MONTH/YEAR: June 2020
NAME/RANK: ECDIS Datums and Bridge Air Clearance
THEME: Stellios Andreas, 2nd Officer
Stellios Andreas searched the applicable datums in ECDIS, the sounding datum, the horizontal datum referring to the common geodetic system (WGS84), and the vertical datum which was finally the idea that fired up a discussion during a Passage Planning with ECDIS seminar.
The WGS84 datum has been revised six times since its original realization in 1987. The most recent version is WGS84 (G2139) implemented on 3 January 2021 and aligned to the International GNSS Service. On the other hand, depths shown on charts are the least depths to be expected under average conditions. Since the chart datum is generally a computed mean or average height at some state of the tide, the depth of water at any particular moment may be less than shown on the chart. For example, if the chart datum is MLLW, the depth of water at lower low water will be less than the charted depth as often as it is greater.