More here: http://www.twoatsea.com/navionics-sonarchart-problem/ Nice analysis.

Vice Commodore, OCC 

More on the topic of Navionics inaccuracies
http://wavetrain.net/techniques-a-tactics/795-tanda-malaika-lost-on-an-unmarked-reef-in-french-polynesia

«[font=sans-serif]Have you had experience with inaccuracies on Navionics charts?[/font]»

Yes.
[ul][li]1. Guadalquivir river, just downstream from Seville: no indication of the overhead power cables existing on the river bypass nor on the city channel into the port.[/li][li]2. Tomás Mestre canal into the Mar Menor near Cartagena: Navionics had a fantasy that the channel was passable only by tender at two separate points. We draw 2.2 meters, went in w/o issue.[/li][li]3. Unnamed cove immediately N of Akra Khondri Pounda, N of Frikes, Ithaca (alternate description: second cove S from Agios Nikólaos Is.). Where Navionics says there are 28 ft., in reality there are 148 ft.[/li][/ul]
The first one, we reported, got a quick reply, and within two weeks our chartset had been updated to accurately include both sets of power cables. The other two, we haven't reported.

Navionics charts are our primary navigation tool because of the richness of detail, wealth of ancillary information, and ease of use. However, we don't trust Navionics more than we need to, and we cross check them against a _minimum_ of two other chartsets (currently, MaxSea TZ and Imray Navigator), sometimes three, plus satellite imagery from Ovitalmap for anchorages, plus forward-looking sonar at very, very slow speed when doubts still remain.
edited by Hasbun on 9/26/2017
edited by Hasbun on 9/26/2017

[color=rgb(144, 148, 156)][font=inherit][font=inherit]Daria Blackwell[/font] shared a link.[/font][/color]
[font=inherit][/font][font=inherit][font=inherit]24 September at 11:46[/font][/font]
OCC Members Neil & Ley Langford have written an important blog post about their grounding experience while using Navionics Sonar Charts in Maine. I have added it and other reports to an OCC Forum post about Navionics charts on iPad. Please contribute your experience there.
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[font=inherit][font=inherit][font=inherit]Daria Blackwell[/font] [font=inherit][font=inherit][font=inherit][font=inherit][font=inherit]The original report from Crystal Blues. [/font]http://svcrystalblues.blogspot.ie/.../urgent-boat-repair[/font][/font][/font][/font][/font][/font][/font][/font][font=inherit][font=inherit]

[font=inherit][font=inherit]Neil Langford[/font] [font=inherit][font=inherit][font=inherit][font=inherit][font=inherit]Daria, the actual original report is here : [/font]http://svcrystalblues.blogspot.com/.../navionics-sonar...[/font][/font][/font][/font][/font]
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[font=inherit][font=inherit][font=inherit][font=inherit][font=inherit][font=Georgia, serif]Navionics Sonar Charts & The Missing Reef[/font]
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[/font][/font][font=inherit][font=inherit][font=inherit]Anne Lloyd[/font] [font=inherit][font=inherit][font=inherit][font=inherit][font=inherit][font=inherit]We also went on a reef in Fiji that was not marked on either Navionics or open Cpn CM93[/font]
[font=inherit]We knew however that in Fiji there are massive inaccuracies in all charts in relation to reefs and indeed whole islands in the Lau[/font]
[font=inherit]I do not however particularly Bla[/font][/font]...See more[/font][/font][/font][/font][/font][/font][font=inherit][font=inherit]

[font=inherit][font=inherit]Sherry Day[/font] [font=inherit][font=inherit][font=inherit][font=inherit][font=inherit]We discovered an uncharted Reef in Fiji also. Fortunately, it was a light bump before we turned quickly to port.[/font][/font][/font][/font][/font][/font][font=inherit][/font]
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[/font][/font][font=inherit][font=inherit][font=inherit][font=inherit]Anne Lloyd[/font] [font=inherit][font=inherit][font=inherit][font=inherit][font=inherit]we were stuck for 12 hours[/font]
[font=inherit]Near run thing I can tell you[/font][/font][/font][/font][/font][/font][font=inherit][/font]
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[font=inherit][font=inherit][font=inherit][font=inherit][font=inherit]Linda Lane Thornton[/font] [font=inherit][font=inherit][font=inherit][font=inherit][font=inherit]One of the cafes in Neiafu in Tonga used to issue a list of uncharted reefs to yachts heading west and south, most of them known only because people had hit them.[/font][/font][/font][/font][/font][/font][font=inherit][/font]
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[/font][/font][/font][font=inherit][font=inherit][font=inherit][font=inherit][font=inherit]Julia Freeland[/font] [font=inherit][font=inherit][font=inherit][font=inherit][font=inherit]Tanda Malika just ran into the reef in Huahini. The reef is not unchartered. It was nothing to do with Navionics.[/font][/font][/font][/font][/font][/font][font=inherit][/font]
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[/font][/font][font=inherit][font=inherit][font=inherit][font=inherit]Neil Langford[/font] [font=inherit][font=inherit][font=inherit][font=inherit][font=inherit]Julia, please read the complete analysis - on Navionics Sonar charts the reef was well out of place and completely mis-represented. True, I would not have been there at night, so close, but the Navionics Sonar Charts were completely wrong. That is what this tory is about.[/font][/font][/font][/font][/font][/font][font=inherit][/font]
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[/font][/font][font=inherit][font=inherit][font=inherit][font=inherit]Julia Freeland[/font] [font=inherit][font=inherit][font=inherit][font=inherit][font=inherit]Neil...we are in the place they hit the reef!!!! It's a mile wide and on every chart...look at Charlie's Charts![/font][/font][/font][/font][/font][/font][font=inherit][/font]
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[/font][font=inherit][font=inherit][font=inherit][font=inherit][font=inherit]Julia Freeland[/font] [font=inherit][font=inherit][font=inherit][font=inherit][font=inherit][font=inherit]We are currently in the lagoon where Tanda Malika hit...the boat is stripped and sitting in someone's garden after been dragged off the reef. Huahini has a fringing reef that is easily seen on all charts. The pass is 6 miles north of where they hit. Th[/font][/font]...See more[/font][/font][/font][/font][/font][font=inherit][/font]
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[/font][/font][/font][font=inherit][font=inherit][font=inherit][font=inherit][font=inherit]Alan Leslie[/font] [font=inherit][font=inherit][font=inherit][font=inherit][font=inherit]And a sensible seaman would time the passage so as not to arrive in the dark. Its hard to understand why he chose to arrive at night. The reef is huge and he should have known it was there, some things don;t add up in this story.[/font][/font][/font][/font][/font][/font][/font][/font][/font][font=inherit][font=inherit]

[font=inherit][font=inherit][font=inherit]Neil Langford[/font] [font=inherit][font=inherit][font=inherit][font=inherit][font=inherit]It's fair to say that most of us would not have planned a close pass by that reef at night, hoever[/font][/font][/font][/font][/font][/font][/font][/font][/font][font=inherit][font=inherit]

[font=inherit][font=inherit][font=inherit]Neil Langford[/font] [font=inherit][font=inherit][font=inherit][font=inherit][font=inherit][font=inherit]Oops finger trouble ..... however, if you follow that sad story all the way through you'll see that very large (gross) errors in the Navionics Sonar charts were identified by Evans Starzinger. If they used those bad charts then they simply had to hit t[/font][/font][font=inherit][font=inherit][font=inherit]he reef. Our own little collision was related to an entire reef being missing on the Sonar Charts, then later we (and other OCC [/font][/font][/font][/font][/font][/font][/font][/font][/font][/font][/font][font=inherit]
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[font=inherit][font=inherit]Julia Freeland[/font] [font=inherit][font=inherit][font=inherit][font=inherit][font=inherit]Neil the reef around Huahini is obvious and we'll charted...it's even shown on tourist maps. We are on Huahini now and it couldn't be any more obvious![/font][/font][/font][/font][/font][/font][font=inherit][/font]
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[/font][/font][font=inherit][font=inherit][font=inherit][font=inherit]Linda Lane Thornton[/font] [font=inherit][font=inherit][font=inherit][font=inherit][font=inherit]Lucky you! We spent nearly three weeks in the deep bay down on the south west corner of the island - all by ourselves.[/font][/font][/font][/font][/font][/font][font=inherit][/font]
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[font=inherit][font=inherit][font=inherit][font=inherit][font=inherit]Anne Lloyd[/font] [font=inherit][font=inherit][font=inherit][font=inherit][font=inherit][font=inherit]I do not have experience of the sonar charts[/font]
[font=inherit]Huahine was quite well charted I thought like most if the French Empire[/font][/font]...See more[/font][/font][/font][/font][/font][font=inherit][/font]
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[/font][/font][/font][font=inherit][font=inherit][font=inherit][font=inherit][font=inherit]Odette Hasbun[/font] [font=inherit][font=inherit][font=inherit][font=inherit][font=inherit]For those interested in digital charts for iPad, MaxSea TZ offers raster (“paper”) charts that strictly come from the official sources (SHOM, UKHO, etc). We always cross-check Navionics against MaxSea.[/font][/font][/font][/font][/font][/font][font=inherit][/font]
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[font=inherit][font=inherit][font=inherit][font=inherit]Julia Freeland[/font] [font=inherit][font=inherit][font=inherit][font=inherit][font=inherit]Navionics can be so much on the money though. In the Tuamotu atolls we were surprised to find many of the coral bombies in the atolls on the chart! Go figure! We still travelled in good light with one of us on the bowsprint using visual checks, but it was quite amazing how our sightings corollated with the charts.[/font][/font][/font][/font][/font][/font][font=inherit][/font]
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[/font][/font][/font][font=inherit][font=inherit][font=inherit][font=inherit]Neil Langford[/font] [font=inherit][font=inherit][font=inherit][font=inherit][font=inherit]Julia, yes I agree it can be onthe money - it was outstanding around Cape May and I went into print about it. However that isn't good enough - it can't simply lose major reefs..... When we pay for nautical charts we are buying knowledge - unfortunately Navionics, with Sonar Charts, have turned that on its head and we pay to give the. Knowledge[/font][/font][/font][/font][/font][/font][font=inherit][/font]
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[/font][/font][font=inherit][font=inherit][font=inherit][font=inherit][font=inherit]Alan Leslie[/font] [font=inherit][font=inherit][font=inherit][font=inherit][font=inherit]Its interesting that we hear A LOT of folk talking / complaining about Navionics, but few about C-Map. In any event relying on one source of information is dangerous. We have C-Map on our Furuno Plotters, C-Map, Navionics on Max-Sea laptop and raster, GE2KAP on OpenCPN laptop. I also have Navionics on a tablet but rarely use it. AND I keep my eyes open and look out the window ![/font][/font][/font][/font][/font][/font][font=inherit][/font]
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[font=inherit][font=inherit][font=inherit][font=inherit]Odette Hasbun[/font] [font=inherit][font=inherit][font=inherit][font=inherit][font=inherit][font=inherit]We used C-Map from the Guadiana river to the Ionian, i.e., for 18 months. This product is not for us. It is the only charting software we have used that, if you are zoomed out, gives no inkling about numerous obstructions that only show up on large, [/font][/font]...See more[/font][/font][/font][/font][/font][font=inherit][/font]
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[font=inherit][font=inherit]Alan Leslie[/font] [font=inherit][font=inherit][font=inherit][font=inherit][font=inherit][font=inherit]My experience is quite the reverse in the South Pacific. I have found C-map to be much better then Navionics in identifying dangers and putting them in view. Maxsea uses either c-map, navionics or raster depending on which chart package you buy...howev[/font][/font]...See more[/font][/font][/font][/font][/font][font=inherit][/font]
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[font=inherit][font=inherit][font=inherit][font=inherit]Neil Langford[/font] [font=inherit][font=inherit][font=inherit][font=inherit][font=inherit][font=inherit]Hello Folks, please allow me to (attempt) to bring this discussion back on message. It is about Navionics Sonar Charts. Not C-Map, not the normal Navionics charts. Yes, all the charting systems have errors and gaps around the world, but no others (that[/font][/font]...See more[/font][/font][/font][/font][/font][font=inherit][/font]
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[font=inherit][font=inherit]Odette Hasbun[/font] [font=inherit][font=inherit][font=inherit][font=inherit][font=inherit][font=inherit]Neil, we have also come across several errors on Navionics Sonar Charts (NSC). Yet NSC is our primary, because of the wealth of detail and excellent user interface. But because we know of the high error rate on NSC, we do the following:[/font]

[font=inherit]1. Always r[/font][/font][font=inherit][font=inherit][font=inherit]un two other charts to cross-check against Navionics. Currently, MaxSea TZ (raster, official charts) and Imray Navigator (raster, proprietary charts).[/font]

[font=inherit]2. When in doubt, fire up our Garmin Bluechart.[/font]

[font=inherit]3. Avoidance or minimal (i.e., 1 knot or less) speed on any "dotted black line" marked area on Navionics. We understand that "dotted black line" means "questionable." On the Crystal Blues blog, Gangway and Grindstone ledges are shown both inside "dotted black lines."[/font]

[font=inherit]4. ScanForward forward-looking sonar is always on if we enter any questionable grounds. Would not enter any NSC "dotted black line" grounds at any speed without ScanForward, unless with local knowledge.[/font]

[font=inherit]5. Since the last 2 months or so, we also run Ovitalmap for extremely easy, automatic-save satellite imagery to compare against the sources mentioned above when deciding where to anchor.[/font]

[font=inherit]It takes some work to make Navionics Sonar Charts one's primary, but the level of detail and ease of use can't be beat.[/font][/font][/font][/font][/font][/font][/font][/font][font=inherit][/font]

[font=inherit][font=inherit][font=inherit][font=inherit]Neil Langford[/font] [font=inherit][font=inherit][font=inherit][font=inherit][font=inherit]Interesting that you'd go to so much trouble to continue using a faulty product, but good on you for persevering. Your comment about the dashed black line is also interesting, thanks. You may note that the reef / ledge we found and collided with was not circled by a dashed line, so nothing is guaranteed unfortunately.[/font][/font][/font][/font][/font][/font][font=inherit][/font]
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[font=inherit][font=inherit][font=inherit]Odette Hasbun[/font] [font=inherit][font=inherit][font=inherit][font=inherit][font=inherit]Well, we have to. We anchor out most of the time, year-round, so the payoff of using the charts with the most detail (Navionics) is being able to anchor in safe, secluded places, often well off the trodden path.[/font][/font][/font][/font][/font][/font][font=inherit][/font]
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[font=inherit][font=inherit][font=inherit][font=inherit][font=inherit]Dierdre Atkinson Wogaman[/font] [font=inherit][font=inherit][font=inherit][font=inherit][font=inherit]We used an IPad with governemnt charts in the USA, but purchased Navionics charts for our cruise to the Canadian Maritimes. We have redundant Candian government charts on our laptop. We found good agreement, but don't use the sonar feature, becasue frankly it drives the navigator crazy to look at it. We always treat crowd sourced data with skepticism.[/font][/font][/font][/font][/font][/font][font=inherit][/font]
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[/font][/font][/font][font=inherit][font=inherit][font=inherit][font=inherit]Neil Langford[/font] [font=inherit][font=inherit][font=inherit][font=inherit][font=inherit]Hi Dierdre, well put, although in the cases we're discussing here it is not the crowd sourced data that is the problem - its the fact that Navionics simply LOST a ton of perfectly good data that was on the Government charts.[/font][/font][/font][/font][/font][/font][font=inherit][/font]
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edited by simoncurrin on 9/27/2017

Daria
Yes we noted plenty of inaccuracies in Navionics this summer. This included reefs that weren't marked, shorelines half a mile adrift from their charted position and, of course, plenty of islands that didn't exist. The trouble is these errors were also present in CMAP and Garmin's Blue Chart all of which we carry. I think the problem in remote waters is that the electronics are all based on paper charts drawn from ancient surveys. Not sure where that leaves us other than to recommend greater use of forward looking sonar, KAP charts from Google Earth and, perhaps, drone surveillance. Interesting one of the first boats to transit the NW passage this season (East about) attributed their success to deploying a drone to reconnoiter the ice conditions.
edited by simoncurrin on 9/25/2017

There is a growing body of evidence that Navionics Sonar Charts, and indeed their regular electronic charts, have major inaccuracies. Two serious accidents have recently been reported. Please read the report from Crystal Blues if you use Navionics charts. They collided with a reef in Maine that was missing on the charts.

http://svcrystalblues.blogspot.ie/2017/09/navionics-sonar-charts-missing-reef.html

Similarly, a family of four sailing Tanda Malaika, a catamaran, collided with a reef in the Pacific. Fortunately, all were rescued unharmed. The yacht was not insured and an expensive salvage operation was required. They had been using Navionics charts.

"[color=rgb(102, 102, 102)][font=Raleway, Helvetica, Arial, sans-serif]When they asked us what happened and we told them that our chart did not show reef, they asked us if we had been using Navionic charts, and I said yes. He then shook his head and said that at least five boats end up on those reefs a year who were using Navionic charts. They walked me over to a large map on the wall and told me to point exactly to where Tanda Malaika was, and I did to the best of my knowledge. They then pointed to two places, our spot being one of them, that all the wrecks seem to happen, then gave us the name of a man who we could call for salvage help. The word ‘salvage’ seemed so cold and final. It sounded to me like death."[/font][/color]

https://adventuresofatribe.com/2017/07/23/mayday/
https://adventuresofatribe.com/2017/07/25/
https://adventuresofatribe.com/2017/07/27/
https://adventuresofatribe.com/2017/07/29/

Have you had experience with inaccuracies on Navionics charts?

Vice Commodore, OCC 

[quote="simoncurrin" post=1109]Never had this problem with an iPad but I wondered if anyone has had any experience of GLONASS - the Russian sat nav system. I bought a new camera last week (just. £200 compact) but it boasts that it fixes position (for geotagging photos) by both GPS and GLONASS. So can all current gps receivers use both GPS or or just the newer ones? Presumably if the Pentagon throws the switch I 'll be able to still navigate by camera!![/quote]

UPDATE: As of 2015 most smartphones now include GLONASS navigation.

Vice Commodore, OCC 

I just read this blog about lightning strikes and wondered if any of you protect your electronics if there are electrical storms around. Any experience with lightning strikes and electronics?

https://yachtpipistrelle.wordpress.com/2015/05/11/lightning-never-strikes-twice/?blogsub=confirmed#blog_subscription-3

Vice Commodore, OCC 

We decided to head off for a sail earlier this week when we heard the Azores high was settling back in over Ireland! As we were leaving our inlet, the GPS (no differential) started dropping in and out of the chartplotter. Alex tried to jiggle wires thinking it was a bad connection. We were waiting for our back up GPS to launch when it suddenly came back into action with differential, about a half hour into it. When we looked at satellite acquisition, there were five satellites out of commission. We had heard that the aging satellite system was going to cause problems with GPS this year, and this is the third time we 've had a problem. I 'll post photos of the anomalies we experienced in Scotland in July as well.

But I LOVE your navigation by camera. Point and shoot naavigation. I just picked up a new Samsung android and the Navionics charts are pretty cool as a backup on there, as long as the gps works.

I still love paper charts.

Vice Commodore, OCC 

Never had this problem with an iPad but I wondered if anyone has had any experience of GLONASS - the Russian sat nav system. I bought a new camera last week (just. £200 compact) but it boasts that it fixes position (for geotagging photos) by both GPS and GLONASS. So can all current gps receivers use both GPS or or just the newer ones? Presumably if the Pentagon throws the switch I 'll be able to still navigate by camera!!