Even when the Datum is correctly set in my
chartplotter, the
CMAP NT
charts for the Lesser Antilles have been off by as much as 1,000 feet. I contacted
CMAP about it and their response was that they made every effort to ensure accuracy, but their
charts are only as good as the input data, which in many cases comes from sources many, many years old, like Admiralty
charts from previous centuries. I had a similar problem with Imray Iolere
charts for the BVI, even after applying the required adjustments. Maybe they all use the same ultimate source data (Admiral Lord Nelson?).
Bottom
line: use
charts outside the U.S. with caution; verify by eyeball navigation.