image similar to the look of
Humminbird’s Down Imag-
ing and Side Imaging systems.
You can also narrow the scan
to any sector, such as a 45-
degree sector ahead of the
boat. The narrower the sec-
tor, the faster the screen updates.
The transducer must be below the bot-
tom of the boat to operate ef ectively. One
option is a motorized transom-mount
pole mechanism that lets you deploy to a
predetermined depth and then retract the
transducer at the press of a fi nger. You can
also mount a transducer to a Minn Kota
bow-mounted trolling motor.
As with other imaging systems, the
slower the boat speed, the more detailed
the images. Also, even moderately high
speeds can damage or tear loose the trans-
ducer pole or trolling motor, lending impe-
tus to the need to keep it under 5 mph.
The Humminbird system will fi t on
boats of 20 feet in length or less. But more
powerful, stand-alone scanning sonar
systems are available from companies
such as Furuno and Koden. These are
designed primarily for large vessels that
fi sh of shore.
Residing in tubes as large as 8 inch-
es in diameter, the sonar-transducerassembly deploys from within a sea chest
and protrudes well below the hull when
in use, then retracts for running at high-
er speeds.
In some systems, the transducer me-
chanically rotates as it transmits. With
more-advanced systems such as the
Furuno CSH-8L Mark 2, the transducer is
stationary. It’s equipped with an array of
420 elements that transmit electronically,
resulting in a sonar image that’s updated in
real time. You can look 360 degrees around
the boat and as far out as 6,000 feet with
some systems.
Skippers who possess experience in us-
ing sonar can easily interpret the returns,
but newcomers might fi nd it di cult,
particularly with sonar using mechani-
cally driven transducers, which might take
more than a minute to make a full-circle
sweep, or “train,” as it is called. Veteran
captains have learned to listen to the au-
dio of the sonar’s “tap, tap, tap.” When a
target appears, the sound becomes more
of a rattle, alerting the captain to check
the display.
The biggest downside to these sys-
tems is the price. One of the least expen-
sive is Furuno’s CH-270 that retails for
$14,000, excluding installation, which
can be fairly pricey. The Furuno CSH-8L
real-time sonar sells for $75,000, exclud-
ing installation. By comparison, Hum-
minbird’s 360 Imaging system costs
about $1,280.
There are also space considerations.
Unless you have a boat that’s at least 35 to
40 feet in length, you won’t have room for
a stand-alone scanning sonar system. Not
to worry. There are plenty of other ways to
see underwater. And with this guide to so-
nar technology, you now have a good idea
of where to look.WITH IMAGING SYS-
TEMS, THE SLOWER
THE BOAT SPEED, THE
MORE DETAILED THE
IMAGES. KEEPING
SPEED UNDER 5 MPH
HELPS ENSURE THE
BEST RETURNS.
Humminbird’s 360 Imaging system gives you a full-circle view around the boat. ILLUSTRATION: TIM BOWER; PHOTOS: (FROM TOP) COURTESY LOWRANCE, COURTESY HUMMINBIRDLarge, powerful
sonar systems
like Furuno’s
CH-270 scan
in a wide
circle around
the boat.90 | BOATINGMAG.COM | APRIL 2018