The fathom
A fathom is a nautical unit of measurement equal to 6 feet (1.8288 m), historically used for measuring the depth of water. The word derives, via the Middle English word fathme, from the Old English word fæðm, which is cognate with the Danish word favn, meaning a ‘pair of outstretched arms’. A burial at sea officially requires a minimum of six fathoms of water, probably being the origin of the phrase ‘to deep six’ as meaning to discard, or dispose of something. The phrase is echoed in Shakespeare’s The Tempest, where Ariel tells Ferdinand, ‘Full fathom five thy father lies’, which means his body is lost deep at sea.
The nautical mile
A nautical mile is defined as exactly 1,852 metres, or 6,076 ft, which equates to 1.151 standard miles. The unit for measuring the speed of a ship called the knot is derived from this unit of measurement – 1 knot being one nautical mile per hour. Historically, a nautical mile was defined as the meridian arc length corresponding to one minute (1/60 of a degree) of latitude at the equator. The word ‘mile’ itself comes from the Latin phrase for a thousand paces: mille passus.
The league
The league is thought to have derived from an ancient Celtic unit later adopted by the Romans – the leuga. It became a common unit of measurement throughout western Europe, although since the Middle Ages many values for this unit of distance have been specified, ranging from 2.2 km/1.4 miles to 7.9 km/4.9 miles. In England it was most commonly specified as being 3 miles. A league might have originally represented the rough distance a person could walk in one hour.
A cable’s length
A cable’s length is a nautical unit of measure equal to one tenth of a nautical mile or approximately 100 fathoms. Owing to anachronisms and varying techniques of measurement, a cable length can be anywhere from 169 to 220 metres (185 to 241 yards), depending on the standard used – 720 feet (219 meters) in the U.S. Navy and 608 feet (185 meters) in the British Navy, the latter country adopting the value. A cable’s length, also cable length or just cable, is the standard length in which cables came. According to the Royal Navy, the length of a ship’s hempen anchor cable was formerly 101 fathoms.
The shackle
A unit used for measuring the lengths of cables and chains equal to 12.5 fathoms (75 feet; 22.9 metres). In 1949, the British navy redefined the shackle to be 15 fathoms (90 feet/27 metres).
The toise
A unit used by the colonial pre-revolutionary French to measure length, area and volume, known by the Portuguese as toesa. According to the Oxford Dictionary, the name is derived from the Latin tensa brachia, meaning “outstretched arms”. One toise was divided into 6 feet (French: pieds) or 72 inches (pouces) or 864 lines (lignes) in France until 1812. When used to measure area, one square toise was about 3.799 square metres (40.89 square feet), being used as a measure for land and masonry area in France before 10th December 1799. For measuring volume 1 toise equals 8 cubic metres (282.5 cubic feet).