How does depth sounder work

For a fisherman, it can almost feel like cheating! These days, depth sounders include large high definition displays, rapid pulse rates, and images so clear they could be mistaken for an MRI reading.

Instead, they had a roll of paper and an ink pin. The roll of paper was much like a roll of receipt paper in an eftpos machine, while the ink pin was like the arm on a record play. The pin would map out the shape of the ocean floor onto the paper, which would roll out as the boat moved. The end result looked a bit like a heart monitor, or a seismometer that you would see in the movies.

Not only do new depth sounders come with high resolution displays, but they also offer improved features and greater accuracy. Take speed, for example—early models of depth sounders used small water wheels to gauge speed; the wheel would spin as the boat moved through the water, and the rate of its revolutions would be used to calculate speed.

But that system was rudimentary and prone to inaccuracy, especially in debris-filled waters or at higher speeds. They are also able to offer depth-sounder GPS combinations, which display both aerial maps and depth imaging on single or split displays. Despite so much technological advancement in the world of depth sounders, one feature stands above all else: side scan technology.

Side scan depth sounders are relatively recent, and they provide some of the most accurate displays available. This makes them perfect for lure fishing. A basic echo sounder will return imagery based on static objects whereas a sounder which is designed to aid fishermen will also reflect back from any object that is denser than the surrounding water, including rocks, metal and mud but also the air filled bladders of fish. Fish that do not have swim bladders such as sharks and rays therefore do not show up on fish finding devices.

Most current applications of fish finding technology show clear and resolute data allowing you to identify single or shoals of fish but some of the older designs require additional interpretation. Each manufacturer varies in design but the visual representation of fish vs plankton or solid objects is relatively easy to determine as the size, composition and position of them moves in the water.

The frequency of the transducer is a crucial factor in the depth of your range but also the level of information provided. Typically the lower the frequency the more practical for deeper waters something like a 50kHz wave will penetrate further whereas kHz is more suitable for shallow waters.

However, the benefit of the higher frequency is that the detail of the imaging returned is much greater than that of the lower ranges. Some devices offer dual or multiple frequencies which provide both range and clarity. As well as the frequency of the transducer it is important to ensure that the device is installed in the best location to get the best results. As important as the transducer itself, the power of your device will determine the speed at which information is transmitted.

A low power device will take longer to return accurate information by which point any advantage of having it installed may have been lost. This is also relative to the depth of water you are using it in. Generally speaking you will need lower power at higher frequency for shallower waters and higher power, lower frequency for deeper waters.

This term refers to the width of the beam that the transducer is sending to the floor of the body of water you are in and a narrow beam will cover less area than a wider beam. More advanced echo sounders have multiple beams including side beams which give greater coverage. What to read next: How to Pick up a Mooring Ball. Please comment, subscribe, and follow me on Facebook and InstaGram! See you there or on the water!

You must be logged in to post a comment. On February 18, By Kimberly. How the depth sounder works The depth meter sends the signal from the transducer at the through-hull fitting to the bottom of the ocean floor.

Sorting out the numbers On most of our 30 to foot sailboats, our magic number is three. Adjusting the readout The transducer reporting digital readout can be adjusted to read zero when you are aground. Three different ways to measure depth 1. Depth from the top of the water to the sea floor.

To get that depth, you would have to add from the transducer to the waterline. Which do you prefer? About Kimberly. You May Also Like.