NOAA charts with depth in meters?

[dmksails]

I was looking at some charts of the waters around Alaska, and came across something curious. Chart 500 shows depths in meters. Other charts, like 530 show depths in fathoms. Seems to be confusing. Anyone know why?

[Joh.Ghurt]

Have you checked when those were surveyed last? Those could be quite ancient charts.

[dmksails]

It was on the NOAA chart site online, so should be the lastest.

[dannc]

Originally Posted by dmksails

It was on the NOAA chart site online, so should be the lastest.

They might be the latest charts but that does not mean the survey itself, could have been done many decades ago. The survey date is on the chart.


Later,
Dan

[Dsanduril]

From the NOAA National Charting Plan:

Metrification of ENC and Raster Charts
The United States is one of only a few countries that routinely use traditional or “Imperial” units of measure, such as gallons, pounds, and feet. The first international hydrographic conference (convened in London in 1919) set in motion the establishment of the International Hydrographic Bureau. The conference passed a resolution that, "strongly recommended that all countries, as soon as convenient, adopt the metric system for their nautical publications." Since that time, nearly a century ago, the Coast Survey made one brief attempt to convert its nautical charts from feet and fathoms to meters in the early 1990s. The effort was abandoned after only a small number of charts were converted.

Coast Survey is now reinvestigating the feasibility of converting all depth values into meters on both ENC and raster charts. This will be a considerable effort, but much less onerous than it was 25 years ago. Now, all chart data is in digital format and new, more efficient computer tools are available. Having all chart formats use the same international units for depth will make chart production more efficient and use of NOAA charts less confusing for U.S. and foreign mariners transiting in and out of U.S. waters. Customers are reminded that they will still be able to choose to convert values to feet and fathoms in their navigation systems.

and

All but a handful of NOAA’s 1,000-plus raster nautical charts show depths in feet or fathoms; however, IHO ENC product specifications state that all depths must be encoded in meters. Therefore, when NOAA digitized paper charts in the 1990s to create the first U.S. ENCs, depth values for soundings, depth curves, and other features with depths were converted from fathoms or feet into meters to populate the ENC database.

I'm guessing 500 was one of those few 1990's conversions?

[dmksails]

That makes sense. I did a bit more digging and all the charts in meters have the title of International Chart Series.

[Bill Seal]

But the question remains, would Sam Clemens have been as famous if he had used the pen name Mark 3.6576?

[Benz]

I have some then-current Canadian charts from less than five years ago with depths in fathoms. They're still printing from older surveys with only the variation gauge and the title altered.

[Paul L]

In the area covered by those charts not only do you deal with meters, fathoms and feet, but the depth datum is different on the US charts vs the adjacent Canadian ones. MLLW and LNT.

[sv_pelagia]

Originally Posted by Benz

I have some then-current Canadian charts from less than five years ago with depths in fathoms. They're still printing from older surveys with only the variation gauge and the title altered.

All new charts are in metres. In many cases, when data from older surveys are used, fathoms are converted to metres.

All Cdn ENC charts in metres (which your software can convert to feet or fathoms).

[Cadence]

Originally Posted by dmksails

I was looking at some charts of the waters around Alaska, and came across something curious. Chart 500 shows depths in meters. Other charts, like 530 show depths in fathoms. Seems to be confusing. Anyone know why?

A 5-10$ hand held calculator would solve your problem. It is what it is as to the units used.

[skipper53]

Maybe all government charts and the electronic industry could agree on using cubits as the measurement standard....

[Cadence]

Originally Posted by skipper53

Maybe all government charts and the electronic industry could agree on using cubits as the measurement standard....

A great ides.

[Cool Hand Luke]

I gotta say... I was born in Europe, but for the life of me I cannot use meters in sailing. I love kts and nm and ft. Maybe because I was taught sailing in the USA. Actually, that's probably it. I'm used to miles and mph in my car, as well.

But, the metric system DOES make more sense

[Benz]

Originally Posted by sv_pelagia

All new charts are in metres. In many cases, when data from older surveys are used, fathoms are converted to metres.

All Cdn ENC charts in metres (which your software can convert to feet or fathoms).

Do you believe they've changed all their soundings on paper charts since >five years ago? Seems like a big job, given how many fathom charts there are around the Gulf of St. Lawrence.