Fish in the water column on 998, where are they??? how far???

I fished a power plant lake several times this winter and there were roaming schools of black crappie. These crappie would always show up in the water column when they swam by and it showed on the graph that they were 20' away or closer to the boat according to the graph's feet ranges. But it never failed that when a school came by that they were more like 50-60' by the fish we caught. On one of the hummingbird "how to" you tube video's they describe that the fish in the water column are as far as it says on the graph, but I'm not sure this is true. If the fish are in the water column on the unit is it not possible that they are much farther away and are only recorded in the water column because of the slant angle of the sidescan. Just speaking from what I experienced each weekend this winter and wondering if anybody else has noticed this.

The dark water column is the distance equal to the water depth as drawn in a complete semi-circle from "water's surface left to water's surface right"...

*Any fish showing in the dark water column will be within this distance equal to the water depth...
*Any fish shown against the bottom detail will be faster away from the boat than a distance equal to the water depth...

http://i477.photobucket.com/albums/r...psm7jtyyhn.jpg

http://i477.photobucket.com/albums/r...ps6v0szivl.jpg

If your water depth was 20ft and you were catching fish 60ft away from the boat....your were not catching the same fish you were marking in the dark water column...

Here is more info on slant range vs horizontal range...
http://forums.sideimagingsoft.com/index.php?topic=946.0

Rickie

So as the angle of the side image goes out, the side image signal I was thinking was apparently shooting under the fish as they got farther out. The fish on my hds showed shadows long before the fish actually arrived, and they were shallow. We were catching them 3ft in 15ft of water as the schools came by as we were anchored. So does this make sense why the farther part of the school didn't show up on the SI. Because they was too shallow for the distance....... But I was on 455 so this isn't right either is it. This would only be right if I was on 800...... According to the chart above the 455 gives you total top to bottom water level coverage to desired range, is this correct. And the 800 will miss shallower fish due to the cone angle?

I'm not sure what you mean by "the fish showed shadows long before they actually arrived"...

I think it's important to realize that it's very possible the fish (or shadows of fish)...you are seeing on the screen might not be the actual fish you are catching at any given moment....

It's even possible for the fish you are catching to come in from the front or the rear, the fish turn around and retreat...and the fish might never even get into the thin slice SI beams...in which case the fish might not ever show on the screen...

If you are anchored, the only way a fish is going to show on the screen is if the fish is 90° left or right of the xducer in the thin slice SI beam...so I'm confused as to how you are seeing these fish "come towards you" while anchored...

http://i477.photobucket.com/albums/r...ing_480ft2.jpg

Rickie

I have a 998 on the back and an HDS8 on the bow so we could tell the direction of travel of the fish. The HDS shows a very good return of fish and a very good shadow, it's almost like in 3d as you can see the fish above and the shadow below when anchored as the fish swim by. It's not like the white streaks and small spots on the 998. As obviously the schools reached out as far as we were casting since we were catching them as soon as it hit the water when the schools was in that direction on the fish finders, I didn't seem to see them on either unit that far out, is what I was wondering about. I thought maybe they had a cone and the fish were above the cone is why they didn't show up.

I know the fish only show when they swim through the slice, but it appears as a 3d looking return on the screen as the shadow of the fish is visible on the lake bottom before the fish return is visible in the water column on the hds. If the fish are at the top they are still directly right or left of the transducer, I get that. I don't get why the entire school didn't ever seem to show the entire distance that they reached out on either unit.

This is an interesting concept...

I've never tried using SI while anchored...

It would be interesting to see a video of this happening on the HDS...

I still don't understand how the shadow can show on the screen before the fish shows in the water column...because both the fish and the shadow should be directly 90° from the xducer to be in the SI thin slice beam...which would seem they both should enter at the top of the screen at the same time...

Rickie

I would think the fish would have to be in the sonar beam before there could be a shadow.

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Originally Posted by justinp61

I would think the fish would have to be in the sonar beam before there could be a shadow.

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What justin said :hesaid

So when you say the radius = water depth when you are in 10ft. of water that is from each side of the boat?and the dark center water column is 20ft. wide with the boat in the center? I always thought opposite that the depth of water was how wide the total dark spot was

It would, otherwise what is there to create the shadow?
What he may be seeing is the shadow while the primary return from the fish is still far enough away to be over the bottom. It’s there but he may not be able to see it yet until it gets close enough that it is now in the water column and easier to see.

The 455kHz Humminbird Si sonar should be showing the entire school as it covers 180 degrees (unless it is being physically blocked), I don’t know what the other brand covers.

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Originally Posted by wilbur

So when you say the radius = water depth when you are in 10ft. of water that is from each side of the boat?and the dark center water column is 20ft. wide with the boat in the center? I always thought opposite that the depth of water was how wide the total dark spot was

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10 feet from each side of the boat.
The width of the dark center would be double the water depth which in this case would be 20 feet wide.
Remember that the distance show is always the distance from the transducer.

Yes that's exactly what I was seeing the shadow before the primary return, the fish were shallow and the water was fairly deep so the shadows came first. But why the entire school didn't show on the graphs I still don't know unless maybe because the lake bottom was too hard....Or I thought the 455 had a cone angle for the transducer beam too until I saw the above pictures. I don't know how well the anchoring and watching SI would work at a regular lake. This was a power plant lake the fish concentrate on the warmest windblown side of the lake in the winter, along with the bait, Some schools are huge as you can tell by how long it takes them to pass both transducers. Jan, Feb we were fishing 55 degree water while the regular lakes were frozen solid. It's kind of a strange lake how the black crappie school up on cloudy days and roam the warmest water. Catch 3-5 foot deep. It's pretty clear water, on Sunny days you can pick up a few dragging bottom 12-15ft or out of grass edge, but the schools split up or go to 30ft on Sunny days. It probably wouldn't work this time of year, haven't had a chance to try, they've probably split up to find spawning beds now. Lake of Egypt, IL where they had the Crappie USA Megatournament is where I was.

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Originally Posted by wilbur

So when you say the radius = water depth when you are in 10ft. of water that is from each side of the boat?and the dark center water column is 20ft. wide with the boat in the center? I always thought opposite that the depth of water was how wide the total dark spot was

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Following is how I explain it in my seminars...:

If we tie a string to the xducer and extend the string straight down to the lake bottom...this is the water depth ("distance x")....

If we now swing this string in a complete semi-circle from the "water's surface left to the water's surface right"...any target in this semi-circle will show in the dark water column ....due to the fact that the target is closer to the xducer than "distance x"....

http://i477.photobucket.com/albums/r...psm7jtyyhn.jpg

Rickie

I guess the school its self could have been blocking the further returns when the big schools were close, I hadn't thought of this, they were pretty tight schools, I don't know. But I had trouble seeing fish past the water column at this particular lake anyway, they just didn't show up no matter how I set my unit. A crappie isn't a very big target though.... Anyways we'll see how they do at my local lake with a soft bottom when I get a chance to go this spring. I do now understand that the fish that I saw in the water column were very close to me. Thank you all for all the reply's.

The angles Rickie is showing represents the HB SI beam angles. The structure scan angles aren't that wide......What did you have the SI range set to on both units?

I usually use 60 feet on both units because I'm usually in 12-16 foot of water. I think unless looking for major structure this seems to be about the limit in that depth or for looking for a stake bed or Christmas tree. I was in 24 fow though at a different lake and the shad schools showed very good on the hds out to 100 foot. Even individual fish showed very good returns in a creek channel at 24 foot...I could see the creek channel with the 998, but no fish returns unless the size of a football.... I don't mean to be pro Lowrance but this is what my initial views are. It may change.... I haven't had time to really use either unit much yet I got the 998 last Dec and hds in Feb. So I have a bit of getting used to and learning to do. I've only had the hds out 3 times. 998 about a dozen or more and it helped me find fish, but fish returns were weak. I don't know if there is actually a functional difference as far as one finding more fish/ structure than the other, athough the down image is actually real on the hds and fish returns are much larger and brighter as well as is the screen. I may keep the 998 for shallow stake bed scouting and the hds on front for DI and closer SI views of the structure I find and when fishing. I had planned to pick a brand, but I may very well find that a combination of both will work best for me. And yes I know I always write too much....

I still catch myself viewing the screen sometimes like a tv of what is around me instead of concentrating on the first few inches and thinking of that thin slice to the left and right when looking for fish to cast at. I'm just now getting over this. And when a school enters that slice it would be very easy for the returns to be blocked before they got far out if you think about it, thus blocking the further part of the school from being recorded on the chart. I think I'm right in theory on this anyway. This could be my answer, and I think likely is.

Anyways this "school chasing" is over for this winter and now I will go to the traditional use for what the SI was meant for, finding structure or structure with fish on it.

If you think about sonar shadows, they are no different than normal shadows cast by any light source. The "players" must line up appropriately, that is, in a direct line. First and foremost, the light source, then the object and finally, the shadow. Your shadow from the sun, for example, will be cast in a line directly behind you when you are facing the sun. In a sonar shadow, the players are first and foremost, the transducer, then the fish and finally, the sonar shadow.

Well that sounds right in theory, but is absolutely backwards in the way they were shown on the HDS. The shadows ALWAYS came first. I would say we got some fish because the shadows are coming, and then soon the shallow fish returns. I don't know why, I guess the hds shows shadows in reverse than they should be due to software or something. If I get a chance to go back and any schooling fish are still doing this I'll take a screenshot and post some day. Remember we were anchored and the fish were swimming through the sonar beam, so this may cause the returns to show up differently as it wasn't meant to be used this way really, so software may actually show returns backwards in this case. I don't know, but I can tell you that the shadows were first. No shadows appeared on the 998, just white streaks or white specs.

Show me a picture of this.

Too bad that crappies don't "ping" like dolphins. I could hone in on them. The bigger fishes have a deep voice ping.

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Originally Posted by jimmyfreeland

Well that sounds right in theory, but is absolutely backwards in the way they were shown on the HDS. The shadows ALWAYS came first. I would say we got some fish because the shadows are coming, and then soon the shallow fish returns. I don't know why, I guess the hds shows shadows in reverse than they should be due to software or something. If I get a chance to go back and any schooling fish are still doing this I'll take a screenshot and post some day. Remember we were anchored and the fish were swimming through the sonar beam, so this may cause the returns to show up differently as it wasn't meant to be used this way really, so software may actually show returns backwards in this case. I don't know, but I can tell you that the shadows were first. No shadows appeared on the 998, just white streaks or white specs.

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HDS units have a dedicated element for down imaging as well as side imaging. Wonder if there is some overlapping between the DI and SI images on the screen. Maybe there is just enough overlap to create the effect you are seeing?

I will take a screenshot if I get back down there. But the schools have probably split up by now, the lake temp was 57 three weeks ago.

Well I tried to get a screen shot today, but after 6 inches of rain my pristine clear lake looked like the Mississippi river at flood stage, it even had sticks and trash floating in it. Water temp varied from 57 - 60 all over the lake even with the power plant not running so no pictures this year. The schools that were seeking the warmer water and the bait it contained have dispersed throughout the lake. I did finally get to scan the lake though, spent 8 hours driving 50 yards or so from the bank looking for brush piles, I think they must be old dozer piles from when they built the lake. Anyways I finally got em marked. Still didn't get all the way around and it's only 2000 acres but it's all fingers. Maybe I can find 'em in the brush piles after they spawn.....

Attachment 157853the results is all I can post from this winter.

Cool that you actually got the power plant in the background of the pic...

Nice blacks...

:ThumbsUp

Rickie