What They Do
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. How They Work
Fishfinders separate and
enhance the information received from a transducer to show underwater objects. Information
is presented on a graphic display, showing a representation of the water column below the
boat rather than with a single digital reading, as with depth sounders.
Every fish finder has a display/control
head and a transducer. They must be matched in frequency in order to work. The
display/control head has three subcomponents: the display, transmitter/receiver,
and the signal processing software. Other components may be added to contribute
additional information including temperature, speed, and navigation information.
What to Look For
Transducer(s)
Several factors affect transducer
selection: normal water depth, frequency, desired beam-width, bottom detail, and
transducer size. See Depth Transducer Pros and Cons later in this section for more
information.
Display Type
There are two main types of fishfinder
displays: Liquid Crystal Displays (LCDs) and Cathode Ray Tubes (CRTs).
LCDs are very compact, draw a
small amount of current, have good contrast in daylight, and are available in resolutions
up to 320 x 200 pixels. Newer technologies such as Film Super Twist provide far greater
contrast and viewing angles than first generation "gray-on-gray" displays. The
protective lens over the display must not cause excessive reflections in sunlight, or the
display will be difficult to see.
CRTs are similar to a
television screen. They are available in both monochrome and full color models. By using
different colors, the relative strength of the echo is shown, for easier discrimination
between different types of targets. The depth of a CRT enclosure is roughly the same as
its diagonal measurement, which fills up a boat's helm station in a hurry. In bright
sunlight, CRTs must be used with a viewing hood, or mounted in a shaded location.
Display Resolution
The resolution of a fishfinder's
display is what determines its ability to see fish near the bottom, separate closely
spaced targets from one another, and see fish on the edges of "bait balls."
Display resolution is determined in two ways: the vertical pixel count from the top to the
bottom of the display, and the number of pixels per square inch. A large number of pixels
vertically will show target depths more accurately. More pixels per square inch will
provide better detail of structures, a better representation of what's below you, and
improve split screen images. But remember: the contrast of the display must also be sharp
in order to use the resolution.
Displayed Image Options
3-Dimensional Images display a perspective
view of the bottom by splitting the transducer beam into sections. While we'd like to see
a TV-quality image, most of the products available display a wire frame representation of
the bottom. While not terribly detailed, they are good for large bottom structures, and
for showing you the location of fish.
Scanning Sonar can
"steer" its signal from a single transducer to "look" to the right and
left, or fore and aft. This allows you to see where fish are within the beam of the
transducer. The Interphase phased-array sonars have dramatically lowered the entry price
into the world of scanning sonar.
Split-Screen or Data Window
displays enable the fishfinder to display different types of information simultaneously.
For instance, you can display a track plot along with the normal underwater display. Data
Windows provide digital information (speed, depth, temp, lat/long) along with the graphic
screens.
Additional Capabilities
Integrated Loran or GPS receivers reduce the clutter on your instrument panel. Since
the graphic display on a fishfinder is a perfectly good place to display navigation
information as well, these dual-function products have become very popular. However, due
to the superiority of GPS, we would not buy one with a built-in Loran.
Temperature capability
detects and displays surface water temperature. Since many fish species are found in
specific water temperatures, a temperature graph or digital readout can be helpful in
finding them. Remember, this is the surface temperature and has little relationship
to the water temperature where the fish are holding!
Speed/Distance capability lets
you display speed and distance so that you can maintain accurate trolling speeds. The
knotmeter will also compute distance so you can see how many miles you've traveled in a
day of fishing.
Grayline®, White Line, or Bottom
Hardness displays the bottom signal as a thin line, with a variable width band beneath
it. This both indicates bottom hardness and allows you to separate targets near the bottom
from the bottom itself. Experienced users will be able to differentiate between mud, sand,
and rocky bottoms.
Fish symbols show intermediate targets as fish icons, with the
size of the icon indicating the relative strength of the return. While it is sort of a
cute feature, it masks the actual signal from the user. Most experienced users will
usually opt for the display that shows targets without fish symbols (called fish arches).
Digital displays require no
interpretation when determining water depth or target depth. While it is true that a good
graph imparts relative information quickly, discrete information like speed, temperature,
and depth is most easily understood with a simple numeric display.
Alarms alert you to one of
four conditions: shallow water, deep water, intermediate targets (fish, we hope), and a
change in water depth (anchor alarm).
Glossary
Auto Settings make it easier for the first-time user to get a useful
picture. This is sort of like using the default settings on a TV or computer.
