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Part of an early "new style" Admiralty chart, of Risavika in Norway, published in 1970. Depth in metres (and tenths of metres for depths less than 20m). Metrication of Admiralty charts began in 1967, and it was decided to synchronise this with the introduction of a new style of chart, with increased use of colour, which continues in use today.
Tidal diamonds are symbols on British admiralty charts and others [a] that indicate the direction and speed of tidal streams. The symbols consist of a letter of the ISO basic Latin alphabet in a rhombus, printed in purple ink. [b] On any particular chart each tidal diamond will have a unique letter starting from "A" and continuing ...
The chart uses symbols to provide pilotage information about the nature and position of features useful to navigators, such as sea bed information, sea mark, and landmarks. Some symbols describe the sea bed with information such as its depth, materials as well as possible navigational hazards such as shipwrecks.
A chart datum is the water level surface serving as origin of depths displayed on a nautical chart and for reporting and predicting tide heights. A chart datum is generally derived from some tidal phase, in which case it is also known as a tidal datum. [1] Common chart datums are lowest astronomical tide (LAT) [1] and mean lower low water (MLLW).
In the UK, the Admiralty issues 76 volumes covering the world and these are used frequently by most merchant ships. [8] In the US, the United States Coast Pilots is a nine-volume American navigation publication distributed yearly by the National Ocean Service. Its purpose is to supplement nautical charts of US waters.
(See chart to the right.) Combinations of these alphanumeric characters are assigned as codes for various standardized messages. For instance, the master of a ship may wish to communicate with another ship, where their own radio may not be working or the other ship's call sign is not known or the other ship may not be maintaining a radio watch.
Graphical and textual descriptions of navigational light sequences and colours are displayed on nautical charts and in Light Lists with the chart symbol for a lighthouse, lightvessel, buoy or sea mark with a light on it. Different lights use different colours, frequencies and light patterns, so mariners can identify which light they are seeing. [1]
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