Navigation General · Chart Datums & Projections
Soundings on most U.S. nautical charts are referenced to which datum?
- AMean Higher High Water (MHHW)
- BMean Sea Level (MSL)
- CMean Lower Low Water (MLLW)✓ Correct
- DLowest Astronomical Tide (LAT)
Explanation
U.S. nautical charts use Mean Lower Low Water (MLLW) as the sounding datum, which represents an average of the lower of the two daily low-water levels. Using MLLW provides a conservative (shallower) reference so that actual depths are usually equal to or greater than charted values.
Authority: Chart No. 1, General Remarks
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