You would benefit from a Lowrance HDS StructureScan plus DownScan unit that presents a panoramic view off the sides and under the boat.
A classic (already old fashioned) sonar of any brand has fewer options. None are reliable for viewing to the side. However, I've turned my trolling motor transducer sideways to make it peer under docks, moored boats, etc, and get fish arches. stumps, etc. However, because of the image return limits, any object on the screen might show as being 1500 feet away. The signal skips along the bottom and right out of the lake, so the machine assumes "infinite" distance to the target. Even so I find that trick useful.
Cheaper units use an 8 to 20 degree cone at around 200 Mhz. A 50 Mhz sonar has a wider 35-45 degree cone, great for trolling in freshwater, or in deep saltwater. Think of a flashlight beam when talking cones. Shooting a narrow beam straight down under the boat a 200 Mhz unit allows a "lit" area of 1/3 of depth. If you are 15' off bottom the screen image shows you an area about 5' wide. If 100' of water it will show a bottom circle 33' wide. Remember the cone tapers ever wider from an inch wide at the boat to feet wide below. Using a wider cone angle allows a larger bottom view with less detail. The same proportion is true if scanning sideways.
Practically, I don't think sonar is good for anything in 5-20 feet of water except to locate structure while passing over it. I find that fish are not "photogenic" enough to stick around to give themselves away. They scoot away when the vibrations get within their comfort range. I've let my sonar run while entering an area full of bass feeding shallow, fins sticking out, only to finds them gone when ready to cast. That's while using a pole, not the trolling motor, being ultra quiet and staying low. I use it shallow simply to identify likely places fish should be, then approach without anything that could interfere. If you already know the shallow area I recommend turning the sonar off. Use it in water 20' or deeper.
Over the years I have logged way too many hours messing with sonar than I should have, time better spent moving baits in the lake. I used to fuss at friends not even turning their units on, but now I realize they got far more actual fishing in and did quite well. It's a tool. I compare it to a router in a cabinet shop. There are many other tools that go toward a finished piece.