Nautical chart
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A nautical chart or hydrographic chart is a graphic representation of a
Data sources
Nautical charts are based on
Publication
Nautical charts are issued by power of the national hydrographic offices in many countries. These charts are considered "official" in contrast to those made by commercial publishers. Many hydrographic offices provide regular, sometimes weekly, manual updates of their charts through their sales agents. Individual hydrographic offices produce national chart series and international chart series. Coordinated by the International Hydrographic Organization, the international chart series is a worldwide system of charts ("INT" chart series), which is being developed with the goal of unifying as many chart systems as possible.
There are also commercially published charts, some of which may carry additional information of particular interest, e.g. for yacht skippers.
Chart correction
The nature of a waterway depicted by a chart may change, and artificial aids to navigation may be altered at short notice. Therefore, old or uncorrected charts should never be used for navigation. Every producer of nautical charts also provides a system to inform mariners of changes that affect the chart. In the United States, chart corrections and notifications of new editions are provided by various governmental agencies by way of
A good way to keep track of corrections is with a Chart and Publication Correction Record Card system. Using this system, the navigator does not immediately update every chart in the portfolio when a new Notice to Mariners arrives, instead creating a card for every chart and noting the correction on this card. When the time comes to use the chart, he pulls the chart and chart's card, and makes the indicated corrections on the chart. This system ensures that every chart is properly corrected prior to use. A prudent mariner should obtain a new chart if he has not kept track of corrections and his chart is more than several months old.
Various Digital Notices to Mariners systems are available on the market such as Digitrace, Voyager, or ChartCo, to correct British Admiralty charts as well as NOAA charts. These systems provide only vessel relevant corrections via e-mail or web downloads, reducing the time needed to sort out corrections for each chart. Tracings to assist corrections are provided at the same time.
The Canadian Coast Guard produces the Notice to Mariners publication which informs mariners of important navigational safety matters affecting Canadian Waters. This electronic publication is published on a monthly basis and can be downloaded from the Notices to Mariners (NOTMAR) Web site. The information in the Notice to Mariners is formatted to simplify the correction of paper charts and navigational publications.
Various and diverse methods exist for the correction of electronic navigational charts.
Limitations
In 1973 the cargo ship MV Muirfield (a merchant vessel named after
A similar incident involving a passenger ship occurred in 1992 when the
Map projection, positions, and bearings
Historically the first projection, invented by Marinus of Tyre ca. AD 100 according to Ptolemy, was what is now called equirectangular projection (historically called plane chart, plate carrée, Portuguese: carta plana quadrada). While it is very convenient for small seas like the Aegean, it is unsuitable for seas larger than Mediterranean or an open ocean, even though early explorers had to use it for want of a better.
The Mercator projection is now used on the vast majority of nautical charts. Since the Mercator projection is conformal, that is, bearings in the chart are identical to the corresponding angles in nature, courses plotted on the chart may be used directly as the course-to-steer at the helm.
The
Positions of places shown on the chart can be measured from the
A
However, the use of the Mercator projection has drawbacks. This projection shows the lines of longitude as parallel. On the real globe, the lines of longitude converge as they approach the north or south pole. This means that east–west distances are exaggerated at high latitudes. To keep the projection conformal, the projection increases the displayed distance between lines of latitude (north–south distances) in proportion; thus a square is shown as a square everywhere on the chart, but a square on the Arctic Circle appears much bigger than a square of the same size at the equator. In practical use, this is less of a problem than it sounds. One minute of latitude is, for practical purposes, a nautical mile. Distances in nautical miles can therefore be measured on the latitude gradations printed on the side of the chart.[6]
Electronic and paper charts
Conventional nautical charts are printed on large sheets of paper at a variety of scales. Mariners will generally carry many charts to provide sufficient detail for the areas they might need to visit. Electronic navigational charts, which use computer software and electronic databases to provide navigation information, can augment or in some cases replace paper charts, though many mariners carry paper charts as a backup in case the electronic charting system fails.
Details on a nautical chart
Many countries' hydrographic agencies publish a "Chart 1", which explains all of the symbols, terms and abbreviations used on charts that they produce for both domestic and international use. Each country starts with the base symbology specified in IHO standard INT 1, and is then permitted to add its own supplemental symbologies to its domestic charts, which are also explained in its version of Chart 1. Ships are typically required to carry copies of Chart 1 with their paper charts.
Labels
Nautical charts must be labeled with navigational and depth information. There are a few commercial software packages that do automatic label placement for any kind of map or chart. Modern systems render electronic charts consistent with the IHO S-52 specification, issued by the International Hydrographic Organization (IHO).[7]
Pilotage information
The chart uses symbols to provide
Colours distinguish between human-made features, dry land, sea bed that dries with the tide, and seabed that is permanently
Depths and heights
Depths which have been measured are indicated by the numbers shown on the chart. Depths on charts published in most parts of the world use metres. Older charts, as well as those published by the United States government, may use
Heights, e.g. a lighthouse, are generally given relative to
The use of HAT for heights and LAT for depths, means that the mariner can quickly look at the chart to ensure that they have sufficient clearance to pass any obstruction, though they may have to calculate height of tide to ensure their safety.
Tidal information
Tidal races and strong currents have special chart symbols. Tidal flow information may be shown on charts using tidal diamonds, indicating the speed and bearing of the tidal flow during each hour of the tidal cycle.
See also
- Aeronautical chart
- Automatic label placement
- Admiralty chart
- Bathymetric chart
- European Atlas of the Seas
- Nautical star
- Navigation room
- Portolan chart
- Dutch maritime cartography in the Age of Discovery(First printed atlas of nautical charts, 1584)
Further reading
- Calder, Nigel (2008). How to Read a Nautical Chart. McGraw-Hill Professional. ISBN 978-0-07-159287-1.
References
- ^ Calder, Nigel. How to Read a Navigational Chart: A Complete Guide to the Symbols, Abbreviations, and Data Displayed on Nautical Charts. International Marine/Ragged Mountain Press, 2002.
- ^ British Admiralty. The Mariner's Handbook. 1999 edition, page 23.
- ^ "Maritime Casualties 1999 And Before". The Cargo Letter. 2007. Retrieved August 25, 2018.
- ^ Marine Investigation Accident Branch (2007) Report Number 18/2007.
- ^ See, for example, NOAA 14860 - Lake Huron 1:500,000 and NOAA 14853 Detroit River 1:15,000.
- ^ Nautical charts on sailingissues.com
- ^ https://iho.int/uploads/user/pubs/standards/s-52/S-52%20Edition%206.1.1%20-%20June%202015.pdf [bare URL PDF]
External links
- The Medieval and Early Modern Nautical Chart: Birth, Evolution and Use, Lisbon-based ERC-funded academic project. They develop and maintain the MEDEA-CHART Database, a sophisticated search engine and aggregator of early nautical charts data.
- Online version of Chart No.1 with "Symbols, Abbreviations and Terms" used in nautical charts
- Portolan Chart of Gabriel de Vallseca, 1439
- The short film "Reading Charts (April 6, 1999)" is available for free viewing and download at the Internet Archive.
- Nautical charts available online (Nautical Free)
- Online Nautical Charts Viewer