CHART WORK Flashcards
What is a routing chart, what projection is it and how to read wind and current off of it?
A routing chart is used for planning ocean passages and are mercator projection. There are 12 seperate charts for each area, showing each month of the year.
The wind is indicated on the wind rose with the longer bar showing the most common wind direction and stregnth for that month.
To read the current, you look for the current lines and the speed of the current is indicated by the number value at the end, indicated in knots.
More information is found on the chart about stregnths
What is the difference between a mercator chart and a Gnomonic?
Mercator Chart:
Projection: Conformal cylindrical projection.
Distortion: It preserves angles and shapes accurately, especially near the equator, but it distorts sizes and distances, particularly toward the poles.
Use: Well-suited for navigation because straight lines on the Mercator chart represent lines of constant compass bearing or rhumb lines, making it easy to plot a course.
Gnomonic Chart:
Projection: Azimuthal (planar) projection.
Distortion: It accurately represents great circles as straight lines but distorts other features, such as shapes, distances, and areas, especially away from the center point.
Use: Particularly useful for planning and navigating along great circle routes, which are the shortest distance between two points on a globe. It’s commonly used for long-distance air and sea travel.
In summary, while both Mercator and Gnomonic charts are used in navigation, the Mercator chart is advantageous for plotting rhumb lines and maintaining shape accuracy, while the Gnomonic chart is preferred for plotting great circle routes.
How do we do Great circle sailing and rhumb line sailing?
Great Circle Sailing:
Definition: A great circle is the shortest path between two points on the surface of a sphere, such as the Earth. It represents the circumference of a circle whose center coincides with the center of the Earth.
Method: To sail a great circle route, navigators plot the great circle arc between the departure and destination points on a navigational chart. This route may not appear as a straight line on a Mercator projection chart but will be the shortest path.
Use: Great circle sailing is preferred for long-distance voyages, such as transoceanic crossings, where minimizing distance traveled is crucial for efficiency.
Rhumb Line Sailing:
Definition: A rhumb line (or loxodrome) is a line crossing all meridians of longitude at the same angle. On a Mercator projection chart, rhumb lines appear as straight lines and represent a constant compass bearing.
Method: To sail a rhumb line route, navigators plot a straight line between the departure and destination points on a Mercator chart, using a constant compass bearing (azimuth). This line will maintain the same direction throughout the voyage.
Use: Rhumb line sailing is useful for short to medium distances and when maintaining a constant compass course is desired, such as coastal navigation.
In summary, great circle sailing follows the shortest path on the Earth’s surface, while rhumb line sailing maintains a constant compass bearing, making it easier to navigate but potentially resulting in longer distances traveled compared to great circle routes.
SYMBOLS: random ones to note
foul grounds
cardinal marks
fishing grounds
pilot station
Radio reporting points
Tidal diamond - what to do with tidal diamond
When are cummulative NM’s printed?
The cumulative list of NTMs is published every six months (in January and July) to aid with the identification of outstanding NtMs and to provide an audit trail for chart and publication corrections.
Whats in the Annual NM summary?
The Annual Summary of NTMs is published annually (in January) and contains the Annual Statutory Notices to Mariners, a summary of the Temporary and Preliminary Notices still in force at the start of the year and a Cumulative Summary of Amendments to Sailing Directions. There are currently 26 annual notices.
Where can we find T’s and P’s?
Weekly NTMs
The cumulative list of NTMs
In the Annual Summary of Admiralty Notices to Mariners (NP 247).
Admiralty Information Overlay (AIO)
Modern way of updating charts?
QR Code scan on bottom of chart
How do we update charts?
For paper charts you can either scan the QR code on the bottom of the chart, or go to the UKHO website and select view update list by chart number. Then see what corrections have been completed on your chart, for ones not completed you can download and print them and apply the correction.
Alernativly, you can chack the cummulative NTMs then the subsequent weeks until you find where your chart is updated to.
For ECS charts you will normally be emailed your weekly updates via email or straight to software like NAVBOX where you plug in a USB into your computer, upload the updates to USB and then follow the updating procedure you can upload weekly updates to your ECDIS
