Structure Scanning for More Fish

Structure Scan Transducer LSS-2

A couple years back when I first received my new Lowrance StructureScan I was a little apprehensive about installing it onboard my vessel Salt Patrol. After all I don’t spend much time fishing shallow water lakes and I’m not a certainly not a bass angler!

After some gently persuasion from the regional Navico representative Mike Campbell that went something like”I don’t care what you think you know about StructureScan get it put on the boat now” so I decided to give it a try.  Well to say I didn’t know what I didn’t know was a giant underestimate of how well it works. Using StructureScan HD in the saltwater is now my number one go to piece of equipment for locating fish since that first day I installed it.

The first day I turned it on and set the side scan feature to 300ft and I was instantly rewarded with the exact location of a school of bait fish that appeared 250ft to the port side of the boat with large salmon marks feeding under it. Like a lightning bolt to the head it became very clear to me that there was indeed a use for this latest Navico product for saltwater anglers.  As I learned how to operate StructureScan and fine tuned its use it quickly became one of my primary tools for locating fish and fish holding bottom structure.

Side Scan of bottom with boulders on both sides of boat. Line down center of image is bottom of boat showing transducer burst 

So how does it work?

Structure Scan HD requires the addition of a transom or thru hull mounted side scanning transducer in addition to your normal sonar transducer.  On HDS units and HDS Gen 2 units the transducer plugs into a StructureScan HD Module and from the module it uses an yellow ethernet connection plug to the HDS sonar unit.  On the new HDS Touch Screen units the transducer can plug directly into the back of the sonar as StructureScan HD is built into the new HDS Touch Screen units. The Structure Scan HD uses 455kHz frequency for distance and 800kHz for greater resolution in 50ft or less of water. 


Side scanning sonar is exactly that, a view directly off both sides of your boat. Being able to view a swath of water 600 ft wide 300ft on either side of my boat is a very power tool when it comes to locating baitfish, salmon, tuna and suspended schools of rockfish. I often find schools of bait or fish that are not visible on the surface, or mark salmon feeding on bait in the ocean and with StructureScan HD it makes it easy for me to stay with the school of fish. Without StructureScan HD after hooking up on a fish and stopping to land it I would quickly lose the school of actively feeding fish and have to begin blind trolling again trying to guess where they went in relationship to where I just landed my recent catch.  With side scan sonar it’s pretty easy to relocate the school and get back on the fish relatively quickly. This past summer, I used the side scan feature on my StructureScan HD to locate fish off Westport. We had been catching kings in 30-40ft of water but the fish moved. By side scanning the shallow water I was able to see the fish moved in closer to the surf line. We found the fish moving down 15-20ft contour of water off the coast. We easily located and targeted these fish and came home with limits. The Side Scan works great in all water depths even if it can’t read bottom. Many times fishing tuna in 3,000 plus feet of water we used it to locate tuna schools around the boat even if it couldn’t read bottom.

Left window standard sonar showing kokanee, right window Down Scan showing fish in school


Down Scan:

StructureScan HD is also equipped with a DownScan feature that shoots under the boat just like your traditional sonar. The difference is you get extremely clear pictures of objects under the boat. These are like graphic paintings of the bottom.  With DownScan it’s very easy to locate submerged debris, boats, abandoned crab pots, large rocks and boulders, underwater shelves, and key fish holding structures in water up to about 230ft. 

Whenever I have a question on my standard HDS sonar, I just bring up my DownScan on the same page and overlay the Structure Scan/Down Scan data over top of the standard sonar; this really helps ID the type of targets you’re looking at.

Structure Map displaying image on American Lake


Structure Map:

Structure map is a tool built into the StructureScan HD that works on HDS-Gen 2 units and HDS Touch Screen Units that allows you to overlay SideScan sonar returns on top of GPS charts, giving you a bird’s-eye view of underwater structure. Imagine looking ahead of your boat and seeing your GPS chart of the bottom and behind the boat then displays an underwater map of what you just cruised over.  This is a great way to map and record data on the HDS Gen 2 unit of the bottom. This works really well when you’re looking for bottom fish haunts or good lingcod holding rocks.  


Left window GPS, Top right standard sonar image, right bottom window Down Scan image of snag on the bottom of Mid Channel Bank with bait on it. Screen shot on Simrad unit

Fine Tuning StructureScan HD:

One trick to getting the most from the side scanning feature is fine tuning it. I manually override the auto range and get the unit out of its factory default settings. Next play with the color palettes that give a real clear image of the targets you’re fishing for. Brown works well for me for salmon. For tuna I had better clarity with an orange palette. For most side scanning I have found the 455kHz frequency works the best to picks up fish at any distance more than 50 yards. Last play with the contrast control to bring in the clearest image on the HDS screen. Run it up to max, and then back it down until you get a crisp clear image.

Why traditional sonar will tell you what’s under your boat you can be missing some great fish opportunities just off either side by not employing StructureScan/Side Scan feature on your Lowrance or Simrad sonar. I quite often run my HDS unit with a left and right view, a down scan view and a traditional sonar view. See what you have been missing! For more information on StructureScan HD visit

Comments are closed.