Side-Imaging Today: The Humminbird 987c SI

Last year, Humminbird introduced a new type of sonar. Their high-end units now add Side-Imaging (SI) sonar standard color sonar imagery and GPS map navigation features. At roughly $2,000, the Humminbird 987c SI is about the most expensive sonar and GPS unit available. I find the SI to be a better searching tool than standard units.

Buyers gain a new search capability that simplifies the process of finding cover and structure likely to hold fish. The SI allows an angler to make passes down a shoreline or around important structures and mark spots as waypoints. The angler can then return to fish each waypoint to see if the spots are productive. Users more rapidly learn new waters and gain knowledge about underwater features they already fish.

Fish returns are smaller and more difficult to identify in SI imagery compared to standard vertical sonars. Schools of small baitfish appear as murky clouds rather than dark blobs. Fish the size of crappies or yellow bass may appear as small white dots, and individual gamefish like bass aren't much different than the returns created by stumps on bottom; but this is a cover-location tool, and effective use always has a learning curve.

Although gamefish and baitfish show as separate returns in SI imagery close to the boat, fish echoes farther to the side are mixed in with returns from the bottom and are more difficult to see. The clue that an SI return is a fish rather than a bottom or cover echo is a matching fish shadow farther away. Side imaging can help an angler locate and relocate moving schools of predator fish in relatively open water, but this is a bonus feature, not a primary benefit.

Beds of underwater vegetation are visible as marbled or bumpy bottom, but the soft edges of many submerged weedbeds may be indefinite. The prime benefit of SI is in definition of hard elements. Rockpiles and the deep edges of riprap are clear. Bridge construction and cover near pilings are revealed. Laydowns and underwater brush seen as blobs on bottom with vertical sonars become distinct logs and trees with defined branches. The clarity of various images recorded with the SI can be seen on the Humminbird website ( The increased fishing capability created by such detail is much like having photographs of exposed cover in a reservoir or lake.

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While the unit has many positive features, anglers should also be aware of its limitations. The SI unit's transducer must be located externally on the stern of a boat. The system works best at speeds under 10 mph and on straight-line courses, as turns distort the imagery.

How the stern is shaped and outboard motor is mounted influence whether the unit can "see" well to either side. Nothing may be placed in the line of sight to the sides of the transducer, and external mounting exposes the transducer to possible damage. Yet, I fish mine in Lake Fork, a water known for its hard-to-navigate stump fields, without damage.

I'm a beginner with the SI system and learn to better identify echoes and use other features on every outing. If you're a non-techie like me, you may find the complexity of menus and some options non-intuitive, but learning the details is rewarding. Users need to buy a map chip and may want another chip to record images for review with a personal computer.

Beyond conventional "fish-finding" sonars, the SI is worth the price if a user wants an advanced search tool.

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