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Old 09-13-2015, 08:06 PM   #1
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Default Help with Sonar Interpretation

I have a B175-H-W transducer to a NSS12. I fish fresh water (Lake Michigan) in relatively shallow water. Very happy with the sonar so far, but do occasionally get some returns I don't understand. I get returns like the one I have attached usually a couple of times every trip. It appears like several targets stacked up, but I doubt this is actually the case.
Also if someone could explain what the thin red line at the top of the screen is it would be helpful. Sometime it appears and sometimes not.
Please advise.
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Last edited by slipfit; 09-13-2015 at 08:31 PM.
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Old 09-13-2015, 08:11 PM   #2
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Thanks for opening this thread, I too have a new Garmin 741xs and I can't tell a fish from a weed from a whatever! I'll try to post some of my pics if you don't mind a bit later but your pic will help a lot with the pros assessments.
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Old 09-13-2015, 08:27 PM   #3
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No problem Hatem. I'm here to learn and help where I can. I'm sure the returns I posted are not weeds or the like. The smaller returns are baitfish and although there are none on this shot, the salmon returns are about the same size, but much more strong (thicker and multicolored with red at the top side of the arch).
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Old 09-13-2015, 08:34 PM   #4
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Thanks, Slipfit, so all of those linear things are the fish's movements? Or is the entire thing a fish?

Like those long ones on the bottom, at first I would've said some type of weed or even eel, but could that be a few fish just moving towards the surface showing their path for that period of time of capture by the sonar?
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Old 09-13-2015, 09:36 PM   #5
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If you have StructureScan, run the DownScan at the same time as 2D CHIRP and you will much easier understand what you see.

What you are seeing might methane bubbles rising.

The red line at the top is surface clutter. Use TVG to decide how much surface clutter to be shown, use TVG with care since it's reducing the sensitivity close to the surface which may mask targets in the upper part of the water column. The amount of disturbances close to the surface and the TVG setting will decide the color, read means strong.

From an old Lowrance sonar tutorial:

Surface Clutter

The markings at the top of the screen can extend many feet below the surface. This is called Surface Clutter. It's caused by many things, including air bubbles created by wind and wave action or boat wakes, bait fish, plankton and algae. Many times larger fish will be seen feeding on the bait fish and other food near the surface.



Why do you operate B175H-W at 200kHz when not using StructureScan? NSS Evo2 with B175H-W have best fish finding performance in CHIRP mode at any depth.

Last edited by abbor; 09-13-2015 at 09:48 PM.
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Old 09-13-2015, 09:57 PM   #6
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Quote:
Originally Posted by abbor View Post
If you have StructureScan, run the DownScan at the same time as 2D CHIRP and you will much easier understand what you see.

What you are seeing might methane bubbles rising.

The red line at the top is surface clutter. Use TVG to decide how much surface clutter to be shown, use TVG with care since it's reducing the sensitivity close to the surface which may mask targets in the upper part of the water column. The amount of disturbances close to the surface and the TVG setting will decide the color, read means strong.

From an old Lowrance sonar tutorial:

Surface Clutter

The markings at the top of the screen can extend many feet below the surface. This is called Surface Clutter. It's caused by many things, including air bubbles created by wind and wave action or boat wakes, bait fish, plankton and algae. Many times larger fish will be seen feeding on the bait fish and other food near the surface.



Why do you operate B175H-W at 200kHz when not using StructureScan? NSS Evo2 with B175H-W have best fish finding performance in CHIRP mode at any depth.


Good question Abbor. I guess the honest answer is that I don't know. I also have structure scan with the LSS2. I don't offten run them together as I prefer my nav screen bigger. But I will start. So I thought my options were 50 hz or 200. How do I select the chirp feature?
Feel pretty dumb for not recognizing this earlier. I'm excited to see the difference that should make
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Old 09-13-2015, 11:04 PM   #7
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Touch Menu when the sonar window is active, then select Frequency . The options for B175H-W are High CHIRP, 200kHz and Customer frequency. Under Custom frequency any fixed frequency from 150 to 210khz can be selected.
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Old 09-13-2015, 11:08 PM   #8
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I now see you asked about the thin red line (which I did not notice on the screen shot when using my smartphone earlier), you have enabled the temperature curve to be drawn.
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Old 09-13-2015, 11:12 PM   #9
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The red line is caused by the sounder switching to receive after transmitting a pulse and the gate allowing some of the transmitted signal in immediately before the true pulse returns. This is why it is at the top of the screen..
1 The same red line would be present even if the transducer was 2 meters below the surface or in air.
2 If the red line was not present it could indicate the transmitter has failed. However the screen may still render a passive target indicating the receiver is working.
3 The red line can increase in size when operating in shallow water as the switching is slow and allows more signal in.
The red line is called "the transmission line"
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Old 09-14-2015, 07:21 PM   #10
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Thanks for the responses and explanations.

The methane bubbles make good sense and is the best explanation I have had to date. That's something I would have never thought of. Seems legit.

One more question if I may. There is an indication on the right side of the screen in my picture. It's above the 40 ft. Mark and says 65 degrees. Is this the surface temp.? And if so, why is it not on the left below the depth indication? I have not updated to the latest software update. Is this the reason?

Also, I was at the boat and switched the frequency to High Chirp. (Thanks Abbor, I feel like a numbskull for that oversight). How do I know I am in 2D as you suggested?

Thanks again. I continue to learn.
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Old 09-14-2015, 08:23 PM   #11
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One point worth mentioning is that the transducer installed must be selected in the setup menu under installation. This applies to many brands.There are 50 or so to select from and factory default is usually set to 'generic'. CHIRP transducer have an ID chip so this is automatic but the other conventional transducers are not and you must select from the list.

The transducer cable usually has it's model number at the plug end and many installers forget to set it.
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Old 10-23-2015, 08:10 PM   #12
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Well, I have a Garmin 741xs and half the time I have no friggin idea if what I'm looking at is a fish or a weed or some floating thing. I know it's not one of those great CC fish finders and is only 9 inches long or from corner to corner but sometimes I do see things that look like fish but just so hard to tell. I suppose practice makes perfect.

I was out in Ocean City of shore about 25 miles with a fellow who had one of the 8000's on his and he said half the time he doesn't even use it because you just can't tell.
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Old 10-23-2015, 08:55 PM   #13
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Your screen shots shows good targets..enough to fish with..but as abbor noted..you would be better to use the full CHIRP with the HW..just a bit of a tweak and you will be sailing!


With the B175C-HW you are best to run in full CHIRP because you will achieve the bet target detection and separation.
Below is a comparison of the standard H and the HW..showing the sensitivity of the HW


Left..standard High band CHIRP.....Next the HW CHIRP.
Again standard H and then again HW.
Furuno DFF1-UHD






And one does not always sees arches..here is bait and salmon .. .
Garmin xs & B175C-HW


Bait....B175C-HW

Last edited by semperfifishing; 10-24-2015 at 12:20 AM.
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