There are 2 yards (6 feet) in a fathom. Based on the distance between the fingertips of a man's outstretched arms, its size varied slightly depending on whether it was defined as a thousandth of an (Admiralty) nautical mile or as a multiple of the imperial yard. Formerly, the term was used for any of several units of length varying around 5 and 5 1/2 feet.
The name derives from the Old English word fæðm meaning embracing arms or a pair of outstretched arms. In Middle English it was fathme, cognate to the Latin patēre to be open, pandere to spread or unfold, and the Greek petannynai to spread out. Hence its earlier meaning, now obsolete: a full stretch of the arms in a straight line, and consequently grasp or reach.
A brass was a unit of length equal to a fathom. A cable length, based on the length of a ship's cable, has been variously reckoned as equal to 100 or 120 fathoms. At one time, a quarter meant a fourth of a fathom.
Abbreviations: f, fath, fm, fth, fthm.
In 1954 the United States and countries of the Commonwealth of Nations defined the length of the international yard to be exactly 0.9144 metres. With the adoption of the metric SI system the use of fathoms declined.
Until early in the 20th century, it was the unit used to measure the depth of mines (mineral extraction) in the United Kingdom. Miners also use it as a unit of area equal to 6 square feet in the plane of a vein. In Britain, it can mean the quantity of wood in a pile of any length measuring 6 feet square in cross section.
Historically, though, the fathom has been used to define depths and layers of the sea and lengths of line (rope).
This technique has been superseded by sonic depth finders for measuring mechanically the depth of water beneath a ship, one version of which is a is the Fathometer (trademark). The record made by such a device is a fathogram. 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.
The fauna and flora of the sea bottom between 100 and 500 fathoms are the mesobenthos. One denizen of this region is the oilfish (Ruvettus pretiosus), which lives at a depth of from 100 to 400 fathoms in the Mediterranean, middle Atlantic and throughout the southern seas.
The deeper parts of the ocean, especially between 100 and 1000 fathoms, are the bathyal zone or bathyal district — the slope from the continental shelf at 100 fathoms to the abyssal zone at 1000 fathoms. One feature on the ocean bottom of this district is a dome, a rounded isolated elevation found at depths greater than 100 fathoms.
In the deep sea, the water has a depth of 1000 fathoms or more. In a deep, a generally long and narrow area in the ocean, the depth generally exceeds 3000 fathoms.
A waterproof watch, its movement enclosed in a case in which the openings for the winding and cover are sealed with gaskets, should be able to withstand pressures equal to several fathoms of submersion.
A line attached to a whaling harpoon was about 150 fathoms long. A forerunner — a piece of cloth tied on a ship's log line some fathoms from the outboard end — marked the limit of drift line. A kite was a drag, towed under water at any depth up to about 40 fathoms, that on striking bottom was upset and rose to the surface.
A shot, one of the forged lengths of chain joined by shackles to form an anchor cable, was usually 15 fathoms long.
|Culture||Name||Length in metres|
|French||toise (circa 1150), brasse (1409)||~1.949|
|German||Klafter, Faden = 6 Fuß||n/a resp. 1.7|
|India (State of Manipur)||Sana lamjel||n/a|
|Russian||morskaya sazhen (морская сажень)||1.852|