By: KEVIN SMITH, Photography by: KEVIN SMITH

Presented by
  • Trade-A-Boat


The correct use of Lowrance’s StructureScan HD can tell you pretty much everything that’s going on beneath the water’s surface. Kevin Smith gives us a guide on how to get the most out of your system.

To fully appreciate StructureScan HD, it helps to understand a bit about sonar and how the image on a screen is created in the first place.

Sonar (SOund NAvigation and Ranging) is another of mankind’s attempts to replicate nature, in this instance the way in which whales and dolphins navigate by creating mental images of their environment from echoes of their squeaks and clicks.

In the modern man-made version used by fishos, a transducer projects a pulse — an audible click — down into the water column, then measures and records the echo over and over.

Software deciphers and interprets the signals, eventually building an image of the object(s) responsible for it. Traditionally this image would consist of squiggles, dots or clumps, which the angler would then have to decipher in order to determine what they’re seeing.

In-store demo displays often render bait on the screen as dense, tightly-packed balls and fish as perfect crescents or arches. It’s important to note that this ideal arch is rarely replicated in actual fishing situations. Typically, a perfect arch is formed when a fish enters a transducer cone and swims through it to the other side. Since the signal is strongest when the fish is in the middle of the cone, and weakens as it enters and exits, this is reproduced on the screen as an arch — dense in the middle and less so on
the ends.


Essentially, StructureScan HD’s key objective is to help take some of the guesswork out of the above process by rendering the environment below the surface in a more realistic manner.

When a mate of mine, Lowrance technical guru John Easton from in South Africa, called me up four years ago to tell me about it, I’ll admit I was more than a little sceptical. He spoke about SideScan and DownScan, which allows the user to see either side of their boat, and a vivid image of what was straight under it.

I used to run professional dive charters in South Africa and always took the opportunity to have a poke around to make sure what I was seeing on the sounder matched what I could see underwater. Apparently, this new gear from Lowrance was so sophisticated that, John assured me, I could stay dry.

With that endorsement, I invested in a new HDS-7 as soon as they became available, later upgrading it to the Gen2 version (two, in fact) with StructureScan HD (as tested).


Rigging up a normal sounder is relatively straightforward, but StructureScan HD is a little bit more involved due to the extra transducer and separate module.

The HDS-7 Gen2 is a fairly conventional affair in contrasting grey and charcoal, with neatly labelled buttons. However, when you open up the StructureScan HD box you’re confronted by an 8in black cylindrical object that wouldn’t look out of place in a Sexpo showbag. And attached to that is a 6m cable that plugs in to a novel-sized processing module.

The black cylinder is in fact the StructureScan transducer, its round shape permitting the wide dispersion (455 and 800kHz instead of the usual 50 and 200kHz) needed to create a 3D-like image on screen. The transducer can either be screwed to a hull flat, such as a planing plank or transom, mounted via the supplied bracket. Or for those who prefer torturing themselves, a shoot-through installation is an option on fibreglass boats.

I found the wiring diagrams fairly easy to follow, but the best bet is to give yourself plenty of time to do it right, or, alternatively, pay an expert for the privilege, and have someone to blame as a bonus. And don’t forget to run power up to the LSS2 Module.

To connect to the HDS-7 module or any other compatible Lowrance head unit, link via the supplied Ethernet cable. Additional cables are readily available through dealers if you wish to link other units.

One consideration to bear in mind: the supplied literature suggests you mount your StructureScan transducer within 30cm of a Lowrance Skimmer transducer if you wish to overlay your DownScan image onto a standard sonar view. Regardless, fit a splash plate because it can throw up one helluva roostertail.


As with any sounder, nothing beats spending lots of time on the water to become intimate with your unit. Sure, you can turn it on and stick to the default settings, but learning to drive it properly will allow you to more fully exploit the HDS-7 / StructureScan combo’s potential. Here’s a rundown to put you on the home straight.


When you engage SideScan, you’re presented with either a combined or individual left and right view. I prefer the combined, in which the surface line in the centre of the screen splits into a left and right view. The dark colour is the water column from surface to bottom, and the lighter colour with weird images is the bottom contour. If this confuses you, you’re on the right track — the easiest way to read it is to turn your head sideways to imitate reading a normal sounder. In other words, it’s the bottom turned on its edge.

Bottom structure is the easiest to decipher with rocks, reef, wrecks and basically anything standing out like a sore thumb. Fish are a different kettle of, well, you know — especially when small. The beauty of the trackback feature is that it allows you to place your cursor anywhere on the screen to zoom in, and when doing so you can often work out if you’re looking at baitfish or single fish.

Larger fish tend to throw shadows — imagine shining a high-powered torch at an object in front of a wall. The dark negative space, or shadow, tells you there is something solid and suspended off the bottom. When this happens, most of the time the images are clear and large, such as the image on the bottom right in which three distinct fish just off the bottom are throwing large shadows. (As it turned out, those were identified as fair-sized bronze whalers, or bull sharks.)


As its name implies, DownScan gives you an almost photographic view (albeit a circa 1920s sepia version) of the fish and terrain under your boat. It’s best used in conjunction with a traditional sonar view in the early stages to allow you to condition yourself to the new view downstairs. DownScan, SideScan or a combination thereof with or without sonar can be accessed by punching the "Pages" button, selecting "Structure" from the carousel and selecting your preferred configuration.


Out on the water, you have the choice of splitting the screens. In my case, I’m lucky enough to have networked dual HDS-7 units, so one unit is used purely for sounding, and my preferred screen is a split of standard sonar and StructureScan HD.

As standard, the StructureScan HD auto settings on the new HDS-7 Gen2 units work a treat but, like any sounder, if you want to get the most out of it,
and especially so on StructureScan HD, you need to change the settings to
suit the depth, water conditions and bottom topography.

So, several years after my friend John first told me about StructureScan HD / SideScan, I have since spent countless hours on the water using and testing the systems and, combined with the use of aids such as Lowrance’s Doctor Sonar DVDs (see TrailerBoat #292, March 2013) and the Fisherman’s Guide To Sonar, the missing links in the brain box finally came together and led me to a better understanding of how they work.

The latest Lowrance Gen2 HDS-7 StructureScan HD unit is now a permanent fixture on my console.


Anyone who is serious about catching fish is sure to benefit from this technology. I regularly use the StructureScan to locate old and new reefs without having to be smack on top of it.

One one occasion I even managed to find a wreck. I set the range out to 100m at a depth of 10m and ended up sighting it 80m off to the side. I then placed the cursor on it and, bang, I was straight on top of it.

I also frequently fish 2-8m depths and this where StructureScan really surpasses standard sonar because you don’t need to sound directly on top of fish, which can spook them.

The more I use StructureScan, the more rapt I am with it. It’s been a very worthwhile addition to my on-board gear, regardless of the cost. The built-in GPS on the HDS-7 is also first-rate, particularly with the inclusion of the optional Platinum Charts and Google Maps overlay. And I haven’t even touched on StructureMap (more on that in a later column).

Next on the list is definitely one of the new Lowrance HDS touch units. I can’t wait to get hold of one.



• Holding down the Pages button will allow you to flip between split screen windows without having to access the menu. It’s particularly handy if you’ve installed the optional Sonichub plug-in iPod sound system.

• Run past some solid vertical structure while in SideScan mode. If the structure shows up on the opposite side of the screen, change the orientation. You can do this by going to the Structure Options menu, selecting Flip Left / Right and pressing Enter.

• Compensate for depth in the range — i.e. if you want 30m out to the side, add your depth as the transducer reads down, then outwards.

• Zoom in on likely targets.

• Observe bait school behaviour. If they are spread out and moving freely, even though larger targets might be hovering underneath, odds are they’re not feeding — yet. Search for tightly-packed baitballs with larger targets sitting higher up in the water column.

• Adjust the gain to suit conditions.

• Adjust the distance to suit — the further away the lower the resolution.

• Use 800kHz in the shallows and 455kHz in deeper water (20m or more).

• Use the cursor to work out how far fish or structure is out to the side.

• Use the cursor to mark the fish and / or structure without having to sound over the top. Save as a waypoint for later.

• The slower you sound, the better — fish images elongate the slower you go. If you park over stationary fish, they will often show up as continuous lines as their echo is being repeated.

• In the case of defined structure like wrecks or prominent bommies, sound from different directions to get the best result on the screen.

• Use Screen Capture for later reference. Select Screen Capture from the System menu and press Enter. Press the Light / Power key to grab a screen shot that will save to the unit and can be downloaded to an SD card later.

• Sonar can also be logged and replayed as video (refer to page 37 of the manual provided).


  • Faster processing
  • Higher resolution on StructureScan HD and DownScan
  • Trackback feature and zooming
  • Screen still viewable through polarised sunglasses


  • Would prefer dual SD card slots
  • Having to install separate LSS2 module — new HDS units integrate them in the one chassis
  • The editor has an HDS12 Gen2 Touch and won’t loan it to me


Display: 6.4in, 16-bit colour full VGA Solarmax

Resolution: Full VGA 480Vx640H

Backlighting: Pure white LED

Operating Frequency: 50 / 83 / 200kHz

Communication: NMEA 2000, 0183 Ethernet

Languages: 23

Media Port: SD / MMC slot


Power Requirements: 12V DC

Max RMS: 500W; peak-to-peak; 4000W

Cable Length: 6m

Transducer Frequencies: Enhanced 455kHz and 800kHz


Navico Australia



Authorised Lowrance dealers


Price as tested: $2289 HDS-7 (combo)

Options fitted: LSS2 StructureScan

Priced from: $1499


Originally published in TrailerBoat #293, March/April 2013

Find Lowrance electronics and boats with Lowrance electronics.


Want the latest stories delivered straight to your inbox? Sign up for the free TradeBoats e-newsletter.