Navionics option for setting baseline water level on Powell

[Sunbeam]

I was just on the phone with Eric at Navionics asking about their Navionics+ program (will write about that in another post), and I mentioned how I had noticed that Garmin had added a feature where you could choose a water level for their charts on Powell and it would then display them accordingly. I thought that sounded nifty and wondered if Navionics might have something similar in the works.

Well not for the chartplotter chips, but there is something like that for the Navionics iPad app, which I had not known about. I haven't activated it yet, but here is how he explained it to me:

First of all, it's an "in app" purchase in the Navionics iPad app. Here is the chain of selections:

1) Open app
2) Menu
3) Charts and Upgrades
4) Features
5) I think this is the point at which you make the in-app purchase, and it is called "Advanced Map Options." (Was scribbling notes while on phone.) Then once you have it on your iPad:
6) Advanced Map Options
7) Water Levels

I didn't ask him how much it was, but presuming it is reasonable, I'm going to try it out.

 

[Pat Anderson]

Well, the channel of the Colorado River in Lake Powell is the channel, regardless of water level! We have the Raymarine Western Lakes chip, which has Lake Powell and the old Navionics app on the iPad with unlimited downloads of chart data, and we have Lake Powell on it. So, we know where the center of the channel is! The water level is really not an issue! You stick to the center of the channel, and then when you go out of the channel, you go really slow! But if you have better chart data, we will be happy to follow you!

 

[Sunbeam]

Well, the channel of the Colorado River in Lake Powell is the channel, regardless of water level! .. we know where the center of the channel is! The water level is really not an issue! You stick to the center of the channel, and then when you go out of the channel, you go really slow!

Oh agreed, the center of the channel is nothing to worry about being too specific on. Likewise, when deep in a side channel, you can just read it like a river, and watch the depth sounder. Where I thought setting a level might be nice is when, say, heading into a side channel and picking your path. You know that the lake is 125' lower than the chart says. Now sure, you can mentally subtract (I did the last two years), but then you also have to think about that slightly submerged rock that is now a 100 foot high "mountain."

I just thought that if there was an option to set the base depth, so the chart would show the 100' "mountain" instead of an underwater mound in 25' of water, well why not select it? I notice that when I get into trouble is when two or three factors "pile up," so anything easy I can do to potentially eliminate one is a help - such as setting the chart datum. If 2-3 other things are going wrong (weather, a boat issue, traffic), not having to mentallly subtract might make the difference (for me) between an issue and not an issue. I can see where others might not need to set the level though (more experienced, better at multi-tasking, have a co-pilot, etc.)

But if you have better chart data, we will be happy to follow you!

Oh I wouldn't recommend that :smileo Sounds like you are more experienced and just more confident all around.

 

[rogerbum]

<stuff clipped>

But if you have better chart data, we will be happy to follow you!

Oh I wouldn't recommend that :smileo Sounds like you are more experienced and just more confident all around.

Yes, and the more experienced ones follow at a distance that will allow them to stop if they hear a "crunch" from or see a sudden stop of the boat in front of them. :lol:

 

[Sunbeam]

I downloaded the "Advanced Map Options" (it was $4.99 IIRC) and looked at the water level adjustment. I was at first thinking I was going to plug in something like "3600'" for the Powell water level, but that's not how it works. The adjustment goes from -150' to +50' - so you are adjusting whatever they already have for a base. I wasn't sure how to find that, but on Wayne's Words someone said the default level was set at 3597.85' Looking at the Castle Rock cut on the Navionics chart on the iPad, this looks about right. Just figured I'd add this in case it's helpful (note: for those who need depth measurements; apparently we don't all :wink )

 

[Discovery]

I've found that navigating Lake Powell is best done by watching your depth sounder and keeping a sharp lookout for shallows and rock pinnacles and tree tops. The underwater mapping is not that accurate on the chart plotter maps I own. Go slow, or stay in the center of the channel. Follow the channel markers, don't cut corners and NEVER run after dark. Just my two cents worth after 40 years on the lake.

 

[Sunbeam]

I agree with you, Discovery. The chart is just an adjunct to eyes/ears/depth sounder. Also it is good to understand how rivers work, since this is/was a river (I used to kayak rivers, so I have a reasonably good idea what to expect under the surface of a river-like waterway).

Still, I thought it was an interesting feature to be able to set the baseline depth on the Navionics chart, and that some people might like the information.

 

[Pat Anderson]

FWIW, Pat and Patty agree with Brent! And damn, it was good to see you two again!

I've found that navigating Lake Powell is best done by watching your depth sounder and keeping a sharp lookout for shallows and rock pinnacles and tree tops. The underwater mapping is not that accurate on the chart plotter maps I own. Go slow, or stay in the center of the channel. Follow the channel markers, don't cut corners and NEVER run after dark. Just my two cents worth after 40 years on the lake.

 

[Sunbeam]

Okay, okay, no more posting about Powell charting, I promise! It's just something the Navionics tech fellow mentioned in passing and I thought folks here might find it to be of interest. I should have added a caveat that I'm not encouraging anyone to run at night, to head out without understanding how rivercourses work (since these are essentially flooded rivercourses), or to be overly dependent on charts or gadgets instead of eyes, ears, and common sense. Ironically, I think my C-Dory is primitive in the "electronics" and outfitting arena compared to many of yours.

Sunbeam

 

[Hunkydory]

This year I noticed Lake Powell's present depth to be very close to 100 feet off the Navionics IPad chart & the same on the Garmins making it very easy to readily calculate the difference between actual & chart suggested depth. I use our annual Lake Powell cruise to practice using the electronic charts while cruising in changing water depths where the charts & the GPS signal cannot be trusted. This is similar to some of the remote areas we have cruised in Southeast Alaska, so I find cutting the corners & staying out of the main channel except for times when I just want to relax a opportunity to learn where a screw up is more a inconvenience & cost factor then possibly life threatening. This year when we first set out from Bullfrog we went at displacement speed up lake to Forgotton Canyon, then down river to the Escalante junction, then up it & several of its tributaries before ending up at Oak Canyon. I cut every corner during this time & saved the track. On the return I used the combination of the tracks & a very careful watch on the charts & visual positioning including the aid of water color to judge depths to do the same on plane on the return back up lake. Of course it's best to stay in the main marked river channel if just wanting to relax & enjoy the scenery, but I also think having a chart match the actual depth for ease of viewing not such a bad idea either, though again, cruising in a lake with varying levels, that don't match the chart is some what similar to shallow water cruising in ocean passage areas where the tide is constantly fluctuating up to 20 some feet, the chart detail not always accurate along with your positioning on it & feel Lake Powell can be used as practice for it.

Jay

 

[Sunbeam]

That was a neat exercise, Jay. Must have been interesting to compare and get a feel for any patterns. I have the habit of using anything/everything available to me (including charts if available). But you do have to have an idea of how trustworthy said charts are, and if there is any known pattern to the inaccuracy that's really useful info.

I actually found the charts I had for Powell to be really good the past couple of years (they were Garmin charts, not the ones mentioned in this thread). I didn't so much stare at the depth numbers (they were almost impossible to read anyway) as I did use them to get a feel for the contours and patterns, but hey, if I can adjust the depth numbers to be closer to accurate, I likely won't pass up the chance. It's only a couple of screen presses. Not that I'm going to trustingly fly through dicey areas just because I "set" the numbers. I don't know that the bottom is listening to my iPad :lol:

What I found fun on Powell was how it brought back the days of yore when I used to do a lot of whitewater kayaking. From that I learned to read rivers, and there were a lot of similarities at Powell, since it's a drowned river. It was so fun having that "back on a bicycle" feeling from a part of life that I really, really enjoyed.

 

[potter water]

I have navionics lakes on my c80. Something is going on magical in the system. Because, When I look at the chart depths, my depth finder will be within 10 feet of the numbers on the topo rings on the chart.

Now, is this because the "lakes" chart I have loaded puts the numbers for the rings at a single nominal lake level that just happens consistently to be when I'm on the lake. OR, is the system using the GPS altitude function to adjust the numbers on the plotter?

If my chart and plotter aren't using the GPS altitude function to adjust the chart depth numbers, then they should be. But, I swear that I've been on the lake at water levels from 1600 to 1650 and had correlation between the plotter depth numbers and my depth finder numbers withing plus or minus 5 feet. Probably just my 70 year old brain and wishful thinking.

If I'm on a slope that the plotter displays as 120 feet, and I cross to a different ring that is at 150 feet, the depth finder will dutifully show that change to within a few feet.

I guess I'll have to do my own factory call. I've been told by knowledgeable C Brats that those depth ring numbers are fixed in memory of the chip and based on a unchanging baseline depth of the lake. If so, I should be adding or subtracting significant numbers from the plotter topo ring numbers to get a number that matches what the depth finder is telling me. ???

 

[Pat Anderson]

Harry, I think there must be gremlins in your C-80! The cartography, including contour lines, has to be hard-coded in the Navionics Western Lakes CF card. As far as I can tell, the C-80 does not even have an elevation function. But then, there is much that is unfathomable about the C-80!