A nautical chart is a map specially prepared for navigation that provides information such as the type of seabed (rock, sand or other…), danger zones, depth of the sea or beacons, among others. They can also be found under the name of maritime charts, navigational charts or simply charts. There are different types of nautical charts that are divided into two main groups, which are used for navigation.
Types of navigational charts
The charts used for navigation are the following:
Used for loxodromic navigation. The Mercator projection is named after Mercado, who developed it. This maritime navigation chart is based on a cylinder, in which the meridians are shown as parallel and equidistant lines. The parallels also appear as straight lines, but in their case, the distance increases as they move away from the equator.
This is an azimuthal projection whose point of perspective is the earth. It consists of great circles as straight lines, regardless of their orientation. This is a very useful projection for navigation, as the larger circles point to the shortest distance routes.
Classification of nautical charts according to their scale
According to their scale, there are also different types of navigational charts: general or oceanic charts, medium coastal charts, coastal charts, approaches charts and portolan charts. The characteristics of each of these are described here:
They cover a great area of coastline and sea and are mainly used in ocean navigation. Their scale ranges from 1/30,000,000 to 1/3,000,000.
Medium coastal charts
These charts are used for medium-sized routes. In terms of scale, they are between 1/3.000.000 and 1/200.000.
Coastal navigation charts
As their name suggests, they are necessary for navigating by surveying the coastline. They have a scale between 1/200.000 and 1/50.000.
Aproaches (landfall navigation)
These navigational charts are intended to help navigators to approach harbours and other geographical features, and to avoid accidents. Their scale is 1/25,000.
Coastal They have a scale of less than 1/25,000 and are used to show in detail a small area of coastline and sea.
In this case the scale has a value of 1/50,000 or even higher. Due to the high accuracy required for navigation, they are only used for reference and rarely for position determination. They are used for navigable rivers with pilotage areas.
Importance of nautical charts
Anyone who has ever been at the helm of a ship knows that this document is of vital importance. It is a map detailing water areas, lines and coastal ports. It also provides valuable information on the depth of the waters in which the vessel is located, restricted areas, recommended routes or obstructions.
The main purpose of the different types of nautical charts is to provide up-to-date information to avoid collisions, grounding or navigating in restricted areas. This allows both the vessel itself and other vessels to navigate safely.
Among the valuable information it contains, a few points can be highlighted:
Marks on land and sea.
Maritime radio, radionavigation and radiodetermination stations.
It is worth noting that, for some time now, most navigators find it quite cumbersome to use a conventional chart and have to make calculations with instruments such as a compass, pencil or parallel rules.
This is why electronic charts are increasingly being used. It plays a very important role because of the speed it offers when certain aspects of navigation need to be consulted.
Nowadays, both formats coexist side by side. Vector or scanned charts are available in digital format. Many navigators ask themselves whether the paper or digital version is more convenient. In order to assess this aspect correctly, it is necessary to take into account some factors:
If a ship’s master has the appropriate local knowledge.
Whether the ship is equipped with an adequate electronic chart display and information system and back-up computers, among others.
The most relevant issue in order to ensure safe operation has to do with how electronic information is used. The most important thing is to see a specific area on the right scale.
It should be noted that there are two types of electronic charts: Raster Navigational Chart and vector Electronic Navigational Chart. Raster charts are based on a scanned image of another chart that was originally produced on paper. Vector charts are digitally processed based on objects such as points, lines or areas.
One of the requirements to be able to comply with the obligation to have nautical charts on board is that they must have been published by a public organisation. Any other type of chart is not official and is usually referred to as a commercial chart.
Raster or scanned charts are digital copies of official charts and have been reproduced based on official international standards. Therefore, their content is endorsed by a governmental organisation and periodically revised with official data.
The electronic navigational chart, on the other hand, is created at the request of a governmental institution or hydrographic service. Any other vector data will not be taken into consideration as they are not of an official nature and do not comply with the mandatory requirements for navigational charts.
In short, it is clear that the different types of nautical charts are of immense help for navigation due to the great precision of the places that are represented on them. In Suisca we are official distributors of Admiralty nautical charts in Spain, published by UKHO for several years. Thanks to the use of nautical charts, not only is it possible to have a great knowledge of the area being navigated, but also to avoid accidents on the boat or with other boats. For this reason, they are also an indispensable element for the safety of the crew.
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