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ICW charts get better ‘magenta line’

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The U.S. Office of Coast Survey announced in mid-January that future editions of nautical charts of the Intracoastal Waterway will be updated to include an improved “magenta line” that has historically aided navigation down the East Coast and around the Gulf Coast.



Additionally, Coast Survey will change the magenta line’s function, from the perceived “recommended route” established more than a hundred years ago, to an advisory directional guide that helps prevent boaters from going astray in the maze of channels that comprise the route.



The decision comes on the heels of a year’s investigation into problems with the magenta line. In early 2013, after receiving reports of groundings by boaters who followed the line into shoals, Coast Survey started to remove the magenta line from Intracoastal Waterway nautical charts.



“We cannot deliberately include chart features that we know may pose a danger to navigation,” explained Rear Admiral Gerd Glang, director of Coast Survey. “The problems of the magenta line’s misplacement, which had been developing over the past seven decades, were aggravated when some boaters assumed that the line indicated a precise route through safe water – although it actually went over land, shoals, or obstructions.”

The U.S. Coast and Geodetic Survey, a NOAA predecessor agency, first installed the line on nautical charts in 1912, when the advent of motor boating produced a demand for charts of the inland waters and shallower waters along the East Coast. The magenta line on Intracoastal Waterway charts received major updates in 1935, thanks to an influx of funding from the Great Depression’s Public Works Administration. Charts rarely recorded updates of the magenta line in the ensuing 70 years.



“Today’s decision to reinstate the magenta line is not a quick fix,” said Capt. Shep Smith, chief of Coast Survey’s Marine Chart Division. “It will take at least three years to fix problems that were 70 years in the making.”



When no depth soundings are on the chart, the line will generally be positioned in the centerline of dredged channels and natural waterways, avoiding shoals or obstructions less than the controlling depth. When the chart data is insufficient for determining the line’s preferred route, Coast Survey will attempt to gather additional data from partner agencies and reliable crowdsourcing.



“We need to hear from boaters who can provide hazard locations,” Capt. Smith said. “Over 200,000 boaters actively share information on ActiveCaptain, and their reports along the Intracoastal Waterway are particularly helpful for revising the ‘magenta line.'”



In cases where information is lacking and the line depiction can lead to risky navigation, Coast Survey will remove the line.

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