BDOC NSS Exam
Major Lights - Answer-a high intensity and reliable light exhibited from a fixed structure or marine site
Primary Major Light - Answer-Established for making landfall from sea
Secondary Major Light - Answer-Established at harbor entrances
Minor Lights - Answer-Low to moderate intensity light used to mark a specific channel or location
Two considerations for minor lights - Answer-o Care should be taken NOT to confuse minor lights with
lighted buoys
o Established in harbors, channels, rivers, and isolated locations
Sector Lights - Answer-o Red: Danger Areas
o Green: Turning Points or best water areas
o White: Good water
Buoy Shapes - Answer-Can, Nun, Pillar, Spar, Sphere
,Purpose of Buoys - Answer-Aids to navigation and used to mark
o Channels
o Shoals
o Obstructions
o Warn of Dangers
IALA A - Answer-Red port, Green Starboard when returing to harbor (Countries in Africa, Asia, Australia,
Europe)
IALA B - Answer-Green port, Red Starboard when returning to harbor (Countries like America, Japan,
Korea, and the Philippines)
Variation - Answer-The angular difference between the true meridian and the magnetic meridian
o True Bearing = Magnetic Bearing + Variation
Deviation - Answer-The deflection right or left of the magnetic meridian caused by magnetic properties
of the vessel
Gyrocompass Error - Answer-The difference between the true heading and gyrocompass heading.
Caused by: friction, ship's motion, electronic malfunction, and power fluctuations
Permenant Magnetism - Answer-The stable magnetic condition of the ship, created by construction and
materials used
Induced Magnetisim - Answer-Magnetism acquired by the ships placement in the earth's magnetic field
, Datum - Answer-The mathematical model of the earth used to calculate position coordinates, heights,
and distances
Datum used by US Navy - Answer-WGS 84 (World Geodetic System 1984)
Three segments of GPS - Answer-Control, User, Space
FOM - Answer-(Figure of Merit): An internal GPS receiver calculation that indicated the best accuracy
achievable from the satellites being tracked
Chart - Answer-Graphical representation of the spherical Earth
Two types of chart projection used by US Navy - Answer-Mercator and Gnomic
Advantages/Disadvatages of Mercator - Answer-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 - Answer-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:
Major Lights - Answer-a high intensity and reliable light exhibited from a fixed structure or marine site
Primary Major Light - Answer-Established for making landfall from sea
Secondary Major Light - Answer-Established at harbor entrances
Minor Lights - Answer-Low to moderate intensity light used to mark a specific channel or location
Two considerations for minor lights - Answer-o Care should be taken NOT to confuse minor lights with
lighted buoys
o Established in harbors, channels, rivers, and isolated locations
Sector Lights - Answer-o Red: Danger Areas
o Green: Turning Points or best water areas
o White: Good water
Buoy Shapes - Answer-Can, Nun, Pillar, Spar, Sphere
,Purpose of Buoys - Answer-Aids to navigation and used to mark
o Channels
o Shoals
o Obstructions
o Warn of Dangers
IALA A - Answer-Red port, Green Starboard when returing to harbor (Countries in Africa, Asia, Australia,
Europe)
IALA B - Answer-Green port, Red Starboard when returning to harbor (Countries like America, Japan,
Korea, and the Philippines)
Variation - Answer-The angular difference between the true meridian and the magnetic meridian
o True Bearing = Magnetic Bearing + Variation
Deviation - Answer-The deflection right or left of the magnetic meridian caused by magnetic properties
of the vessel
Gyrocompass Error - Answer-The difference between the true heading and gyrocompass heading.
Caused by: friction, ship's motion, electronic malfunction, and power fluctuations
Permenant Magnetism - Answer-The stable magnetic condition of the ship, created by construction and
materials used
Induced Magnetisim - Answer-Magnetism acquired by the ships placement in the earth's magnetic field
, Datum - Answer-The mathematical model of the earth used to calculate position coordinates, heights,
and distances
Datum used by US Navy - Answer-WGS 84 (World Geodetic System 1984)
Three segments of GPS - Answer-Control, User, Space
FOM - Answer-(Figure of Merit): An internal GPS receiver calculation that indicated the best accuracy
achievable from the satellites being tracked
Chart - Answer-Graphical representation of the spherical Earth
Two types of chart projection used by US Navy - Answer-Mercator and Gnomic
Advantages/Disadvatages of Mercator - Answer-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 - Answer-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:
