CHARTWORK

Question 1

Correcting Charts

Answer 1

• Current Cumulative List. Check latest edition date against date of chart.
• Check for corrections that apply to the chart, listed in the Cumulative List.
• Check Weekly NtoMs published since the Cumulative List for subsequent corrections and new editions.
• Look at bottom left hand corner of the chart and see which corrections have or have not been applied to the chart.

Question 2

Correcting Publications

Answer 2

Annual Summary of NtoMs - Part 2.
then check any subsequent Weekly NtoMs.
Check and Record amendments in front of book.

Question 3

Explain a DR

Answer 3

Calculated rough position derived from the Vessel’s course and STW.

Shown on the chart with a small cross and time.

Question 4

Explain an EP

Answer 4

Most accurate position calculated using:
leeway,
current and or tide.

Shown on the chart as a triangle with time.

Question 5

Explain a Running Fix

Answer 5

1. EP from a random point on position line 1 (visual brg)
2. Transfer position line 1 through EP and position line 2. (double ended arrows)
3. Position is where the transferred line intersects the second position line.

Question 6

Geographical Range

Answer 6

MAX distance a light can be seen.
Determined by:
-height of eye
-height of structure
-curvature of the Earth

Question 7

Luminous Range

Answer 7

MAX distance a light can be seen.
Determined ONLY by:
- intensity of the light
- visibility at the time.
NO account of elevation, observer’s height of eye, or curvature of Earth.

Question 8

Nominal Range

Answer 8

Luminous range for a meteorological visibility of 10 miles.
Details of these ranges, and diagrams for use with them - Admiralty List of Lights.

Question 9

Chart Features

Answer 9

NP5011, used to be called Chart 5011.
Learn for Paper Charts and ECDIS.

Question 10

Explain Tidal Diamonds

Set and rate?

Answer 10

• SET. Direction that a given current or tidal stream is moving. (degrees)
• RATE. Velocity of the current or tidal stream (knots)

Question 11

Explain primary ports use of ATT

Question 12

Types of Chart Projections

Answer 12

Mercator
Transverse Mercator
Gnomonic

Question 13

Mercator

Answer 13

Rhumb Lines - straight lines.
Great Circles - curved.
Used for normal Nav.
Appropriate Lat scale for measuring.
Land distorted N and S.
Parallels of long equally spaced.

Question 14

Transverse Mercator

Answer 14

Used for large scale charts.
Mercator turned through 90 deg.
Parallels of Lat now equally spaced.
Parallels of long NOT equally spaced.
Land distorted E and W.
Distance measured on scale along bottom.

Question 15

Gnomonic

Answer 15

Used for Ocean Navigation PLANNING
Parallels of lat are curved
Parallels of long converge at poles.
Great Circles - straight
Rhumb lines - curved

Question 16

Great Circle

Answer 16

Great Circle:
Used for long ocean passages
Shortest distance between any 2 points on the Earth’s Sphere.

Question 17

Composite Track

Answer 17

Used when a great circle goes into unnecessarily high latitudes or passes over land.
Follows the course due East or West along the limiting latitude between the two great circle routes.

Question 18

Variation

What is it?

What is it affected by?

Answer 18

TVMDC

The angular difference between True North and Magnetic North.
Measured in degrees
Named E / W of True North.

Dependent on EARTHS MAGNETIC FIELD

Isogonal Chart / Compass Rose

Question 19

Deviation

What is it?

What is it affected by?

Answer 19

TVMDC

The angular difference between Magnetic North and Compass North.
Measured in degrees
Named E / W of Magnetic North.

Dependent on SHIPS HEADIING

Question 20

Rhumb Lines

Answer 20

A line which cuts all meridians at the same angle.

Question 21

Tides

Causes, effects and information source?

Answer 21

Gravitational pull of the Sun and moon.

Tides are the periodic vertical movements of the water on the Earth’s surface.
Tidal streams are the periodic movements of the water that result from the tides.

Height of Tide: vertical distance between the water level and chart datum.

ADMIRALTY Tide Tables and Tidal Stream Atlas. (ATT)

Question 22

What is a Sextant and its uses?

Answer 22

Tool to measure the angle between two objects.

• Vertical Sextant Angles
• Horizontal Sextant Angles
• Ocean Navigation

Question 23

Fixed Errors (SEXTANT)

Answer 23

Depends on the quality of the sextant:

-Graduation Error
When the graduations on the arc, micrometer and/or the screw thread are not cut accurately.

-Collimation Error
Telescope is not parallel with the plane of the instrument.

-Centring Error
Pivot of the Index Bar is not at the centre of the circle of which the arc forms a part.

-Optical errors (shade errors)
Shades are not optically flat.
AKA Prismatic Error

Question 24

Adjustable Errors (SEXTANT)

Answer 24

P S I

Perpendicularly Error
Index Mirror is not perpendicular to the plane of the instrument.

Side Error
Horizon mirror is not perpendicular with the plane of the instrument.

Index Error
Index and horizon mirrors are not parallel with each other when the arc is set to zero.

Question 25

Ways to find position

Answer 25

• 3 Point Fix
• Running Fix
• Dipping Height (norries)
• HSA (Sextant / Compass)
• VSA (Sextant + norries)
  -Contour lines (Echosounder) and visual bearing
  -3 RADAR ranges
  -RADAR Range and Bearing (VRM + EBL)
• GPS!

Question 26

How often to do a fix?

Answer 26

Often enough that the vessel does not come into danger between fixes.

This is dependent upon:
- Ships Speed (RULE 6!!)
- Proximity to Navigational Hazards

Question 27

Explain a VSA

Answer 27

Visual bearing, vertical sextant angle and height of object, adjust for HoT difference MHWS.

Norries Nautical Tables - “Range by VSA”

Question 28

Explain a HSA

Answer 28

The angular separation between three points is measured by using the sextant horizontally to give us the angle.

On a chart
Using a station pointer or a protractor.

Position is where the two position circles intersect.

Question 29

Explain Leeway

Answer 29

The sideways drift of a ship to leeward of the desired course.

Question 30

Explain CTS

Answer 30

When determining a course to steer, the tidal stream, current and the effect of wind/leeway must be predicted. Leeway is applied last.

From last known position, extend ground track past destination.
Apply tidal vector from the same last known position.
Using a pair of dividers or compass mark out the distance you will travel in one hour across the intended ground track, this could be before or after the destination.
Draw a line from the end of the tidal vector to the point the arc made on the ground track. This is the water track.
Work out the leeway to be applied, add or subtract it depending on the direction of the wind. Once you have this course to steer then convert to compass.