Sunday 3 September 2017

Navionics Sonar Charts & The Missing Reef

Part Of The Keel Damage
Early on August 9 we departed Potts Harbour, heading for Booth Bay, Maine. Leaving the anchorage we collided with a submerged reef, bringing the mighty Crystal Blues to an instant stop from around 5 knots. Ouch. Our first computer assisted grounding!

Fact is, we were lucky.  The mast and rig stayed up, the hull was not breached and the damage could be repaired fairly simply. However a boat built less heavily would have been in severe trouble. The story that follows is intended to serve as a warning for others, to help prevent further accidents. So how did it happen ?

First off, I made the mistake of trusting Navionics Sonar Charts, which I'm unlikely to do again. Secondly, I failed to check any secondary navigation aids or references. So with more care I could have avoided the reef. Dodging lobster pots, early in the morning, I was busy at the helm and trusted the charts that had brought us into harbor the afternoon before. Never again...

It's ironic that I was actually looking at the charts (on the iPad) as we connected with the reef - when Ley stumbled up the companionway and I picked myself up off the wheel, we both looked at the chart on the iPad - it showed over 13 meters of water depth. Wrong. In fact very wrong.

Crystal Blues was at that point bobbing on the gentle swell, afloat, but occasionally colliding with the reef on the bottom of the swells and occasionally hitting something as she rocked from side to side. Not wanting to start the engine in unknown waters, we lowered the dinghy and towed her away to deep water using the outboard motor. We lifted the floor boards and inspected the bilges for damage or leaks, and then (more than a little shaken) proceeded to Booth Bay, where I dived on the boat and captured the image above.

Pulling Away From The Reef

So now, over three weeks later, we're hauled out of the water at Journey's End Marina in Rockland, Maine, working towards repairing and refinishing the keel. In the time since the accident both we and others have had time to look at the Navionics charts for the area in some detail, and the results are not good.

The Missing Reef

First of all, this problem has nothing to do with zoom levels on the screen. No matter how close in you zoom, that reef was not shown. So here is what we were viewing on screen right when the collision occurred :

With the wisdom of hindsight, it does look weird. The yellow line is our track, and it shows just over 13 meters where we came to a sudden stop. When we checked the standard Navionics chart (not the Sonar Chart version), a serious chart error became apparent :

You can see that this version shows a depth of 5.4 meters nearby, and the dark blue zone adds to the message that we shouldn't be there. However it gets worse, much worse.

The official government chart, above, shows a minimum depth on that reef of less than 1 meter. Yoiks ! So, not only the Navionics Sonar Charts were wrong, but also the "standard" Navionics charts.  How can this be ? How widespread is this problem ?

Soon after the accident, we anchored in Rockland Harbour to arrange for the haulout, repairs and a marine surveyor to inspect the damage. Other cruising friends, also OCC members, came to visit and share a meal with us. They explained that they too were using the Sonar Charts when navigating in harbors, as they valued the extra detail provided, and were shocked to hear of our collision. They were nervous enough to examine our accident site in detail, and then to cast more widely around the region looking for similar charting errors. Apparently it took only 10 minutes for them to find several more in the vicinity of Potts Harbour. As our friends said, these things are dangerous !

I had quickly notified Navionics of the chart error, and they proudly committed to correcting the error before the end of August. We checked recently, updating the charts on just one of our systems, and yes the Sonar Charts now appear to be correct for that reef, showing a minimum depth of 1.2 meters :

My follow up response to Navionics was more specific - I explained that we (and others) had since found numerous examples of dangerous errors in their charts, and suggested that they had a systemic problem that needed fixing - were they going to simply correct the charts when advised of errors, or were they going to address the wider issue of fixing the system that created them? Navionics response was less than pleasing :

"Dear Neil Langford,

I'm sorry you feel this way. We investigate the reports as they are brought to our attention. We have guidelines that we follow for the logs to process; however there can be issues with the processing so we welcome any feedback provided. If you have found numerous instances, please feel free to provide the coordinates of the locations so we can further investigate as we cannot be in all places at once and will be happy to work with anyone who would like to report this information.

For additional support, access Navionics online Help or Chat Now with a live agent.

Best regards,
Jennifer Pereira
Navionics Customer Service"

OK, so they can't be in all places at once ? What does that mean ? And there can be issues with processing ? And they'll be happy to correct their mistakes if only we'll report them.... I had hoped for a more positive response!

Navionics web site advertising says :

"Navionics integrates the sonar logs from individual users with existing data to ensure the SonarChart™ becomes more and more precise"

What they haven't yet explained is how often they actually lose large chunks of the existing data - like entire reefs.

Loss Of The Leopard Catamaran Tanda Malaika, French Polynesia

Just a few days ago I learned of another accident where Navionics charting errors were possibly a contributing factor. The catamaran was a total loss, though very fortunately the family on board survived. You can read about it here, including a range of comments from many cruisers.

For me the interesting comments came from one observer who took a good look at the Navionics charts and found errors that look similar to those we found. These are his images. He said :

"I have never seen an error like this before. It is not missing data, and it is not old/obsolete survey data, and it is not a data layer issue (the three typical errors). I don't really understand how the sounding got warped that way."

From that sad story, we can see that the Navionic charting problems may not be associated only with the rocky coast of Potts Harbour, Maine.
Take A Look At Other Areas

When I learned from friends that they had found other significant chart errors, near Potts Harbour, I was naturally concerned. But when I read of the errors in French Polynesia, I started to think that Navionics may have a wider systemic problem. Since we're in Rockland as I write this, I started looking at the coast close to this harbor and it took only 10 minutes to find yet another set of significant and dangerous errors.

Government Chart
This is the Upper Gangway Ledge, and the Inner Grindstone Ledge, just south-east of Ash Island near Rockland, Maine. These are clearly dangerous places to be, with depths down to 1.5 meters. Experienced locals tell me they see breaking seas there in heavier weather. So how are these shown on Navionics Sonar charts?

Navionics Sonar Chart

What a very dangerous representation - the Gangway Ledge (1.5 meters) is shown as being over 16 meters deep! Inner Grindstone is shown as 5 meters deep, when in reality it is around 2.4 meters. If I can find this area in just a few minutes of local searching, how many other reefs, ledges and rocks are missing (or wrongly plotted) on these charts ? This really is dangerous charting.

The Raymarine Version

If you've followed the story to this point, you're probably wondering if the problem is limited just to Navionics charts when displayed on the iPad - and I was wondering the same thing. So, immediately after our collision I checked the Navionics data on our Raymarine chart display. Raymarine and Navionics are closely linked - yes, you can run many other types of charts on Raymarine displays, but the most common charts supplied with Raymarine systems are made by Navionics. Additionally, Raymarine displays are used to collect the crowd sourced data that Navionics uses to create their Sonar Charts.

On our system (to their eternal credit) Raymarine displayed a large warning when I selected the Sonar Charts - Not For Navigation it said. To be fair, a similar warning is also available on the iPad, covering all Navionics charts - though it is hidden and you can start the software without reading it - as I'm sure most people do.

Sure enough, the missing reef problem existed on the Raymarine display system as well - the reef we hit was clearly displayed on the standard charts, but not displayed on the Sonar charts, when viewed on our C97 multi function display.

Un-Reality Abounds

There is a sense of un-reality about this situation. Here we have a long established and reputable manufacturer, Navionics, who publish electronic chart data aimed at the marine industry.

Navionics marketing includes promotion of Sonar Charts for use on marine chart plotter displays, claiming extraordinary detail.

So check the wording in the email I received today, at right. See any warnings there about "Not For Navigation"?

On the Navionics website (see it here) Sonar Charts are promoted like this :

"Get the most up-to-date charts every day.  Navionics integrates the sonar logs from individual users with existing data to ensure the SonarChart becomes more and more precise, even in the ever-changing conditions of sea, lake and river bottoms."

Once again, I don't see any warnings in that text saying these charts are actually not for navigation. So I have to ask, if I can't use them for navigation, what will I actually do with these Sonar Charts ?

Fact is, the marketing of  Navionics Sonar Charts places them on a pedestal, supposedly better than the standard charts - after all, the idea of crowd sourcing depth data and using it to improve the government charts is exceptionally attractive. If only they could be trusted. If only they could be used for actual navigation. If only Navionics could integrate the crowd sourced data, without actually losing significant and well known dangerous features.

So how do we deal with this? Specially if you have a Raymarine system supplied with Navionics charts? Well, first up I won't use Sonar Charts at all from this point. Secondly, I'll use the government charts whenever possible, as even the standard Navionics Chart showed the depth at our accident site incorrectly as 5.4 meters - the 0.9 meter shallow spot was completely missing (they've now fixed that since my report). Note that the official government charts are available in the Navionics iPad app.

Also, for US coastal navigation we'll use the US NOAA vector charts that can be downloaded for free and run in Open CPN. Or, for $9.99 you can license the NOAA vector charts for the US Eastern Seaboard, from the Raymarine chart store online. Better still, purchase the C-Map charts to run on your Raymarine system - I suspect you'll sleep more soundly knowing the data is actually intended for navigation.


  1. Receiving quite a lot of stories from other sailors who have found missing data in the standard Navionics charts - including one complete island that was missing.

  2. Do you know if the same defects exist with Garmin GPS marine mapping? Many of us sailors here in the U.S. use Garmin GPS systems.

    1. Sorry, I'm not aware of who produces (or updates) the charts that Garmin sells. Can anyone assist ?

    2. Garmin makes their own charts, BlueCharts. Includes updates by GARMIN for LNM Local Notice to Mariner (USCG) and Notice to Mariners NTM (NGA).

  3. Hi Neil. Sorry to hear of the accident. Why is C-map better than Navionics?
    David McKay

    1. David - Check out the comment from Robin Kydd, re-posted below.

  4. David, C-Map offer professional cartography services to the maritime industry - they license UK HMO data, among others, and distribute this to the professional maritime industry. If you go to you'll see the two distinct marketing arms of their business. I would certainly trust their charts more than Navionics, though it should be said that I am aware of cases over the years where critical reefs and features have been missing from C-Map and Jepperson cartography. None of these products are perfect, but the large number of Navionics errors is far greater than I have ever seen. To my knowledge Navionics does not have any significant commercial customer base.

  5. And just for good measure, this comment from my friend Robin Kydd, who posted on my Facebook link :

    "You know my opinion of Navionics and as am ex MD of Navionics Australia I write with some authority.
    Marketing has led the world to believe Navionics is a serious product.
    Equally disturbing is that C Map Jepperson is now owned by a merchant bank so may also be chasing $ rather that quality any time soon.
    No electronic chart sold for navigation has any excuse for not being as good as the government charts which in the USA they get free with out copyright issues that hinder good electronic charting in the ex British parts of the world."

  6. I'm sorry you had that problem with the charts. I also have Navionics on an iPad and will be transiting that area over the next couple of weeks. I may have missed it but could you possibly provide the precise coordinates of the issue as well as any location info available for the other chart discrepancies found in the area? Thanks

    1. Sure Karl,co-ordinates as follows :
      43deg 43.533 north, 70deg 3.039 west
      Update your Navionics charts online and you'll see that location as it really is. Problem is it seems that most updates in this part of the world will be because somebody hit something. My friend Bill Woodroffe has coined a new democratic descriptor for these charts - he calls them False Views. Just remember, besides the one that I hit, there are lots of these undocumented obstacles out there. Use the government charts if you can.

  7. My friend Dana Fowlkes had this to say, via email :

    " We have had similar experiences with the Navionics Sonarcharts in Thailand and I turned them off. They are worse than useless as they encourage you to think you have data. :(

    They do not exist for Indonesia and besides, in Indonesia the Garmin and Navionics charts vary between good and off by 3 NMs. No joking. After our first pass through Indonesia, I decided to buy the official ID government electronic charts S63 versions that could be used with OpenCPN. They were amazingly good and were a real benefit to have onboard. Since they are good, then why can't Navionics and Garmin get them? Or at the very least warn us that their charts are fantasy? "

    Dana, re the Indonesian charts, I had heard from an industry source that some companies have paid for them,others have decided not to. You can figure from this that Navionics have (thus far) made a business decision not to buy the high quality Indonesian data.

  8. Sorry to hear of your crash and happy that neither of you were hurt or the damage significant.

    We feel that there is a disturbing trend: navigating by tablet with tablet based apps and Navionics charts, or similar. Almost everyone is doing it and virtually every crash we hear about happened with these kind of charts and a tablet being used, sometimes mounted in a bracket, often on some bodies' lap or in their hand. We get two or three crashes a year here in Mexico. Routes, if used at all, were planned on the tablet. Navionics route planning is primitive at best. iNav-x is better, still not great.
    We have the greatest respect for your seamanship and skills however these crashes, yours included, and particularly Tanda Malaika, were onto a reef or land which is clearly present on the CM93 charts which most people have on their OpenCPN systems. None of the crashes we read about would have occurred had the proper route planning been performed and the yacht been following the planned route. (You would have never plotted a route over that spot on your OpenCpn system at the nav station.)
    We need to get the word out:
    Proper navigation includes prior route planning on a proper system with a keyboard, preferably at the nav station, and using the best charts available (part of a navigator's responsibility is to obtain and use the best chart for any given location). After developing the planned route then close inspection, at high zoom levels, is required and corrections made before setting out. Then during the passage the ship's progress along the route must be monitored, preferably by a second person, not the helm's man, and not by referencing a tablet computer in the cockpit.
    Navigation is made easy with these tools that everyone uses but it is not sound navigation and it is dangerous and anyone who navigates this way will eventually hit stuff.
    Fred & Judy SV Wings, La Cruz Huancaxtle

  9. Does it not make sense that crowd-sourced sonar charts would have the most serious data deficiencies around those very shallow areas one would want to avoid? After all, fewer boats will have transmitted these hazardous areas.

    Therefore, it makes sense to not use sonar charts for navigation deferring instead to official or more robust soundings. (The sonar charts are probably useful to divers & fishing folk but navigators beware...)

    1. That should read:
      ‘transited these hazardous areas.’

  10. We too have found and reported on problems with Navionics charts, both in Mexico [] and here in Canada. []

    When we were cruising Mexico's Sea of Cortez, C-MAP was somewhat better than Navionics (though I wouldn't be surprised to find the opposites in some areas).

    I certainly wouldn't trust the Sonar Charts. Interpolating already sparse data and/or including possibly inaccurate crowd-sourced data can't result in accurate results.


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