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Old 12-03-2013, 10:08 PM   #1
Diver1111
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Default Varied terrain side-scan-sonar shots

The bottom of Winnipesaukee varies greatly. Unless you've dived it you really don't know just how varied it can be. From huge plains of plain mud to house sized boulders to gravel beds to boulder fields to embankments that drop off very rapidly into deep water (East Rattlesnake for ex.), I never really know what I will see when I start to scan.

Some terrain shots are attached, most taken at very low altitude meaning the towfish is flying close to the bottom. Flying low has certain clear advantages, and certain dis-advantages. Slamming the fish into a rock or drilling it into the bottom are two of them.

The white line down the center of each image represents the boat path and the wake. When the bottom closes in towards the white line the depth is changing-getting shallower. Sometimes really fast.

- Image 1: Bottom changes from small boulders and gravel to mud;

- Image 2: Bottom comes up then down then up again; Towfish is really close to the bottom-really close;

- Image 3: Scanning left & right out to 50 Meters each side and about 5 Meters off the bottom; Clear clean patches of rock and smaller boulders show up nicely on the sonar; Left channel shows cabling of sorts on the bottom running a long distance parallel to direction of travel; I found two more sets of long cabling in this area as well, need to dive it; Could be pipe but I doubt it;

- Image 4: Small boulders fields between patches of mud

- Image 5: Same sort of thing

- Image 6: Bottom came up on me super fast-I just lucked out by not banging up the fish-never connected with the rock although that's as close as you can get without actual contact; Upper right red box show target of some kind; Confident it's man-made, perhaps a barge, and it has something coming off of it that is up in the water column thus you see a big, long, twin shadow. Need to dive it. Large long thin shadows just below center of image in left & right sonar channels are the sharp edges of rock protruding up into the water column;

Image 7: Fractured rock in left channel with bottom coming up fast. Smooth mud on the right the large boulders;

All images can be zoomed in on for better clarity.
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Old 12-03-2013, 10:50 PM   #2
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Default Great pics!

The last one on the left has some very curious looking rocks. They are so square.
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Old 12-04-2013, 06:16 AM   #3
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Interesting stuff. Thanks for the explanations, it helps me understand what I'm looking at. It took me a while to understand how these images were laid out, and the newer unit with much higher resolution also helps.
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Old 12-04-2013, 07:29 AM   #4
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Yes thank you for explaining the images. Very interesting!
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Old 12-06-2013, 04:49 PM   #5
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Quote:
- Image 6: Bottom came up on me super fast-I just lucked out by not banging up the fish-never connected with the rock although that's as close as you can get without actual contact; Upper right red box show target of some kind; Confident it's man-made, perhaps a barge, and it has something coming off of it that is up in the water column thus you see a big, long, twin shadow. Need to dive it. Large long thin shadows just below center of image in left & right sonar channels are the sharp edges of rock protruding up into the water column;
As always, can't wait to see the pics and video.
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Old 12-09-2013, 04:46 PM   #6
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Default More terrain shots

The depression image is a shot in Alton of the sonar beam going over the top edge of what is basically a hole; The dark area is the hole itself on the backside/left side, of the edge of the embankment.

Don't know how the scour marks were created; One poss. is from anchor drag but that's alot of anchors doing alot of dragging. I just don't know for sure.

The mooring block image shows both the hole in the block itself and links in the chain-the alternating light/dark sections as it trails off to the right of the block.
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Old 12-09-2013, 06:35 PM   #7
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Default Fresh water Conch?

I have seen similar trails in the Caribbean caused by Conch moving across the bottom. Large fresh water snails? Possible cusk rooting along the bottom for small organisms.
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Old 12-10-2013, 09:48 PM   #8
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Yes possible. The trenches they dig are quite clear when you swim over them even though the snails themselves average about 3" long. It would also account for why there are so many. The sonar is good enough to pick them up depending on how clear they are i.e. not silted in etc., distance from the towfish, frequency I'm scanning at etc..
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