How accurate are nautical charts?

Some of the data on NOAA charts dates back 150 years with some from Captain Cooks voyage in 1778. A given chart might have data that dates back to 1890 with the depths taken with a lead line and positions by a sextant while other areas of the chart the depths are from a full-coverage shallow-water multibeam echo sounder taken in the last few years. NOAA is starting to indicate on charts when the position and depth data was taken and the expected accuracy,  knowing that parts of a chart might have horizontal accuracy worse than +/- 1,600 feet lets a mariner better understand the limits of the chart. (NOAA has been showing the date the depth was last surveyed on many charts for several years)

Hats off to NOAA for adding yet another tool to the navigators toolbox.

Charts will provide more information on “zone of confidence”

It is a major challenge – some might say an impossibility – to keep all thousand U.S. nautical charts up to date. But exactly how out of date is the chart data? Chart users will get a better idea now that Coast Survey is gradually rolling out a new chart feature called the zone of confidence, or “ZOC” box. It will replace the source diagram that is currently on large-scale charts. Source diagrams, and now the improved ZOC, help mariners assess hydrographic survey data and the associated level of risk to navigate in a particular area.

The first charts to show the new ZOC box are 18622, 18682, 18754, and 11328. They were released on April 7.

Both source diagrams and ZOC diagrams consist of a graphic representation of the extents of hydrographic surveys within the chart…

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