Chart Work

Question 2

What publication explains chart symbols?

Answer 2

Admiralty Chart 5011 – Chart Symbols & Abbreviations.

Question 3

Why check notes/warnings on charts?

Answer 3

They contain critical safety information & datum corrections.

Question 4

What datum do GPS & modern charts use?

Answer 4

WGS84 (World Geodetic System 1984).

Question 5

What projection is used for standard navigation charts?

Answer 5

Mercator Projection – rhumb lines straight, great circles curved.

Question 6

What are the limitations of Mercator projection?

Answer 6

Distortion increases away from equator; distance must be measured at chart’s latitude.

Question 7

Where is Transverse Mercator used?

Answer 7

Large-scale charts like harbour plans.

Question 8

Where is Gnomonic projection used?

Answer 8

Ocean passage planning – great circles appear as straight lines.

Question 9

Why is Great Circle shortest?

Answer 9

It’s the arc of a circle centered at Earth’s core.

Question 10

Why not sail directly on Great Circle?

Answer 10

Requires constant course changes → impractical.

Question 11

How is Great Circle sailing applied in practice?

Answer 11

Plotted on Gnomonic → transferred to Mercator as series of rhumb lines.

Question 12

What is a composite track?

Answer 12

Great Circle modified to avoid high latitudes or land → joins GC arcs via limiting parallel.

Question 13

Steps to correct charts/publications?

Answer 13

Check latest Cumulative List.

Apply Weekly Notices to Mariners (NMs).

Use blocks or pencil (T&P notices).

Replace with New Editions (NE) if required.

Question 14

Types of Notices to Mariners?

Answer 14

Permanent, Temporary, Preliminary.

Local NMs (harbour authority).

New Charts / New Editions.

Question 15

Example: Fl(3) WRG 15s 21m 15–11M – decode?

Answer 15

Group Flashing, 3 flashes.

White/Red/Green sectors.

Period 15 sec.

Elevation 21m.

Range: White 15M, Green 11M, Red 11–15M.

Question 16

Difference between Geographical, Luminous & Nominal range?

Answer 16

Geographical – limited by Earth’s curvature/height of eye.

Luminous – limited by light intensity & visibility.

Nominal – luminous range at 10M visibility.

Question 17

What is Variation?

Answer 17

Angle between true north & magnetic north.

Question 18

What is Deviation?

Answer 18

Error from ship’s own magnetic field → differs with heading.

Question 19

Acronym for applying variation/deviation?

Answer 19

“True Virgins Make Dull Companions At Weddings – Add whisky.”

Question 20

What is Aid to Navigation?

Answer 20

External device/structure to assist navigation.

Question 21

What is a Topmark?

Answer 21

Distinctive shape on buoy/beacon for ID.

Question 22

What is a Lateral Mark?

Answer 22

Defines channel sides.

Question 23

What is a Cardinal Mark?

Answer 23

Danger shown relative to cardinal points.

Question 24

What is a Clearing Bearing/Mark?

Answer 24

Transit line/bearing showing vessel is clear of danger.

Question 25

What is a Sector Light?

Answer 25

Different colours in defined bearings.

Question 26

What are Leading Line/Range Lights?

Answer 26

Transit line guiding safe channel.

Question 27

What publication explains all chart symbols and abbreviations?

Answer 27

Admiralty Chart 5011.

Question 28

What chart datum is commonly used today with GPS?

Answer 28

WGS84 (World Geodetic System 1984).

Question 29

Why must chart notes and warnings always be checked?

Answer 29

They contain critical information on hazards, datums, T&Ps, and limitations.

Question 30

What is the main projection used in navigation charts?

Answer 30

Mercator Projection.

Question 31

What are the limitations of Mercator projection?

Answer 31

Distortion increases with latitude; distances must be measured at the correct latitude.

Question 32

What projection is used for ocean passage planning?

Answer 32

Gnomonic projection (great circles appear straight).

Question 33

Where is Transverse Mercator projection used?

Answer 33

Large-scale harbour and coastal charts.

Question 34

Why is a Great Circle the shortest distance?

Answer 34

It is the arc of a circle with Earth’s centre as radius.

Question 35

Why don’t ships follow a Great Circle track exactly?

Answer 35

Requires constant course changes; impractical.

Question 36

What is a composite track?

Answer 36

A modified Great Circle avoiding high latitudes/land, joined with rhumb lines.

Question 37

How are Admiralty charts kept up to date?

Answer 37

Weekly Notices to Mariners, Cumulative List, Blocks, New Editions.

Question 38

What are the 3 types of Notices to Mariners?

Answer 38

Permanent, Temporary, Preliminary.

Question 39

What are Local Notices to Mariners?

Answer 39

Updates from local harbour or port authorities.

Question 40

Decode: Fl(3) WRG 15s 21m 15–11M.

Answer 40

Group Flashing 3; White/Red/Green sectors; 15s period; 21m height; range W=15M, G=11M, R=11–15M.

Question 41

What is the difference between Nominal, Luminous, and Geographical range?

Answer 41

Nominal: Range at 10M visibility. Luminous: Based on light intensity & actual visibility. Geographical: Limited by Earth’s curvature & height of eye.

Question 42

What is a sector light used for?

Answer 42

To indicate safe channel limits (different colours for bearings).

Question 43

What is a leading line or range lights?

Answer 43

Two lights in transit giving a safe bearing.

Question 44

Define Variation and Deviation.

Answer 44

Variation = True vs Magnetic north. Deviation = Compass error from ship’s magnetism.

Question 45

How do you remember whether to add or subtract Variation/Deviation?

Answer 45

“True Virgins Make Dull Companions At Weddings – Add West.”

Question 46

What is Compass Error?

Answer 46

Total of Variation + Deviation (east/west corrected by signs).