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Author Topic: Seymour depth charts and navionics inaccurate?  (Read 655 times)

Offline troutcrazy

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Seymour depth charts and navionics inaccurate?
« on: Feb 28, 2018, 06:47 PM »
I'm on Seymour.  Both Navionics and the state depth
charts seem to be wildly inaccurate, though they agree with each-other.

The first hole I drilled, I expected to be 45+ feet.  It was actually 16!  Now I'm in 46' but both depth charts say 90+ feet.

Weird.  Anybody know what's up with that?

Nothing's biting.  I'm just trying to catch a few smelt to use as bait in the morning.

Offline WVBoy

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Re: Seymour depth charts and navionics inaccurate?
« Reply #1 on: Feb 28, 2018, 08:24 PM »
Strange...the only issue I've had is the App locking up on me and telling me I'm in the wrong place. App re-boot fixes that usually.
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Offline Gills-only

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Re: Seymour depth charts and navionics inaccurate?
« Reply #2 on: Feb 28, 2018, 08:57 PM »
I have used navionics, and for the most part what I have on my flasher is very close to what it says. Have checked it many times and within 3í most of time.

Offline keithm87

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Re: Seymour depth charts and navionics inaccurate?
« Reply #3 on: Mar 01, 2018, 05:35 AM »
Navionics is terrible on the lakes with sudden drops. No fault of their own really. sonars Donít pick up sudden drops well, which you can see in he summer when a sonar will read 200ft but the when looking at the screen the bottom will be way shallower. Then there is the overlay accuracy. Navionics overlays on the lake, and if they are off a couple feet one side or the other the whole map will be slightly off which when it comes to a drop can be a lot, and then there is the gps accuracy. Most are accurate to like 3-5 meters, but again that can be a big difference in water depth.

Offline thefishingweatherman

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Re: Seymour depth charts and navionics inaccurate?
« Reply #4 on: Mar 01, 2018, 06:48 AM »
The fact that navionics and the state depth charts are off in the same way is odd. I don't know if navionics bases their maps on the state depth charts, but if you are talking about the following map, it was created using sonar in 2003 by the EPA:

http://dec.vermont.gov/sites/dec/files/wsm/lakes/images/lp_seymour_new.pdf

I would be shocked if this were inaccurate. What is more likely is that either there's something causing your GPS to misplace your position, or your sonar is not reporting depth correctly.

Offline Icemanvt

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Re: Seymour depth charts and navionics inaccurate?
« Reply #5 on: Mar 05, 2018, 10:53 AM »
I think it has more to do with gps being off more than the sonar charts being inaccurate.  Some lakes i'll be standing 10' from shore and it will say im 10' on shore.. :-\
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Offline Light liner

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Re: Seymour depth charts and navionics inaccurate?
« Reply #6 on: Mar 05, 2018, 11:33 AM »
2007 called, they want their iPhone back!!!!!
The GPS is pretty much non existent in those things.
You cannot trust them for accuracy.
Champlain

Offline Hideebeez

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Re: Seymour depth charts and navionics inaccurate?
« Reply #7 on: Mar 06, 2018, 12:23 PM »
Willoughby is consistently 30 ish feet too deep in navionics vs my vexilar.

Offline dickbaker

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Re: Seymour depth charts and navionics inaccurate?
« Reply #8 on: Mar 06, 2018, 06:49 PM »
The fact that navionics and the state depth charts are off in the same way is odd. I don't know if navionics bases their maps on the state depth charts, but if you are talking about the following map, it was created using sonar in 2003 by the EPA:

http://dec.vermont.gov/sites/dec/files/wsm/lakes/images/lp_seymour_new.pdf

I would be shocked if this were inaccurate. What is more likely is that either there's something causing your GPS to misplace your position, or your sonar is not reporting depth correctly.

Note that EPA map provides only 25 foot contours and doesn't recommend the map use for navigational use. 
Dick

Offline troutcrazy

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Re: Seymour depth charts and navionics inaccurate?
« Reply #9 on: Mar 06, 2018, 11:30 PM »
I just compared the two maps (Navionics and EPA) more carefully, and they don't actually agree like I thought they did.  The EPA map is much closer to the actual depth, in the spot in question.  I'm talking about the southeast part of the lake.  Navionics makes it look like a steeper dropoff than it is.

Navionics wasn't as wonky on the west side of the lake, where it actually drops off a little more.

GPS accuracy is definitely an issue on those iphones!  In this case it was way too far off for that to explain it, but yeah... I'm kind of sick of iphones.  I guess it's a good thing mine went down the hole last night as I was googling "how to catch brown trout at night".... and a brown bit.  I'm thinking it's time to switch to one of those Androids that is built for outdoorsmen.  (it was mangled already-- the camera was busted and the screen was glitchy-- I was ready to replace it).

I've had trouble with Navionics on the south end of Iroquois, trying to find the humps by the island.  Navionics is way off.

I've also had trouble on the south end of Dunmore.

 



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