Back in the 1970s, there was so much standing timber in legendary southern fishing lakes like Toledo Bend on the Texas/Louisiana border that about the only way to get around on them was following boat lanes cut through the trees.

Schools of bass also used these lanes, tearing up the surface chasing shad and attracting fishermen. Called schoolies, these bass had the frustrating habit of chasing the bait down deep as you got to them, and then resurfacing minutes later well out of casting range.

Flashers were the high-tech fish finders of the day, and some anglers discovered that leaving the clamp holding the puck transducer on their trolling motor loose enough to slide the puck up the side of the motor allowed them to scan sideways and follow these fish. The trick was to slide the puck up far enough to see the fish but not so high that it got reflections from the underside of the water's surface.

Knowing where the fish were let us cast sinking lures at them as we tracked them with motors cranked up on high, ready to swap the deep rod for one rigged with a topwater the instant they broke the surface again.

This side-looking technique didn't work very well with most of the early LCD graph fish finders, partly because some of their automatic operation keyed in on measuring the strength of the bottom echo you didn't get when you aimed the transducer sideways.

If you set the range, sensitivity and filter controls manually, you could make them work, but it was more trouble than doing it with a flasher.

All that changed back about 1992 when an Idaho-based company called Bottom Line introduced Sidefinders, sonar units with LCD screens designed to show fish off to the sides of your boat. Sidefinders used software that filtered out the bottom, the underside of the water surface and everything else except the suspended objects their computers determined were most likely to be fish. They displayed a mark on the screen showing how far each "fish" was from the transducer.

I tested the units, and found they worked surprisingly well. I also appreciated their advertising, which asked why you would want a fish finder that only looked straight down when more than 99 percent of the fish in the lake were somewhere else.

Interphase, a California-based sonar manufacturer, introduced units designed to look out ahead of a boat and show you both fish and bottom structure. Their transducers could be oriented vertically to show a 90-degree arc from straight below the boat out almost to the water's surface straight ahead. It could also be mounted horizontally and aimed slightly downward to scan 90 degrees from side to side ahead of the boat like an underwater radar.

Fishermen found they could mount the transducers on their trolling motors and scan wide areas without moving the motor.

In one test, I was able to stop in the mouth of a cove and see both fish and structure from one side to the other without moving the boat or trolling motor. It takes a bit of practice to read these units, but they work.

Interphase (interphase-tech.com) continues to improve this technology and markets both stand-alone and computer-based units mostly for larger boats.

Humminbird (humminbird.com) introduced its revolutionary Side Imaging (SI) technology back in 2004, and I saw it as the best side-scanning technology for recreational fishermen developed up to that time. It virtually erased the need for a learning curve to interpret sonar readings. Rocks look like rocks, trees look like trees, weeds look like weeds and fish look sort of like skinny cigars when displayed in Humminbird's side views.

SI even offered two frequencies, 800kHz for super detail and 455kHz for very good detail, and more range. The feature's only shortcoming was its inability to show the same kind of detail when looking straight down.

That capability is scheduled to be included in Humminbird's next free software update, and it will be called Down Imaging. When you pass directly over an object, SI splits it in two and shows half of it in the right side view and half in the left view. Humminbird engineers developed software that recombines the two halves into a single vertical view. The new update should be available by the time you read this.

Lowrance (Lowrance.com) brought out its similar and excellent dual-frequency StructureScan technology last year as an accessory for its HDS series models. It comes with a Downscan feature that presents objects straight down below the transducer in the same photo-like detail seen in StructureScan's side views. The Lowrance StructureScan transducer includes two elements dedicated to providing the Downscan view.

Both Humminbird and Lowrance side-looking units can also show a conventional vertical sonar view. Humminbird does this by building traditional transducer elements into its SI transducer, and Lowrance does it with a separate Skimmer or puck transducer. If you mount Lowrance's StructureScan transducer and a secondary Skimmer or puck transducer within two feet of each other, a unique Downscan overlay can be added to your conventional sonar view.

This feature would make a terrific teaching tool for new sonar users because it shows both a realistic Downscan view of an object superimposed on top of the arched, rounded-off conventional sonar view.

Both Humminbird and Lowrance units can be used in freshwater or saltwater, with slightly less maximum reach in the salt. Both manufacturers recommend using their side-looking features at less than 10 mph for best detail, but I have gotten usable detail from both at up to 37 mph. As always, the quality of your transducer installation affects performance at higher speeds.

The principles of sonar may not have changed since World War II, but innovation in their application continues to expand. I can't wait to see what's next!