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Understanding The Side Scan Fish Finder

Understanding The Side Scan Fish Finder

It’s time to discover or rediscover Side Imascan fish finder mode. Side Imaging, Structure Scan, SideVü are terms that cover very similar technologies. This is the mode par excellence to use for the discovery of a plan or a watercourse. Thanks to this technology you will be able to establish an almost photographic vision of what lies beneath the surface. As with the Down Imaging mode, we are getting closer to what is happening in medical imaging. Like an MRI (Magnetic Resonance Imaging), the probe makes background images in the form of very thin layers. Put side by side, these images give you a very faithful representation of the background, finally provided you respect certain simple principles. Let’s see what are the undisputed advantages of this mode and how to use it.

The first advantage is the most obvious: discover what is beneath the surface! Simply put, just put your boat in the water, navigate and watch the bottom scrolling on your screen. You can either fish directly for hot spots that you discover or mark them as a waypoint and come back later.

How to interpret what we see on a sonar in Side Scan?

Solar Scan

Above all, it is important to understand how this mode works. As can be seen in the diagram above, it is a beam that sweeps the entire height of water as far as one can set in the settings (see box). You must imagine a ray of light that, when it encounters an object, casts a shadow. On the first capture of this article, we clearly see the “shadow” projected by the branches. These shadows can also be created by anything suspended in the water column under the boat: fish, line buoys … Still in this capture, we see in this water column, which is materialized by the black zone central image, bubbles created by a spillway just above the station. The more important the return (background or dense object) the more it will be “bright”, conversely the more the image is “dull” plus the return is low. It’s a bit the same principle as the difference in color returns in 2D mode.

The Side Imaging/scan, how it works ?

The sounder will send a signal with frequencies of 455 kHz and 800 kHz, this very fine signal but very “lateral” allows to obtain a very detailed image of the bottom under the boat and on the sides up to a distance of 120- 150m depending on the manufacturer and depending on the depth.

3d vertical fish finder

This background image is, like Vertical 3D technology, designed to identify structures on the bottom, better understand the echoes visible in traditional 2D vision.

This technique is systematically associated with GPS functions, this technology will only be found on GPS-sonar handsets. Indeed, the software that uses all the sonar data, associated with the GPS positioning, allows you to locate, “georeferencing” a structure present on the sounder image. A waypoint marking makes it easy to return to this point with a very high level of precision.

A wreck located with the sonar image, even on the side can be marked very quickly and simply with GPS.

It is possible to obtain very high quality images when the sea is calm, the speed of the boat between 3 and 7 knots, on a rectilinear trajectory (to avoid distortions). Sonar GPS handsets equipped with this technology also provide 3D Vertical Vision.

3D technologies provide a better understanding of background tracking images. They are an asset to facilitate the interpretation of data, to identify the best fishing areas.

Side Imaging Beams

Two side beams sweep on the sides, with a theoretical range of 120 m each.

Unlike conventional conical-shaped beams, Side Imaging beams are very thin in their horizontal dimension, but very wide in their vertical dimension.

To get a good idea, it is important for the boat to move at a constant speed (between 4 and 8 knots), preferably in a straight line to avoid distortion.

Side Imaging/scan , effective everywhere

Side Image Fish Finder Scan

Second advantage of this mode is that even by very shallow water it is quite effective. Indeed, as for the Down Imaging, with the Side Imaging there is no loss of beam power. This is a considerable asset on the large shallow lakes such as Lacanau or Biscarosse where, in the middle of large sandy areas, there are herbaria, refuges suitable for fish. If the fishing is complicated, do not hesitate to go far, far from the posts and mark the area with Way Points. The trick is to come back with the probes off and use only the GPS to avoid alerting predators, sometimes it makes the difference!

A window open on the bottom

Third advantage: understand the structures that lie beneath the surface. Unlike 2D or Down Imaging mode, this mode provides a “top-down” view that is much easier to understand, even for the uninitiated

As for the capture in the previous issue, we clearly see the concrete bases, the submerged cable that connects them and the erosion created by the passage of the current around the bases. On the right side, in the upper third of the image, in the water column under the boat, 3-4 balls of small fish are seen as well as 2-3 isolated fish much larger given the width of the covered area. Even further to the right of the image, on the 36m line, we perceive a ditch that is in fact an old small stream.

In a future article, we’ll go even further in understanding what’s the difference between the side scan of some very known trades and the advantages of each one,  lowrance side imaging vs humminbird side imaging

The settings

The settings are just as simple as for the basic system. The first setting will be the color choice of the palette. By default, amber, allows you to have maximum details without being too aggressive for the eyes. Blue remains a color where the details appear relatively well. This criterion remains a personal choice.

The prospecting range is the distance at which you will carry your signal. Take for example a depth of 10 meters, you establish your prospecting on average at 3 times this value, 30 meters to the right, 30 meters to the left. This will be a criterion to change regularly. If there is only one side activated, you can push the setting to 40 meters. Enabled only one side, it adds a level of detail.

The frequency, is defined according to the type of prospection that one wishes to obtain. The 455 khz will allow you a broader survey, but less detailed, the 800 khz will be the opposite. The speed of scrolling, will be adapted as for the usual surveys depending on the speed of movement of the boat. This will be a criterion to change regularly. You will then have the possibility to adjust the sensitivity, and the contrast. By default, they are adjusted to half, depending on the situation you have to increase the sensitivity slightly to have a better definition. Turn off the sharpness setting,  which adds grain to the image, and prevents proper analysis.A contrast set between 10-12 and the same for sensitivity are the basic values.

Image analysis

Once the catches are made, we must now be able to read them, and especially analyze them quickly and reliably. First, it will be necessary to ensure that the image capture is representative of the background, that is to say having opted for the proper speed of scrolling. Once the image on the screen and representative how to read it? The line symbolized in the center, defines the path traveled compared to the instant “T”. It is located where the symbol of the boat (in blue) appears. The black layer, is the depth at the bottom of the boat. Then if you materialize the situation, the more you go to the outside of the screen, the further you get away from the boat (distance set in range SI). To summarize, the first color relief after the water layer will be the ground immediately above the boat. Now that you have understood the principle, an object that will be symbolized on the ground will generate a shadow, the more the shadow is projected (long), the higher the structure will be. Imagine standing upright on your boat, lighting the ground with a flashlight horizontally, this will create contrasts of light and create shadows, and well the image Side, it’s the same principle.

A very useful tip is to use the directional pad to freeze the capture, and this will bring up a cursor. Once this cursor appears, you move it on the screen and position it for example on a rock head. You then press the “MARK” button and a Waypoint is created. You will see the generated point, on the map, it will be offset from your path, and this is normal, since the aircraft will have analyzed the distance to which the boat was in relation to the object.

Another tip, pressing the zoom keys, you will see a frame, zoom, you can also move it with the directional pad, and allow you to analyze an object, structure, or relief in detail.

A fairly smooth body of water will favor beautiful catches. In terms of depth, in 40 or 50 meters, you will have to master the settings of your device to have a valued image. Otherwise in the rest of the cases Side Imaging is a great asset to save you time. With experience and adapting the settings, the image will become more and more precise, and will push your fishing to be, too, more and more pointed. The system requires a little bit of practice before you can pin it down. An internet support exists, if you have questions. Professionals, as well as current users will know how to inform you, and share their experiences

Multiple features

Devices equipped with this system offer several features: conventional sounder (vertical sounding), precision sounding (Down-Imaging), lateral sounding (Side Imaging) and GPS chartplotter / card reader.

These functions can be used in turn or simultaneously as needed, knowing that they are both complementary and closely related.

Sharing the screen

Humminbird Fish Finder

This system is dependent on other handset tools. It will be used in addition to information. The cartography will situate you in space. The sonar 2 D, will give you information on the nature of the funds, and the presence of fish. Down Imaging and Side Imaging will complement this information by analysing the underwater soil structure. Reading the screen will be easier if you divide the page into three parts, a quarter page for the 2D sounder, a quarter page for the Down Imaging function, and half page for the Side Imaging.

You will have the choice to define the side where the Side is active, left side, right side, or both. Ideally, for a quick survey, activate both sides allows you to have a vision of what surrounds you, ideal for the identification of a structure in 10 or 20 meters of water. During navigation the propeller often disturbs the left side of the Side, so it can only be activated on the right side. You can also slightly trim your engine if your signal is obstructed by cavitation of the propeller. For a survey of wrecks in much deeper, it is better to activate one side only. Preferably we activate the side that is not hidden by the engine, the right. This option allows us to have a wider window and offers us the possibility to increase the SI range.

check out our article https://www.fishloversguide.com/lowrance-side-imaging-vs-humminbird-side-imaging/

Example of setting tips

Concretely here are the settings that accompany expert of fishing most of the time everyday in their fisheries. the choice of screen sharing associated with their shortcuts: Choice 1, Carto / 2D sonar; Choice 2, 2D sounder / full screen; Choice 3 A quarter of page Sonar 2D + a quarter of page DI + half page SI.

My settings for a survey in 10 to 20 meters of water.

Color: Amber

Frequency: 800 khz

SI beach: 45 m

Sensitivity: 13

Contrast: 11

Sharpness: disabled

Scrolling speed, variable.

SI side: Right + Left (engine slightly trimmed)

Do not forget to activate the distance lines, which allow you to split the screen and identify the distance of an object from your boat.

This system allows you to locate faults, plateaus, sand dunes, but also wreck-like structures. This will save you a lot of time on your prospection.


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