Sonar Smack-Down: Traditional Fishfinder vs. Down-looking Scanner-Imager vs. CHIRP

With all the new-fangled fishfinder technology available these days, how are you supposed to know which is the best to invest in? We tested three different moderately-priced modern sonar technologies side by side, to help you make the right call.

20th September 2013.
By Lenny Rudow

To all fishermen in search of a new fishfinder: if your head is swimming with gigamajigs, LCD screams, and watt-evers, you’re not alone. A frequency frenzy has struck the world of sonar, and while we used to be able to compare a few specs, functions, and prices before drawing a reasonable conclusion as to which unit to buy, today the process is enough to make your head really kilohertz. Now there are entirely different forms of fishfinder technologies on the market and even for the most educated buyer, choosing between them is no easy call. We decided to help ease the digital delirium by matching up comparable technologies including traditional, scanning/imaging, and CHIRP, head to head.

To keep the playing field level we capped the price range of the units we included at $800. This represents a sweet-spot for fishfinder manufacturers since most boat owners can afford a unit at this price or below, regardless of whether they cast for largemouth from a bass boat, troll for stripers in the bay, or jig for cod off the coastline. Sure, there’s a lot more—and more advanced—technology available at higher price-points, but some cost as much as a small car and the vast majority of us will be living with something a little more affordable. So we put our focus here, in this moderate price range. We also tried to spread the field among the major manufacturers, which wasn’t difficult since different companies have taken different technological routes to help get you to the fish.

What about those side-scanning fishfinders everyone’s heard so much about? All of them break our price range. But they do provide a lot of utility to anglers. You’d like to boost the budget a bit? Luckily, we’ve already spent a lot of time testing them. To learn more about side-scanning sonar, read Seeing Sideways.

Playing the Field

garmin 547xs

The Garmin 547xs in our test was pinging through the depths with 200/50 kHz.

Traditional fishfinders utilizing a standard 50/200 kHz beam were represented by Garmin, with their just-introduced 547xs, and Furuno, with their brand-spanking-new FCV series. Garmin sells the 547xs (which has a 480 x 640 pixel, 5” display) for a hair under $800. This unit also has 40 – 210 kHz CHIRP capability in its brain, but the least-expensive CHIRP transducer it’ll work with (the 95 – 155 kHz Airmar TM 150M) costs $300 and sends the package well out of our competitive price range. To get the full 40 – 210 kHz spread of CHIRP, you’d have to spend even more, so in this case, we’re sticking with the standard-issue capabilities. The 600-watt Furuno FCV627, meanwhile, can be bought for around $700 and has a 640 x 480 pixel 5.7” display. Although we ran an 8.4” FCV587 for the purposes of this article, it was only because this model line is so new that a 627 wasn’t yet available for testing. Screen size is the only significant difference between these units, so using the 587 doesn’t make any difference for comparing technology – but when you look at the pictures, don’t let the large size of the Furuno fool you.

furuno fcv

Furuno’s new FCV units utilize 200/50 kHz and include Bottom Discrimination and Accu Fish.

The FCV’s do include a few new enhancements which should be noted: Bottom Discrimination, which displays bottom type (sand, gravel, mud, or rock), and Accu-Fish, which denotes fish size. I found that Bottom Discrimination eliminated a lot of the usual guesswork associated with determining bottom type and felt it was quite helpful. Accu-Fish was a bit less impressive but I didn’t spend enough time actually fishing with this unit—and reeling up what I saw on-screen—to make a firm call, so I’m reserving judgment on it for now. Though it has these added perks, you’ll also want to note that this is the only unit in our bunch that didn’t have an integrated GPS antenna and chartplotting capabilities.

humminbird fishfinder

The Humminbird 587ci HD DI Combo features Down Imaging, and was the least expensive finder in the mix.

Our second batch of technology focused on down-looking scanners/imagers, which operate on a much higher sonar frequency to paint a picture of what lies below with vastly enhanced detail. In a nutshell, high-frequency sonar waves are much more sensitive than the lower frequency waves used by traditional fishfinders; the down-side is weaker depth penetration. Here’s an easy way to picture the difference between high- and low-frequency sonar waves: think of them like the ripples in a pond. If you toss a pebble into the pond, it sends out a series of small, tight, fast-moving waves which are easily reflected back. These waves are like those produced by high-frequency transmissions. But if you throw a boulder into the pond, it makes larger, slower, widely-spaced waves. Those large waves will go a lot farther than the pebble’s ripples—but they’ll also roll right over small items, instead of being reflected back. These are your low-frequency waves. In other words, your traditional 200/50 kHz fishfinder takes a far-looking X-ray, but your higher frequency 455/800 kHz scanner takes a short-range MRI.

lowrance elite 7x

Lorance’s Elite 7x not only provides DownScan Imaging, it also has the largest screen of these competitors.

We tested this technology with two very different units. The first was the 500-watt Humminbird 587ci HD DI Combo, which is the least-expensive sonar in the mix, coming in at a mere $450. It utilizes Humminbird’s Down Imaging, and has a 640 x 480 pixel, 4.5” screen. The Lowrance Elite 7x HDI with DownScan Imaging was our other scanner/imager. It runs about $550, puts out 250 watts, and has a 7” screen that significantly out-sizes the others available at this price-point, with 800 x 480 pixels. Both of these units send out their pings at 455/800 kHz and can also operate in 200 kHz traditional mode, with Lowrance adding 50 or 83 kHz options.

Our final player was the Raymarine Dragonfly, the first relatively inexpensive (just over $600), scaled-down CHIRP unit combined with scanning/imaging abilities (Raymarine calls it “DownVision”) to hit the market. Just what the heck exactly is CHIRP, anyway? Think back to those ripples in the pond. But this time, instead of throwing in a single pebble or boulder, you’re going to line up a series of rocks from small to large and throw them into the water in rapid succession. A Chirp unit uses the same concept by putting out pings through a spectrum of frequencies in a short blast, to gain the best of both worlds—plus everything in-between. Yes, we are over-simplifying things a bit; if you want to geek-out on CHIRP, just click that mouse one more time and read New Wave Fishinders.

raymarine dragonfly

Raymarine’s Dragonfly: the first CHIRP-light with imaging capabilities.

Most of the more advanced, much more expensive CHIRP units blast out a range from 25 – 250 kHz, while the Dragonfly sticks to a pair of smaller ranges. Raymarine says the 600-watt sonar, which displays the results from all that pinging on an exceptionally bright 5.7” 480 x 640 pixel LCD, is “centered” at 200 kHz while DownVision is “centered” at 350 kHz. According to Raymarine sources we spoke with when the Dragonfly was introduced at the 2013 Miami International Boat Show, the ranges are “about” 170 to 230 kHz and 320 to 380 kHz. So let’s call this option CHIRP-light, and note for the record that Lowrance says they have a CHIRP-light/scanner/imager unit of their own in the works.

Out of the Lab and On the Water

It was time to hit the water and find out how these technologies performed side by side. We mounted the five displays on a test board and mounted their transducers on a sled that could be towed behind the boat. This naturally subjected the transducers to a bit more turbulence than a proper transom-mounting, but our testing took place at slow speeds or while stopped, and all five transducers were equally affected. Besides, I wasn’t about to drill 20 more holes into the transom of my boat.

The rigging process proved to be quite educational, exposing a few high points and low points that may not be related to technology, but which I’d certainly want to know about if I were buying one of these units. For starters, the Dragonfly’s mount looks slick and curvaceous, but it’s too flimsy. It’s also a bear to get the unit into and out of the mount, and frankly, I think they should replace it. The single-plug connection, however, is easy to rig and looks clean. The Garmin, meanwhile, feels plenty sturdy and sits securely in its mount. But the plugs don’t twist-lock into place. You simply push them in—over and over again, because when you adjust the unit, a plug sometimes falls out. The Lowrance’s plugs do have a twist-lock, and in my opinion are second only to the Furuno in ruggedness. In fact, the Furuno is over-built in every way possible, from the huge sturdy plugs to the stout mount to the heavy casing. If I had to bet on which unit would stand up best to long-term use and abuse, this would be the one.

For the shallow water test I headed out into the South River, a Chesapeake Bay tributary that’s about 25’ at its deepest. The first stop was a creek where there were some eelgrass beds, because the manufacturers of scanning/imaging units often claim their units are much better at picking up wispy targets like weeds—an ability that’s quite important to some anglers. And from what I saw on-screen, those manufacturer claims are correct. The scanner/imagers showed the grasses clearly. CHIRP-light picked up slightly less conclusive returns. I could tell there was something there and with experience I think I’d know the difference between weeds and whatever, but the picture wasn’t as crystal-clear. Meanwhile, the traditional frequency units pinged right through the grass without showing it on-screen. But the real shocker came when I went over a tree branch. Both scanners showed it laying on the bottom in amazing detail and I could clearly see the branches shooting off the main trunk. The Dragonfly also showed it, though in a bit less detail. The traditional sounders, however, showed just a red streak breaking slightly off of the bottom. You could tell something was down there, but you’d never identify exactly what.

sonar-imaging

Though it was impossible to get identical shots from all of these units at exactly the same time and place due to the motion of the boat and interference between the units, this stock screen shot gets the point across. Detail levels with the scanner/imagers, seen at right, is greatly enhanced.

Digging Deeper

Next I moved to a steep drop-off from 10’ to 25’ with a rockpile at the bottom. Scattered stripers commonly meander about here, and I caught a few just to make sure they were around. I saw them occasionally on the traditional sounders and on the Dragonfly, but it was very rare to spot them on the scanning/imaging screens. The rockpile, on the other hand, was visible in much higher detail on both the scanners/imagers and CHIRP-light, and was correctly identified as rocks by the Furuno’s Bottom Discrimination.

Why were scattered fish less visible to the scanner/imagers, which gave an improved visual of the structure? It’s known that different species of fish show up better or worse in different frequency ranges. Unfortunately, there’s very little hard data on which types of fish appear better or worse in which frequency beams. But this experience matched up well with what I’ve seen in the past: very high frequency sonar doesn’t mark fish (or at least, certain species of fish) as clearly as structure, when compared to the traditional 200 kHz beam or CHIRP. They still pick them up, but often on the display this translates into little more than a dot or two instead of a bright arch, and it’s much harder to discriminate between fish and screen clutter. With large fish or schools of fish the issue is much less noticeable. But if you want to locate smaller or more isolated fish, lower frequencies get the job done better.

fishfinder transducer beams

The image to the left shows a 200 kHz beam’s reading, while the one to the right is a 455 kHz beam. The white arrow points out an identifiable arch created by a small fish, as well as two targets above it which are likely fish that didn’t provide as solid a return; none of these targets appear very well in the higher-frequency beam.

To test the units in a greater depth, I pulled the sled and headed for a wreck sitting in 70’ of water. All five units picked it up without a problem. But again, the scanner/imagers and CHIRP-light showed significantly more detail. In fact, I could differentiate the bow of the wreck from the stern, and clearly make out the cabin. On the traditional sonars, all I could see was a big red blob.

It was time to head for even deeper water. To really push these units to the extreme, I towed my boat to Ocean City, cruised through the inlet, and headed out into the open Atlantic. I decided to double the depth tested thus far, and not pull back the throttles until I had 150’ of water under the keel. When I did so and fired up all the units, the results were similar to what I’d seen thus far but the detail advantages of the imagers/scanners began to fade. Clutter crept onto the screens, as gain went up to maintain a hold on the bottom. So I kept going, on to 200’, and then to 250’. Here, the story began to change even more as the Elite 7x scanner/imager had trouble holding a bottom reading. In 300’ it was gone completely. Meanwhile, the 587ci screen showed gobs of clutter and when I moved on to 350’, the Humminbird could no longer hold bottom either. The Dragonfly held fast in 350′ but clutter was beginning to take over. And when I pushed on to 400’ CHIRP-light couldn’t hold bottom, either. The Garmin’s hold on bottom at this depth became a bit tenuous, and was completely gone in 500’. The only unit still getting a consistent bottom reading at this depth was the Furuno. It held on all the way out to 600’, which was the deepest water we went through during testing.

We should note at this point that these depths should not be taken as firm limits for these units. How far a fishfinder penetrates can vary quite a bit depending on suspended solids, sea state, and even the presence of marine life—a concentration of algae or jellyfish, for example, can dramatically alter performance. All of these manufacturers rate these units to go to significantly more depth than seen here, and I’m sure that on paper and in certain conditions they can in fact go much deeper. But what happens in the real world rarely (as in, never) matches up to mathematical equations and lab experiments. What’s important to pay attention to in this case is not the specific depths each unit worked to, but how the performance of each technology compared to the others in the exact same conditions.

So let’s boil it all down to the bottom line. If you fish relatively shallow water and you want maximum detail levels when you’re looking at structure, a scanner/imager is probably going to be your first choice. But recognize that if you go this route it may be a bit tougher to spot scattered and/or smaller fish in some conditions, in scanning/imaging modes. If you venture into deeper waters with any kind of regularity, traditional sonar is going to be more appropriate for your needs. And if you fall right into the middle of the spectrum, CHIRP-light seems like a darn good option.

Of course, while choosing your next fishfinder you’ll still have to consider all of those old-school factors like screen size and ruggedness. But hopefully, this comparison of modern, moderately-priced fishfinder technologies will help you make the right call—without getting a headache that kilohertz so bad it makes you want to LCD scream.


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About the author:

Lenny Rudow

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Lenny Rudow is Senior Editor for Dominion Marine Media, including Boats.com and Yachtworld.com. With over two decades of experience in marine journalism, he has contributed to publications including Boating Magazine, Marlin Magazine, Boating World, Saltwater Sportsman, Texas Fish & Game, and many others. Lenny is a graduate of the Westlawn School of Yacht Design who has won 28 BWI and OWAA writing awards.
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