[CA] [CA11] Side scan issue

[Chief]

I don’t believe the side scan is producing complete image.
I am attaching some screen captures for you to see.
I have quite a few I can provide. If you want to see additional images please let me know what you want to see, i may have it in another capture.
Attached is a file as I pass under a bridge with solid concrete supports. I appears to provide returns from the other side of the solid structure. I also lose bottom return closer to the boat than I would expect. I think this is having an impact on the 3D picture as well.
The second video shows both side scan and 3D.
Axiom Pro 12” and 9”. RV220 transducers. All other sonar and downvision work very well.

Thanks
John

[Chuck - Raymarine - Moderator]

John,

We believe what you are seeing is normal, and it’s a matter of expecting the system to perform one way while it actually behaves differently. My first few times on the water with RV3D were similarly challenging, and disappointing, until I understood better how it works.

The SideVision channels transmit basically horizontally (slightly angled down) and effectively have much farther reach than the 3D does. If you take the SideVision out of auto range and select it manually, you can get it to see quite a distance with some detail. Its reach for all practical purposes in infinite, limited only by signal strength.

RealVision 3D on the other hand, can only see out to the sides about as far as the water is deep. The pattern of its beam is more of a radius that scrapes the bottom under the boat. To the sides, it does not have as much contact with the bottom. For this reason, its possible to pass relatively close to object that you would think it should see in 3D, and it in fact does not. At the same time, the 2D SideVision does pick them up.

Your situation may be a bit easier to interpret if we know the depth of the water when the video was taken, and whether or not the SideVision was in manual or automatic range control. The RealVision 3D’s range scale follows that of the SideVision, however, it can’t see as far as the SideVision can because of its radiused beam.

Sometimes when you get some thick bait, or noise on the RealVision 3D, you can actually see the radius of its beam in the returns, similar to spokes of a bicycle wheel.

Notice in your video how well the RV3D and SideVision both painted the bait pod he went through. It was well within the radius of the RV3D beam.

Take a look at the Brown’s Bridge Image attached below. This one is very impressive. Let me explain why. The water is nearly 90-feet deep, and the concrete bridge supports are only 25-feet away. In this case the RV3D beam is a 90-foot radius around the transducer, so we’re seeing the structure very nicely. Look at the SideVision image. It has solid returns on the bottom all the way to 120-feet away. Look at the horizontal scale on the RV3D though. Its bottom fades out at about 100-feet. Just a bit more than the water depth. The arc of the 3D beams is no longer in contact with the water out there.



Please additionally note that sonar improvements were included within the LH3 v3.11.42 software update and it would be recommended that this version of software be installed should it not already have been.

[Chief]

Chuck,
The bridges are located on Kent Island MD.
38.58.260N 76.14.847W
The system is running 3.11.42 and to that point, the upgrade made a big improvement in the clarity of the sonar image. No change in the side scan or 3D. This has been consistent since new install this spring.
I would estimate the span width at approx 40’.
See attached photos. Concrete piles stand on solid concrete bases.

[Chuck - Raymarine - Moderator]

John,

Please review my updated prior response. I see the water depth is not much more than 10' in the specified location ... is this correct? No photos have been attached. Should you have issues with photo sizes, then please click here to view a FAQ addressing how to resize photos.

[Chief]

Chuck,
15-20ft is closer but yes, not very deep. Bridge image attached.
The video was passing through the section to the right of the drawbridge.

Below is a link to a screen capture in 25-30’ of water.
no 3D in operation and the bottom returns seem to disappear at 75-90’.
I would expect returns significantly further out than that based on other images I have seen.
I always use sidescan in manual range because the default in auto is usually less than 40’.

https://click.email.vimeo.com/?qs=157dfa...5338668bbf

This is another capture.
Again, no 3D is active but the bottom return drops out much closer than I would expect.

https://click.email.vimeo.com/?qs=dae14f...7f04bceab5

I appreciate the feedback.

John

[Chuck - Raymarine - Moderator]

John,

The links to these videos expired. Please place host them on a video hosting site which will permit them be remain until you pull them down.

[Chief]

Chuck,
Try these links

https://vimeo.com/380564519

https://vimeo.com/380570413

Same 2 videos. I hope these are the correct links.

Just to be clear, the 3D seems to work great within that cone you described. It’s the 2d sidescan past about 90ft that seems to be missing regardless of depth or manual setting.

Thanks again,

John

[Chuck - Raymarine - Moderator]

John,

The imaging shown within the video looks very good to me and to be that of a properly working system operating over a relatively nondescript bottom. The humps which hold fish appear to render correctly within CHIRP conical sonar and within side imaging. The maximum practical range for side imaging is 180'. Accordingly, it would not be recommended that it be ranged out to 240' and greater as was shown in your video. Like DownVision, SideVision is most useful in locating and identifying structure ... and structure often attracts and holds fish. CHIRP conical sonar is best for locating fish.

[Chief]

Thanks for the feedback Chuck.

John

[Chuck - Raymarine - Moderator]

You're welcome.