ENC vs RNC and no more RNC

[transmitterdan]

As the sage philosopher Mick Jagger said:
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You can't always get what you want
But if you try sometime
You'll find
You get what you need
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[Dsanduril]

One of the things I appreciate about ENCs, and one of the easiest things for a new user to adjust are the shallow, safety, and deep contours. With RNCs we're at the mercy of the mapmaker and 5, 10, and 20 fathoms are not really critical to me. I can float in 1 meter, consider 2 meters quite safe, and 10 meters is "deep". Using the Caesar Creek example from earlier (just because Snore brought it up) the default mapping on an ENC shows everything as being "shallow" blue. But if I adjust for 1/2/10 meters suddenly I can clearly see the channel that is suitable for my vessel. I really appreciate just this simple feature of ENCs. Since it is all still based on ancient surveys and the contours are drawn by algorithm you have to practice responsible navigation, but the same is true regardless of ENC/RNC.

[ranger58sb]

Just recently we went out for fuel, and the destination dock is in a known-to-be-shallow area. I used the lastest NOAA raster charts on our plotter going in and out, worked OK, but we saw some surprisingly low readings... more inline with the AquaMap vector charts we used as backup.

Afterwards, I checked NOAA, iSailor, and AquaMap vector charts more closely, and all three showed soundings 1 foot less deep than the NOAA raster chart for the same area.

The three soundings I needed most were 7, 6, and 6' for the best route in according to the raster chart, and the same soundings were 6, 5, and 5' on the three vector charts.

-Chris

[bcn]

What do the meta data of the charts tell about updates included - "last edited"...?

[requiem]

Originally Posted by bcn

What do the meta data of the charts tell about updates included - "last edited"...?

Both quality and date are good.

Here's a table that explains how the quality of the survey impacts soundings and positions on charts:
https://www.admiralty.co.uk/Admiralt...OC%20Table.pdf

A chart saying 6', even with an accurate modern survey, really means 6' ± x'.

[svspirited]

Originally Posted by Dsanduril

ENCs can be quite nice, but there is definitely a learning curve when moving from RNCs, and there are still odd things that the computer just doesn't get quite right. And there is also some information that is disappearing compared with RNCs, I will miss some of the land information that is simply no longer present.

Agreed, the loss of land detail makes it more difficult to verify your chart position with traditional navigation techniques. That bit is unfortunate but the ability to customize the ENC to your vessel and navigation needs is very powerful and once you learn how to tweak them you will likely never go back to raster charts. Also worth noting is the ability to change the color scheme for low light situations, far superior to the red filter or super dim lighting that you get with raster charts. I know for navigating at night the various dark modes save my eyes a lot of strain.

[transmitterdan]

Charted depths are in relation to a specified tidal condition (e.g. mean low water). Compare the specified condition of each chart before you compare the depth numbers.

[transmitterdan]

Some “recreational” chart vendors have been known to subtract an offset from NOAA depths. They don’t admit it but they get fewer complaints if they fudge the depth values down some. More people complain about grounding than those who complain about waters actually being deeper than charted.

[ranger58sb]

Originally Posted by transmitterdan

Charted depths are in relation to a specified tidal condition (e.g. mean low water). Compare the specified condition of each chart before you compare the depth numbers.

Originally Posted by transmitterdan

Some “recreational” chart vendors have been known to subtract an offset from NOAA depths. They don’t admit it but they get fewer complaints if they fudge the depth values down some. More people complain about grounding than those who complain about waters actually being deeper than charted.

My look at the area charts included a direct comparison of NOAA to NOAA charts. And they're also both the latest "generation" of charts in each format that I could get for our plotter (happened to be circa May 2019 for each).

Perhaps Transas (now Wartsila) and AquaMap did that fudge thing, but I'd have thought NOAA soundings are NOAA soundings, without regard to chart format.

-Chris

[Coquina]

I have AquaMap on my phone and one of their claims to fame is downloading survey data as it becomes available, so their depth might be a lot newer than some NOAA products and NOAA RNC and ENC probably don't update on the same schedule either.

[Coquina]

Back to the original question - I have used various types of vector products dating back to when C-Map was monochrome on a green CRT. I have no issue with the concept at all.

I have only used RNC on OpenCPN and was a bit surprised at how bad an ENC could look when adjusted wrong. I have a template now I like and I will probably switch over. Apparently we will all have to do so at some point, like it or not.

[bcn]

Originally Posted by Coquina

I have AquaMap on my phone and one of their claims to fame is downloading survey data as it becomes available.

How do the surveys get available?
When the relevant Hydrographical Service - for example NOAA - releases new charts.
We are not aware of surveys from official bodies that are out there for simple licensing. And not getting reflected in the official charts.


The release cycles for updates of ENC and RNC are very often different, indeed. As today all the chart work is digital, new data get into the data bases and ENCs are generated from that. RNC require additional editing work. That's why the HOs tend to get rid of them.

[ranger58sb]

Originally Posted by Coquina

I have AquaMap on my phone and one of their claims to fame is downloading survey data as it becomes available, so their depth might be a lot newer than some NOAA products and NOAA RNC and ENC probably don't update on the same schedule either.

Yes. In the area I posted about, Aqua Map doesn't have any USACE survey overlays just now. So the comparison was latest NOAA raster to latest NOAA, AquaMap, and iSailor vector charts and to a slightly older Plan2Nav (C-Map) vector chart.

Originally Posted by bcn

How do the surveys get available?
When the relevant Hydrographical Service - for example NOAA - releases new charts.
We are not aware of surveys from official bodies that are out there for simple licensing. And not getting reflected in the official charts.

No clue how AQ gets the USACE survey maps, but they're quite obvious in the chart display. Chart grid updates happen often, but I can't tell whether an update is from a new survey or from some other update within a given AQ chart grid.

-Chris

[bcn]

We don't make a follow up for the US ENCs but we see for the weekly updates of the oeSENC sources weeks with 5-10% of the charts with releases by some Hydrographic Office.


That's why I tend to smile when some commercial chart provider talk about "thousands of updates each week". Sure easily, if you count the objects that come in by new editions or updates...

[bdbcat]

Coquina...


And will you share your nicer ENC template, or screenshot of the settings page? Perhaps it will find its way into the next release as default....


Dave