• Sonar interpretation?

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Talk about your boats, trailers, and boating specific topics here. Sponsored by Life Proof Boats.
 #238158  by TrackerPro16
 Fri Aug 11, 2017 8:57 am
Larry3215 wrote:Try lowering the trolling motor down a little lower in the water if possible. Im guessing its sucking air in from the surface at higher speeds.


I did try that. I bought an extra long shaft for my boat as I don't mind the extra sticking up over the top of the boat. Better to have more to drop in than not enough to keep the prop in the water. I will drop it all the way down to see if it makes a difference but it is already quite a ways under the surface. If not I may change the prop to see if that helps. There are little lines and bent tips on the prop so it may be beating the air out of the water and causing the bubbles. I am wondering now if the long shaft is bending and putting a bad angle on the motor.
I set up a sidevu/downvu/panoptix/traditional screen and played a bunch while cruising slow by the shoreline. It was pretty fun seeing the detail it shows, particularly in less than 20 feet of water.
I scouted until I found a ‘fish ball’ on the sidevu, spot locked, and started fishing. While I setting up the fish went to the front of the boat and lit up the panoptix. YaHoo!
As usual, the fish were right along the weed line and I could toss my lure in different directions to catch (generally) different fish. Into the weeds to catch Rock Bass, along or away from the weeds for perch. The Seahawks were practicing so they had the ‘BOOMING’ music going for part of the time. Not sure if it excited the fish to bite but it was LOUD.
Caught a lot of fish. It was a good day!
 #238164  by Larry3215
 Sat Aug 12, 2017 5:00 pm
You could also be seeing turbulence from the prop if its strong enough, but I dont usually see that on sidevu. Turbulence shows up really well on Panoptix though.

One of the coolest things about Panoptix is "sight" fishing with it. Its awesome being able to "see" fish so you can cast right to them and watch them take your lure!

On the other hand, it is really really frustrating seeing those same fish ignore everything you throw at them!!
 #238202  by samr
 Wed Aug 16, 2017 12:34 pm
So after an hour or so of reading I think I am slowly starting to understand what you are saying. My question is this, on an HDS 7 G2, in 2d mode, are fish going show up in small "arcs" or are they a different shape? I did not pay attention to this before as I had the "fish" icon turned on and after reading early on in this thread I will turn it off. But I'm now trying to figure out what I should be seeing instead!

Thank you for your posts, Very insightful!
 #238206  by Larry3215
 Wed Aug 16, 2017 6:44 pm
How they end up looking on the screen can very a lot depending on the details. There are several things that can mess up the arches or make them look odd.

One of the key things to getting good arches is boat speed. The boat must be moving.

Remember that GIF I posted early on?


fish arch.gif
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Whats going on here is one of the most basic keys to how things look on your screen.

On the left side is the boat and the right side is what it looks like on your plotter screen as a fish moves into and out of the sonar cone. That "into and out of is critical to the formation of arches. If the fish doesnt do the in/out thing you will not get arches.

If the boat is sitting still, the fish wont move smoothly into and out of the arch and you wont get an arch. You will get streaks or lines or sometimes blobs. The slower the boat is moving, or the faster the screen is scrolling, the longer the arches will be. If the boat is moving fast and/or the screen is scrolling slowly, the arches will be shorter.

The next thing to notice is that the arch starts out thin and at a lower depth when the fish first enters the beam/cone for two basic reasons. On the outer edge of the cone, the signal is weaker than it is in the center, so the return or arch is thinner and lighter in color. Its also slightly farther from the fish to the transducer on the outer edge of the beam because of the angle of the cone. When the fish is in the center of the cone, the signal is strongest, so the arch is thickest. The fish is also slightly closer to the transducer, so the top of the arch is higher than the leading and trailing edges.

If the fish is moving at the same time - diving or climbing in the water, or the boat is pitching or rolling in waves, the arches will be odd shapes depending on how far and how fast the fish moves.
Last edited by Larry3215 on Wed Aug 16, 2017 6:57 pm, edited 1 time in total.
 #238247  by Larry3215
 Fri Aug 18, 2017 9:11 am
Anything that reflects the sonar 'pings' from the transducer will get drawn on the screen and can make a nice arch. There is no way to tell what it actually is unless you have a camera down there - or - you catch one :)

I have been in situations where I thought there were a million fish, but it turns out is was just bubbles coming up from the bottom. That was at Potholes. Another time, on the Columbia, I finally decided it was junk being carried down stream in the flow - weeds, leaves, etc, in a hi water run.

Last year we were on Spencer early in the season and the pads were not yet above the water and those bulbs on the heads made for tons of "fish" hugging the bottom. We were real excited until I looked over the side and we could see them down there in 5 ft of water :)
 #238281  by TrackerPro16
 Sun Aug 20, 2017 7:52 pm
Took all the toys out today and tried for Cutthroat for a couple hours but could see fish come up and look but not really interested with a number of presentations. Bagged it and went looking for 'bigger' perch. I went to an area that looked 'interesting' but would not be your typical spot for panfish. First I set up the 7610 with a four way split screen. Panoptix forward, Sidevu, Clearvu (down) and Traditional. Then I set up my new/used Honda four stroke (first four stroke!)7.5 and the Terrova bow mount so I was running at about 3 mph and hugging the bank at about 20-25 feet deep. I hung my dropshot over the side and waited. When I saw a 'fish ball' appear on the down, side and traditional I would let it drop. I would keep going about 20 feet then hit 'spotlock' while letting line out. Then I would start twitching the pole. I will say 75% of the time I would have a strike within 20 seconds.
I don't know if it is because of the 'odd' area but most of the fish I caught there were on the large side. Once I caught a fish I would drop straight down or use the Panoptix to locate the school and cast the dropshot just past them, then reel, twitch in.
Great way to spend the day!
 #238568  by TrackerPro16
 Fri Sep 01, 2017 7:06 pm
Went out to fish and play more to get more time on the electronics. Hit an area where I have had some 'hang ups' with the downrigger. First pass is East to West. Second was South to North back over it. No wonder it was hanging up!

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Last edited by TrackerPro16 on Fri Sep 01, 2017 10:54 pm, edited 1 time in total.
 #238570  by TrackerPro16
 Fri Sep 01, 2017 7:12 pm
These were a couple other shots I got. One looks like a sailboat with the mast about 50' up. The other looks like a power boat. I think you can make out an outboard on the back of it on the right side of the picture. Pretty fun!
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 #238573  by Larry3215
 Fri Sep 01, 2017 11:24 pm
Nice shots! Where were those at?

Can you post larger images? Those are too small for my old eyes to make out any details :)

By the way, you can get even better shots if you press and hold the HOME button for about 4 or 5 seconds. That will save a hi res BMP image in a folder labeled SCRN inside the Garmin folder on the SD card.
 #238580  by TrackerPro16
 Sat Sep 02, 2017 11:00 am
The structure is in Lake Washington in front of the Boeing plant. After asking around I understand they had a very long, large dock for the boats and float planes they used to build and sunk it at some point. I may try to line up on it and run the length. I was still at a slight angle when I went N/S.
As far as the pictures go they are crystal clear on my phone and can be blown up nice. They got a bit fuzzy when I put them on here. Probably the small size I saved them at. The sailboat (I think) and powerboat (I think) are on the west side of Mercer Island. The powerboat is only in about 25' of water so I am kicking around trying to get a better look at it and maybe using my grappling hook on it... Now this stuff has me thinking about buying an underwater camera! Lake Wa is really murky though so I am not sure how useful it would be.
 #238586  by Larry3215
 Sat Sep 02, 2017 1:48 pm
Much better, thanks!

Screen captures are another step up though. You dont have any shadows and reflections and glare that hide details and make it hard to see whats going on. For example, parts of that last image are completely hidden by sun glare and your reflection. I can actually see your face almost as well as the boat :)

On another note, I would think that sunken dock would be a great place to jig fish on spot lock with your TM. You shouldnt loose as much gear, but I bet its still going to be snaggy.

Nice find!
 #238587  by Amx
 Sat Sep 02, 2017 1:54 pm
Great pictures. I really like that dock situation. Too bad it's too deep.

I've done the screen capture a couple times, but not on depth stuff, only on the properties/software on the computer thing inside the depth finders (2) to compare what makes them work different and so getting different chart images. and need to practice it a FEW times for the depth stuff. :)
 #238588  by TrackerPro16
 Sat Sep 02, 2017 3:01 pm
I'm thinking for 'ease of use' I might take a jacket and put it over me and the screen when I take a picture... [thumbsup]
Maybe I should throw some of the LARGE fish balls I got on screen. Easier fish to catch than avoiding structure!
 #238590  by Larry3215
 Sat Sep 02, 2017 5:18 pm
Amx wrote:Great pictures. I really like that dock situation. Too bad it's too deep.

I've done the screen capture a couple times, but not on depth stuff, only on the properties/software on the computer thing inside the depth finders (2) to compare what makes them work different and so getting different chart images. and need to practice it a FEW times for the depth stuff. :)


I would think it starts close to shore, so it should be shallower closer in?
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