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 CH250 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 CH250’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 CH250 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 CH250 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 CH250 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.
It’s not quite like shooting fish in a barrel, but it’s darn close.
Contact: Furuno USA, (360) 834-9300; www.furunousa.com.