Coastal Navigation & Chart Work Flashcards

A depth contour line labelled '10' on an Admiralty chart means:

Answer: All points on this line have a depth of 10 metres at chart datum

Depth contours connect points of equal depth referenced to chart datum (CD), which is typically the lowest astronomical tide (LAT).

What is meant by 'chart datum' (CD) on UK Admiralty charts?

Answer: Approximately the level of the Lowest Astronomical Tide (LAT)

Chart datum on UK Admiralty charts is set at approximately LAT (Lowest Astronomical Tide) — the lowest level the sea is predicted to reach under average meteorological conditions.

A mariner takes a single compass bearing of 040°C on a lighthouse. Variation is 4°W and deviation is 0°. The true bearing of the lighthouse FROM the vessel is:

Answer: 036°T

Compass to True: apply deviation (0) → 040°M; apply variation (W means subtract to go to True) → 040 − 4 = 036°T. The vessel lies on the reciprocal (216°T) from the lighthouse.

On a chart, a blue circle with 'PA' next to a depth sounding means:

Answer: Position Approximate — the sounding position is not precise

PA stands for Position Approximate, indicating that the sounding or feature has been placed on the chart with limited positional accuracy.

What does 'set' mean in the context of tidal stream?

Answer: The direction toward which the tidal stream flows, expressed as a true bearing

Set is the direction the tidal stream is flowing toward (e.g., 090° set means the stream is flowing eastward). Rate is the speed of that stream in knots.

A pilot book states a waypoint should be kept to port. What does this mean for a vessel proceeding on passage?

Answer: The waypoint (hazard or mark) should be on the vessel's port (left) side as she passes

'Keep to port' means the mark or hazard should be on the left side of the vessel when passing. This is standard pilotage language.