What confidence do you have in your charts?

[El Pinguino]

What confidence do you have in your charts - be they paper or electronic?
Bear in mind that both paper and electronic use the same 'source material'

This should be essential reading for all.
https://www.hydro.gov.au/prodserv/im..._of_charts.pdf
Note - this is undated but was written when raster charts were still considered OK.

Prior to my retirement our charts still had the 'reliability diagrams' rather than 'ZoC diagrams' and I was very aware that all the northern Tasmanian coastal survey work had been done by HMAS Warrego in the 40's and 50's ( at which time she surveyed a huge area of the Australian coast and most of those surveys are still in use).
https://www.navy.gov.au/hmas-warrego-ii - ' In the post war period Warrego (II) made a significant contribution to the survey of Australian waters, steaming some 271,000 miles on post war survey duties alone.'
The soundings in central Bass Strait were and still are from HMS Beagle's work in the 1840s.

In fact the only areas covered by recent surveys are port approaches and 'deep draught' passages ie the waters of interest to the commercial chaps..

Some more interesting information here
https://maritime-mutual.com/risk-bul...gators-beware/

And speaking of raster charts AMSA has this to say
'Use of ENCs
The ENC coverage of Australian waters is 100 per cent. The use of raster navigational charts (RNC), when ENCs  are  available, is not permitted in Australia. ' That I think it is safe to say refers to 'commercial' shipping.

https://www.amsa.gov.au/safety-navig...m/electronic-0

Now I think I am correct in saying that all the electronic charts on the plotters found on yachts would come under
'Official and Unofficial Data
An ECDIS can determine if data is from either an ENC or a private source by interrogating the Agency Code (a two character combination which is unique for any data producer) embedded in the data.
Using this code an ECDIS will warn mariners that they must navigate with an official up to date paper chart if data from a private source is in use. The ECDIS will show a warning on the ECDIS screen:
«No Official Data -Refer to paper chart »'
Thats the IHO viewpoint found here https://iho.int/iho_pubs/standard/S-...inal_Clean.pdf

I think thats enough reading for today but the big takeaway for me is that while I have reliability information on my paper charts I don't have any of that info on opencpn - willing to stand corrected on that point.

Do any of the Raymarine/Navionics/Garmin etc etc plotters provide that reliability/confidence information?

[Mike OReilly]

Originally Posted by El Pinguino

What confidence do you have in your charts - be they paper or electronic?

Didn't read all the references Ping, but I can easily answer your basic question: I have confidence that my charts are a general facsimile of reality.

By that I mean, I realize my charts may, or may not, be exceedingly accurate. They show some useful information about the area, which makes them useful tools. But I NEVER assume they are perfectly accurate, and NEVER place my vessel in a situation where I am blindly or solely relying on them.

I know full well that many areas I travel are poorly charted. The "source material" might be soundings that date back over 100 years in some areas. And it's quite clear some are offset from reality by up to a mile or more.

So I think I have the appropriate level of confidence in my charts. IOW, they are useful tools, but I never assume they are fully accurate. This is why in a trade, I'd rather have my depth sounder and radar over my chartplotter, or even paper charts. The former shows actual reality, while the latter displays a representation of the world which is at least two steps removed from actual world.

[requiem]

Originally Posted by El Pinguino

I think thats enough reading for today but the big takeaway for me is that while I have reliability information on my paper charts I don't have any of that info on opencpn - willing to stand corrected on that point.

Under the View menu, "Show ENC Data Quality" will overlay the appropriate CATZOC symbols. Right-clicking a point and selecting "Object Query..." will bring up additional information, in this case you'd likely be interested in the "Quality of data" section, specifically the SURSTA and SUREND values if present.

Originally Posted by El Pinguino

Do any of the Raymarine/Navionics/Garmin etc etc plotters provide that reliability/confidence information?

Hahahaha... no.

[RaymondR]

With about 45,000 nm of coastal cruising around northern Australia under my keel I've found the 800 series paper charts very reliable. However there were a couple of times with older charts in the Northern Territory (All that was available in 2002) where I would have been a mile or so inland had I sailed to some of the waypoints taken from the older charts when using GPS.

[El Pinguino]

Originally Posted by requiem

Under the View menu, "Show ENC Data Quality" will overlay the appropriate CATZOC symbols. Right-clicking a point and selecting "Object Query..." will bring up additional information, in this case you'd likely be interested in the "Quality of data" section, specifically the SURSTA and SUREND values if present.



Hahahaha... no.

Under the view menu the 'data quality' is shaded but -being cheap - I am using CM93 and RNC charts - no ENC.

This thread was prompted by a number of recent threads where some people seemed to think that the centimetric accuracy of GPS etc gave them whizbang navigational accuracy.

PS you can buy a complete Australian Portfolio of ENCs for $793.50 ( South Pacific Pesos ) https://www.boatbooks-aust.com.au/pr...ustralia-pack/

Pretty good value I reckon.

[requiem]

Originally Posted by El Pinguino

Under the view menu the 'data quality' is shaded but -being cheap - I am using CM93 and RNC charts - no ENC.

Yep, the 3rd party charts may be a mix-n-match of various sources and often won't have the quality data. Sometimes they may mention the source, or you can guess based on what notes are present. On the other hand, if you're lucky they may include more recent data.

To add an illustration to the thread, here's a figure from S-67 Ed 100 Mariners Guide to Accuracy of Depth Information in ENC:

[hpeer]

I don't have your depth of knowledge but have some experience and have done a wee bit of research.

Some Canadian charts have source material back to French surveys in the 1800's.

I have seen electronic charts disagree with GPS plots by about a kilometer, it shows me sailing through headlands.

I have seen USA charts with significant off sets, I plowed a lot of cornfield going through the Erie Canal.

The Bahamas are interesting. To my knowledge the government charts are either poor or non-existent. A private company (Explorer) made their own surveys and these are very highly regarded. You can directly buy Explorer charts from the company or through some chart applications (e.g. iNavex or AquaMap). Last I heard Navionics was using a PARTIAL set of Explorer data, but not clear which bits come from what source. Both Navionics and Explorer have marked preferred routes. At least one Navionics preferred route leads over a reef and has brought grief to multiple boats. Last I heard that was not fixed.

Navionics has this "sonar view" feature which implies extra detail about the depth. Apparently they crowd source this info in some locations. However, where they don't have info it appears to be merely extrapolating even curves between known readings. That this is true is pretty clear when you look at infrequently traveled areas with few soundings. In short, they are making it up.

On the other end of the spectrum, and inline with your question, the US Army Corps of Engineers does special soundings for problem areas and publishes that data. AquaMap makes that data available, for a small fee. It is presented as a color coded overlay on the base chart. Data up to 3 years old is presented, older data is more faint than newer data. Survey date is available by a long click. This is really useful when trying to transit the ICW with a deep draft.

[rslifkin]

If you have radar and the ability to overlay it on a chart, assessing whether the chart is position-shifted from reality is easy enough. You can use that to compare the real position of land with the one on the chart. Of course, that doesn't give you any information about how old the soundings are, whether some are interpolated, etc.

[singlespeed]

For many passages from Monserrat to Guadeloupe in the Eastern Carribean, our RayMarine chart plotter had us sailing right through Redonda, despite upgrading the maps on each cycle. I never sail in unknown shallow waters at night, only in depths reported to be over 100'.

[Benz]

I think the advent of the GPS has exposed, or perhaps created, a lot of shortcomings in cartography that didn't matter when you didn't have the ability to pinpoint a set of coordinates on a graticule.
In the San Blas islands, for instance, to navigate by taking GPS coordinates off a chart can get you in trouble, which is why the current popular guide created routes through the coral using coordinates taken by the editor without regard to the existing charts. But to navigate by eye and compass bearings, the charts are perfectly acceptable, and I've gunkholed the entire length of the archipelago without relying on the GPS.
Likewise in Newfoundland, piloting by compass and eye, the charts from Captain Cook's surveys are perfectly usable, and better than the current issue Canadian Government ones, that leave soundings out of vast areas.
I certainly won't trust anything on a chartplotter until I'm persuaded that the charts have been updated by GPS surveys, so that the GPS and the chart are both using the same graticule.
We're a long way from all that just now, but progress is being made.

[CaptTom]

Originally Posted by Benz

...pinpoint a set of coordinates on a graticule...

...so that the GPS and the chart are both using the same graticule...

I learned a new word today! Thanks!

[davil]

Originally Posted by Benz

I think the advent of the GPS has exposed, or perhaps created, a lot of shortcomings in cartography that didn't matter when you didn't have the ability to pinpoint a set of coordinates on a graticule.
In the San Blas islands, for instance, to navigate by taking GPS coordinates off a chart can get you in trouble, which is why the current popular guide created routes through the coral using coordinates taken by the editor without regard to the existing charts. But to navigate by eye and compass bearings, the charts are perfectly acceptable, and I've gunkholed the entire length of the archipelago without relying on the GPS.
Likewise in Newfoundland, piloting by compass and eye, the charts from Captain Cook's surveys are perfectly usable, and better than the current issue Canadian Government ones, that leave soundings out of vast areas.
I certainly won't trust anything on a chartplotter until I'm persuaded that the charts have been updated by GPS surveys, so that the GPS and the chart are both using the same graticule.
We're a long way from all that just now, but progress is being made.

================================

Yes, I cruised the San Blas 1998 to 2000, and I remember there was a correction to be made to the charts.

If I remember correctly the difference was explained as the old charts were drafted by surveyors reading from sea level (smaller boats, ships, etc) and did not match the readings from a satellite reading down (GPS), made sense.

[RaymondR]

Originally Posted by CaptTom

I learned a new word today! Thanks!

You'll end up confused.

A graticule is how Cartesian coordinates are represented on a sphere.

A grid how they are on a flat plane. Land maps of relatively small areas, such as UTM system, are presented on a grid.

[requiem]

Originally Posted by Benz

I think the advent of the GPS has exposed, or perhaps created, a lot of shortcomings in cartography that didn't matter when you didn't have the ability to pinpoint a set of coordinates on a graticule.

In the San Blas islands, for instance, to navigate by taking GPS coordinates off a chart can get you in trouble, which is why the current popular guide created routes through the coral using coordinates taken by the editor without regard to the existing charts. But to navigate by eye and compass bearings, the charts are perfectly acceptable, and I've gunkholed the entire length of the archipelago without relying on the GPS.

I've seen it described as more a reversal; in the old days the charts would be considered more accurate and the ship's position uncertain. Now, the ship's position is considered more certain, and the charts less accurate.

E.g. for Captain Cook the ship's position error might be 10,000 meters, an island might be fixed to 1,000 meters, and now with GPS we can fix the ship to 10 meters.

I think moderns forget that for Cook, the charts could be considered quite accurate because once in sight of an island he would be using it as the reference rather than GPS.

[jo_sail]

I normally look for a A) good paper chart, which is at least based on official nautical chart information. And I amend this with B) most recent up to date infos on seamarks and points for special attention found in the OpenSeaMap and C) satellite images for additional coastal anchorage detail information, changing colors so, that in many areas you most easily recognize even small obstacles of less then 2 m depth.

I have quite bad experience with Navionics and OsmAnd depth information, less in vertical (30 m) but significant in horizontal offsets, 100 to 300 m in some examples in Kykladic islands. So I deeply mistrust such digital and all globe satellite based depth information.

I hope ongoing international hydrographic projects will improve this also in open access information during this decade.