|Physical quantity (s)||speed|
|In SI units|
|Named after||Knot (tying)|
|Derived from||Nautical mile , hour|
The knot (kn) is a measure of speed in sea and aviation or meteorology , which is based on the unit of length nautical mile ( sm ) or nautical mile ( NM, nmi, n.mi. ). One nautical mile is exactly 1852 meters . The unit symbol is kn (English formerly kt ).
Origin and use
The name is derived from the knots that are made in the line of the log to mark certain distances. The distances are ideally a fraction of a nautical mile. The number of knots that are covered in a certain time results in the so-called ride through water ( FdW ). The time was set by the log glass , a special hourglass.
Nowadays, this journey through the water is determined much more precisely by other logging systems (hydrostatic, hydrodynamic, electric, etc.). What is more important for navigation , however, is the ground speed , which is determined either with other navigation aids such as GNSS , terrestrial navigation, radio navigation or by taking the ocean current into account .
The nautical mile or nautical mile (German: sm , English: NM ) corresponds to a difference in geographical latitude of one angular minute (1 '), and thus 60 nautical miles correspond to one degree of latitude . A ship traveling exactly north or south at a speed of 20 knots covers one degree of latitude in three hours.
An easy-to-remember rule of thumb for converting knots into kilometers per hour is: "Times two, minus 10%" (or "minus 10%, times two").
The rough conversion as a formula:
The error in this calculation is less than 3%.