen than the same size school of fish located in 140 metres of water. This is due to the shorter distance the sound waves have travelled to and from their target.

The advantage of using TVG is that it avoids the illusion of fish located in deeper water looking a lot smaller than they actually are, or that they may go undetected altogether. The TVG function looks at the overall strength of the fish targets and records it proportionally to their depth. It does this by reducing the signal strength of the fish targets located in the shallower water and increasing the signal strength of the fish targets in the deeper water.

My experience has been that fishers who are not catching fish with their existing sounder will generally not benefit from upgrading to a new sounder. In many instances, fishers are better to stay with their existing unit and learn more about how to use them. Making a few adjustments to the settings can dramatically improve the sounders overall performance. And as the fisher’s ambitions increase, the argument for a more powerful echo sounder unit increases.

I hope you will enjoy learning about echo fishing as much as I have.

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