Another Navionics Victim in Georgetown

[Normanskier]

My current version on Navionics show that entrance entirely closed due to coral reef and rocks.

[GinoDelG]

I’ve been sailing in the Bahamas, including Georgetown, for the past two winters. I rely on Navionics Sonar charts almost exclusively, although I have paper charts as well. I can’t believe how accurate they are. My wife and I even went through Eluthera’s Infamous Devil’s Backbone this year without a pilot and the charts were spot on. I did have my wife on the bow as a backup, but it wasn’t needed.

[Tollesbury]

Originally Posted by quackedo

Actually, Garmin/Navionics is probably at fault to a great degree. When Garmin bought Navionics something became corrupted in the process. Information that was clearly shown on previous Navionics Charting suddenly changed or was completely lost. I ran aground off Man O War Cay on a spot clearly showing 8 feet of water on updated Navionics Charting. I checked an old phone with Un-updated Navionics charts and they showed the 4 foot shoal that I was sitting on. Somehow it and many other things were lost in the Garmin/Navionics transfer. I discussed it with Garmin and they are clueless as to how or why. Beware of updated Navionics Charts! They went from being the best to now untrustable. A big step backwards.

Thanks, I respect your viewpoint, but to paraphrase, “beware of navigators who rely on charts - e-charts or paper - rather than on navigation skill”.

[captainwoody]

I'm sure this was covered somewhere in the comments.
Never enter an area like this or any shallow area new to you or any area after a hurricane, using charts alone. Time your entry when the sun is directly above or behind you, watch the water colors change and tip toe in slowly.

On deliveries we often catch new crew staring at the video game (the plotter) instead of looking around. It's wrong often and on so many levels. Plotters are supposed to back up what you think you see. Not the other way around.

Be careful out there.

I'm a longtime delivery captain with many Bahamas visits.

[Triumphant]

I am always been very worried about the option that Navionics offers for users to update chart information without any challenge as to their validity

A current example in another area

The entrance of the Rio Dulce in Guatemala is currently showing a buoyed channel WHICH IS NOT THERE AND IS ALSO IN THE WRONG POSITION, these are result of a user update.

The better route with deeper water is marked by the Walker icons, these were a result of a Cruiser doing a survey using sonar equipment in February 2019.

[lestersails]

Originally Posted by a64pilot

The GPS depends solely on the Chart datum to display where you are on the chart.
While it of course helps to review your paper chart prior to and during navigation in difficult areas, as long as the datum is the same, your paper chart isn’t going to tell you anything that isn’t on the plotter.

While GPS isn’t infallible, it is the most accurate, reliable form of navigation there is. 999 times out of 1000 if the GPS tells you your somewhere you don’t think you are, your wrong.

I’ve used GPS since before it was available to the general public, initially it would only display current position and you could program a way point and get a heading and distance, but this moving map stuff was pure science fiction.
I have never, ever seen a GPS error, I’ve seen high DOP or EPE depending on brand of GPS and loss of satellite reception, but never ever seen one display position in error, not when you confirm satellite reception.

I have once over the Gulf of Mexico had my Garmin 396 simply lock up or freeze, I couldn’t even turn it off, had to remove the battery and reinsert to make it come back, and that fault never, ever reoccurred, but that was a GPS fault, that was the hardware.

DOP = dilution of precision, EPE = estimated position error

OK - so it is almost always right, except when it is wrong. The only thing that matters to me is if it is perfect or it is not. I don't consider myself to be all that good, but sailing into Sprat Bay on Peter Island my depth gauge was decreasing too fast and I just felt that my eyeball distance from the land to starboard was just too far (which can be hard to do - to move closer to the shoreline to get more water). I switched from GPS to eyeball (and also relying on my recall from the narrative of the entrance in the cruising guide). Tied up on the dock and looked down at the GPS and according to that, I was up on land. When leaving the next day, all was right with the GPS. I have no idea what was going on but my goodness, I would have put her on that reef in front of the resort if I steered the GPS. So, 90% or 99% or 99.9% - it ain't 100%.

[skipmac]

Originally Posted by lestersails

OK - so it is almost always right, except when it is wrong. The only thing that matters to me is if it is perfect or it is not. I don't consider myself to be all that good, but sailing into Sprat Bay on Peter Island my depth gauge was decreasing too fast and I just felt that my eyeball distance from the land to starboard was just too far (which can be hard to do - to move closer to the shoreline to get more water). I switched from GPS to eyeball (and also relying on my recall from the narrative of the entrance in the cruising guide). Tied up on the dock and looked down at the GPS and according to that, I was up on land. When leaving the next day, all was right with the GPS. I have no idea what was going on but my goodness, I would have put her on that reef in front of the resort if I steered the GPS. So, 90% or 99% or 99.9% - it ain't 100%.

Have had similar experiences several times. Once rented a 21' center console in Savannah to ride around with the family. Went up a river about 10 miles, stopped for lunch and a look around and went back down the river. The track going back in places where I knew from landmarks I was in the exact same place, were 100 yards or more different and didn't really match up anywhere on the whole run.

Just about every time I can recall doing the same thing, short trip there and back on the same day, the tracks never matched up.

[DreamWeaver III]

Any chart is only as good as its base information and subsequent updates. as previously mentioned the sonarchart and community edits are to try and increase the accuracy of the information presented but it only works when uploaded and verified. I guess it would also depend upon the vintage of the e-chart used and if the daily updates were done

[Fidsplice]

We are seduced by the apparent accuracy of electronic charts. 1/2 metre bathymetric lines, lights, anchorages etc. Wonderful, except that as soon as you identify one error, the entire product becomes seriously questionable. As other posts have noted, keep your head up! Use every resource available.

Recently in The Caribbean I noticed 2 serious errors.
1: there are 2 lights on the SSW coast of Dominica (not Republic of...) which are hopelessly out of place
2: St Barthelemy - there is a small boat passage shown between Ile de la Pointe and the main island (NW) with a depth of around 10m. Damn me, those Caribbean waters are healthy! Make the legs grow because you can walk across the passage!

Gather ALL information, but trust no-one. Worked well for the Royalty of mediaval Europe.

[bcn]

Take crowdsourced sonar charts, for missing data provide interpolation, and hey: here you go with super detailed electronic charts.

Quality control? Who has checked the content? How?
Can go well, yes - examples mentioned above. Or not, other examples mentioned above.

The Explorer Charts for the Nassau case looks like below. Gives an idea that the missing detail does not mean "in between just interpolate..."

[MartinR]

Most of the charts we are using are based on official bathymetric information. Basically meaning the area may have been last surveyed in 1808 or so. Especially in areas with little commercial shipping. I am sure, neither Garmin nor Navionics are doing any hydrographic surveying. They just present the available info in different ways. Sometimes they may have access to other data than official data, though.

Crowdsourcing will introduce new problems, so might not be the perfect solution either.

Also, sands shift, coral heads grow. There is a simple solution to this. Lookout!

[Exile]

Originally Posted by MartinR

Most of the charts we are using are based on official bathymetric information. Basically meaning the area may have been last surveyed in 1808 or so. Especially in areas with little commercial shipping. I am sure, neither Garmin nor Navionics are doing any hydrographic surveying. They just present the available info in different ways. Sometimes they may have access to other data than official data, though.

Crowdsourcing will introduce new problems, so might not be the perfect solution either.

Also, sands shift, coral heads grow. There is a simple solution to this. Lookout!

I thought the well-acclaimed Explorer charts for the Bahamas were considered more up to date and therefore accurate. If so, then it poses a dilemma for Garmin users. Use updated charts which are apparently from Navionics, or don't update and use the old Explorer charts.

[AiniA]

Originally Posted by GinoDelG

I’ve been sailing in the Bahamas, including Georgetown, for the past two winters. I rely on Navionics Sonar charts almost exclusively, although I have paper charts as well. I can’t believe how accurate they are. My wife and I even went through Eluthera’s Infamous Devil’s Backbone this year without a pilot and the charts were spot on. I did have my wife on the bow as a backup, but it wasn’t needed.

I think there is a flaw in this reasoning. Your wife in the bow is the primary data source with the charts in support. It is not a video game.

I am late to this thread and looked at the chart excerpts shown earlier. Can't imagine why anyone would try to go through the charted narrow (and shallow) bits. There is jus not enough data there and what there is is not promising. How much time would this save - an hour? What is the rush?

[AiniA]

Originally Posted by Exile

I thought the well-acclaimed Explorer charts for the Bahamas were considered more up to date and therefore accurate. If so, then it poses a dilemma for Garmin users. Use updated charts which are apparently from Navionics, or don't update and use the old Explorer charts.

We found the Explorer Charts to be fabulous in the Bahamas and used them in preference to electronics. When you need to you can get your lat/lon from the plotter and put it on the Explorer Chart. My understanding is that Garmin charts back then 10-12 years ago had licensed Explorer data but Navionics had not (we had Navionics).

[bcn]

After buying Navionics Garmin has stopped to license the Explorer Charts material since this spring.

The Explorer charts will be getting available as electronic raster charts for OpenCPN in some weeks. Three sets corresponding to the three books.