Choose a passage with enough water
Soundings, draught and clearance margin. Developing level, about 3 min. Chart reading. Chart 1 · soundings and contours.
The situation
The fictional chart shows a western bank sounding 0.6 m and an eastern passage sounding 4.2 m. Water level is +1.4 m above chart datum. Your draught is 1.8 m and this exercise requires a 0.5 m margin. These values are explicit exercise facts.
Which passage meets the stated clearance requirement?
- Take the eastern passage: 4.2 + 1.4 − 1.8 − 0.5 = 3.3 m remaining.
- Take the western bank: There is water above it.
- Continue between the soundings without checking: Assume the nearby number applies everywhere.
Answers and explanations
Lookout: Add the water level to charted depth, then subtract draught and the authored margin.
The sound answer
Take the eastern passage
The eastern passage meets the stated margin. The western bank has only 2.0 m actual depth, leaving 0.2 m under the keel and failing the exercise’s 0.5 m margin.
Why the other options fall short
Take the western bank
Water covering a bank does not establish clearance. Its actual depth is 2.0 m and leaves only 0.2 m under your keel.
Continue between the soundings without checking
A sounding describes its measured position. Use the surrounding depths and authored safe passage; a number nearby is not a depth guarantee.
Chart 1 · soundings and contours
Use depth relative to chart datum together with water level, draught and an appropriate margin. A sounding is not a guarantee of uniform depth across the surrounding water.