Chart Navigation & Plotting · Tides — Charted Depth
Charted depths (soundings) on a U.S. chart are referenced to:
- AMean high water
- BMean sea level
- CMean lower low water (the sounding datum)✓ Correct
- DThe highest astronomical tide
Explanation
U.S. nautical chart soundings use mean lower low water (MLLW) as the datum, so actual depth = charted depth + height of tide. Vertical clearances under bridges are instead referenced to mean high water.
Authority: NOAA charts; Chart No. 1
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