In books about sea voyages or adventures, in films about desperate sailors, in articles on a geographical theme and in conversation between sailors, the term "nautical mile" often slips. It's time to figure out what this measure of length is in shipping, and why sailors do not use the kilometers we are used to.
What is 1 nautical mile?
Initially, this value corresponded to the length of 1/60 degree of the arc of a circle on the surface of the Earth with a center coinciding with the center of the planet. In other words, if we consider any meridian, then a nautical mile will be approximately equal to the length of one minute of latitude. Since the shape of the Earth is somewhat different from the outlines of an ideal ball, the length of 1 minute of a degree of the considered meridian may differ slightly depending on the latitude. This distance is greatest at the poles - 1861.6 m, and least of all at the equator - 1842.9 m. To avoid confusion, it was proposed to unify the length of the nautical mile. The length of 1 minute of a degree at 45º of latitude (1852, 2 m) was taken as the basis. Suchthe definition led to the fact that the nautical mile became convenient for calculating navigational tasks. For example, if you need to measure a distance of 20 miles on a map, then it will be enough to measure 20 arc minutes with a compass on any meridian plotted on the map.
Starting in 1954, the United States began to use the international nautical mile (1852 m). In practice, it is often rounded up to 1800 meters. The official designation of this unit was never adopted. Sometimes the abbreviation "nmi", "nm" or "NM" is encountered. By the way, "nm" is the generally accepted designation of the nanometer. 1/10 international nautical mile=1 cable=185.2 meters. And 3 miles equals 1 nautical league. In the UK, their own nautical mile, equal to 1853.184 m, was often used before. In 1929, an international conference was held in Monaco on various issues of hydrography, at which the length of the nautical mile was determined at 1852.00 meters. Do not forget that a mile is not only sea, but also land. In this case, its length is 1.151 times less than the sea.
What is the relationship between a nautical mile and a knot?
The nautical mile, or, as it is sometimes called, geographic or navigation, has become widespread in geography, aviation and navigation. Closely related to it is the concept of the sea knot, which is used in shipping as the basic unit of speed. One knot is equal to one mile traveled per hour of the vessel's movement. The name "knot" is due to the fact that in the old days onships used a log to measure speed. It was a log or board in the shape of a triangle, to which the load was tied. A line (rope) was tied to such a floating anchor, on which knots were tied after a certain distance. The log was thrown overboard, after which for a selected period of time (from 15 seconds to 1 minute) it was calculated how many knots would go into the water.
There are different versions regarding the distance between nodes. Some believe that it was 25 feet (7.62 m), and if one knot left in 15 seconds, then one nautical mile (100 feet / min) was obtained. According to the second version, the knots were tied after 47 feet and 3 inches (14.4018 m), and the countdown was 28 seconds. In this case, one knot showed a speed of 101.25 ft/min.
We hope now you will have no difficulty in understanding marine terminology, and miles with knots will become as clear as usual kilometers.
