Underwater Illustrations

Today’s sounders find fish fast and provide photolike bottom imagery.

Electronics, Marine
Today’s sounders find fish fast and provide photolike bottom imagery. Yachting

Attend enough new-product presentations and it can feel like successive generations of technology strive to refine rather than revolutionize. The perception makes sense given the advanced state of today’s marine electronics, but it’s a great feeling to walk away from a new-product announcement gobsmacked by a breakthrough. This happened to me at last fall’s METS trade show in ­Amsterdam during a Humminbird presentation for its Mega Imaging sonar. The lights dimmed, the slideshow started, and my jaw promptly found the floor. I stared, mesmerized, at photographlike sonar images of the bottom structure and — in some cases — shadows on a lake bed cast by rocks, trees and fish.

Sonar technology emerged before World War I and was originally used to detect submarines. In the late 1940s, it made the jump aboard commercial fishing vessels to help bolster catch numbers. Over time, different frequencies, transmission schemes and other technologies have been developed to provide varying depth ranges and on-screen resolution levels, but none (as of this writing) are as pyrotechnic as Humminbird’s Mega Imaging sonar.

Mega Imaging may have limited ­down-view and side-view ranges when compared with other sonar frequencies, and it works best with certain bottom types, but its photographlike imagery makes it possible for anglers of all skill levels to understand underwater topography and stalk piscatorial prizes.


Traditional sonar transmits an electrical pulse to an underwater transducer that converts the energy into a discrete-frequency sound wave and broadcasts it into the water column. These systems typically broadcast on two channels — high frequency (ballpark 200 to 210 kHz) and low frequency (40 to 80 kHz) — and offer a power output of approximately 600 W to 1 kW. Just like radar, a sonar’s “ping” travels until it hits something — say, a fish or bottom structure — before bouncing back to the transducer.

Electronics, Marine
Simrad’s S5100 High-Performance Chirp Sonar Module. Courtesy Simrad

The sounder receives the information, and it’s analyzed to determine the target’s size, shape and depth, which are depicted graphically on a screen or a ­multifunction display (MFD). Higher-frequency sonar waves provide higher-resolution imagery, while lower-frequency waves provide better range (think AM and FM radio, where FM signals provide superior sound quality but can’t propagate as far as their AM brethren).

In all cases, the quality of returned sonar information depends greatly on the power and frequency of the transmitted pulse. Recent years have seen the rise of chirp sonars that simultaneously broadcast transmissions over a sweep of predetermined frequencies at a power output ranging between 300 W and 3 kW, delivering better image resolution and target separation. These transmissions are broadcast as siren-like shrills that are inaudible to human ears but that let the sounder “peer” through targets, such as tightly packed bait schools, by comparing the original transmission (and its time stamp) with the returned sonar energy.


If you’re seeking the latest sonar for depths exceeding 150 feet, Simrad’s S5100 High-Performance Chirp Sonar Module offers three independent sonar channels in one black-box housing. Owners of compatible Simrad equipment — including NSS evo2 and NSS evo3 MFDs, NSO evo2 glass-bridge systems and S2000-series fish finders — can monitor sonar imagery from multiple depths simultaneously. The S5100 ($1,999) is compatible with 600 W to 3 kW transducers and can be configured using three single-channel transducers, or one single-channel transducer and one dual-channel transducer. Imagery is sent via Ethernet to three independent MFDs/screens, or to one MFD that’s operating in split-screen mode plus a second single-screen display. Users can select chirp frequencies from 28 to 250 kHz, and they can adjust the power output depending on their intended targets.

Realizing that chirp sonars’ significantly higher-frequency signals yield significantly better short-range sonar imagery, Humminbird’s engineers created Mega Imaging, which comes bundled on select Helix and Solix MFDs. Customers can choose between MFDs that offer just Mega Down Imaging (DI) or ones that offer both Down Imaging and Side Imaging (SI). “With Mega Imaging, we went from ‘it looks like a roadbed’ to ‘it looks like a roadbed with a cinder block or a two-by-four lying there,'” says Humminbird’s brand manager, Ray Schaffart. He likened the jump from traditional sonar to Mega Imaging to the sea-change leap from console TVs to high-definition flat-screen TVs. “In 30 feet of water, you can see the sand ripples,” he says.

By harnessing frequencies between 1.125 MHz and 1.3 MHz, Mega Imaging delivers eye-popping imagery 125 feet below the transducer and 125 feet to each side. The system requires at least one special, multi-element transducer that includes a dedicated Down Imaging beam.

“The majority of the technology is in the transducer,” says Schaffart, adding that Mega Imaging isn’t just a software upgrade. “You also need the capability in the MFD.”

Electronics, Marine
Humminbird MFDs can display Mega Imaging in one split screen and a chart plotter in the other. Courtesy Humminbird

To extend the system’s range, Mega Imaging transducers include elements that broadcast at 455 kHz, which ­allows compatible Humminbird MFDs to create hybrid sonar imagery. For ­example, Mega Imaging delivers 250 feet of high-resolution Side Imaging using the transducer’s ­higher-frequency ­elements and an additional 800 feet of traditional sonar imagery using the 455 kHz elements. The transducers also provide 125 feet of downward-looking Mega Imaging, plus 1,375 feet of traditional lower-frequency sonar.

An optional Airmar transducer plunges that last metric to 5,000 feet, says ­Schaffart, who suggested spec’ing a transom Mega Imaging transducer for low-speed work and one or two networked through-hull transducers for high-speed soundings.

Compatible Humminbird MFDs have peak-to-peak power output of 8,000 W, but draw depends on screen size. For example, the top-of-the-line Solix 15 SI ($3,499) draws 4.56 amps, while the Helix 9 Chirp Mega SI GPS G2N ($1,299) draws 2.5 amps.


As with all sonars, Mega Imaging renders crisper imagery when operating above hard, dense seafloor. “Bottom type changes what the [Mega Imaging] looks like,” says Schaffart, who advises adjusting settings when operating above soft, murky bottoms, which can absorb and disperse sonar signals.

While some saltwater anglers will want more range, all anglers will likely agree that — when operating in the correct depths and bottom types — Humminbird’s Mega Imaging sonar technology is impressive. Given its photographlike image quality, Mega Imaging could make a significant impact in the fish-finding world, allowing angling neophytes to find fish quickly.

It will be interesting to see how this technology performs in the wild, and whether the competition also switches to megahertz frequencies to bolster their short-range performance too.


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