By Steve Katz

When it comes to finding the best fishing grounds, some captains seem to have that fifth sense. Such helmsmen can consistently navigate to productive waters using little more than visual observation of the conditions and a chart or two. On the opposite end of the spectrum, some captains won’t leave the dock without the latest in high-tech gadgetry– satellite images, altimetry data and multiple on-board fish finding sonars and the like. For most captains, it is a happy medium that combines local knowledge with the right amount of technology that guides their search for productive water.

Finding productive-looking water is just the first step in the equation. Once there, how do you know that the fish are there? Most of us use a finely tuned echo sounder/fishfinder/ sonar. Others deploy the spread to see what awaits. What if there was something even better, a way to “see” if there are any fish around your boat in real time?

How a Fish Finder Works

At its most basic level, a fishfinder has a transducer that sends out sound waves in the shape of an inverted (upside down) cone. The transducer then listens for the echo of the waves as they bounce off of an object to determine the target’s distance—whether it be a fish, the bottom, or some other object.  The processor and display then convert these echoed sound waves into a useful image. This picture is a historical view of what was below the bottom of the boat as you move along.

There have been a lot of advances in fishfinders. These include CHIRP, wide angle, forward looking transducers—all that include faster and more detailed data processing capabilities. These improvements  mean that modern fishfinders—from the most basic and inexpensive to the top of the line– all do a great displaying the bottom structure and fish under the boat.

Fishfinder technology in the sportfishing space has recently been revolutionized by technologies that were once reserved for military and commercial fishing applications. Chief among these advancements are multibeam sonar and scanning sonar. Early adopters of this new sportfishing technology benefit from increased clarity and accuracy of imagery. Some products even provide data in near real-time.

Multibeam Sonars

A multibeam sonar has an array of multiple sonar emitters in one fixed transducer. These multiple beams are digital. They are “moved” to scan a wide angle, often 120-degree coverage, using hardware and software. How revolutionary is this 120-degree coverage? A traditional echosounder has a beam as narrow as 4-degrees. 

Examples of multibeam sonar used in sportfishing include Garmin Panoptix, Simrad StructureScan® 3D and Furuno DFF-3D. These systems allow you to see a historical view of what your boat passed over. Their wide view allows you to “see” the water column to the sides of boat, helping you learn if you are in an area where there are fish or structure.

Scanning Sonar

A scanning sonar works like your radar underwater– you can think of it kind of like “The Hunt for Red October.” Scanning sonars include a transducer housing that is lowered into the water from a storage tube within the hull of the boat. This transceiver can be rotated and tilted within the housing.  The transducer can rotate up to 360 degrees creating an image of the water area all around the boat. 

The tilt angle is adjustable for varying water depths and different applications. The Furuno “Searchlight” CH-50 is the most well know scanning sonar options used in the sportfish and commercial fishing markets. While this technology may seem new, the original CH-250 model has been in use for over 10 years—and newer models are currently available.

Technology has enabled the development of newer scanning sonar that does not need to rotate mechanically to capture the 360 degree are under the boat. The newest scanning sonar uses a transducer that deploys downward from the hull, like the Searchlight but consists of multiple stacked elements to transmit the sonar signal in all directions simultaneously. The combination of the processing power of the hardware and the multiple sonar elements allows the system to provide a real-time image of the water below the boat. Yes, that means you can see fishing moving in and out of the sonar beam coverage area!

While there are other manufacturers of scanning sonar, the Furuno Omni (CSH-8L MARK -2) scanning sonar is the most popular with sportfish boats. This unit is fast, able to complete a full circle scan in a half a second, as compared to 32 seconds with the Searchlight sonar. The Furuno Omni sonar uses a retractable transducer that is about 8” in diameter, with 14 layers of transducer elements. These multiple elements are combined electronically in the processor to display a full 360 image. The unit transmits its sonar signal on a fixed frequency of 85 kHz.  The beam angle, how far up or down the transducer “looks” can be adjusted from near zero – which is parallel to the sea surface to 55 degrees pointed downward toward the bottom.

The Omni sonar was originally designed for and used by commercial fishing boats and is a popular unit in Japan. Once the Omni sonar was installed on a sportfish boat and captains saw and caught more fish, word got out and it has become a must have for serious tournament sportfish.  

The most complex part of the Omni sonar is the transducer. You need a suitable area in the machinery space to install the sonar– up to about five feet of clearance inside the hull for a long travel hull unit.  Additionally, the system contains a transceiver, processor and control unit. This is a “black box” system, which can use most any standard marine monitor. As you might expect, a scanning sonar system is more costly than traditional systems, starting at $20,000 for the searchlight CH300 and $75,000 for the Omni CSH-8L Mark 2.  Understandably the complex installation of the system will add to the cost

The Benefits to A Sportfishing Boat

What does a fast scan get you? It allows a real time picture of the fish or lack of fish around the boat.  A traditional echosounder beam “looks” below the bottom of the boat and reports on the screen on the area you just passed over. The Omni scanning sonar can “look” around the boat, in a full 360 degrees with a range out to about 1000’ – a typical range when used for sport fishing. 

The specifications include much longer ranges, though the practical application is dependent on water depth, wave heights and other factors. This Omni sonar allows you to change the tilt angle, something that can’t be done with a traditional echosounder. Increasing the tilt angle allows you to scan more downward and a smaller angle allows you to focus on the top of the water column.

All of these scanning sonars use a stabilization component (motion sensor) to allow the system to calculate and compensate for the boat’s roll, pitch and yaw. Proper stabilization of the image allows the system to draw the sonar picture relative to the ship.

The Learning Curve

There is a learning curve when operating scanning sonar compared to a traditional echosounder.  Interpreting the results on the screen takes some practice. To fine tune your system, you will need to make some adjustments as well.  

Some users supplement the screen image with the audio feature, which emits varying tones when objects are detected in a monitoring zone. Many captains find this audio feature quite helpful.  It allows the sonar to monitor the forward sector of the vessel, while the captain keeps his gaze fixed behind the boat on the spread. He can watch for the rise of a sailfish or marlin, awaiting the squeak indicating the presence of a fish ahead of the boat. 

How do you operate and analyze the data from these scanning sonars?

A quick glance at the screen of scanning sonar often shows a red, doughnut-shaped image. What is this really telling you? Before you can interpret the screen, you need to learn more about the settings and adjustments necessary to understand what you are seeing. As the image is real-time, the Omni sonar is more intuitive to operate and interpret. 

Some of the necessary adjustments are similar to a traditional echo sounder– range, gain, TVG and the like. Other adjustments are exclusive to the Omni sonar. These include transmit power, pulse length, TX cycle, noise limiter, color curve, horizontal and vertical beam width and, most importantly, tilt angle. Beyond the adjustments, there are also many automatic functions– such as tilt angle and train sector (rotation) and auto retract (a critical function that retracts the transducer at a predetermined speed– the unit is not designed to operate at speeds over 16 knots).

Conclusion

Technology that was once reserved for science fiction books or for hunting submarines is transforming the sportfishing space. Captains on the Gulf Coast are reported to run up to oil rigs and scan them. If they “see” a marlin they stay and fish, if they don’t—it’s on to the next. Revolutionary technology indeed. 

What Furuno dealers are saying about the CSH8LMK2 Omni Sonar

“It’s a game-changer. The biggest advantage of the CSH8LMK2 is how quickly it paints. You’re not just looking at the water column, but you are actively hunting individual fish. If you’re fishing against one of these boats who have this machine and you don’t, you have a very serious disadvantage. They have one up on you.” Todd Tally. – Atlantic Marine Electronics

Captain Steve Katz is the owner of Steve’s Marine Service Inc in Ocean City, Maryland. He is the Vice Chairman of Board of Directors – National Marine Electronics Association (NMEA) and holds ABYC Master Technician certification, NMEA AMEI, NMEA2000 certificates along with factory training from many manufacturers. To contact Steve, email info@inthebite.com.

Originally published in the June 2018 issue of InTheBite Magazine.