Looking at your fish finder and you just can’t figure out what the screen is showing. Keep reading because we are going to give you a high level summary of what you are looking at. We will be showing images from the NSS Evo 3s but the principals are the same for most fish finders.
Understanding How A Fish Finder Works
Sound waves traveling through the water
To truly understand the screens you are looking at, let’s go back to the basics of understanding how the technology works. The way a fish finder works or traditional sounder, they mean the same thing, is a sound signal is sent from the transducer that’s usually on the back of the boat sending out different frequency signals through the water in the direction you have set up on the unit. The signals travel through the water and hit things along the way until it hits a surface (stone, plants, fish, ground, etc.). Once the signal hits a surface of a structure, fish or the bottom, that signal is then bounced back to the transducer and is interpreted by the machine. The machine then interprets the density based on the sound waves that were returned and calculates the depth based on how long it took to get back to the unit.
Based on the color palette that is chosen or assigned, you will see different colors on the screen. We will take a closer look at how to interpret the colors.
Basic Echo Sounder - Traditional Sounder Screen
Traditional Sounder Screen
Let’s start with the traditional broadband sonar view, which you will find in most fish finder sounders and can see the bottom or other objects . This screen in the above image is showing you the bottom and any structures that might be along the bottom. We are using a model that has chirp, which provides a better defined image of the bottom, structures and objects. The chirp technology will allow you to better identify individual fish that are hanging just off the surface of the bottom. Without chirp technology if you had a lot of fish gathered together at the bottom you wouldn’t be able to tell if it was fish or structure.
In the image you see a really thick red line, which can be interpreted as a very dark or hard bottom. The thicker the red is the denser it is, so we’ve got a hard bottom. It could be hard packed sand or rock.
Arcs represent fish
If you look at the image now, it is showing you a thicker red area, so we can assume we’ve got rocks or something hard because the sound waves coming back from the sounder shows a much thicker red area. The sound signal isn’t getting absorbed by the structure or object and it’s bouncing back with a strong signal to the transducer.
Soft muddy bottom
A thin red line with a lot of yellow and green, could mean that it’s a soft muddy bottom or there is a lot of vegetation that is absorbing the sound signal. There are settings in some units that allow you to have actual fish symbols, so you can see when there are fish of various sizes hanging in the water column. Even though it is nice to have the fish symbol, it is a better representation of the fish size to have the arcs.
When you see objects that look like they are suspended, those could be fish. The sound signal is bouncing off the swim bladder of the fish (because this is the densest part of the fish and reflects the sound signals very well). The bigger the swim bladder means the bigger the fish, which you will see as a bigger arc. This setting can be turned on and off through the menu in the machine. Just keep in mind that the arc would be in comparison to the things in the water, like vegetation or structures.
The screen will always show a scale for your depth.
If you see an area that you may want to investigate later, you can create a waypoint by putting the crosshairs on the area and saving the waypoint. Remember that you are traveling so you will see the screen scroll through and the imagery you see is usually something that you have already passed. It is better to travel at slow or idle speed then going fast to make sure you see the imagery clearly.
Down Scan - Down View
The screen might have some similar elements to the traditional view but it does provide you different information. The imagery looks more like a 3d image. You will see some shadowing and other features. The sound signals that are being transmitted from the transducer in the down scan is not a single cone shape waiting for the sound signal to bounce back to the unit. In down scan there are multiple signals being sent out from the transducer in a wafer and as the information returns to the unit, that information gets processed and compressed into the image you see on the screen.
A good rule to remember is that higher frequencies will work better in shallow waters and lower frequencies will work better in deeper water. If you aren’t getting a good reading or the imagery doesn’t look clear, always try adjusting your frequency.
Always look at the equipment and make sure you have the right equipment for the fishing you plan on doing. Most of the transducers that come pre-packaged with the units sold will be adequate for a good percentage of fishing but if you plan on doing deep sea fishing within canyons, you will want to look at purchasing a transducer that has that capability
Another way to understand how sound signals work, if you think about a spot light shining directly under your boat straight to the bottom. You will see crevices, nooks and crannies from structures or vegetation in the water. The sound signal that is being pushed through the water is bouncing around all of those things and bouncing back into the unit, which the unit will interpret and create the imagery you see on the screen.
Let’s take a look at this image showing a different color palette. Instead of seeing the color showing the bottom in red it is showing the bottom in white. If you saw a complete speckled tan bottom it would be a softer material at the bottom such as silt, sand or mud. The signal would be absorbed into the material at the bottom.
With this specific unit from Simrad it offers an exclusive in their units with either an arc to identify fish or an actual fish image. They call it Fish Reveal. The way it works is that they are taking the arcs from their chirp screen and from their echo screen and identify the fish by overlaying that on your down view screen so you’re getting the best of both worlds. You’ll be able to see where your fish are very easily as well as having your really nice depth defined bottom with your down view. It’s exclusive to Simrad and Lowrance.
Side Scan
Now let’s try and understand side scan on our fish finder. It is similar to down scan but the signals are now being sent on either side of the boat. The signal is being sent on port and starboard. The transducer is right at the top of your boat and the line you see on the screen is created by your transducer.
The area you see that is black on the screen, that is your water column. That is the area from your boat to the bottom or an object. But remember the signal is being pushed to the side of the boat. If you see an mark on either side of the centerline, you will know which side of the boat to cast. It is great to use a combination of down scan and side scan to know where to fish. Down scan will give you a good visual of the bottom or any objects under the boat but side scan will give you a good representation of where the fish might be in relation to the center of the boat.
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