For a navigating officer on board a merchant vessel, the most essential and fundamental tool is the Nautical Charts. It is the soul of safe and effective navigation of a vessel all around the world. The art of planning a passage and stay on the course, fixing the ship’s position graphically, laying a safe course to destination, and checking the ship’s position whilst on, the course to ensure the vessel’s safe arrival to the destination is only possible because of the nautical charts. Navigational/Nautical charts are mostly drawn on Mercator’s projection, which ensures that each and every meridian and parallels of latitude appears to be straight lines, at right angles to each other and all angles on the earth’s surface are equal to that particular angles drawn on the chart. A pecularity of this projection is that rhumb lines are represented as straight line. The Hydrographic Department of the British Admiralty (UKHO) issues charts for almost all the parts of the world. This task has now become easier because the Admiralty gets the necessary information from the Hydrographic Departments of the countries, which are responsible for the publication of the charts for the waters under their jurisdiction. After the chart is published, it must be kept up-to-date by assimilating any changes or corrections, which may have occurred subsequently. These corrections and changes in chart are issued as “Notices to Mariners” by the Hydrographic Departments.
Chart Folio is an arrangement by which charts are kept onboard a ship. The charts may be kept as per Admiralty Chart Folio for Indian Chart Folio Publication. In the ship’s bridge, the charts are kept according to various areas of the world on the other hand in some ships these are kept as per the increasing chart number. By keeping it in order it becomes easier for the navigator to take out the chart as required at that time.
What are four types of nautical charts?
Navigational charts may be generally classified into four categories:
These charts are prepared on a very small scale, covering large portions of the Earth’s surface e.g. Pacific Ocean, Indian Ocean, and the Atlantic Ocean. In these charts, only the outstanding coastal features and important ports, etc. are shown. These charts are used for planning and executing long voyages across the oceans and are not at all suitable for coastal navigation.
These are medium-scale charts that covers just a segment or a piece of the coast. They show all the aids to navigation e.g. lights (their characteristics), Radio & D.F. beacons, important navigation marks including off-lying rocks, and other dangers. Such charts are used when the ship is being navigated along the coast. Coastal charts thus highlight the features on and along the coast and the adjoining portions of the seas.
These charts are drawn on a very large scale and each plan covers only a small or congested area e.g. ENGLISH CHANNEL, MALACCA, and SINGAPORE STRAIT. They contain all the information required when navigating a ship in harbors, enclosed waters. Every possible information of use to a navigator is shown in great detail and it helps in preparing the Passage Plan through these congested waterways. The scale of these plans enables the mariner to plot his position with great accuracy and thus avoid the dangers.
Some special types
- LORAN-C CHARTS: used in vessels with Loran-C Navigational equipment.
- DECCA CHARTS: used in vessels with Decca Navigational equipment.
- ROUTEING CHARTS: published for North and South Atlantic, North and South Pacific, Indian Ocean. Each region has twelve charts, as per every month which assists in planning passage, as it depicts usual routes, distances, wind and weather, air and sea temperatures, ocean currents, load line zones, etc.
- OCEAN SOUNDING CHARTS (OSC)
- TIME ZONE CHARTS
- LOADLINE ZONE CHARTS
- TIDAL STREAM ATLASES
- CO-TIDAL AND CO-RANGE CHARTS
- MAGNETIC VARIATION CHARTS
- INSTRUCTIONAL CHARTS: used for practice and examination purpose only.
- SHIP’S BOAT CHARTS
- ELECTRONIC NAVIGATION CHARTS (ENC): it’s the database, standardized as to content, structure, and format, issued for use with ECDIS. It contains all the chart info necessary for safe and effective navigation and may contain supplementary info in addition to that contained in the paper chart assisting navigation.
What are Nautical Charts used for?
Onboard ship nautical charts play a vital role in safe and effective navigation, it illustrates and portrays all the conditions and circumstances that a vessel will be confronting in her voyage. For a navigator in a merchant vessel, Nautical Charts are the most essential part of their daily navigating operations.
Numerous dangers to navigation such as grounding, severe storms, collisions, etc. can be avoided. Thus effective navigation saves time and expense, making a promising amount of profits for the owners and companies. As the dangers are predicted and avoided way beforehand this reduces the chances of cargo damage and increasing the outturn. Therefore, Nautical Charts are helping for both safeties of personnel, cargo, and the vessel itself.
Parts of Nautical Charts
- TITLE OF THE CHART
The title of each chart is printed in some convenient, prominent place on a chart, where it does not hinder the navigational use of it. Under the title, the information about projection, cautions, lights, scale, datum, Admiralties to be used, etc are shown.
- NATURAL SCALE
It is the ratio of the distance on the map to the correlative distance on the ground. The numerator of the fraction is usually unity, and both the lengths i.e. on the earth and that on the chart must be in the same units. e.g. 1:25,000 means a feature of 25,000 cm on length on the earth appears to be a length of 1 cm on the chart.
- NUMBER OF THE CHART
This is shown at the bottom right-hand corner and the top left-hand corner, outside the margin. Each and every chart has a serial number assigned to it.
- DATE OF PUBLICATION
The date of publication along with the name of the Hydrographer of the Admiralty or Government authority is printed outside the margin in the bottom middle.
- DATE OF PRINTING
It is printed at the top right-hand corner, outside the margin.
- SOUNDINGS AND THE CHART DATUM
The units used for Soundings are clearly shown below the “Title” of the chart and the sounding number denotes the water below the chart datum and it is considered one of the most important features of the Nautical Chart.
- COMPASS ROSE
It is used to display the orientation of the cardinal directions to take calculate bearings.
- TIDE TABLE
These are printed at a convenient place where it does not hinder the navigational use of the nautical chart.
- SOURCE DATA
It is a scaled replica of the nautical chart, which shows the entire, sub-sections of the coverage, dates, scales, show areas of shallow banks or routing measures, to assist in relating the sources to the chart and authority for various types of source material used. The Electronic Navigation Charts do not have ‘source data’, instead have a “category of zones of confidence (CATZOC)”, which gives an estimate of the reliability of source data.
How to read Nautical Charts?
It is shown under the title of the chart and distance can be measured between two points on a map using the longitudinal scale.
The depth note under the title shows the unit of measurement that is used to indicate the depths on the chart e.g. ‘SOUNDINGS IN METERS or IN FEET & FATHOMS. Sounding in fathoms and feet indicates that soundings are in fathoms with a subscript in feet. The larger number indicates fathoms, and the small number indicates feet, similarly sounding in meters indicates that the soundings are in meters and decimeters.
We can convert between meters, feet, and fathoms by using the depth conversion table provided on the chart. The depths indicated on the chart are all based on Chart Datum. This could be the Mean Lower Low Water, or the Mean Low Water, or another tidal datum. To avoid grounding you have to take into consideration the height of the tide and the tidal range.
- CONTOUR LINES
This particular line joins all the areas on the chart having an equal amount of sounding.
- COLOUR CODES
Beige/Tan color indicates Land
White color indicates Deep Waters
Light Blue color indicates Shallow Waters
The green color indicates that the land is covered with water during high tide but exposed in low tide.
- USE OF COMPASS ROSE
Positions can be plot on a nautical charts by taking bearings from a terrestrial or a celestial body and the bearings can be plotted on the chart using the compass rose. The magnetic field over the Earth changes over time, magnetic compass or an updated map becomes necessary to make use of the compass rose.
- NAVIGATIONAL GUIDES
Soundings, depths in fairways and areas, depth contours, types of the seabed and intertidal areas, extremities of TSS, location of buoys, beacons, lighthouse, extremities of land, Pilot Boarding Points, Reporting Points, Anchorage Berth, etc. Dangers including rocks, wrecks, and any obstructions to the navigation.
- CHART CATALOGUE
It is a book that contains details of all charts and publications used in the navigation on board ship we keep admiralty chart catalogue NP 131. It is published at the beginning of every year any correction related to the catalogue published via the weekly notice to Mariner and every time a change is made an entry is to be done on the inner page of the front cover it is used to select the chart. On the selected pages of the charts- the scale of the chart, edition, date, remarks is given. Chart Catalogue also gives information regarding ENC.
- ADMIRALTIES PUBLICATIONS
Additional information can be taken from the publications such as Adm. List of Light and Fog Signal, Adm. List of Radio Signals, Mariners Handbook, and Guide to Port Entry, etc. which are mandatory to be carried onboard.
Nautical Charts Symbols
Abbreviations used for the nature of the Sea bed–
Sand – S
Soft- so Hard- h
Symbols of electronic chart display and information system-