Admiralty chart

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An 1845 Admiralty Chart of the Houtman Abrolhos, Australia, surveyed from HMS Beagle

Admiralty charts are nautical charts issued by the United Kingdom Hydrographic Office[1] (UKHO) and subject to Crown Copyright. Over 3,500 Standard Nautical Charts (SNCs) and 14,000 Electronic Navigational Charts (ENCs) are available with the Admiralty portfolio offering the widest official coverage of international shipping routes and ports, in varying detail.

Admiralty charts have been produced by UKHO for over 200 years, with the primary aim of saving and protecting lives at sea. The core market for these charts includes over 40,000 defence and merchant ships globally. Today, their products are used by over 90% of ships trading internationally.

The scale of the charts can vary according to purpose; large-scale charts often cover approaches to harbours, such as Port Approach Guides, medium-scale charts often cover frequently used coastal areas, and small-scale charts are regularly used for navigation in more open areas. A series of small craft charts are also available at even smaller scales.

Admiralty charts include information on: depths (chart datum), coastline, buoyage, land and underwater contour lines, seabed composition, hazards, tidal information (indicated by "tidal diamonds"), prominent land features , traffic separation schemes radio direction finding (RDF) information, lights, and other information to assist in navigation.

Passage charts at smaller scales use the Mercator projection, so that bearings can be directly transferred between charts, although allowances for magnetic variation and magnetic deviation must be considered for accuracy The straight lines drawn on the Mercator projection represent lines of constant bearing; in reality, these lines are not straight but are segments of a three-dimensional “loxodromic” spiral, or rhumb line. In contrast, coastal charts use the transverse Mercator projection, in order to depict the shape of the shoreline with greater accuracy.

Admiralty charts are issued by the UKHO for a variety of users; Standard Nautical Charts (SNCs) are issued to mariners subject to the Safety of Life at Sea (SOLAS) convention , while chart folios, at a convenient A2 size, are produced for leisure users. Alongside its paper charts, UKHO produces an expanding range of digital products to fulfil the impending compulsory carriage requirements of ECDIS/ENCs, as issued by the International Maritime Organization (IMO).

The digital range comprises of Electronic Navigational Charts (ENCs) for use with an Electronic Chart Display and Information System (ECDIS), which can be displayed and interrogated through Admiralty Vector Chart Service (AVCS). The range also includes Admiralty Raster Chart Service (ARCS), which allows paper nautical charts to be viewed in raster form on an ECDIS.

Due to the changing nature of the seabed and other charted features, chart users’ information must be up-to-date to maintain accuracy and general safety. This is ensured by UKHO through continually assessing hydrographic data for vital safety information, with urgent updates issued via weekly Notices to Mariners (NMs)

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