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Fishfinders & Sonar
Helpful Product Advice
Fishfinders (fishing sonars, echo sounders) display a representation of what is below the boat, including the bottom, fish, vegetation and structures, to help you locate fish and navigate safely. Unlike depth sounders, navigation instruments that only show a number to indicate depth, fishfinders show you a graphic representation of the bottom. Fishfinders have three essential parts: a speaker/microphone, a stopwatch and a display. The transducer (the speaker/mike) sends and receives underwater high-frequency sound waves. Software in the display head (the stopwatch) calculates the time interval between the sending and receiving of these “pings.” Since the fishfinder knows how fast sound travels under water (slightly less than a mile per second), it can figure out the distance to detected objects. A graphic display plots this information, using shades of gray or a selection of bright colors to highlight differences in the strength of the returned echoes, highlighting structures of the bottom, layers of water of different temperatures and fish, individually or in schools.
What to look for
Display type
There are two main types of fishfinder displays: Passive Matrix monochrome and color LCDs, and Active Matrix TFT (thin film transistor) color LCDs. Both types have advantages and disadvantages. Color Cathode Ray Tubes (CRTs), hotter and heavier units similar to TV screens, are still being produced for seriously old-school anglers who like their higher contrast ratios and wider variety of screen resolutions, but these folks can get info from the SiTex and Furuno web sites.
Passive matrix LCD
Monochrome: Film super-twisted nematic (FSTN) displays use a circuit for each row and column of liquid-crystal pixels located between two sheets of polarized glass, with a backlight behind the screen. Requiring little power, they’re available in resolutions up to 640 x 320 pixels, with four or 16 different shades of gray, and are the least expensive type of display. Okay economy choice, but lacking in user-friendliness.
Color: Color super-twisted nematic (CSTN) is similar to the above, with 256-color capability. Recent technical advances make CSTN a viable, and more affordable alternative to smaller active matrix displays, but with dimmer colors and reduced contrast.
Active matrix LCD
Thin Film Transistor (TFT) displays include a dedicated transistor that controls each individual pixel, and are common in high-quality displays on chartplotters and fishfinders. 256-color capability is the minimum, and large displays meet the VGA (video graphics array) or SVGA (super VGA) standards, and have a theoretically unlimited range of different colors.
Transflective screens: A good compromise between daylight readability in bright sun and high contrast in dim ambient light. Transflective displays act as a transmissive screen, passing light from behind-screen backlight in dark conditions, and as a reflective screen in daylight, reflecting a portion of the bright outdoor light. Look for terms like “sunlight-viewable,” “anti-reflection” and “anti-glare.”
Display resolution
The resolution of a fishfinder’s display is what determines its ability to see fish near the bottom, to separate closely spaced targets from one another, and to see fish on the edges of “bait balls.” LCD displays are made of a grid of “picture elements,” tiny dots that individually darken when electrical current is applied, with their name shortened in common usage to “pixel.” More vertical pixels mean higher depth resolution, as each pixel represents less depth. If your screen has 100 vertical pixels, and you search for fish in the 0' to 50' depth range, then each pixel represents 6" of depth. This blocky display won’t let you see subtle details. A display with 240 pixels in each vertical column will show about 2 1/2" of depth; one with 480 pixels will resolve to 1 1/4", giving you a clearer picture. The number of pixels in a screen’s horizontal axis determines how long objects stay onscreen before they scroll out of view, of significant importance with split-screen displays showing narrow columns of side-by-side information. More pixels per square inch will provide better detail of structures, a better representation of what’s below you, and improved split-screen images. But remember: the contrast of the display must also be sharp in order to use the resolution. Like many features, you get what you pay for with display resolution—the more the better.
Connectivity options
Three fishfinder choices are available; standalone fishfinders that perform no other function, combination products that also include a chartplotter, and fully-networked systems offering a smorgasbord of potential functions, all viewable through one or more multi-function displays.
