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What is a Fishfinder ? A fishfinder is an echo sounder (sonar) specifically designed to detect the presence of fish in the underwater environs of the host boat. In addition to locating fish, bait, and structure, a fishfinder also measures the overall depth of the water. Water depth is also important navigation and safety data. A fish-finder uses echo-location to reflect electronic pulses off fish and other underwater features and converts this information into a graphic rendition, most often a full-color high-definition screen or liquid crystal display unit. The image on the screen, which represents individual fish with a small icon or as a series of arcs, enables fishermen to identify suitable targets and lower their baits or lures to the correct depth or over chosen structure. The units function by transmitting an electrical impulse which is converted into a sound wave by a transducer or hydrophone mounted on the underside of the hull and sent into the water. When the sound wave strikes something such as a fish or bottom relief, it is reflected back and displays size, composition and shape. The level of detail and precision depends on the frequency and power of the pulse transmitted. The signal is amplified and sent to the display unit. The display screen graphically represents the distance to the fish or object that reflected the sound wave. This process can be repeated up to 40 times per second. Fish-finder's are fast becoming an essential electronic tool, enabling fishermen to become more efficient in locating fish and fish-holding structure. Modern units are relatively inexpensive, easy to install and operate, and used on both commercial and recreational fishing vessels of all sizes and descriptions.