A cable length or cable's length is a nautical unit of measure equal to one tenth of a nautical mile or approximately 100 fathoms. The unit is named after the length of a ship's anchor
cable in the age of sail. The definition varies:
International: 1⁄10 nautical mile, or 185.2 m
Imperial (Admiralty): 1⁄10 Admiralty mile, or 608 ft (185.32 m), about 101 fathoms
The traditional British fathom varied from 5Ĺ feet to 7 feet in the Merchant Navy
U.S. customary (US Navy): 120 fathoms (720 feet, 219.456 m)
fathom (abbreviation: ftm) = 6 feet or 1.8288 metres, is a unit of length in the old imperial and the U.S. customary systems, used especially for measuring the depth
There are two yards (6 feet) in an imperial fathom. Originally based on the distance between 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 5–5 1⁄2 feet (1.5–1.7 m).
1 fathom =
1.82880 m 182.880 cm
US customary / Imperial units
6.00000 ft 72.0000 in
As you can see, the problems stem from
1- The difference between US and Imperial measurements
2- International Standards (IS) and US and Imperial measurements.
The same errors occur when discussing f.eks. gallons the imperial gallon is not the same as the US gallons.
A cables length is frequently used as a measurement in the UK, as is Fathom. So depending on the audience, it is natural this is used.
Just to add to the confusion:
What about Beaufort/Knots/meters per second for wind
speeds? (rough conversions: 2 x beaufort
= meters per second X 2 = knots
Of course, not to mention the metric system versus yards/feet/inches