Going back eons to the time when cavemen named Og tried to hook dinner while perched atop  a drifting log, man has wished he could see the fish below his boat. Then just 60 or so years ago, the first fishfinders were developed. We peered at the flashing lights, waiting to see the blip of our quarry. Next came LCD screens, and suddenly we were able to spot Nemo easily from afar. Color fishfinders became commonplace, and then we could even judge a fish’s size and species with a mere glance at the screen. But we could only look in one direction: down. And, since man is never truly satisfied, we wished we could see fish off to our sides. Og would have been thrilled with an old-time flasher, but even today’s tech-savvy anglers will be blown away when they experiment with Lowrance’s new side-looking StructureScan—I know I was.

The white line down the middle is the sonar "bang," where your boat is, and to either side you can clearly see fish-attracting structures like these rocks.

StructureScan utilizes a pair of 455-khz and 800-khz beams shot out to either side of the boat with 500-watts of power, from a transom mounted or trolling motor mounted transducer. Normal down-lookers commonly use 200-khz or 50-khz. What’s the difference? Think of the sonar waves like ripples in a pond. Toss a pebble, and when it strikes the water’s surface it sends out a series of small, tight, fast-moving waves which are easily reflected. These waves are like those produced by the high kilohertz transmissions. Chuck in a boulder, however, and it makes larger, slower, widely-spaced waves which go farther but may roll right over items instead of being reflected. These are more like lower kilohertz waves. In other words, your 200/50-khz fishfinder takes a far-looking X-ray, but your 455/800-khz StructureScan takes a short-range MRI.

How far out to the sides can this MRI see? That depends on depth. When I first tried out StructureScan on my boat, I was confused because I could only see 30’ in either direction. But when depth dropped down below 10’ my vision increased to 60’. Then the bottom dropped another 10’ or so, and I could see 120’ out to the sides. Maximum range is 250’.

It takes some experimentation and some getting used to before you’ll feel comfortable identifying items and fish on-screen. For at least six or seven trips, I simply couldn’t tell what I was looking at, and there are so many color palette options it took a lot of trial and error to find the ones I liked. But after some experience seeing items like rocks, pilings, and lighthouses which protruded both above and below the water’s surface, I got a feel for how items looked with the StructureScan’s “eyes.” And the advantages don’t all come from looking off to the sides; in DownScan mode, you get just as detailed a view of what’s directly below because the regular transducer and the LSS-1 StructureScan transducer work together to paint a hyper-detailed down-looking image.  (For this function to work, the two transducers must be mounted within a foot of each other).

Surprisingly, seeing fish really isn’t the feature I found most useful with this system. They don’t show up incredibly well on-screen, often producing a wispy image and smaller returns than on the regular HDS down-looker. The real advantage comes from being able to spot items like rocks, wrecks, and coral heads from off to the side, because once the unit sees them it’s easy to put your boat right on top of them. Let’s say you see a boulder on the bottom, 100’ off to the starboard, for example. You can move the fishfinder’s cursor over to the image of the rock, hit “enter,” and create a waypoint. Then use your chartplotter window to navigate to the mark (if you have an HDS8 or larger unit; with the smaller HDS units, which can only display two screens at a time, you’ll have to switch windows to bring up your chartplotter screen). There’s also a “TrackBack” feature that lets you scroll backwards through the StructureScan’s history, set waypoints on interesting-looking structure, and navigate to them.

I discovered just how handy this function can be while casting jigs to striped bass, on a rocky ridge in 15’ of water. I spotted an unusual outcropping on the StructureScan and we caught fish off of it as we drifted past, but between the strong current and the breeze, I couldn’t re-locate the hotspot. Until, that is, I scrolled back and created a waypoint on it. Moments later, we were catching fish again.

What are the down-sides? Just those you’d expect: additional cost (the base system goes for $600), installation work, and the time it takes to get used to looking at side-imagery. If you have other accessories using the HDS Ethernet port, like Sirius weather or Broadband radar, you’ll also need a $150 Ethernet expansion port.  And remember, this is a system add-on for Lowrance HDS displays, only. There are also some speed constraints; both side- and down-scanning works best at 10-mph or less.

The bottom line? This is an entirely new—and better—way of looking at the bottom, both beneath your boat and off to the sides. If Og could see it he’d be so astonished, he’d roll right off of his log.

Editor's Note: For more detail about Lenny's experience with the Lowrance StructureScan, read his Boatermouth blogs.