How Fish Finders Work

• 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.
  
  

Transducers

• 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.
  
  

Displays

• 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.
  
  

Power

• 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.
  
  

Mounting

• Fish finders can be both portable and mounted. A portable unit comes with a transducer that attaches to the boat's hull with a suction cup. The use of portable fish finders in kayaks has increased dramatically in recent years. For permanently mounted transponders, a hole is drilled in the hull away from any prop turbulence. There are also kits available to mount fish finder transducers onto trolling motors.
  
  

Other Fish Finder Features

• Manufacturers are now combining fish finders with GPS units. These are especially appealing to ocean anglers who find themselves navigating in open water.
  
  Side scanning sonar fish finders are another development. Manufacturers now produce transducers whose beams can be directed out from the boat parallel to the surface of the water and rotated 360 degrees. These are intended to complement traditional fish finders that only find fish directly beneath the boat.