BDOC NSS Exam Questions With Proper
Answers
Major Lights CORRECT ANSWERS a high intensity and reliable light exhibited from a
fixed structure or marine site
Primary Major Light CORRECT ANSWERS Established for making landfall from sea
Secondary Major Light CORRECT ANSWERS Established at harbor entrances
Minor Lights CORRECT ANSWERS Low to moderate intensity light used to mark a
specific channel or location
Two considerations for minor lights CORRECT ANSWERS o Care should be taken
NOT to confuse minor lights with lighted buoys
o Established in harbors, channels, rivers, and isolated locations
Sector Lights CORRECT ANSWERS o Red: Danger Areas
o Green: Turning Points or best water areas
o White: Good water
Buoy Shapes CORRECT ANSWERS Can, Nun, Pillar, Spar, Sphere
Purpose of Buoys CORRECT ANSWERS Aids to navigation and used to mark
o Channels
o Shoals
o Obstructions
o Warn of Dangers
IALA A CORRECT ANSWERS Red port, Green Starboard when returing to harbor
(Countries in Africa, Asia, Australia, Europe)
IALA B CORRECT ANSWERS Green port, Red Starboard when returning to harbor
(Countries like America, Japan, Korea, and the Philippines)
Variation CORRECT ANSWERS The angular difference between the true meridian and
the magnetic meridian
o True Bearing = Magnetic Bearing + Variation
Deviation CORRECT ANSWERS The deflection right or left of the magnetic meridian
caused by magnetic properties of the vessel
, Gyrocompass Error CORRECT ANSWERS The difference between the true heading
and gyrocompass heading. Caused by: friction, ship's motion, electronic malfunction,
and power fluctuations
Permenant Magnetism CORRECT ANSWERS The stable magnetic condition of the
ship, created by construction and materials used
Induced Magnetisim CORRECT ANSWERS Magnetism acquired by the ships
placement in the earth's magnetic field
Datum CORRECT ANSWERS The mathematical model of the earth used to calculate
position coordinates, heights, and distances
Datum used by US Navy CORRECT ANSWERS WGS 84 (World Geodetic System
1984)
Three segments of GPS CORRECT ANSWERS Control, User, Space
FOM CORRECT ANSWERS (Figure of Merit): An internal GPS receiver calculation that
indicated the best accuracy achievable from the satellites being tracked
Chart CORRECT ANSWERS Graphical representation of the spherical Earth
Two types of chart projection used by US Navy CORRECT ANSWERS Mercator and
Gnomic
Advantages/Disadvatages of Mercator CORRECT ANSWERS o Advantages:
Rhumb lines plot as straight lines
Provides for easy measuring of distance, direction, and position
Latitude and Longitude draw as straight lines and their correct angular relationships are
maintained
o Disadvantages:
Great circles plot as curves
There may be minor distortion of features at extreme latitudes
Advantages/Disadvantages of Gnomic CORRECT ANSWERS o Advantages:
Great circles plot as straight lines on a gnomic projection, which are ideal for long
transoceanic voyages
Distortion on a gnomic chart is tolerable within 1000 nm of the point of tangency
o Disadvantages:
Rhumb lines plot as curved lines on a gnomic projection and do not plot direction or
measure distances easily on the chart
True shapes of the earth are not represented
Great Circle CORRECT ANSWERS The intersection of a sphere and a plane through
its center (Meridians and the equator)
Answers
Major Lights CORRECT ANSWERS a high intensity and reliable light exhibited from a
fixed structure or marine site
Primary Major Light CORRECT ANSWERS Established for making landfall from sea
Secondary Major Light CORRECT ANSWERS Established at harbor entrances
Minor Lights CORRECT ANSWERS Low to moderate intensity light used to mark a
specific channel or location
Two considerations for minor lights CORRECT ANSWERS o Care should be taken
NOT to confuse minor lights with lighted buoys
o Established in harbors, channels, rivers, and isolated locations
Sector Lights CORRECT ANSWERS o Red: Danger Areas
o Green: Turning Points or best water areas
o White: Good water
Buoy Shapes CORRECT ANSWERS Can, Nun, Pillar, Spar, Sphere
Purpose of Buoys CORRECT ANSWERS Aids to navigation and used to mark
o Channels
o Shoals
o Obstructions
o Warn of Dangers
IALA A CORRECT ANSWERS Red port, Green Starboard when returing to harbor
(Countries in Africa, Asia, Australia, Europe)
IALA B CORRECT ANSWERS Green port, Red Starboard when returning to harbor
(Countries like America, Japan, Korea, and the Philippines)
Variation CORRECT ANSWERS The angular difference between the true meridian and
the magnetic meridian
o True Bearing = Magnetic Bearing + Variation
Deviation CORRECT ANSWERS The deflection right or left of the magnetic meridian
caused by magnetic properties of the vessel
, Gyrocompass Error CORRECT ANSWERS The difference between the true heading
and gyrocompass heading. Caused by: friction, ship's motion, electronic malfunction,
and power fluctuations
Permenant Magnetism CORRECT ANSWERS The stable magnetic condition of the
ship, created by construction and materials used
Induced Magnetisim CORRECT ANSWERS Magnetism acquired by the ships
placement in the earth's magnetic field
Datum CORRECT ANSWERS The mathematical model of the earth used to calculate
position coordinates, heights, and distances
Datum used by US Navy CORRECT ANSWERS WGS 84 (World Geodetic System
1984)
Three segments of GPS CORRECT ANSWERS Control, User, Space
FOM CORRECT ANSWERS (Figure of Merit): An internal GPS receiver calculation that
indicated the best accuracy achievable from the satellites being tracked
Chart CORRECT ANSWERS Graphical representation of the spherical Earth
Two types of chart projection used by US Navy CORRECT ANSWERS Mercator and
Gnomic
Advantages/Disadvatages of Mercator CORRECT ANSWERS o Advantages:
Rhumb lines plot as straight lines
Provides for easy measuring of distance, direction, and position
Latitude and Longitude draw as straight lines and their correct angular relationships are
maintained
o Disadvantages:
Great circles plot as curves
There may be minor distortion of features at extreme latitudes
Advantages/Disadvantages of Gnomic CORRECT ANSWERS o Advantages:
Great circles plot as straight lines on a gnomic projection, which are ideal for long
transoceanic voyages
Distortion on a gnomic chart is tolerable within 1000 nm of the point of tangency
o Disadvantages:
Rhumb lines plot as curved lines on a gnomic projection and do not plot direction or
measure distances easily on the chart
True shapes of the earth are not represented
Great Circle CORRECT ANSWERS The intersection of a sphere and a plane through
its center (Meridians and the equator)
