Certainly one of the questions most commonly asked by passengers on the vessels I work on is "How deep is it here?" For most of them, it is simply a matter of curiosity, but for the mariner knowing how much water is "under the keel" is essential for safe navigation.
Full fathom five thy Father lies,
Of his bones are Corrall made:
Those are pearles that were his eies,
Nothing of him that doth fade,
But doth suffer a Sea-change
Into something rich & strange
Sea-Nymphs hourly ring his knell.
Harke now I heare them, ding-dong, bell.