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Searchlight Sonar is by far the most common and cost effective and works by transmitting a single ultrasonic beam into the water column before moving a set amount of degrees and repeating the process. In this way a Searchlight Sonar can search a wide area sequentially. High frequency ultrasonic waves take a comparatively long time travelling through the water. To increase the speed of searchlight sonar search capabilities, Furuno has developed the high speed training feature which is available in the CH-500/600 Searchlight series sonars. This allows the sonar to update the display with high resolution echoes much quicker than previous Searchlight sonars. The user can set the training speed by adjusting the step scan speed by selecting the best setting to suit vessel speed and species. It provides 6 selectable step variations (6°,12°,15°,18°,21° and 24°) for high scanning speed that can cover sectors widths from 24° to 360° in a couple of seconds. The CH-500/600 can rapidly scan a large area providing the ultimate fishing Searchlight sonar experience.

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CSH-5L Mk2
CSH-8L Mk2
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Scanning Sonar is the ultimate fishing tool! It can search 360 degrees around the vessel in an instant. Due to the wide beam, no dead zones (zones that will not get displayed properly due to narrow beam width) will appear in the horizontal direction. Since the Scanning Sonar searches 360 degrees around the vessel, the same fish school can be identified multiple times. Based on the information received by the Sonar it is also possible to estimate where the fish school is heading, and at what speed.

Scanning Sonar can display information "full circle" at 360 degrees, or "semi-circle" at 180 degrees at a time.

Sector scanning has a scan area of 90 degrees or 45 degrees at a time. Sector scanning works much like Searchlight Sonar, except that the beam width is much wider.


For the purpose of fishing sonar is defined as a device that can search both horizontally and vertically while a fish finder can search only vertically directly underneath the vessel.

Sonars transmit and receive sound waves into the water via a transducer that is lowered by means of a raise/lower motor.  The sonar receives the returning echoes from the surrounding water column and anything that gets hit by these ultrasonic waves will give a returning echo that shows up on the sonar display and also via an audible speaker.

To locate fish schools, sonar shows a radar-like image of the surroundings of the ship. This image stretches from left to right and back and forth, showing the distribution and density of fish schools. Purse seiners, tuna fishermen and trawlers worldwide rely on Sonar on a daily basis to locate their catch. Sonar is know as the "unfair advantage" and quickly becomes the eyes and ears of a successful professional fisherman.

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Need some help understanding your sonar? Click on the play icons on the left to hear examples on what the sonar sounds like for different types of returns. You can also download the Sonar Tips Book by clicking on the icon below.