Problems with Navionics Sonar Charts.

[Steadman Uhlich]

Originally Posted by Gypsy23

Very salutory message. Personally I have not been induced to use the sonar chart display, I prefer the chart presentation. This has been particularly true since Navionics started their user/community input of sonar data. That scared me. How could Navionics validate the data? Sure some new dangers may be identified but also mis-identified.

I have looked at 'user/community' data marks which have been published on the ipad/android chart systems for places I know and I have frequently found them to be inaccurate when I go there myself. Too much room for error to rely on.

As for the sonar community info, it is axiomatic that there will be very little accurate information from users about the MOST shallow spots - 99.9% of boaters don't go there because they are too shallow - so even if you provide valid data to Navionics close by to the shallow reef it does not include the most shallow points.

Maybe the problem is as simple as Navionics getting so much data from user input which indicates sufficient depth (say 5m near the 1m reef) that their algorithm to blend the information just adopts the more frequent deeper readings and earlier shallow data from hydrographic surveys is over-ridden/swamped.

Whatever the root cause, Navionics are certainly tainting their product and brand and need to resolve it.

For me, I'll stay away from the sonar displays and also continue use my C-Map android app as a cross-check to the Navionics on android and my Raymarine E120W.

Interesting hypothesis or good points.

Your comment also reminds me of a statement I remember from seeing it on official pilot charts, paraphrased as: the reports of storms and seas are underrepresented and their frequency and height is likely to be more severe than this data shows on this chart. This is caused by the fact that most ships avoid those places.

[AJ_n_Audrey]

I found some ridiculous errors on the Navionics charts in the Bahamas, whereas the Explorer-based Garmin charts were spot on. I agree with others who have said that Navionics has a serious problem with their methodology and needs to address the algorithms and other processes they are using.

[Emerald Sea]

Detailed contoured marine charts, of which SonarCharts are mimicking, of any real accuracy are executed with a survey vessel towing a bathymetry spread ie echosounders, GPS positioning and a surveyor analyzing, interpreting and correcting the results for anomalies, tides, overlaps, etc. This takes $$$. Only areas where sustained commercial shipping traffic or other interests get such funding for these surveys, whether gov't or publicly funded. Many western gov'ts have funded such surveys and some have provided these charts to the public for recreation use. A majority of coastal regions of the world have never been subjected to such detailed surveys. Many rely only on the soundings from eons ago with rudimentary tools where inaccuracies abound.

So along comes Navionics with their SonarCharts. Where did they get the detailed sonar data for regions like Madagascar's NW coast (for example - one of two areas where I had a near-miss using Sonarcharts)? The fact is, they didn't! Navionics is not funding any detailed bathymetric surveys of these remote regions yet they create and publish detailed bathy charts. I can only imagine that a Navionics cartographer (if they have any), as a minimum, has taken whatever depth data he/she has available and extrapolates this between the high and low depths. And it would seem that before publishing such data that its not even quality checked even against satellite imaging (for surface referencing and any surface protrusions). This is outright dangerous and, if the case, negligent. Stating 'not for navigation' is unfounded as a majority of its subscribers use their charts wholly for this purpose.

A few years ago I was comparing in detail between Sonarcharts and my depth sounder in a number of coastal regions around the Indian Ocean and soon came to the conclusion they were rubbish. I have since turned off Sonarcharts as they give a complete false sense of security.

[Zabriskie]

Navionics have been replacing official chart data (that which appears on navigational charts of national hydrographic offices) with data that they have sourced elsewhere.

Hence the difference between their chart data and some of their rivals in the market.

[zboss]

The initial data from sonar charts was seeded from another source. If that source is incorrect, the sonar charts will be also - if there has been no-one travelling over that specific path, the sonar chart will reflect the data from the seeded data (which is hydrographic data from government sources) and not data from other boats.

In a new area, it pays to use more than one charting system until the you have verified the sonarchart data yourself.

I've been doing a lot of charting on sonar charts on the ICW and there are many many locations where the seed data is way off.

[JPA Cate]

Originally Posted by hogHunter

Navionics does not especially replace the data. They use algorithms to attempt to put together data from Navionics users, government data and data collected by Navionics to create the most accurate and up to date charts.
FYI is any Navionics user sees a place that's wrong or incomplete on the charts they can make a noteof it on the chart for all Navionics users to see using community edits.

This all sounds reasonable, until you start to think about groundings, sometimes catastrophic--no pun intended in the case of the Tanda Malaita.

While it was definitely a piloting error that led to its loss, the fact that there had already been enough Navionics assisted groundings that got the rescue folks on Huahine involved that that was the first thing they asked indicates to this reader that Navionics has a serious problem. It is foolish to expect users to fix up an erroneous data base. Just how long will that take? And if it was a serious grounding, don't Navionics consider that the people in distress will be taking care of themselves, not thinking of Navionics' benefit? Get real.

Ann

Just my opinion, and I don't know what they are or are not doing about it, but they have a serious problem.

[billknny]

In almost 20,000 miles I have never seen "bad data" when using Navionics chart presentation. I am sure there is some, but NOAA charts have lots of crap too.

BUT, the sonar database used to create the detailed contures is a disaster. Do NOT EVER use that to navigate! It’s ok to find a fishing spot, but not for more than that.

It’s easy to turn off the "crowd sourced" data. Just do it.

[zboss]

Originally Posted by billknny

In almost 20,000 miles I have never seen "bad data" when using Navionics chart presentation. I am sure there is some, but NOAA charts have lots of crap too.

BUT, the sonar database used to create the detailed contures is a disaster. Do NOT EVER use that to navigate! It’s ok to find a fishing spot, but not for more than that.

It’s easy to turn off the "crowd sourced" data. Just do it.

How do you differentiate between data that is seeded and data that is calculated?

[Zabriskie]

Originally Posted by hogHunter

Navionics does not especially replace the data. They use algorithms to attempt to put together data from Navionics users, government data and data collected by Navionics to create the most accurate and up to date charts.
FYI is any Navionics user sees a place that's wrong or incomplete on the charts they can make a noteof it on the chart for all Navionics users to see using community edits.

I think you will find that Navionics will advise you that they have totally replaced government data in many parts of the world and that they are not using the official data in their algorithms.

[Hoosiersailor]

This isn't necessarily just a Navionics issue. Most of the chart companies have some sort of community based sonar chart you can use. Only a matter of time before someone has an issue with their chart as well.

Garmin Quickdraw Community
C-MAP Genesis

[ArmyDaveNY]

Garmin just bought Navionics. It will be interesting to see what, if any, changes take place. I also wonder how long this sale has been pending and if the negotiations had any effect on what we're talking about.

[Jammer]

I use the Sonarcharts data. A lot.

The thing to realize is that for many remote locations, it is the best depth data available anywhere. I've used Sonarcharts in previously uncharted waters and accumulated data, which Navionics publishes, so that there is at least something available rather than a blank space on the chart.

The best data one might hope for is that collected by shallower draft vessels since they can approach obstacles more closely, or cross over them, and provide accurate data.

As for Navionics, my wish is that they would provide some sort of data quality metric along with the contours, to indicate their relative confidence in the data in some way. Their algorithms know whether they have data from one boat or a hundred of them.

And as for navigation, well, the charting products I use let you choose whether to see the sonarchart contours or whatever other charts you have downloaded/paid for. Each has different drawbacks. Choose carefully.

Navionics has a hard job. Make the algorithm too conservative and you'll capture the reefs but miss the channel. Could they do better? I imagine they could, but I am glad that I have the data they provide.

[zboss]

I’m also a huge user of sonar charts and also contributor. I use a dragonfly on my RIB to chart popular anchorages on the ICW and in the keys.

My concern is people that don’t have their system configured correctly with the correct depth offsets or where they have a custom depth set that is only meaningful to them.

This information then gets propagated into the soundings. I agree there needs to be very many confirmations before the data gets integrated. Then, you should be able to filter on the shallowest/deepest/etc returns regardless of the provider.