Knot is a unit of speed, equal to one nautical mile per hour. A nautical mile or sea mile is a unit of Length. It corresponds approximately to one minute of Latitude along any meridian.
The abbreviation preferred by maritime authorities in the USA[1], and Canada [2], as well as the Institute of Electrical and Electronics Engineers and the International Bureau of Weights and Measures is kn. The Institute of Electrical and Electronics Engineers or IEEE (read eye-triple-e) is an international Non-profit, professional organization The International Bureau of Weights and Measures ( Bureau international des poids et mesures, in French) is an international Standards organization, one [3] [4] The abbreviation kt is also in widespread use, sometimes with kts for the plural (knots). It is a non-SI unit accepted for use with the SI. [3] It is used around the world in meteorology and for maritime and aviation purposes. Meteorology (from Greek grc μετέωρος metéōros, "high in the sky" and grc -λογία -logia) is the Interdisciplinary Shipping is physical process of Transporting goods and Cargo. Aviation refers to activities involving man-made flying devices ( Aircraft) including the people organizations and regulatory bodies involved with them A vessel traveling at 1 knot along a meridian, covers one sixtieth of a degree geographic latitude in one hour. This article is about the geographical concept For other uses of the word see Meridian. The term knot was first used by mariners who measured how many knots on the line paid out in a given time period when the chip log was deployed. A chip log, also called common log, ship log or just log, is a Navigation tool used by Mariners to estimate Speed of a vessel
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Definition
1 international knot = 1 nautical mile per hour = 1. A nautical mile or sea mile is a unit of Length. It corresponds approximately to one minute of Latitude along any meridian. The hour (symbol h) is a unit of Time. It is not an SI unit but is accepted for use with the SI 852 kilometres per hour exactly, or (approximately) 1 international knot = 1. (For the South African airport with IATA code "KMH" see Johan Pienaar Airport. 1507794 miles per hour = 0. 51444444 meters per second.
This is based on the internationally agreed length of the nautical mile. The international definition was adopted by the US in 1954 (which previously used the US nautical mile of 1853. 248 m). [5] The international definition was adopted by the UK in 1970 which previously used the UK or Admiralty nautical mile of 6080 feet (1853. 184 m). This is the definition used in most, if not all, modern circumstances. A common error that should be avoided is to use the term 'knot' to refer to the nautical mile itself.
The speed of a vessel relative to the fluid in which it travels is usually measured in knots. This may be referred to as 'boat speed', 'vessel speed' and, for aircraft, 'air speed'. Airspeed is the speed of an Aircraft relative to the air There are several different measures of airspeed indicated airspeed calibrated airspeed equivalent airspeed and true For consistency in navigation, the speed of relevant fluids, such as tidal stream, river current and wind speed, is also usually specified in knots. Tidal power, sometimes called tidal energy, is a form of Hydropower that converts the energy of Tides into electricity or other useful forms of power "Riverine" redirects here For the use of that term in Maritime geography, see there Wind speed is the Speed of Wind, the movement of air or other gases in an atmosphere Knots are then also used to describe the actual speed of a vessel over the ground (SOG) ground speed (GS) in aircraft and for its rate of progress toward a distant point ('velocity made good' or VMG). Ground speed is the speed of an Aircraft relative to the ground In Physics, velocity is defined as the rate of change of Position.
Origin
Until the mid-19th century vessel speed at sea was measured using a chip log. A chip log, also called common log, ship log or just log, is a Navigation tool used by Mariners to estimate Speed of a vessel This consisted of a wooden panel, weighted on one edge to float upright and thus have substantial water resistance, attached by line to a reel. The chip log was "cast" over the stern of the moving vessel and the line allowed to pay out. Knots placed at a distance of 47 feet 3 inches (14. KNOT (1450 AM) is a commercial Classic Country music Radio station in Prescott Arizona, broadcasting to the Flagstaff - Prescott A foot (plural feet or foot; symbol or abbreviation ft or sometimes &prime – the prime symbol) is a non-SI unit Inches redirects here To see the Les Savy Fav album see Inches. 4018 m) passed through a sailor's fingers, while another sailor used a 30 second sandglass (28 second sandglass is the current accepted timing) to time the operation. An hourglass, also known as a sandglass, sand timer or sand clock, is a device for the measurement of Time. [6] The knot count would be reported and used in the sailing master's dead reckoning and navigation. Dead reckoning ( DR) is the process of estimating one's current position based upon a previously determined position or fix, and advancing that position based upon Navigation is the process of reading and controlling the movement of a craft or vehicle from one place to another This method gives a value for the knot of 20. 25 in/s, or 1. 85166 km·h−1. The difference from the modern definition is less than 0. 02%.
Modern use
Although the unit "knots" does not fit within the primary SI system, its retention for nautical and aviation use is important for navigational reasons, since the length of a nautical mile is almost identical to a minute of latitude. Latitude, usually denoted symbolically by the Greek letter phi ( Φ) gives the location of a place on Earth (or other planetary body north or south of the As a result, distance in nautical miles on a navigational chart can easily be measured by using dividers and the latitude indicators on the side of the chart.
Nautical speed is sometimes erroneously expressed as "knots per hour" which would actually be a measure of acceleration, as in "nautical miles per hour per hour. "
Aeronautical terms
Prior to 1969, airworthiness standards for civil aircraft in the USA Federal Aviation Regulations specified that distances were to be in statute miles, and speeds in miles per hour. The Federal Aviation Regulations, or FAR s are rules prescribed by the Federal Aviation Administration (FAA governing all Aviation activities in the In 1969 these standards[7] were progressively amended to specify that distances were to be in nautical miles, and speeds in knots.
The following abbreviations[8] are used to distinguish between various measurements of airspeed. Airspeed is the speed of an Aircraft relative to the air There are several different measures of airspeed indicated airspeed calibrated airspeed equivalent airspeed and true
- KTAS is "knots true airspeed", the airspeed of an aircraft relative to undisturbed air. True airspeed ( TAS) is the speed of an aircraft relative to the airmass in which it flies i
- KIAS is "knots indicated airspeed", the speed shown on an aircraft's pitot-static airspeed indicator. Indicated airspeed (IAS is the Airspeed read directly from the Airspeed indicator on an aircraft driven by the Pitot-static system. A pitot-static system is a System of Pressure -sensitive instruments that is most often used in aviation to determine an aircraft's Airspeed, Mach number The airspeed indicator or airspeed gauge is an instrument used in an Aircraft to display the craft's Airspeed, typically in knots, to the
- KCAS is "knots calibrated airspeed", the indicated airspeed corrected for position error and instrument error. Calibrated airspeed (CAS is the speed shown by a conventional Airspeed indicator after correction for instrument error and Position error. Position error is one of the errors affecting the systems in an aircraft for measuring Airspeed and altitude.
- KEAS is "knots equivalent airspeed", the calibrated airspeed corrected for adiabatic compressible flow for the particular altitude. Equivalent airspeed (EAS is the airspeed at sea level which represents the same Dynamic pressure as that flying at the True airspeed (TAS at altitude This article covers adiabatic processes in Thermodynamics. For adiabatic processes in Quantum mechanics, see Adiabatic process (quantum mechanics A flow is considered to be a compressible flow if the change in Density of the flow with respect to Pressure is non-zero along a streamline.
External links
- Non-SI units accepted for use with the SI, and units based on fundamental constants - At one time, the knot, along with the nautical mile, was discouraged for use by the BIPM, but it is now officially accepted for use (as of the 8th edition of the SI brochure), since its use is "expected to continue indefinitely", as well as having an exact SI definition.
See also
- Hull speed, which deals with theoretical estimates of practical maximum speed of displacement hulls. Hull speed, sometimes referred to as displacement speed, is a Rule of thumb used to provide an approximate maximum efficient speed for a hull
- Metre per second
- Nautical mile
- Orders of magnitude (speed)
References
- ^ Positions, Distances, Directions, Compass; Office of Coastal Survey, NOAA, USA
- ^ POSITIONS, DISTANCES, DIRECTIONS, COMPASS, Ministry of Fisheries and Oceans, Canada
- ^ a b See BIPM website on accepted non-SI units, in particular note f. A nautical mile or sea mile is a unit of Length. It corresponds approximately to one minute of Latitude along any meridian. To help compare different Orders of magnitude, the following list describes various Speed levels between 1
- ^ IEEE guidelines for authors
- ^ Louis E. Barbrow and Lewis V. Judson (1976). Appendix 4 The international nautical mile (PDF). Weights and Measures Standards of the United States, A brief history. NIST Physics Laboratory. Retrieved on 2007-08-02. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 338 BC - A Macedonian army led by Philip II defeated the combined forces of Athens and Thebes in the
- ^ Oxford Companion to Ships and the Sea. Page 454.
- ^ For example, Part 23 of the Federal Aviation Regulations, amendment 23-7, September 14, 1969
- ^ USA Federal Aviation Regulations, Part 1, §1. The Federal Aviation Regulations, or FAR s are rules prescribed by the Federal Aviation Administration (FAA governing all Aviation activities in the 1 and §1. 2
- Kemp, Peter (editor). The Oxford Companion to Ships and the Sea. Oxford university Press, 1976. ISBN 0-19-282084-2
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