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Fathom
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A fathom is a unit of length in the Imperial system (and the derived U.S. customary units), used especially for measuring the depth of water.
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 5½ 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.
A brass was a unit of length equal to a fathom.
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Encyclopedia
A fathom is a unit of length in the Imperial system (and the derived U.S. customary units), used especially for measuring the depth of water.
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 5½ 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.
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.
International fathom
One fathom is equal to:
- 1.8288 metres (1 metre is about 0.5468 fathoms)
- 2 yards (1 yard is exactly 0.5 fathoms)
- 6 feet (1 foot is about 0.1667 fathoms)
- 18 hands
- 72 inches
In 1959 the United States, Australia, Canada, New Zealand, South Africa, and the United Kingdom defined the length of the international yard to be exactly 0.9144 metre. With the adoption of the metric SI system the use of fathoms declined.
British fathom
The British Admiralty defined a fathom to be a thousandth of an imperial nautical mile (which was 6080 ft) or 6.08 feet. In practice the fathom was always regarded as exactly 6 feet. No conflict in the real world existed as depths on Imperial nautical charts were indicated in feet if less than 30 feet and in fathoms for depths above that.
Use of the fathom
Water depth
Most nautical charts produced by hydrographic offices worldwide, with the notable except of those produced by the U.S. Hydrographic Office, which uses feet and fathoms, now indicate depths in metres. Nevertheless, most English-speaking mariners are familiar with the unit. A nautical chart will always explicitly indicate the units of depth used.
To measure the depth of shallow waters, boatmen used a sounding line containing fathom points, some marked and others in between, called deeps, unmarked but estimated by the user. Water near the coast and not too deep to be fathomed by a hand sounding line was referred to as in soundings or on soundings. The area offshore beyond the 100 fathom line, too deep to be fathomed by a hand sounding line, was referred to as offsoundings or out of soundings. A deep-sea lead, the heaviest of sounding leads, was used in water exceeding 100 fathoms in depth.
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.
Line length
The components of a commercial fisherman’s setline were measured in fathoms. The rope called groundline, used to form the main line of a setline, was usually provided in bundles of 300 fathoms. A single 50-fathom skein of this rope was referred to as a line. Especially in Pacific coast fisheries the setline was composed of units called skates, each consisting of several hundred fathoms of groundline, with gangions and hooks attached. A tuck seine or tuck net about 70 fathoms long and very deep in the middle was used to take fish from a larger seine.
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.
Burial
It is customary, when burying the dead, to inter the corpse at a fathom's depth, or six feet under. A burial at sea (where the body is weighted to force it to the bottom) requires a minimum of six fathoms of water. This is the origin of the phrase to deep six, meaning to discard, or dispose of.
On land
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.
Other fathoms and similar units of length
Units of length similar to the size of the fathom can be found in many cultures. Some are listed below.
| Culture | Name | Length in metres |
|---|
| Croatian | hvat | 1.896484 | | Czech | sáh | 1.7928 | | Danish | favn | 1.883124 | | Dutch | vadem, vaam | 1.883679 | | Estonian | süld | 2.1336 | | Finnish | syli | n/a | | French | toise (circa 1150), brasse (1409) | ~1.949 | | German | Klafter, Faden = 6 Fuß | n/a resp. 1.7 | | Ancient Greek | orguia | 1.8542 | | Hungarian | öl | 1.8964838 (Viennese) | | India (State of Manipur) | Sana lamjel | n/a | | Italian | braccio | ~1.65 | | Japanese | hiro | ~1.818 | | Maltese | qasba | ~2.096 | | Norwegian | favn | 1.882 | | Polish | sazen | 1.728 | | Portuguese | braça | 2.2 | | Russian | morskaya sazhen (??????? ??????) | 1.852 | | Turkish | kulaç | 1.83 | | Sanskrit | vyama | n/a | | Serbian | ???? | n/a | | Slovak | siaha | n/a | | Spanish | braza | 1.6718 | | Swedish | famn | 1.7814 |
See also
External links
- (retrieved Sept 2005).
- 1911 Encyclopedia Britannica - Free Online.
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