Navigation & Charting Flashcards

On a nautical chart, what does a blue tint in shallow water areas indicate?

Answer: Water depth less than the chart datum sounding

Blue tinting on nautical charts indicates shallow water areas where depths are less than the charted datum, warning mariners of potential hazards.

What is the magnetic variation on a nautical chart?

Answer: The difference between true north and magnetic north due to Earth's magnetic field

Magnetic variation is the angular difference between true north (geographic) and magnetic north caused by the Earth's magnetic field, shown on a chart's compass rose.

When plotting a running fix, what is the minimum number of LOPs required?

Answer: One LOP advanced to a second bearing

A running fix uses one LOP advanced along the course line to intersect a second LOP taken later, accounting for the vessel's movement between observations.

A light characterized as 'Fl (3) 15s' means the light:

Answer: Shows 3 flashes in a group, with the full cycle lasting 15 seconds

Fl (3) 15s indicates a flashing light that shows a group of 3 flashes, with the complete cycle (flashes plus eclipse) totaling 15 seconds.

What does the abbreviation 'PA' on a nautical chart signify?

Answer: Position approximate

PA (Position Approximate) on a chart indicates that the plotted position of an object or feature is not precisely determined and should be treated with caution.

Which of the following correctly describes a 'cocked hat' in celestial navigation?

Answer: A small triangle formed when three LOPs do not meet at a single point

A cocked hat is the small triangle formed when three lines of position fail to intersect at a single point, indicating observational or plotting errors.

On a NOAA nautical chart, a number printed in italics within the water area represents:

Answer: A depth in feet below chart datum

Italic numbers on NOAA nautical charts represent water depths (soundings) in feet or meters below chart datum, typically mean lower low water (MLLW).