All a depthfinder is a sonar unit, it shoots soundwaves through the water and when the waves hit something it bounces back. Most transducers shoot straight down. Some transducers are mounted with a bracket on the back of the boat and have the ability to swivel, backwards, straight down, or towards the front of the boat. There are also transducers that are epoxied into the fiberglass in the hull of the boat, those always shoot sound waves straight down. the advantage of the transducers epoxied into the hull is that they won't get damaged by underwater hazards. The reason a depthfinder constantly scrolls across the screen is because it is constantly regenerating an updated reading of what it is seeing. If you are sitting still in your boat and there is a fish below that is sitting still below it, the screen will show a straight line. The sound waves are constantly reflecting the same area of the fish, hence giving you the same reading on the screen. If you are moving your boat and it passes over a stationary fish it will show an arch. As the sound waves pass over the tail and move toward the head it will give you arch, just like the top profile of a fish, or it could be head to tail. If you are stationary in your boat and see a line that is moving across the screen but is moving upwards or down there is a good chance that fish is actively swimming through the cone (area covered by your sonar). The Lowrance website has a great tutorial and can probably answer most of your questions. Thank you for your service and stay safe, trust me, we have left plenty of fish for you.
