Electronics
There are a variety of electronics to help you determine the depth of fish. First, obtain a hydrographic chart or underwater contour map of the area you're fishing. These are readily available from appropriate government agencies. They will show a clear picture of what structural elements lie beneath the surface. If available, the combined use of an aerial photo and these maps will aid in converting the two-dimensional representations into three-dimensional reality. Then turn on your depth sounder and use it like a compass in combination with your map and perhaps the aerial photo to put the boat exactly where you want it.
Since smallmouths are seldom found deeper than 40 feet, a shallow-water flasher is a good choice. These units have an extra wide angle transducer cone designed to give accurate readings in shallow water. With practice, a flasher can tell you a lot about depth, structure, bottom content, and vegetation. You may want to add a shallow-water graph, but it's certainly a luxury. This unit actually draws a picture of what lies beneath the boat, sometimes including fish, but there is some evidence that its strong signal can spook shallow-water fish.
Don't be like some anglers who, when they purchase an electronic depth sounder or other equipment, go blind, or at least stop using their eyes. No question, electronics can help you but don't forget to look for visual signs of fish location. A quick scan of a lakeshore line will tell you a lot about the contours and bottom content of what lies below. Keep your eyes open for swirls and jumping minnows -- they're sure signs of active smallmouths. Check for visual clues about vegetation types and thickness. The only way to find that all-important broken rock is to look for it!