I dare say I’m the only angler in the history of the Chesapeake Bay to have bronzini on the end of my fishing line. Bronzini, also known as Mediterranean sea bass, don’t normally swim within a thousand miles of the Chesapeake. Nor are they swimming here today—the Bronzini were thoroughly expired when I bought them at my local Safeway seafood department. (Are you listening, accounting department? It’s a valid expense.)

I chose them for one specific reason—because they were the only fish sold whole in the Safeway, and I needed whole fish to carry out a series of experiments with side-scanning fishfinders. My mission: to debunk the myths that have sprouted up about these systems, and to determine how side-scanning technologies from Garmin, Lowrance, and Raymarine stack up against each other.


With bronzini in the water and three side-scanners on the boat, we put Garmin, Lowrance, and Raymarine systems head to head.

We’ve heard an awful lot about how awesome side-scanners are, and their popularity has grown by leaps and bounds these past few years. And while they certainly have value to anglers, in my experience, side-scanning fishfinders don’t live up to the marketing hype in several respects. If these units will help you become a more successful angler, understanding their limitations—and thus understanding how to best use them in your angling endeavors—will help even more.

MYTH: Side-scanners can see fish from afar.

While side-scanners are great for finding structure, they just aren’t all that great at showing you the fish themselves. Sure, dense schools of fish show up just fine on the screen, but talk to anglers who have these units on their boat and many will say that it’s easier to identify individual fish on traditional down-looking units. Part of this has to do with the formation of arches on down-lookers, but I suspected it was also partially due the relatively large swaths of water being represented by side-scanners on LCD screens. Whatever range the side-scanner is set at, it’s representing twice that distance on the screen (since it’s displaying both port and starboard views)—yet it has the same number of pixels to work with as a down-looker would have at half the range. Then there’s frequency to consider. Side-scanners use much higher-frequency pings, and they’re bound to “see” a bit differently.

There was only one way to put the theory to the test: tether some fish at a suspended depth next to easily-identifiable structure, and make multiple passes from different distances with side-scanning units from each of the major manufacturers. Hence, the bronzini. At two pounds they would be large enough to interest most anglers, but small enough to present a challenge to the side-finders. I strung them up on a length of fishing line that would be weighted at the bottom and buoyed at the top with a milk jug. Then I deployed the bronzini so they sat about 10’ below the surface, next to a cluster of pilings and close to a large dock, with seawalls on either side.

With the Garmin system fired up, we made our first pass from 25 feet away at clutch-speed. There were the bronzini, a pair of white dots next to the larger piling blobs. The next pass was at 50’, then at 75’, where yes, I could still make out my makeshift Mediterranean fish-markers. But at this distance the fish had become mere specks on the screen. If I hadn’t known exactly what and where they were, I doubt I would have been able to ID them as fish among the other on-screen speckles. So I doubled back, switched units, and tried again with the Lowrance, and then the Raymarine. My results were more or less identical. At 50 feet the fish were clearly fish; beyond that it became hard if not impossible to tell what they were, if anything, as I ranged out the side-finder.


At 50 feet, the pilings (marks casting shadows, to right) were clear along with the bronzini (white marks to left). But beyond this distance...

While 75 feet may seem like a lot at first, let’s put it into context. That's barely 25 yards—significantly less than the maximum casting distance of any competent angler. And in all honesty, there's a good chance that I only knew what the returns were because I had put the fish there and could see a visual marker of their location. The specks displayed on-screen blended in with clutter and false returns. Had I been idling alongside the pilings looking for fish, even at 50 feet I'm not positive I would have felt confident enough of their existence to actually stop and cast.

MYTH: Side-scanners can see a fifth of a mile or more.

Depending on what documentation you read, the claimed range for these systems is 500-750 feet out to either side. If this were accurate, you’d be able to cover over a fifth of a mile of water with each sweep. But that’s a big “if”. Fishfinder ranges vary quite a bit depending on variables like the water’s suspended solids, temperature, and fresh or salty nature. And while the frequencies used by down-lookers (commonly 120 or so kHz for up to a few hundred feet of depth, and 50 or so kHz beyond that) are tuned to balance depth penetration with fish detection, side-scanners use much higher frequencies to paint their more detailed picture—even as high as 800 kHz. The reason is enhanced detail. Low-frequency sonar waves are like large ocean rollers. They travel for long distances before dissipating, but they roll right over small objects without being reflected back. High frequency waves, on the other hand, are more like ripples on a pond. They don’t go terribly far, but they’re easily reflected by items as tiny as a twig or a leaf. As a result, the detail level you get from high-frequency pings is similar to that of an MRI, as opposed to the X-ray-like image provided by a traditional fishfinder. But the higher detail comes at a price—namely, reduced range.

Due to the competitive nature of the market, some manufacturers have ceased supplying information on the exact frequencies they’re utilizing. But we do know that Garmin pings sideways at dual CHIRP ranges of 425 to 485 kHz and 790 to 850 kHz, Lowrance claims the use of “enhanced” 455/800 kHz sweeps, and Raymarine pings through a 60 kHz CHIRP-ed spread in the mid-300-kHz range. You can see the difference (to some degree) in the transducers. Garmin’s transducer is by far the widest, while Lowrance’s is the longest. In fact, it’s long enough to present a transom-mounting problem for boats with very limited mounting space, where the transducer has to be located near the drive unit. Raymarine is the only manufacturer to mount the left and right transducers side-by-side instead of combining them in a single casing. The advantage here is an ability to adjust their individual angles somewhat, to get improved deep or shallow water performance. But making the adjustment is difficult—you’ll need an Allen wrench and the boat has to be out of the water—so this advantage is marginal at best.


At distances over a couple hundred feet, the Raymarine seemed to work best. The two white dots above the (added) red arrow are a pair of pilings, seen from 300 feet.

Just how far would these units see in the real world? Would the pilings and seawalls remain clearly visible, long after the fish disappeared? The answer was a solid yes. At 100, 200, and even 250 foot ranges, on all of the units I could pick out the seawalls. At the far end of this range picking out the pilings might have been iffy without knowing they were there, but I could still see them on-screen.

At 300 feet, however, they were lost on the Garmin. I could still make them out on the Lowrance, but just barely, and they were only visible at long ranges after I set the unit to the dedicated 450 kHz mode.

Raymarine seemed to provide slightly clearer imagery at long ranges, stayed in the game at over 300 feet, and the pilings were still visible on about half of the passes I made at 400 feet.

Seeing them beyond 400 feet was hopeless on all of the units.

MYTH: Unlike early versions, modern side-finder systems are relatively easy to install and use.

The idea of this article was to test the technology each manufacturer uses, not their specific units. But there are some factors that affect each manufacturer across their model lines, which definitely need to be considered—and which will debunk this myth.

For starters, Raymarine’s side-scanning system requires a CP200 black-box, which makes mounting and wiring notably more complex than those from Lowrance or Garmin—which both have side-scanning software built right into their MFD brains. Considering the trend to incorporate all possible functions into single head units and the fact that Raymarine jumped into side-scanning barely a year ago, I’d expect them to begin building side-scanning capabilities into their MFDs sooner rather than later.

Note that you’re stuck with the same problem when adding side-scanning to all but the newest Garmin systems (they’ve been producing their SideVu systems since late 2013); only the latest and greatest models eliminate this extra step. Lowrance has been working at seeing sideways with StructureScan a bit longer, but pre-2012 units may still need an additional box, and some other units will need software updating.

raymarine cp200

Systems from Lowrance and Garmin may or may not need a "black box" for side-finding. Raymarine presently requires the CP200 for all systems.

The transducers for these systems also present an issue. This is the one piece of hardware that remains (mostly) the same for side-scanning throughout a given manufacturer’s model line, and with all side-scanning units you’ll need to mount a dedicated transducer. Naturally, the recommend location is exactly the same as it is for other transducers. Chances are you’ve already got one there. That means you’ll have to find a secondary location and plan to adjust and re-adjust as necessary, to get (cross your fingers) acceptable performance. Garmin and Lowrance do offer through-hull options, but Raymarine’s CPT-200 CHIRP SideVision transducer can only be transom-mounted. Raymarine says they’re always considering expanding installation options, but doesn’t have anything solid to report regarding through-hulls at this point in time.

Sideways Glance

Hopefully, by now it’s clear that while there certainly is value to side-scanners, a lot of the claims you hear about them are in fact a bit inflated. Sure they can see individual fish, but with all the speckles and dots you see on-screen, you’ll have trouble knowing that they’re fish even at relatively close ranges. Yes they can reach out for quite a distance, but when ranged-out to such distances you’ll have trouble picking out things, even things as large as clusters of pilings. And even in the best-case scenario their maximum ranges may be a bit overblown. Finally, while some of the newest of these units are simplified when compared to earlier generations, there’s still a long ways to go in this regard. Transducers, in particular, present a number of potential problems.

There are some easy ways to mitigate the issues of fish-spotting and range. For starters, get the unit with the largest LCD screen you can shoe-horn into your helm. If at all possible, run side-scan on a dedicated screen instead of splitting it with a chartplotter and/or down-looker. Remember: the bigger a display area you have at your disposal, the better you’ll be able to pick out individual fish. The larger screen will also be of benefit when ranging out to long distances, and you can enhance your long-range ability by setting the side-scanner to look only in one direction. This doubles your effective viewing area, turning pin-prick marks into visible blobs.

Finally, if installation simplicity is a major concern and you’re rigging up a new electronics system from scratch, you’ll probably be happiest eliminating the black-box unit by going with Garmin or Lowrance. But if maximum range is of more importance, the results of my day on the water point to Raymarine as the top dog. The lower kHz range they chirp through does seem to reach out a bit farther, and as far as I could tell looking at pilings, seawalls and bronzini, if there’s a detail loss it’s negligible.

Then again, how often do you get to look at bronzini, in the Chesapeake Bay?

For more information on each individual system, visit Garmin, Lowrance, and Raymarine.