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A fathom line or fathom curve, a usually sinuous line on a nautical chart, joins all points having the same depth of water, thereby indicating the contour of the ocean floor. [24] Some extensive flat areas of the sea bottom with constant depth are known by their fathom number, like the Broad Fourteens or the Long Forties, both in the North Sea.
Fathom: Length: Knot: Speed: League: Length: Nautical mile: Length: Rhumb: Angle: The angle between two successive points of the thirty-two point compass (11 degrees 15 minutes) (rare) [1] Shackle: Length: Before 1949, 12.5 fathoms; later 15 fathoms. [2] Toise: Length: Toise was also used for measures of area and volume Twenty-foot equivalent ...
If the depth was at a mark he would call "by the mark" followed by the number, while if it was between two marks, he would call "by the deep" followed by the estimated number; thus "by the mark five", since there is a five-fathom mark, but "by the deep six", since there is no six-fathom mark.
On nautical charts, the top of the chart is always true north, rather than magnetic north, towards which a compass points. Most charts include a compass rose depicting the variation between magnetic and true north. However, the use of the Mercator projection has drawbacks. This projection shows the lines of longitude as parallel.
fathom: kalamos, akaina or dekapous κάλαμος, ἄκαινα, δεκάπους: 10 podes 3.08 m (10.1 ft) 10 feet hamma ἅμμα: 60 podes 18.5 m (20.2 yd) knot, link of a chain plethron: πλέθρον: 100 podes 30.8 m (33.7 yd) 100 feet stadion: στάδιον: 600 podes 184.9 m (202.2 yd) an eighth of a Roman mile diaulos ...
The General Bathymetric Chart of the Oceans (GEBCO) is a publicly available bathymetric chart of the world's oceans. The project was conceived with the aim of preparing a global series of charts showing the general shape of the seafloor. Over the years it has become a reference map of the bathymetry of the world's oceans for scientists and others.
Bathymetric surveys and charts are associated with the science of oceanography, particularly marine geology, and underwater engineering or other specialized purposes. Bathymetric map of Medicine Lake, California. Bathymetric data used to produce charts can also be converted to bathymetric profiles which are vertical sections through a feature.
These works are all in the public domain. Roger Morris, Hydrographer from 1985 to 1990, published Charts and Surveys in Peace and War 1919-1970, a further continuation of Memoirs. [8] A less formal account of British Naval Hydrography in the 19th-Century is given by Steve Ritchie, Hydrographer 1966–1971, in The Admiralty Chart. [5]