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

[jimmyfreeland]

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.

[rnvinc]

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...





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

[jimmyfreeland]

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?

[rnvinc]

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...



Rickie

[jimmyfreeland]

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.

[jimmyfreeland]

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.

[rnvinc]

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

[justinp61]

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

[BrownTrout]

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

What justin said

[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