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A Little History of Fishfinders

As an offshoot of the sonar technology developed for military submarines, fishermen began to use large, bulky vacuum tube sonar units to find fish in the ‘50s.

All fish finders use sonar. Sonar sends sound waves through the water. When the waves bounce off an object, they echo back to the fish finder and are displayed on the screen. Any object will cause an echo: fish, seabed or lakebed, weeds or debris. Some fish finders will also plot the depth of thermoclines, areas where there is a sudden change in water temperature.

The sound waves are sent out and received by a small transducer. As they are emitted from the transducer they gradually spread out in size creating a cone-shaped pattern. Anything within this cone will be displayed on the fish-finder screen.

Fishermen try to match the cone angle of their fish finders to the depth of the water where they are fishing. Shallow and medium-depth water requires a broader cone beam. Many fish finders use only one cone-beam angle, while some allow users to switch between two or more cone angles by simply making a change to the fish finder's settings.

LCD screens are common on less expensive fish finders.

In the early years, all fish-finder displays were dials, much like the speedometer on a car. Bright lines appeared at the depths where the sonar detected fish. More advanced dial models are still available. Today, most inexpensive fish finders have black and white LCD screens while the higher-end models use color CRT displays.

LCDs offer less resolution but they are often easier to see in bright sunlight. They are also generally more rugged and waterproof than color displays. Color displays have greater resolution and can give the fisherman more information by color-coding different sized fish and features.

How well a fish finder operates in deep or murky waters has much to do with its power rating and the frequency of the transducer signal.

Highly powered fish finders pick up more details in murky water and are more reliable in deeper water. Generally, manufacturers will express the unit's power rating in watts.

There are two basic operating frequencies for fish finders: 50 kHz and 200 kHz. The slower frequency functions reliably to greater depths while the faster units pick up more detail at moderate depths. Some fish finders operate at only one of these frequencies, while a few allow anglers to switch back and forth between them.