Topic: Waypointing suspended fish while using Side-Imaging

[ITGEEK]

Folks,
I have a question:

Sometimes while I'm looking around using Side-Imaging, I see schools of
suspended fish high in the water column, which are probably Crappie.

I have tried a few times but have been unsuccessful to waypoint them and get back
over them.
If you freeze your frame, and move your cursor over to these fish pods,
and press mark to create a waypoint.
Should this be accurate?
I know that waypointing stuff on the bottom is accurate, but what about
stuff just below the surface?

Thanks in advance.

[sonar2000]

ITG, it is my understanding that the mark function or the cursor on takes into account the slant angle and does indeed project the GPS position.

How accurate is any bodies guess..

Chuck

[Bob B]

Itgeek,
There is a sonar term called slant range correction that you need to do some research about.....be prepared to burn a few brain cells.

It is my understanding that the slant range correction in SI assumes that objects are on the bottom.  Objects that are higher in the water column may not show the corrrect range to the side.

Here is one to get you started.  http://forums.sideimagingsoft.com/index.php?topic=946.msg4876#msg4876   Do a search for "slant range" and you should find several serious discussions about it.

[sonar2000]

Adding to this is the relationship of the gps antenna to the transducer. We have seen on a boat the con cerns of a bow or transom mounted transducer and the location of the gps on the boat console.
this could be a 15 foot difference to start with.
Now consider a tow fish 100 feet behind the boat and away from the gps antenna,, so now whereis the actual positon on the screen. Slant range angle only applies to the left or right of the transducer.
The user will have to account for the distance behind the boat..

chuck

[Weekend Warrior]

Ok gang be gentle, but I'm going to stick my neck out here....  Since I've been studying the manual now for two days straight, it seems by selecting the SI Enhance sub menu under the Side Imaging Express menu, then selecting "Contour Mode On", you remove the water column from the SI display, which according to the manual, ".....allows the display to show targets at their linear horizontal distance.  The location of a target may be easier to interpret when the water column is removed."  Possibly this might help ITGEEK find his schools of suspended crappies?

Please feel free to slap me upside the head if I'm totally off base here.  LOL

Mark

PS.  The information quoted is from pgs. 66 and 67 of the 800/900 series manual.

[ITGEEK]

Bob B:
Wouldn't the engineers at Humminbird build in
the necessary SI corrections?

Weekend Warrior:
Some of the fish schools are pretty high up.
If I remove the water column, I fear
that I may not be able to see the schools
anymore.

[Weekend Warrior]

ITGEEK, I hope this thread continues to pick up steam b/c being able to find schools of suspended crappie is going be of great interest to me as well as soon as the weather improves here.  Contour mode ON could be something to try to make the way points more accurate and avoid having to calculate a slant range correction.

Mark

[Humminbird_Greg]

Folks,
I have a question:

Sometimes while I'm looking around using Side-Imaging, I see schools of
suspended fish high in the water column, which are probably Crappie.

I have tried a few times but have been unsuccessful to waypoint them and get back
over them.
If you freeze your frame, and move your cursor over to these fish pods,
and press mark to create a waypoint.
Should this be accurate?
I know that waypointing stuff on the bottom is accurate, but what about
stuff just below the surface?

Thanks in advance.

ITG,
It really is dependant on how deep those Crappie actually are.  The closer to the surface of the water they are; the more accurate the waypoint will be.  If they are deep than they will be somewhere between where the waypoint was marked and the boat.  Maybe this picture will help explain it:

[sonar2000]

what about turning SI range lines on.  that shows some relative positioning and distance..
I think that option may depend on code level..
chuck

[Bob B]

http://forums.sideimagingsoft.com/index.php?topic=1164.msg6140#msg6140

http://forums.sideimagingsoft.com/index.php?topic=1526.msg12502#msg12502

http://forums.sideimagingsoft.com/index.php?topic=715.msg3358#msg3358

http://forums.sideimagingsoft.com/index.php?topic=2005.msg11103#msg11103

[newkid4si]

Weekend Warrior
      If you get over on Shenango and see a LUND with " micro spoons  " on the side, stop "chaunc" and ask him.
      I think he has a HB sideimage. If anyone has figured it out, Ken will know. He will give you straight info.

[SonarTRX]

Hi all,

The only two things you can typically be sure of when using SI to determine the position of the fish is:

1.The fish is within the vertical plane perpendicular to the axis of the boat (i.e. within the sound waves from the SI transducers)
2.The fish is at the range seen on the SI-display (...when not in the contour mode.)

The above two "criterias" defines a vertical CIRCLE, as illustrated by the yellow 40' range-line in Greg's figure.
(The fish could be anywhere on that circle-segment: Either directly below the boat, or up towards one of the two sides.)

If the circle radius (ie. range) is larger than the water-depth, the circle is clipped as illustrated by the 50' 60' and 70' range-lines shown on Greg's figure.
i.e. you know that the fish cannot be directly below the boat (by simple trigonometry)


It is impossible to know exactly where the fish is located based on the above information:
As mentioned by Greg, you need to know how far below the surface the fish is located.

To improve your chances of coming back to the right place, you could define TWO waypoints, and return to the line between them:

WP1: At the boat position
WP2: At the range of the fish (as shown on the screen when not in the contour mode)

If you think the fish was deep, you should move closer to WP1
If you think the fish was shallow, you should move towards WP2.


...My 2 cents,

Tore

[sonar2000]

Wow, Tore......That makes fishing a little more even for the fish..
From a SAR view good thing we are only looking at the bottom or just a few feet above...

Chuck

[Weekend Warrior]

I'm trying to grasp all of this and having some newbie frustration(as you might imagine).   In the diagram above, Let me focus on the fish on the yellow arc at approximately the 5 o'clock position.  The fish is in ~32 ft. of water, and from the diagram, we can see that it is 25 from the center line of of the transducer horizontally.  The distance shown to the fish will be 40 ft.  What I want to know, is if I'm able to mark the fish with a way point, how far away from the boat horizontally will the way point be?  Roughly 50 ft. if the Unit places the fish on the bottom like I've read?

[Humminbird_Greg]

If you mark a fish (or structure) that is being shown 25 feet away from the transducer, than the waypoint will be 25 feet from the centerline.

That fish (shown 25 feet horizontally across the surface of the water) is about 32 feet deep in the water.

The fish shown 36 feet horizontally across the surface of the water is approximately 17 feet deep.

[sonar2000]

so if we turn on si distance and water depth lines we can get where the fish is without having to mark (waypoint) it ?  Or must we mark?

chuck

[Weekend Warrior]

Chuck, now that I "think" I understand somewhat, your comment "From a SAR view good thing we are only looking at the bottom or just a few feet above..."  doesn't seem to make sense.  Let's say you have a "target" on the bottom at the 50 foot arc in the diagram and mark it with a way point.  Your way point will be 50 feet away from the transducer horizontally(on the water's surface)even though your "target" is only ~25 ft. from the transducer/boat(on the water's surface).  So I don't see how it's a "good thing" that your just using the SI to find things on the bottom.  Please help me "get" this.  Every time I think I understand the concept of distance and way points in SI, someone says something to the contrary. Thanks  Maybe I should just go back to a traditional 2D sonar.

In a nutshell, it seem's you would navigate 25 ft. past the spot of being vertically overhead of your target.....

[Humminbird_Greg]

Chuck, now that I "think" I understand somewhat, your comment "From a SAR view good thing we are only looking at the bottom or just a few feet above..."  doesn't seem to make sense.  Let's say you have a "target" on the bottom at the 50 foot arc in the diagram and mark it with a way point.  Your way point will be 50 feet away from the transducer horizontally(on the water's surface)even though your "target" is only ~25 ft. from the transducer/boat(on the water's surface).  So I don't see how it's a "good thing" that your just using the SI to find things on the bottom.  Please help me "get" this.  Every time I think I understand the concept of distance and way points in SI, someone says something to the contrary. Thanks  Maybe I should just go back to a traditional 2D sonar.

In a nutshell, it seem's you would navigate 25 ft. past the spot of being vertically overhead of your target.....

No, you got that correct Weekend Warrior.

[Humminbird_Greg]

so if we turn on si distance and water depth lines we can get where the fish is without having to mark (waypoint) it ?  Or must we mark?

chuck

Not sure what you are calling "si distance" lines here.  Are you meaning the SI Range Lines?  If so than that will not help you any more than the waypoint (even less so because with the waypoint you have a set of coordinates to go by versus just XX feet away from wherever it was that the boat was at when I saw the fish).
You don't ever "have to" mark a fish or other object with a waypoint but you can to help find it again.

[sonar2000]

So tell me now how do I go back to a target and be within 10 feet of the position..?

How do we locate the position accurately.
a lot of explaination and a picture.... but how does the diver go to where he is needed..

Chuck

[Humminbird_Greg]

Mark the structure/object with the Si sonar and than circle back to the waypoint using 2D sonar.  This will get you close to the waypoint.  Even with the 2D sonar you will not always be able to drop a weight right on top of what you are looking for due to the spread of the sonar beam and water depth.

[sonar2000]

Now I am confused.  If I look at a recording in humviewer and move the cursor to a particular point  it gives me depth, distance to the side and a gps position.
If I look at the recording in yellowFin and go to the same point the cursor will match the humviewer position within less than a 1/100th of meter. the GPS position difference is only 1/1000  of a decimal minute.
If we navigte to the GPS position and drop a marker the diver is usually within 5 feet of target.
the depth is as indicated on the HV or YF recording..

Now to unconfuse me.  Are we ok with the bottom target and it will be the suspended target we will have trouble with..?

Chuck

[Roddy]

Chuck, Mark the target, drop a marker, dive it you will be within a few feet.

As fishing goes mark the boat,mark the fish,turn around and fish along the line

[sonar2000]

Rody, thanks, that is what we have been doing and always within a few feet of the target.

I suppose that maybe a suspended target may be different but we are always on the bottom..

Chuck..

[lcookie]

Not a suspended fish question but same concept.  If I am in 60 FOW and I run directly across a tree that is 30 ft tall should I - (1) mark a waypoint at the top of the tree in the water column or (2) mark a waypoint where the base of the tree meets the bottom?  I have been marking the base but from the examples above it seems that the higher in the water column the more accurate the waypoint.  Maybe I will mark both and see which one is more accurate.

[Roddy]

Lcookie, With GPS Error, not much difference.

[Humminbird_Greg]

I would mark the base of the tree as you don’t know whether the tree is leaning to one side or another.  The base is also the one location of the tree that would not change (being in a perfect world) with a change in the direction that you scan the tree from.

[sonar2000]

The thing to remember here is that a stationary fixed object will be there when you come back.
So top or bottom of tree will not make much difference. The marked spot will guide you back and then use SI to reconfirm the target.
Now fish on the other hand will probably not be as reliable and cooperative so as to remain there until you come back..

But your point is well taken on suspended objects and that is where in the heck do I toss the lure...

Chuck

[fishshtick]

The greatest distance distortion is going to occur for fish shown in the water column sections of the image and in the very closest sections of down imaging (i.e., where the bottom already tends to have a bit of that funky curved look to it).  Once you start considering fish that are marked at distances somewhere beyond about 2.0 times the water depth, the sound waves are basically travelling parallel enough to the water surface that you will likely come close enough to the actual location of the fish that this distortion is not likely to be your major limiting factor in catching them.  Unless you fish extremely deep water, GPS accuracy and your ability to place the bait are probably going to be more limiting.  This is not true of fish shown as being in the water column part of the image or the nearest part of the side image showing substrate, as noted above. Of course, this is where use of the other sonar options (i.e., traditional sonar and down imaging) can clarify the issue a bit, and that is why I use the combined SI, DI, Sonar screen for much of my searching.

SO HERE IS MY TIP AND METHOD FOR DEALING WITH THIS ISSUE - use your whole sonar and make more than one pass.

MORE SPECIFICALLY: If the fish are shown as being located beyond about twice as far from the boat as the water depth, then put a waypoint on the FISH.  If they are in the water column part of the SI, then look at your other sonar screens (200 khz sonar and DI) to see if the fish are approximately under you.  If they are there, then put your waypoint right on the BOAT track.  If you are unsure if the fish are under you, or they appear in that iffy zone (out to about twice the water depth), then place a waypoint on your BOAT position relative to the fish and loop back around on a parallel track, but FURTHER away from your target (I shoot for being further away from my old track / waypoint by a distance about equal to the water depth).  If you spot the fish on that second run, then they should now be far enough out in the SI image that you can accurately waypoint them and GPS to them.  By tracking parallel to your first track but a bit further away you reduce your risk of disturbance a bit more than coming from other angles (which is also possible). In truth, I usually find myself doing multiple passes when it comes to spotting fish because I am the kind of person who just doesn't believe they are really there unless I see it more than once.