Editing Fathom

{{short description|Unit of length}}
{{About|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 (unit)|foot]] (''schuch'', Modern German ''Schuh'' "shoe") and [[ell]] (''öln'', Modern German ''Elle'').
| standard = [[Imperial units|imperial]]/[[US customary units|US]]&nbsp;units
| quantity = [[length]]
| units1   = imperial/US&nbsp;units
| inunits1 = {{val|6|ul=ft}}
| units2   = [[SI unit|SI unit equivalent]]
| inunits2 = {{convert|6|ft|disp=out|lk=on|sigfig=5}}
}}
A '''fathom''' is a [[Units of measurement|unit]] of [[length]] in the [[Imperial unit|imperial]] and the [[United States customary units|U.S. customary]] systems equal to {{convert|6|ft|4}}, used especially for [[Depth sounding|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 [[yard]]s (6 [[Foot (length)|feet]]) in an imperial fathom.<ref name=britannica11>{{cite EB1911 |wstitle=Fathom |volume=10 |page=201}}</ref> Originally the span of a man's [[Arm span|outstretched arms]], the size of a fathom has varied slightly depending on whether it was defined as a thousandth of an [[Nautical mile|(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 {{convert|5|-|5+1/2|ft|m}}.

{{anchor|Etymology}}

==Etymology==
The term (pronounced {{IPAc-en|'|f|ae|D|@|m}}) derives (via [[Middle English language|Middle English]] ''fathme'') from the [[Old English language|Old English]] ''fæðm'', which is [[cognate (linguistics)|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;</ref><ref>{{cite book
 |last        = Bosworth
 |first       = Joseph
 |author-link  = Joseph Bosworth
 |editor      = Thomas Toller
 |title       = An Anglo-Saxon Dictionary
 |publisher   = Clarendon Press
 |date        = 1898
 |location    = Oxford, England
 |url         = http://beowulf.engl.uky.edu/cgi-bin/Bosworth-Toller/ebind2html3.cgi/bosworth?seq=285
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20070314093510/http://beowulf.engl.uky.edu/cgi-bin/Bosworth-Toller/ebind2html3.cgi/bosworth?seq=285
 |archive-date = 2007-03-14
}}</ref><ref>{{cite web|url=http://www.merriam-webster.com/dictionary/fathom|title=Definition of FATHOM|website=www.merriam-webster.com|access-date=21 March 2018}}</ref><ref>{{Cite web|url=http://www.etymologiebank.nl/trefwoord/vadem|title = Zoekresultaten}}</ref><ref>[https://www.dwds.de/wb/Faden Definition and etymology of ''Faden''] in the dictionary dwds.de (in German)</ref>

==Forms==
{{anchor|Greek|Orguia|Greek fathom|Greek fathoms}}<!--linked-->

===Ancient fathoms===
The [[Ancient Greek units of measurement|Ancient Greek measure]] known as the '''orguia''' ({{langx|grc|ὀργυιά}}, ''orgyiá'', <small>{{abbr|lit|literally}}.</small>{{nbsp}}"outstretched") is usually translated as "fathom".<ref>{{citation |contribution-url=http://biblehub.com/greek/3712.htm |contribution=3712. orguia |title=Bible Hub |date=2016 }}.</ref> By the [[Byzantine Empire|Byzantine period]], this [[Byzantine units of measurement|unit]] came in two forms: a "simple orguia" ({{lang|grc|ἁπλὴ ὀργυιά}}, ''haplē orguiá'') roughly equivalent to the old Greek fathom (6 [[Byzantine units#Length|Byzantine feet]], {{c.|1.87}}{{nbsp}}[[meter (unit)|m]]) and an "imperial" ({{lang|grc|βασιλικὴ}}, ''basilikē'') or "geometric orguia" ({{lang|grc|γεωμετρικὴ ὀργυιά}}, ''geōmetrikē orguiá'') that was one-eighth longer (6 feet and a [[palmspan|span]], {{c.|2.10}}{{nbsp}}m).<ref>{{Citation |last=Loizos |first=Demetris I. |title=Digital Humanities: Diophant Ancient Measures Converter |contribution-url=http://www.anistor.gr/history/Byzantine_Units.pdf |contribution=Byzantine Measures |date=2010 |access-date=6 April 2015 |pages=1–2 }}.</ref><ref>{{citation |last=Schilbach |first=E. |author2=A. Cutler |display-authors=1 | editor-first = Alexander | editor-last = Kazhdan |editor-link=Alexander Kazhdan |display-editors=0 | encyclopedia = [[The Oxford Dictionary of Byzantium]] | publisher = Oxford University Press | year = 1991 | isbn = 978-0-19-504652-6 | ref={{harvid|ODB}} |contribution=Orgyia |pages=1532–1533 }}.</ref>

=== International fathom ===
One  international fathom is equal to:
* 1.8288 [[metre]]s exactly (Official international definition of the fathom)<ref>{{cite book|title=Admiralty Manual of Seamanship|year=1995|publisher=[[HMSO]]|isbn=0-11-772696-6|page=1·19|chapter=Sea measures}}</ref>
=== British fathom ===
The [[British Admiralty]] defined a fathom to be a thousandth of an [[Nautical mile|imperial nautical mile]] (which was 6080&nbsp;ft) or {{convert|6.08|ft|m}}. In practice the "warship fathom" of exactly {{convert|6|ft|m}} was used in Britain and the United States.<ref name=Fenna/> No conflict between the definitions existed in practice,{{citation needed|date=July 2023}} since depths on imperial nautical charts were indicated in feet if less than {{convert|30|ft|m}} and in fathoms for depths greater than that. Until the 19th century in England, the length of the fathom was more variable: from {{frac|5|1|2}}&nbsp;feet on merchant vessels to either {{convert|5|or|7|ft|m}} on fishing vessels (from {{convert|5+1/2|to|5|or|7|ft|m|disp=output only}}).<ref name=Fenna>Fenna (2000: 88-89)</ref>

=== Other definitions ===
Other definitions of fathom include:
* 1.828804&nbsp;m (Obsolete measurement of the fathom based on the [[US survey foot]], only for use of historical and legacy applications)<ref>[https://www.nist.gov/physical-measurement-laboratory/nist-guide-si-appendix-b NIST Guide to the SI, Appendix B: Conversion Factors]</ref>
* 2 [[yard]]s exactly
* 18 [[Hand (unit)|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.<ref>{{cite web |title=NGS and NIST to Retire U.S. Survey Foot after 2022 |url=https://www.ngs.noaa.gov/web/news/us-survey-foot.shtml |publisher=National Geodetic Survey |access-date=4 March 2020 |date=31 October 2019}}</ref><ref>{{cite web |title=U.S. Survey Foot: Revised Unit Conversion Factors |url=https://www.nist.gov/pml/us-surveyfoot/revised-unit-conversion-factors |publisher=NIST |access-date=4 March 2020 |date=16 October 2019}}</ref>

==Derived units==
At one time, a ''quarter'' meant one-quarter of a fathom.{{cn|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.{{cn|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 {{coord|16|114.5|display=inline|nosave=true}}, 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.<ref>Nautical chart of the Macclesfield Bank by the Hydrographic Office 1920</ref> Click for broader map and to enable varied magnification.
}}
Most modern nautical charts indicate depth in metres. However, the [[Naval Oceanographic Office|U.S. Hydrographic Office]] uses feet and fathoms.<ref>{{cite web
  | title =NOAA Chart
  | url =http://www.oceangrafix.com/o.g/Charts/chartViewer.html?viewRegion=GreatLakes&viewChart=Lake-Huron
  | access-date =2008-05-22
  | archive-date =2011-10-03
  | archive-url =https://web.archive.org/web/20111003001522/http://www.oceangrafix.com/o.g/Charts/chartViewer.html?viewRegion=GreatLakes&viewChart=Lake-Huron
  | url-status =dead
  }}</ref> A [[nautical chart]] will always explicitly indicate the units of depth used.<ref>{{Cite book| isbn = 978-1-4729-4343-9| last = Cunliffe| first = Tom| title = The complete yachtmaster: sailing, seamanship and navigation for the modern yacht skipper| date = 2017|page=114| publisher = Bloomsbury USA|quote=The scale of a paper or raster chart is shown near the title, as are the units used for soundings (these are normally metres or fathoms, though occasionally they may be in feet).  Make sure you take notice of this or you'll have some surprises.}}</ref>

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.<ref>[http://www.navyandmarine.org/ondeck/1800soundinglead.htm Sounding lead.] By James Mathews. Navy & Marine Living History Association.</ref> 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''.<ref>{{cite web|url=http://www.bruzelius.info/Nautica/Etymology/English/Burney(1901)_dict.html|title=Burney: "Vocabulary of Sea Terms", 1876.|website=www.bruzelius.info|access-date=21 March 2018}}</ref> 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''.<ref>[http://www.marinewaypoints.com/learn/glossary/glossary.shtml MarineWaypoints.com - Nautical Glossary.] SandyBay.net - Marine Directory (MarineWaypoints.com) and Reference Directory (StarDots.com).</ref> A ''deep-sea lead'', the heaviest of sounding leads, was used in water exceeding 100 fathoms in depth.<ref>[https://query.nytimes.com/gst/abstract.html?res=9D03EFDC1538E233A25755C0A9609C94639ED7CF The new way and the old; how the sounding machine has superseded the deep sea lead.] The New York Times, June 6, 1892, page 5.</ref>

This technique has been superseded by sonic [[Echo sounding|depth finders]] for measuring mechanically the depth of water beneath a ship, one version of which is the ''Fathometer'' (trademark).<ref>[http://nauticalcharts.noaa.gov/hsd/fpm/FPM_MAY2008.pdf ''Field Procedures Manual'', National Oceanic and Atmospheric Administration (NOAA), Office of Coast Survey.] {{Webarchive|url=https://web.archive.org/web/20170703202052/https://nauticalcharts.noaa.gov/hsd/fpm/FPM_MAY2008.pdf |date=2017-07-03 }} May 2008. In chapter 7, Glossary, page 252.</ref> The record made by such a device is a ''fathogram''.<ref>[http://www.thsoa.org/pdf/hm1960/hm1960.pdf ''Hydrographic Manual''.] {{webarchive|url=https://web.archive.org/web/20080704123437/http://www.thsoa.org/pdf/hm1960/hm1960.pdf |date=2008-07-04 }} By Captain Karl B. Jeffers. Publication 20-2, Coast and Geodetic Survey, U. S. Department Of Commerce. Posted by the Hydrographic Society of America.</ref> 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 line|contour]] of the ocean floor.<ref>[http://www.irbs.com/bowditch/pdf/glossary/gloss-d.pdf Glossary of Marine Navigation.] {{webarchive|url=https://web.archive.org/web/20081218130659/http://www.irbs.com/bowditch/pdf/glossary/gloss-d.pdf |date=2008-12-18 }} Page 763. I'd Rather Be Sailing.</ref>

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 {{convert|50|fathom|ft m|adj=on}} [[wikt:skein#en-n-1|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 [[wikt:gangion|gangions]] and hooks attached. A ''tuck seine'' or ''tuck net'' about {{cvt|70|fathom|ft m}} long, and very deep in the middle, was used to take fish from a larger [[Seine fishing|seine]].

A ''line'' attached to a [[whaling]] [[harpoon]] was about {{cvt|150|fathom|ft m}}. 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.<ref>{{cite book |last1=Scofield |first1=William Launce |title=Drift and set line fishing gear in California |date=1947 |publisher=California State Printing Office |location=[[Sacramento, California]] |via=[[Calisphere]] |url= http://content.cdlib.org/view?docId=kt5x0nb13m;NAAN=13030&doc.view=frames&chunk.id=d0e245&toc.depth=1&toc.id=d0e245&brand=calisphere |access-date=18 May 2017 |quote=As opposed to drifting, a piece of fishing gear is considered set when it is anchored or attached to the bottom or shore so that it is not free to move about with water or wind currents. By contrast, a drift line or net has no such attachment to the bottom or shore and is therefore free to drift or move with any currents.}}</ref> A ''kite'' was a drag, towed under water at any depth up to about {{cvt|40|fathom|ft m}}, 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 {{cvt|15|fathom|ft m}}.<ref>{{Cite book|title = Dept. of the Army Technical Bulletin TB 43-0144: Painting of Watercraft|publisher = U.S. Government Printing Office|year = 1990|pages = D-2}}</ref>

A ''shackle'', a length of cable or chain equal to {{cvt|12+1/2|fathom|ft m}}.<ref>{{cite book|title=Oxford English Dictionary|url=http://www.oed.com/view/Entry/177171?rskey=dLfO0E&result=1#eid|access-date=23 February 2015|chapter=Shackle n.1, 9.}}</ref> In 1949, the British navy redefined the shackle to be {{cvt|15|fathom|ft m}}.<ref name=Jerrard1986>{{cite book|last1=Jerrard|first1=H. G.|last2=McNeill|first2=D. B.|title=A Dictionary of Scientific Units|date=1986|publisher=Springer Science & Business Media|isbn=9789400941113|url=https://books.google.com/books?id=ApFfBgAAQBAJ&q=shackle+unit+of+length&pg=PT198|access-date=3 March 2015}}</ref>

The [[Finland|Finnish]] fathom (''syli'') is occasionally used: {{frac|1000}} [[nautical mile]] or {{frac|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.<ref>{{cite book
  | last1=Hirsch Jr
  | first1=E.D.
  | last2=Kett
  | first2=Joseph F.
  | last3=Trefi
  | first3=James
  | title=The New Dictionary of Cultural Literacy
  | publisher=Houghton Mifflin
  | date=2002
  | location=Boston, MA
  | url=https://archive.org/details/newdictionaryofc00hirs
  | isbn=0-618-22647-8
  | url-access=registration
  }}</ref>

The phrase is echoed in Shakespeare's ''[[The Tempest]]'', where [[Ariel (The Tempest)|Ariel]] tells [[Ferdinand (The Tempest)|Ferdinand]], "[[Full Fathom Five (Tempest)|Full fathom five]] thy father lies".

===On land===
Until early in the 20th century, it was the unit used to measure the depth of [[Mining|mines]] (mineral extraction) in the [[United Kingdom]].<ref>{{cite web
  | title =Mining Encyclopaedia
  | publisher =U.K. Mine and Quarry Information and Exploration
  | url =http://www.mine-explorer.co.uk/open-htm-white-paper.asp?id=4
  | access-date =2007-05-28
  | archive-date =2006-05-15
  | archive-url =https://web.archive.org/web/20060515235815/http://www.mine-explorer.co.uk/open-htm-white-paper.asp?id=4
  | url-status =dead
  }}</ref> 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 {{convert|6|ft|m}} 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 ("[[:hu:Öl#Magyarorsz.C3.A1gon|négyszögöl]]") is still in use as an unofficial measure of land area, primarily for small lots suitable for construction.{{clarify|date=September 2016}}

==See also==
{{div col|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===
{{Reflist|30em}}

===Bibliography===
*{{Cite book | last=Fenna | first=Donald | year = 2002 | chapter = fathom | title = A Dictionary of Weights, Measures, and Units | location = Oxford | publisher = University Press | isbn = 0-19-860522-6 }}.

==External links==
{{Wiktionary}}

*[http://www.navyandmarine.org/planspatterns/soundingline.htm An explanation of the fathom marks used at sea] (retrieved Sept 2005).
*[https://web.archive.org/web/20060901101317/http://nyuz.elte.hu/archiv13/szam4/mondok1.htm Hungarian web page that refers to the length of a "bécsi öl"]

{{Imperial units}}

[[Category:Human-based units of measurement]]
[[Category:Nautical terminology]]
[[Category:Units of length]]
[[Category:Customary units of measurement in the United States]]