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John J. Casey, the justifiably proud
owner of Macushla, a new 61-foot Viking sportfisherman, could have been
forgiven had he lapsed into a daydream of tracking enemy submarines
off Palm Beach, Florida. His newly installed
Furuno CH250 Searchlight
Sonar illuminated the underwater scene with a beam of sonic energy,
rotating through 360 degrees like a radar—only scanning downward instead
of parallel to the surface.
At the straight-down tilt angle of
90 degrees and with a list price of more than $13,000, plus installation,
the
Furuno CH250 Sonar serves as the most expensive fishfinder/depth sounder on the
market. It is a virtual underwater radar, a fascinating experience in
multidirectional scanning and accuracy.
Casey began his search for fish with
the help of Furuno's Steve Bradburn, who demonstrated the new unit.
The boat slowed (to a maximum of 15 knots) so the sonar head could be
safely deployed from its stowage tunnel. Bradburn set the system in
horizontal mode, scanning through 360 degrees around the boat, with
the transducer's tilt angle adjusted to keep the sonar beam's upper
limit far enough below the bottom of the waves to eliminate reflections.
Bradburn adjusted the range to look
for targets within 500 feet. Almost immediately, Casey saw a group of
targets about 30 degrees to starboard, 400 feet away. The system's two-axis
motion sensor stabilized the on-screen image, which, unlike that of
a radar, is affected by moderate rolling and pitching.
The boat slowed to trolling speed,
and Bradburn changed the scan from 360 degrees to a 72-degree sector
scan centered on the bow. Again, almost immediately, Casey had a clear
view of groups of fish swimming near a small ledge on the sea floor.
A short time later, the boat's conventional fishfinder showed the same
targets as the fish entered its sonar beam.
The term "searchlight sonar describes
the Furuno CH250 Sonar's operating modes. The horizontal scan mode can search through
360 degrees, or in sectors selected from a menu of 16 choices beginning
at 6 degrees. The train angle, or direction of the center of a sector
scan relative to the boat's bow, can be selected in 6-degree increments.
The user adjusts the beam's tilt angle to suit the search task.
The center of the beam can be set in
one-degree increments from 5 degrees upward to 90 degrees downward.
Tilt angles of 30 to 40 degrees show the entire sea floor. Angles of
10 to 20 degrees show half the seabed; the rest of the scanning beam
illuminates the sea above the bottom. Tilt angles of 0 to 5 degrees
may show no bottom detail at all, but may clearly display the presence
of fish near the bottom.
In addition to selecting the scan,
train and tilt angles, the operator must select the training speed,
or how fast the sonar beam moves across the scan sector. This depends
on the ultrasonic frequency used (fixed by the type of transducer installed)
and the maximum range setting. A 360-degree search at distances up to
300 feet takes seven seconds, while a search at maximum range (3,500
feet) requires 81 seconds at normal speed and 45 seconds at fast train
speed.
All these adjustment choices, of course,
mean the
Furuno CH250
Sonar is not a device you can walk up to and use to best effect.
However, the logic of the controls and the excellent on-screen menus
will greatly shorten most buyers' learning period. During our 31/2-hour
foray, Macushla's captain learned enough about the system to be handy
with the shortcut menus.
In vertical fan mode, the system operates
like a conventional fishfinder, except the area scanned can extend from
the surface ahead of the vessel to the surface aft or to any segment
of that 180-degree sector. The scan may be oriented in any direction.
We used the fan mode while searching for fish and navigating a narrow
channel. The system functioned as a forward-looking depth sounder.
Data and menus can be displayed on
the MU—100C, 10.4-inch diagonal color LCD monitor or a multipurpose
screen. A small inset panel on the screen displays an entire set of
navigation data.
Owners can place the control-panel
module anywhere. Aboard Macushla, it was in a protected well adjacent
to the helm and below the bank of display screens. The arrangement of
the module's five rotary knobs, single cursor control and 22 push buttons
makes it possible to enter most commands without having to look at the
control module.
The similarity to radar continues in
the CH250's time variable gain control, which functions like the short-time
constant control of a radar and reduces the receiver's sensitivity to
quick-returning, close-in signal returns. Like modern radar sets, the
Furuno CH250
Sonar provides choices of display organization and color pallet.
The sonar head retracts into a tank
mounted to the boat's bottom. This tank should be placed one-third to
one-half of the boat's length from the bow, and as close to centerline
as possible. It has a diameter of about 15 inches, is about 2 feet high
and requires about 3 feet of vertical clearance above its top to allow
for the retraction mechanism.
A hull-speed signal triggers automatic
retraction of the transducer when boat speed becomes too high—usually
around 12 knots.
The
Furuno CH250
Sonar has an on-screen cursor that
measures horizontal range, depth and bearing to a target. An event marker
interfaced with the vessel's navigation system allows storage of the
precise location of fish and the bottom structures where they live,
and the target lock modes keep the sonar beam trained on a target as
the boat maneuvers on the surface.
The
Furuno CH250
Sonar is not quite like shooting fish in
a barrel, but it's darn close.
Other Great Furuno Sonar Systems for Fishfinding:
•
Furuno CH250 Sonar
•
Furuno CH250BB Black Box Sonar
•
Furuno CH270 Sonar
•
Furuno CH270BB Black Box Sonar
•
Furuno CH300 Sonar
•
Furuno CH300BB Black Box Sonar
•
Furuno CH37 Sonar (Sector Scanning, 162 KHz)
•
Furuno CSH5LLB/55 Sonar (Omni Sonar, 55 KHz)
Contact: Furuno Sales at PSICOMPANY.COM,
Tel: 1-800-826-2907;
http://www.psicompany.com
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