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The knot (/ n ɒ t /) is a unit of speed equal to one nautical mile per hour, exactly 1.852 km/h (approximately 1.151 mph or 0.514 m/s). [ 1 ] [ 2 ] The ISO standard symbol for the knot is kn . [ 3 ]
A nautical mile is a unit of length used in air, marine, and space navigation, and for the definition of territorial waters. [2] [3] [4] Historically, it was defined as the meridian arc length corresponding to one minute ( 1 / 60 of a degree) of latitude at the equator, so that Earth's polar circumference is very near to 21,600 nautical miles (that is 60 minutes × 360 degrees).
With the introduction of the nautical mile as a standard unit of measure at sea in the 15th century, they began to mark the line at equal intervals proportional to the nautical mile and to the time interval used for measurement. Initially, the markings were simply knots in the line. Later, sailors worked knotted cords into the log-line.
Knot: Speed: League: Length: Nautical mile: Length: Rhumb: Angle: The angle between two successive points of the thirty-two point compass (11 degrees 15 minutes) (rare) [1] Shackle: Length: Before 1949, 12.5 fathoms; later 15 fathoms. [2] Toise: Length: Toise was also used for measures of area and volume Twenty-foot equivalent unit or TEU: Volume
At sea level one minute of arc along the equator equals exactly one geographical mile (not to be confused with international mile or statute mile) along the Earth's equator or approximately one nautical mile (1,852 metres; 1.151 miles). [14] A second of arc, one sixtieth of this amount, is roughly 30 metres (98 feet).
The radar mile is a unit of time (in the same way that the light year is a unit of distance), equal to the time required for a radar pulse to travel a distance of two miles (one mile each way). Thus, the radar statute mile is 10.8 μs and the radar nautical mile is 12.4 μs. [91]
Step 5. Measure length of course by using speed of 8.8 knots and converting into nautical miles via the time, speed, and distance scale; Step 6. Connect the two ends of the vectors from the current course to the course made good. Thus creating your set and drift vector; Step 7. Using the navigational triangle, place on set and drift vector.
As one degree is 1 / 360 of a circle, one minute of arc is 1 / 21600 of a circle – such that the polar circumference of the Earth would be exactly 21,600 miles. Gunter used Snellius's circumference to define a nautical mile as 6,080 feet, the length of one minute of arc at 48 degrees latitude. [24]