Author Topic: Straight down or off to the side?  (Read 472 times)

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Offline Knight48

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  • Unit(s): Helix 7 Chirp Mega si
Straight down or off to the side?
« on: September 16, 2019, 04:54:40 PM »
Hey guys, what's happening?
 Down in Florida here, fish the Indian River in Sebastian a lot. 
  Had my Helix 5 for a while now and getting better each time I think but just a few questions.
In this photo you can clearly see the fish but in order to mark them I need to move my cursor on them
and then hit the mark button.  It just seems that I am putting the cursor (out) to the side when really
these fish are straight down aren't they?  Should I just put my cursor straight behind the boat or
do as I am doing and put the cursor (right on ) the fish?  Does that make sense?

 In the second photo the fish (are) out to the side so I can understand putting the cursor out to the side
but not sure about the first one..

Thanks guys!

 Cursor is (not) on the fish in the second photo but the fish are to the right..
« Last Edit: September 16, 2019, 04:57:41 PM by Knight48 »


Offline rnvinc

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Re: Straight down or off to the side?
« Reply #1 on: September 16, 2019, 10:07:39 PM »
Marking targets out to the side in SI is a mathematical calculation from the GPS coordinates logged at the center line directly perpendicular to the target  ...

In other words the GPS coordinates on the center line are actual logged GPS antenna positions as the boat moved along the center line  ... Targets out to the side are "calculated" from those logged GPS positions  ....

Also take into account that depth of targets out to the side are "unknown" (only depth at the boat position is "known")  ... So the deeper that target is - the farther from the xducer that target actually is  ...

Therefore that "calculated" Waypoint (out to side in SI) is a best guess and not accurate  ...

For marking structure in SI - it is always recommended to reposition the boat, verify the structure with 2d, and adjust the Waypoint for better accuracy  ...

For suspended targets - mark the targets directly and hope they're still close by when you return  ...

Rickie
« Last Edit: September 16, 2019, 10:11:36 PM by rnvinc »

Offline Knight48

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Re: Straight down or off to the side?
« Reply #2 on: September 16, 2019, 10:58:20 PM »
Rickie,
  Yeh ok , that sounds logical.
 Guess I just need to play around with the unit more and do you like you say and reposition the boat and use 2D.
  I guess we really need to also think about how far away the unit is from the transducer right?
I mean if I mark a fish I'm actually marking where the unit is but because the transducer is maybe 7 feet back
we should maybe put our mark just a tad behind the fish, yeh?
Pete
 

Offline rnvinc

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Re: Straight down or off to the side?
« Reply #3 on: September 17, 2019, 08:58:52 PM »
Rickie,
  Yeh ok , that sounds logical.
 Guess I just need to play around with the unit more and do you like you say and reposition the boat and use 2D.
  I guess we really need to also think about how far away the unit is from the transducer right?
I mean if I mark a fish I'm actually marking where the unit is but because the transducer is maybe 7 feet back
we should maybe put our mark just a tad behind the fish, yeh?
Pete

Marking a Waypoint does indeed assign the GPS coordinate location of the antenna  ... so that does also incur added inaccuracy  ...especially if using the internal GPS in the head unit  ...

Rickie

Offline Knight48

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Re: Straight down or off to the side?
« Reply #4 on: September 17, 2019, 11:03:54 PM »
Marking a Waypoint does indeed assign the GPS coordinate location of the antenna  ... so that does also incur added inaccuracy  ...especially if using the internal GPS in the head unit  ...

Rickie

  Got it bud!
Thank you
Pete


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