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Navionics Lake Level offset

I just got the Vankyo Matrixpad S10 tablet and downloaded the Navionics app then downloaded the Lake Powell map for use when on the houseboat when out on the lake. I have a Humminbird Helix with the Lakemaster chip on the fishing boat. I absolutely love the Lakemaster chip. I have been from Lone Rock to White Canyon and the backs of everything in between. With the Lakemaster your lake level offset correction is from full pool 3700. It is incredible accurate until you get to a place that has had silting since the original pre-dam topograpy survey. I.e. the mudflats outside of White, and the bitter ends of the Escalante and San Juan. Did not see the need for a fancy Humminbird on the houseboat but with the low levels this year I thought something for the houseboat was a good investment since before I was just flying by the seat of my pants.

I am not sure of what base elevation to use for the Navionics map of Lake Powell. I seem to recall seeing something on WW that you used 3600 as the base elevation to set your lake level offset with the Navionics Lake Powell map. I could not find anything in the Navionics app that stated what water level to start at for Lake Powell. I used 3600 and set the offset to minus 33 feet for recent elevation of 3567. Based on just looking at the corrected app map around Wahweap Bay and trusting my memory of the shoreline I am not convinced that 3600 is the correct baseline to use. So I emailed Navionics help line about the baseline to use for Lake Powell. Here is their reply:
**************************************************************************
Thank you for contacting Navionics.
Please note that the Navionics charting (not including SonarChart™) for the freshwater lakes (not including the Great Lakes) are done in full pool elevation. Seasonal changes or yearly changes to pool elevations - such as spring levels, summer levels, droughts or over abundance - are not reflected on our charting. These differences in pool levels would need to be calculated when reviewing the current lake levels that can be found on the government's website listings for each individual lake. Currently there is no unit function that allows for these calculation changes. Within our mobile apps, the Water Level can be adjusted under Menu > Map Options > Water Level.
Best regards,
Marcelo
PRODUCT SUPPORT SPECIALIST
****************************************************************

Based on this answer I am not am not sure of what base elevation to use to correct for actual level. Are you Navionics users using 3600 or something else? I do not think it is 3700 full pool but not sure about 3600 either.

Headed up Tuesday 3/30 for a week. HB = Red Sky At Night.... Center console fishboat = Capt's Rx.
Thanks for your help!
Kevin
 

Maverick5207

Well-Known Member
I too contacted Navionics for this same reason last year in July and got the same response but later found out that the level they use for Lake Powell is 3606 because that was the water level at the time of their survey.
3606 ASL is the baseline water level for the Navionics App. and I have the exact same setup. A 10 inch Android Vankyo 10 tablet with the Navionics App.
Something I've learned using the Navionics software is that the lake level adjustments don't work on the plotter part of the app when plotting a course in "automatic mode". ALWAYS plot your course in "manual mode" unless the lake level is 3606 ASL or above.
It takes a bit more time at the start of your trip but worth every second.
 
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Skibum

Well-Known Member
A heads up addition to the recent closed Navionics Thread re: does my device know my location?. On iDevices it was pointed out that you have to give the app permission first and will then always have it on the phone. The caveat is only iPads with a cellular chip have a GPS Chip. The cellular chip does not have to be active, just present internally to give accurate positioning. If you have a non cellular device, Bad Elf and Garmin Glo products, for ~ a Ben Franklin each, provide GPS. I have used an earlier 32 pin version of a Bad Elf for WAAS accuracy on the original iPad ~2010. Only drawback in my 4-5 hr continuous use was it sucked the battery I think the power density on newer iPads has improved. IIRC, the Garmin Glo is wireless via Bluetooth and supports up to 4 devices using its own power supply (Corded or battery).
One other note...keep the iPad out of direct sun. Even out of direct sun, they will occasionally, but fortunately rarely, turn off if ambient is too hot. ...My experience at Sky Harbor last year was inop @ ~100° ambient without cooling.

Question for the current app users. I see they allow family share for 6 devices, but is it correct to assume you only get current shoreline presentation on only one device? I currently use a older Garmin WAAS GPSMAP with 10’ contours that are referenced to 3700 as full pool and no way to adjust the current shoreline. I know the lake well, but for the price of 2 gal of gas and an ice cream, I plan to try it this year. TIA.
 
I'm running the Navionics app on my phone. I've been concerned about the '3606 - #feet below full pool = current depth' routine. But, Navionics definitely did not use full pool (3700) as the basis for their maps. Such a bummer that they don't give a sh!t to give us Powell Boaters accurate information!

What I need to do is go to a spot on the lake, sit there, and compare Navionics stated depth with my depth finder. But, the depth finder I just installed was used and needs calibration or some such routine. It could be a couple feet off. So, I'm just eyeballing shallows and trying to compare that to the stated depth coming from Navionics.

Any accurate information about what # full pool is on Navionics is greatly appreciated. -kirk out

P.S.- Apple is bizarre. My next tablet will be an Android device. I had to make sure I bought an Ipad with Cellular to get the GPS to run Foreflight. What a bummer you would have to connect a peripheral to your tablet to get GPS!
 

Skibum

Well-Known Member
Several posters on various Navionics threads here apparently were told by the company that 3606’ is what they considered full pool at the time they mapped the contours. To have the entire lake mapped at the same level suggests they are combining known survey with satellite data and extrapolating some areas and crowd sourcing others from users who upload their bathymetry data. I’m going to play with it and see what happens. I had the original Navionics app and really never used it.

I use ForeFlight also and like it too much to switch, so I’m stuck with IPad. Unfortunately, ForeFlight/Boeing only supports the iOS platform.
 

Mrs. BigDogGuy

Well-Known Member
I am playing with the Navionics app, downloading maps to try it on the lake tomorrow.
With the offset for water level, I see Red dots in the blue ‘water.’ Am I correct to assume that is the offset showing me the new lake edges?

What are the two purple lines that go up lake following what I am guessing is the channel marker route at lake level 3606? Can that be turned off? It’s kind of distracting at this lake level.

Anything else good to know about using it on the lake? I’m taking a phone and tablet to try both and just generally test it out. This is about 7’ lower than the lowest lake level I’ve personally boated. I wish it was easier to read from Wahweap to the channel. That’s a tough area.
 
I am playing with the Navionics app, downloading maps to try it on the lake tomorrow.
With the offset for water level, I see Red dots in the blue ‘water.’ Am I correct to assume that is the offset showing me the new lake edges?

What are the two purple lines that go up lake following what I am guessing is the channel marker route at lake level 3606? Can that be turned off? It’s kind of distracting at this lake level.

Anything else good to know about using it on the lake? I’m taking a phone and tablet to try both and just generally test it out. This is about 7’ lower than the lowest lake level I’ve personally boated. I wish it was easier to read from Wahweap to the channel. That’s a tough area.
give us an update how did it work?
 

Mrs. BigDogGuy

Well-Known Member
I am still not certain what the two purple lines are, it looks like it might be the 'channel' at the time of the reading, lake level 3606?

It was reassuring to be able to see the underlying channel, given the low lake level, especially in Last Chance. In 2014, when it was super low, but 8' higher, we spotted the now small islands on the left, but those could have been an ugly surprise

I had to reset the lock screen mode so it would not keep turning itself off, but overall it was reassuring.

On my ipad (not cellular connected) with the water level adjustment made, I saw little red dots which I assume showed the new shoreline; however it did not work on the lake, so I will have to play around to figure out more about just what the water level adjustments look like before trusting it.

The crosshairs are confusing with the wrong water level, but subtracting 40' wasn't too difficult.
 
I am still not certain what the two purple lines are, it looks like it might be the 'channel' at the time of the reading, lake level 3606?

It was reassuring to be able to see the underlying channel, given the low lake level, especially in Last Chance. In 2014, when it was super low, but 8' higher, we spotted the now small islands on the left, but those could have been an ugly surprise

I had to reset the lock screen mode so it would not keep turning itself off, but overall it was reassuring.

On my ipad (not cellular connected) with the water level adjustment made, I saw little red dots which I assume showed the new shoreline; however it did not work on the lake, so I will have to play around to figure out more about just what the water level adjustments look like before trusting it.

The crosshairs are confusing with the wrong water level, but subtracting 40' wasn't too difficult.
I believe the red dots are a setting in the depth, I set mine to 20ft, so at least it gives you a warning you are in a shallower area. You can also remove that if you desire. I am trying mine in 4 weeks for 1st time
 

Mrs. BigDogGuy

Well-Known Member
I believe the red dots are a setting in the depth, I set mine to 20ft, so at least it gives you a warning you are in a shallower area. You can also remove that if you desire. I am trying mine in 4 weeks for 1st time
Yah, since the red dots only showed on the iPad, I could not really test it out. Since Navionics charted the lake at 3606, I offset by 40'
 

nzaugg

Well-Known Member
I am still not certain what the two purple lines are, it looks like it might be the 'channel' at the time of the reading, lake level 3606?

It was reassuring to be able to see the underlying channel, given the low lake level, especially in Last Chance. In 2014, when it was super low, but 8' higher, we spotted the now small islands on the left, but those could have been an ugly surprise

I had to reset the lock screen mode so it would not keep turning itself off, but overall it was reassuring.

On my ipad (not cellular connected) with the water level adjustment made, I saw little red dots which I assume showed the new shoreline; however it did not work on the lake, so I will have to play around to figure out more about just what the water level adjustments look like before trusting it.

The crosshairs are confusing with the wrong water level, but subtracting 40' wasn't too difficult.
I think the two solid purple lines are the historic river channel, but like you I am not certain. There is also a dashed purple line indicating the county boundaries. I think these both came from old survey data used to create the topography for the map as well.

The red dots are certainly from the depth warning adjustment. You do the offset value for the map and then you can create a draft warning for your individual boat and it marks the areas under the depth with the red dots. I really hate that it doesn't change the water level in the crosshairs though. It would make it much easier to confirm that you have the right offset values. It does show features shaded properly as you change the values though.

Also, regarding tablet use. You don't need to get an iPad with cellular connectivity. You can pair the iPad with your phone and it will pull the GPS values from your phone, but only if you have an iPhone.
 

Mrs. BigDogGuy

Well-Known Member
The two purple lines are more like the marked channel at 3606 than the river channel as there were spots where they did not follow the river channel at all.
 
Got back from the lake a few days ago. I compared Lakemaster and Navionics. I am using Navionics on an Android / Vankyo setup and do not know if this is different than an I-pad. I went back to a very small rock lined cove with a narrow inlet in the rear left hand side of Padre Canyon. There is no drainage into this area so changing of the bottom contours from silting should not be a factor. The Lakemaster with offset set for current lake level (3700 - 133 = 3567) showed the small cove just about as I observed it visually. It was very close! I had to adjust the Navionics to an offset of 20 feet from whatever baseline Navionics is using to get this little cove on the app screen to look like it did with my eyes. This meant that the Navionics baseline was 3587. Way different then the 3606 that has been mentioned!

Can someone please correct me if I am misunderstanding what mapmakers are using for Glen Canyon topography. I was under the impression that Lakemaster, Lake Level, FishnMap and Navionics depth contours are all based on the detailed survey that was conducted before the dam was built. Any thoughts on that?

I also note that both Lakemaster and Navionics are off on a few obvious whales that I saw during my recent trip. There is a well marked whale (top at about 3574) marked by NPS just off the red side of the main channel very near MM 20 that does not show in the topography of Lakemaster or Navionics. There is also a privately marked whale (top at about 3571) in the middle southern part of Gunsight Bay that is SSW of where the Gunsight to Padre Bay cutoff would be if the lake were higher. So the lesson is you still have to keep your eyes on the water ahead and not looking at an app. Navigation is not a video game!
 

birdsnest

Well-Known Member
I'm running the Navionics app on my phone. I've been concerned about the '3606 - #feet below full pool = current depth' routine. But, Navionics definitely did not use full pool (3700) as the basis for their maps. Such a bummer that they don't give a sh!t to give us Powell Boaters accurate information!

What I need to do is go to a spot on the lake, sit there, and compare Navionics stated depth with my depth finder. But, the depth finder I just installed was used and needs calibration or some such routine. It could be a couple feet off. So, I'm just eyeballing shallows and trying to compare that to the stated depth coming from Navionics.

Any accurate information about what # full pool is on Navionics is greatly appreciated. -kirk out

P.S.- Apple is bizarre. My next tablet will be an Android device. I had to make sure I bought an Ipad with Cellular to get the GPS to run Foreflight. What a bummer you would have to connect a peripheral to your tablet to get GPS!
James T. Kirk never used the s work.... Kids,kids and more kids are here.
 
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