Observe and identify
Foundation level, about 3 min. Chart reading.
The situation
The chart shows a drying rock with an underlined height of 0.8 m. The authored water level is 1.4 m above chart datum. Read the glyph and height; you cannot rely on the rock being visible.
What is the water depth above the rock at this water level?
- 0.6 m; the rock is covered
- 0.8 m above the surface
- 2.2 m; add the two numbers
Answers and explanations
Lookout: A drying height is above chart datum. Subtract it from the water level.
The sound answer
0.6 m; the rock is covered
There is 0.6 m of water over the rock. Your 1.8 m draught cannot clear it; a covered drying feature can be harder to see.
Why the other options fall short
0.8 m above the surface
The underline refers to height above chart datum, not above the current water surface.
2.2 m; add the two numbers
A drying height lies above datum. Subtract it from water level, rather than adding it as a sounding.
Chart 1 · drying features and datum
Drying heights are above chart datum. Present water depth above a drying feature equals water level above datum minus its drying height.