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Nautical time divides the globe into 24 nautical time zones with hourly clock offsets, spaced at 15 degrees by longitudinal coordinate, with no political deviation. Nautical timekeeping dates back to the early 20th century as a standard way to keep time at sea, although it largely only applied to military fleets pre–World War 2.
Green is used for drying (intertidal) areas, and magenta to indicate lights and beacons. Thus the chart coloration gave a clear indication to users as to whether they were using a chart with depths in fathoms or feet. While depths and heights were in metres, the nautical mile continued to be an international standard. Derived from the length of ...
Since the length of a nautical mile, for practical purposes, is equivalent to about a minute of latitude, a distance in nautical miles on a chart can easily be measured by using dividers and the latitude scales on the sides of the chart. Recent British Admiralty charts have a latitude scale down the middle to make this even easier. [10]
The times on the table are related to the high water of the standard port displayed on the table. To calculate the rate at an intermediate tide between neap and spring, interpolation is required. Traditionally this has been done using a "calculation of rates" chart. [3]
Such designations can be ambiguous; for example, "CST" can mean China Standard Time (UTC+08:00), Cuba Standard Time (UTC−05:00), and (North American) Central Standard Time (UTC−06:00), and it is also a widely used variant of ACST (Australian Central Standard Time, UTC+9:30). Such designations predate both ISO 8601 and the internet era; in ...
The 15° gore that is offset from GMT or UT1 (not UTC) by twelve hours is bisected by the nautical date line into two 7.5° gores that differ from GMT by ±12 hours. In reality nautical time zones are used only for radio communication etc. Internally on the ship, e.g. for work and meal hours, the ship may use a suitable time of its own choosing.
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.
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