157Depth sounders and fishfinders can be
among the most troublesome of all categories of
marine electronics because they are sensitive to
both over- and undervoltage situations. In addi-
tion, the transducer that sends and receives sig-
nals from the bottom can be fouled by marine
growth and needs periodic cleaning. It also
must be carefully installed in the correct loca-
tion on the boat’s bottom to ensure maximum
functionality. To keep these devices performing
properly, a first-class installation is paramount.
Displays and Cables
Depth sounders have four types of displays:
LCD screen (color and black and white), CRT
(similar to a television screen), paper graph, and
spinning wheel flasher. When choosing a depth
sounder or fishfinder, be sure to check the read-
ability of the screen, especially in daylight.
The cable that connects the transducer to the
display is carefully impedance matched to the sys-
tem, so under no circumstances should you alter
its length or wire gauge. Doing so would severely
affect the performance of the system. When
installing, carefully route the cable to avoid inter-
ference from other electrical equipment.
Transducers
The transducer is mounted on the bottom of the
boat. Its purpose is to convert the electrical signal,
or pulse, from the depth sounder to a sound,
called a ping, and transmit it through the water.
The sound wave travels until it hits something,
and then echoes back. The transducer captures
the echo, converts the sound back to an electric
signal, and sends this back to the depth sounder.
This process of transmitting, echoing, and receiv-
ing can happen up to forty times per second.
Transducers on simple, numerical depth
sounders are intended to point straight down (or
nearly so), while on the most sophisticated units
they may have sideways- or forward-transmitting
installing depth sounders, weather systems, and autopilotscompare:0’200’600’1,200’1,800’2,100’2,400’2,700’3,000’50 kHz 200 kHzThe beam of a high-frequency (200 kHz) depth sounder is narrow, cov-
ering a 10- to 15-degree arc. This is good for close focus on the bottom
and will give maximum bottom detail. At 50 kHz, the beam is wider and
generally better for scanning greater depths and providing a broad
view with fewer details. Another consideration is power output. A
1,000-watt unit can reach greater depths than a 600-watt unit.