From en.wikipedia.org:
[Unit of length] [the unit of length] {{Infobox unit | name = fathom | image =
Regensburg - Altes Rathaus - Masse - 2016.jpg | caption = Standard units in
Regensburg: the metal rods are (from left to right) a fathom (_klafter_), foot
(_schuch_, Modern German _Schuh_ "shoe") and ell (_öln_, Modern German
_Elle_). | standard = imperial/US units | quantity = length | units1 =
imperial/US units | inunits1 = [6] | units2 = SI unit equivalent | inunits2 =
[6] }} A FATHOM is a unit of length in the imperial and the U.S. customary
systems equal to [6], used especially for measuring the depth of water.<ref
name=britannica11/> The fathom is neither an international standard (SI) unit,
nor an internationally accepted non-SI unit. Historically it was the maritime
measure of depth in the English-speaking world but, apart from within the US,
charts now use metres.
There are two yards (6 feet) in an imperial fathom.<ref
name=britannica11>[wstitle=Fathom ] Originally the span of a man's
outstretched arms, the size of a fathom has 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].
[Etymology]
** Etymology
The term (pronounced [']) derives (via Middle English _fathme_) from the Old
English _fæðm_, which is cognate with the Danish word _favn_ and means
"embracing arms" or "pair of outstretched arms". It is maybe also cognate
with the Old High German word "fadum", which has the same meaning and also
means "yarn (originally stretching between the outstretched fingertips)".<ref
name=oed>_Oxford English Dictionary_, second edition, 1989;[1][2][3][4]
** Forms
[Greek]<!--linked-->
*** Ancient fathoms
The Ancient Greek measure known as the ORGUIA ([grc], _orgyiá_,
<small>[lit].</small>[nbsp]"outstretched") is usually translated as
"fathom".[5] By the Byzantine period, this unit came in two forms: a "simple
orguia" ([grc], _haplē orguiá_) roughly equivalent to the old Greek fathom (6
Byzantine feet, [1.87][nbsp]m) and an "imperial" ([grc], _basilikē_) or
"geometric orguia" ([grc], _geōmetrikē orguiá_) that was one-eighth longer (6
feet and a span, [2.10][nbsp]m).[6][7]
*** International fathom
One international fathom is equal to:
- 1.8288 metre s exactly (Official international definition of the fathom) [8]
*** British fathom
The British Admiralty defined a fathom to be a thousandth of an imperial
nautical mile (which was 6080 ft) or [6.08]. In practice the "warship fathom"
of exactly [6] was used in Britain and the United States.<ref name=Fenna/> No
conflict between the definitions existed in practice,[date=July 2023] since
depths on imperial nautical charts were indicated in feet if less than [30]
and in fathoms for depths greater than that. Until the 19th century in
England, the length of the fathom was more variable: from [5] feet on merchant
vessels to either [5] on fishing vessels (from [5+1/2]).<ref name=Fenna>Fenna
(2000: 88-89)
*** Other definitions
Other definitions of fathom include:
- 1.828804 m (Obsolete measurement of the fathom based on the US survey foot , only for use of historical and legacy applications) [9]
- 2 yard s exactly
- 18 hands
One metre is about 0.5468 fathoms.
In the international yard and pound agreement of 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. In 1959
United States kept the US survey foot as definition for the fathom.
In October 2019, the U.S. National Geodetic Survey and the National Institute
of Standards and Technology announced their joint intent to retire the U.S.
survey foot, with effect from the end of 2022. The fathom in U.S. Customary
units is thereafter defined based on the International 1959 foot, giving the
length of the fathom as exactly 1.8288 metres in the United States as
well.[10][11]
** Derived units
At one time, a _quarter_ meant one-quarter of a fathom.[date=December 2024]
A _cable length_, based on the length of a ship's cable, has been variously
reckoned as equal to 100 or 120 fathoms.[date=December 2024]
** Use of the fathom
*** Water depth
{{Annotated image | image = Macclesfield Bank 1920 nautical chart.jpg |
image-width = 1500 | image-left = -600 | image-top = -500 | width = 300 |
height = 250 | float = right | annotations = <!-- empty or not, this must be
included --> | caption = Excerpt of a 1920 map centred at [16], a notable
focal bank of the South China Sea, with depths in whole fathoms only. The
Hydrographic Office highlights hazardous depth shallows (shoals) with dashed
lines.[12] Click for broader map and to enable varied magnification. }} Most
modern nautical charts indicate depth in metres. However, the U.S.
Hydrographic Office uses feet and fathoms.[13] A nautical chart will always
explicitly indicate the units of depth used.[14]
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.[15] 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_.[16] The area offshore beyond the 100 fathom line, too deep to
be fathomed by a hand sounding line, was referred to as _out of soundings_ or
_off soundings_.[17] A _deep-sea lead_, the heaviest of sounding leads, was
used in water exceeding 100 fathoms in depth.[18]
This technique has been superseded by sonic depth finders for measuring
mechanically the depth of water beneath a ship, one version of which is the
_Fathometer_ (trademark).[19] The record made by such a device is a
_fathogram_.[20] 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.[21]
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.
*** Line length
The components of a commercial fisherman's setline were measured in fathoms.
The rope called a _groundline_, used to form the main line of a setline, was
usually provided in bundles of 300 fathoms. A single [50] 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] 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]. 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.[22] A _kite_ was a drag, towed under water
at any depth up to about [40], which upon 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].[23]
A _shackle_, a length of cable or chain equal to [12+1/2].[24] In 1949, the
British navy redefined the shackle to be [15].<ref
name=Jerrard1986>[last1=Jerrard]
The Finnish fathom (_syli_) is occasionally used: [1000] nautical mile or
[100] cable length.
*** Burial
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_" as meaning to discard, or dispose of.[25]
The phrase is echoed in Shakespeare's _The Tempest_, where Ariel tells
Ferdinand, "Full fathom five thy father lies".
*** 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.[26] Miners also use it as a
unit of area equal to 6 feet square (3.34 m<sup>2</sup>) in the plane of a
vein.<ref name=oed/> In Britain, it can mean the quantity of wood in a pile of
any length measuring [6] square in cross section.<ref name=oed/> In Central
Europe, the klafter was the corresponding unit of comparable length, as was
the toise in France. In Hungary the square fathom ("négyszögöl") is still in
use as an unofficial measure of land area, primarily for small lots suitable
for construction.[date=September 2016]
** See also
[colwidth=22em]
- Ancient Greek units of measurement
- Anthropic units
- Bathymetry
- English units
- Hvat
- Imperial units
- International System of Units
- Klafter
- Sounding line
- Toise
- United States customary units
[div col end]
** References
*** Citations
[30em]
*** Bibliography
- [ last=Fenna ] .
** External links
[Wiktionary]
- An explanation of the fathom marks used at sea (see http://www.navyandmarine.org/planspatterns/soundingline.htm) (retrieved Sept 2005).
- Hungarian web page that refers to the length of a "bécsi öl" (see https://web.archive.org/web/20060901101317/http://nyuz.elte.hu/archiv13/szam4/mondok1.htm)
[Imperial units]
Category:Human-based units of measurement Category:Nautical terminology
Category:Units of length Category:Customary units of measurement in the United
States