CHARTWORK Flashcards
Correcting Charts
- 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.
Correcting Publications
Annual Summary of NtoMs - Part 2.
-latest edition + updates applied?
then check any subsequent Weekly NtoMs.
Check and Record amendments in front of book.
Explain a DR
+ How is it shown on a chart?
Calculated rough position derived from the Vessel’s course and STW.
Shown on the chart with a small cross and time.
Explain an EP
Most accurate position calculated using:
leeway,
current and or tide.
Shown on the chart as a triangle with time.
Explain a Running Fix
(6)
- Visual brg of charted object (note time and speed)
- Convert to True brg using compass error for the ships head.
- Run for a fixed amount of time + take 2nd brg of the same object and plot on chart.
- Using any start point on the 1st brg line and lay ships heading including leeway for the time period measured. Then add in the tidal vector to find an EP.
- The final stage is to transfer the first position line across to run thorough the EP and extend it till it crosses the second position line.
- The resultant position is a fix.
Geographical Range
MAX distance a light can be seen.
Determined by:
-height of eye
-height of structure
-curvature of the Earth
Luminous Range
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.
Nominal Range
+ where can you find this info?
Luminous range @ meteorological visibility of 10 miles.
Details of these ranges - Admiralty List of Lights.
Chart Features
NP5011, used to be called Chart 5011.
Learn for Paper Charts and ECDIS.
Explain Tidal Diamonds
Set and rate?
- SET. Direction that a given current or tidal stream is moving. (degrees)
- RATE. Velocity of the current or tidal stream (knots)
Explain primary ports use of ATT
The Admiralty Tide Tables
Part I: tidal predictions for Standard Ports. These are the tabulated predictions for the time and height of High and Low Water at the specific port.
Part II: time and height differences for predicting the tide at Secondary Ports.
Types of Chart Projections
Mercator
Transverse Mercator
Gnomonic
Mercator
(6)
- 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.
Transverse Mercator
(6)
- 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 as normal
Gnomonic
(5)
- Used for Ocean Navigation PLANNING
- Parallels of lat are curved
- Parallels of long converge at poles.
- Great Circles - straight
- Rhumb lines - curved
Great Circle
Great Circle:
Used for long ocean passages
Shortest distance between any 2 points on the Earth’s Sphere.
Composite Track
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.
Variation
What is it?
What is it affected by?
Where is the information shown?
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
Deviation
What is it?
What is it affected by?
TVMDC
The angular difference between Magnetic North and Compass North.
Measured in degrees
Named E / W of Magnetic North.
Dependent on SHIPS HEADIING
Rhumb Lines
A line which cuts all meridians at the same angle.
Explain
-Tides + its cause
-Tidal Streams
-HoT
Information sources?
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)
What is a Sextant and its uses?
(3)
Tool to measure the angle between two objects.
- Vertical Sextant Angles
- Horizontal Sextant Angles
- Ocean Navigation
GOCC
Fixed Errors (SEXTANT)
(4)
Depends on the quality of the sextant:
-Graduation Error
Graduations on the arc / micrometer / screw thread are not cut accurately.
-Collimation Error
Telescope not parallel with plane of the instrument.
-Centring Error
Pivot of the Index Bar is not at the centre of the circle.
-Optical errors (shade errors)
Shades are not optically flat.
AKA Prismatic Error
P S I
Adjustable Errors (SEXTANT)
P S I
Perpendicularity 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.
