Chartwork Flashcards
What is the Principle of a Mercator projection?
Rhumb lines are straight lines
Great circles are curved
Used for normal navigation
Land features are distorted N/S
Parallels of longitude equally spaced
What is the Principle of a Transverse Mercator projection?
Used for Large scale charts, Harbour plans
Drawn as Mercator but turned through 90 degrees
Parallels of Latitude are evenly spaced
Longitude is not evenly spaced, land distorted E/W
Distance measured on the bottom scale
What is the Principle of a Gnomic projection?
Used for Ocean passage planning, and Polar Charts
Parallels of latitude are curved, Parallels of Longitude converge at the Poles
Great circles are straight lines, Rhumb lines are curved
What is a Rhumb line?
A line which cuts all the meridians at the same angle
What is a Great Circle?
On any sphere, the shortest distance between any two points is the circumference of the circle which joins them and whose centre is at the centre of the sphere.
Procedure for plotting great circles from Gnomic charts, onto Mercator charts
Draw a rhumb line from point to point on Gnomic chart
Plot waypoints, (every 15 degrees matches time zone change)
Transfer waypoints to Mercator projection
Draw rhumb lines between waypoints
Composite Track
If a vessel needs to limit their passage northwards due to weather, she may ‘cut out’ a portion of the plotted great circle on a Mercator projection, and head E/W until the waypoint at which the track is again heading South.
How to correct charts and publications
- Look up current Cumulative list to check the latest edition against the date of the chart
- Check for corrections that apply to the chart, listed in the cumulative list
- Check weekly Notices to Mariners published since the Cumulative list, for any more recent corrections and any new editions
- Look at bottom left hand corner of the chart and see which corrections have or have not been applied
- Apply correction, using stencils, magenta pen, T’s n P’s in pencil.
- Annotate in bottom left hand corner
- Record in NP133A
What is NP133A
Paper chart maintenance record log
What is a Temporary notice?
A notice for a given period of time, to be updated on a chart. I.e wreck etc
What is a Preliminary Notice?
Something that WILL SOON be there, I.e Breakwall being built
We do we get chart corrections from?
From a chart agent, or online
What are the Contents of the Weekly Notice to Mariners, In order?
I Explanatory Notes, Publications List
II Admiralty Notices to Mariners, Updates to standard Nautical Charts
III Reprints of NAVAREA I navigational warnings
IV Updates to Admiralty sailing directions
V Updates to Admiralty. List of Lights and Fog Signals
VI Updates to Admiralty List of Radio signals
VII Updates to misc. Admiralty Nautical Publications
VIII Updates to Admiralty Digital Services
Light description on a chart
Class of light
Colour of light
Period Time from beginning to end of sequence
Elevation of light above MHWS
Nominal Range
What does ‘nominal range’ mean?
The luminous range of a light in a homogeneous atmosphere in which the meteorological visibility is 10 nautical Miles
