USCG Exam Practice · Chart symbols and abbreviations (Chart No. 1)
A chart shows a sounding unit of 'fathoms' in the title block. A mariner reads a sounding of '3' in a channel. What depth does this represent, and to what datum is it referenced?
- A3 feet, referenced to Mean High Water.
- B3 fathoms (18 feet), referenced to Mean Lower Low Water.✓ correct
- C3 metres, referenced to Mean Sea Level.
- D3 fathoms (18 feet), referenced to Mean Low Water.
Why B is correct
When the chart title states fathoms, each sounding unit equals 6 feet, so a sounding of 3 equals 18 feet. All US chart soundings are referenced to MLLW. The mariner must verify the unit in the chart title before plotting. Bowditch Ch. 4 §403.
Cited:Bowditch Ch. 4 §403
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