Fishfinder

The fishfinder is also called echo, ecometer, fishfinder, depthsounder or echosounder, although in nautical jargon the most commonly used terms are fishfinder to indicate an instrument capable of measuring depth only and fishfinder that stands for an instrument capable of displaying the bottom graphically and show fish.

The fishfinder sends an ultrasonic pulse to the bottom that is analyzed on its return, to determine through a sophisticated algorithm the depth and details of the bottom.

Three components are involved in this function:

• The transmitter, inside the fishfinder, sends an electrical impulse to the transducer
• The transducer receives the electrical impulse and transforms it into an ultrasonic wave that is sent to the bottom and from the same recovered and sent back to the receiver in the form of an electrical impulse.
• The receiver, inside the fishfinder, receives the electrical impulse which is then processed by the software to be shown as an image.

The workmanship of these 3 components is obviously fundamental to determine the quality of an echo-sounder:

• The transmitter must be powerful and low noise
• The transducer must have a good resonance box and be sensitive to hear the return echo again.
• The receiver must be sensitive

But it is not only these 3 components that are fundamental, it is in fact appropriate that a good fishfinder has:

• A sophisticated image analysis and structuring algorithm
• A large, bright and defined display

When choosing an echo-sounder, the analysis of the technical specifications is also very important, the following being the most important ones:

• The transmission power eco
• The transmission frequency echo
• The number of transducer elements and their transmission angle
• The presence of noise filters

There are also other important technical data, unfortunately almost never mentioned by the manufacturers:

• Ping Rate
• Internal receiver sensitivity

Adjustments

Today, all fishfinders do their job perfectly in automatic mode. In this mode the fishfinder can automatically adjust several factors including sensitivity (gain) and depth scales, but some also adjust the ping rate, transmission power, etc..
However, the more experienced can sometimes achieve better results by acting on the sensitivity and depth scales, especially in critical conditions, ie where the fishfinder can not detect reliable parameters and then "disorients" showing details far from reliable.

The display of the seabed

The techniques used to extrapolate useful details from the images that appear on the display vary according to the type of fishfinder and the brand. For example, the colors used to determine the consistency of an object may vary from one brand to another. So it's hard to draw up general rules.
But one rule applies to all fishfinders: the actual and simultaneous reading of the background is only on the first column of vertical pixels (the one on the right), the other columns are only a storage of previous data. So the whole image of the display even if it is intended to imitate the background, is only an image that identifies the history of what we have detected and is almost always not related to the real image of the background.
Let's suppose, for example, that we are boiling with the boat at anchor and that we are above the end of the apex of a submerged rock, the fishfinder will detect an image as if we were on a flat bottom, precisely because the reading of the first vertical column is always the same (the boat is stationary) and the columns of the historian will always report the same information.

The first use of sonar technology is attributed to Leonardo da Vinci in 1490, but the first prototypes capable of measuring the bottom through sonar technology appeared in 1912, when following the sinking of the Titanic there was a general spur to the use of new technologies aimed at giving greater security to navigation.

It is attributed to a group of English meteorologists the construction of the first prototype fishfinder in 1912, the following year also a group of German scientists succeeded in this goal. But the first one able to actually carry out the expected functionalities was that of the Canadian Reginald Fessenden (from whom his technology took its name: Fessenden Oscillator) who presented the prototype to the U.S. Navy in 1915.

About ten years later, Grove Dorsey, who had also worked with Fessenden, developed his first Fathometer, which could also measure depths of several hundred meters.

From that moment on, a series of prototypes and models followed one another, but all intended for military use or for hydrographic institutes.

The first commercial echoes appeared in the late 1950s, but it was only in the 1960s that they began to spread among fishing vessels.

The first commercial echoes were of the flasher type with circular bulbs that lit according to the depth detected. But almost at the same time, the first writing fishfinders appeared, able to give an unprecedented perception of the background and to have the historical background drawn on paper at one's disposal.

So it was that in the sixties there was a real race to the depth sounder written by all the fleets of fishing boats and the technology was recognized as so useful, that in case of failure of the depth sounder (very frequent for the valve technology of the time) the owner preferred to wait for the repair technician to face the fishing trip without the help of this tool.

In the recreational sector, technology began to spread only in the early 80's when the first echoes appeared with cathode ray tube monitors. But a great diffusion started only at the end of the 80's when the market started to present the first monochrome LCD screens that made the fishfinders compact for the first time.

The early 1990s marked an attempt to promote other technologies, such as Interphase forward scanning and Humminbird 3D visualization, which were initially well received but now cover a very limited audience.
Also in the same period, there were the first models able to integrate a positioning tool (at the time the Loran) in the fishfinder, in this was the queen of the U.S. brand Impulse (no longer on the market today).

It was only in the mid-1990s that the first TFT colour LCDs (Humminbird) appeared, a technology that still accompanies us today, but with much brighter and more defined displays, capable of presenting useful and inviting graphics.