What is the sea mile and what is the sea knot equal to?

In books on sea travel or adventures, in films about desperate navigators, 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 in shipping is equal to, and why seamen do not use the kilometers we are accustomed to.

What is 1 nautical mile?

Initially, this value corresponded to the length of a 1/60 degree arc of the 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, the nautical mile will be Approximately equal to the length of one minute of latitude. Since the shape of the Earth is somewhat different from that of the ideal ball, the length of 1 minute of the degree of the meridian under consideration may differ somewhat depending on the latitude. Most of this distance at the poles is 1,861.6 m, and least at the equator - 1842.9 m. To avoid confusion, it was suggested to unify the length of the nautical mile. The length of 1 minute of a degree to 45º of latitude (1852.2 m) was taken as a basis. This definition led to the fact that the nautical mile became convenient for calculating navigational tasks. For example, if you need to measure the distance of 20 miles on a map, then it will be enough to measure by circling 20 arc minutes on any meridian marked on the map.

Since 1954, in the United States began to use the international nautical mile (1852 m). In practice, it is often rounded to 1800 meters. The official designation of this unit was never adopted. Sometimes there is a reduction in "nmi", "nm" or "NM". By the way, "nm" is the generally accepted designation of a nanometer. 1/10 international sea mile = 1 cable = 185.2 meters. And 3 miles are equal to 1 sea league. In the UK, it used to often use its own nautical mile, equal to 1853,184 m. In 1929 an international conference was held in Monaco devoted to various issues of hydrography, in which the length of the sea mile was determined at 1852.00 m. Do not forget that the mile is not only sea, but also land. In this case, its length is 1,151 times smaller than the sea.

What is the relationship between a sea mile and a node?

Mile sea (nautical mile) or, as it is sometimes called, geographical or navigational, has become widespread in geography, aviation and navigation. The concept of a sea knot, used in navigation as the basic unit of speed, is closely connected with it. One node is equal to one mile traveled per hour of vessel movement. The name "knot" is due to the fact that in the old days lags used to measure speed. It was a log or a board in the form of a triangle, to which the load was tied. A line (rope) was tied to such a floating anchor , on which nodes were knotted after a certain distance. The log was thrown overboard, after which for a selected period of time (from 15 seconds to 1 minute), counted how many nodes would go into the water.

There are different versions regarding the distance between nodes. Some consider it to be 25 feet (7.62 meters), and if one node left in 15 seconds, it eventually turned out to be one nautical mile (100 ft / min). According to the second version, the nodes were tied through 47 feet and 3 inches (14,4018 meters), and the count went in 28 seconds. In this case, one node showed a speed of 101.25 feet / minute.

We hope that now you will not have any difficulty understanding the marine terminology, and miles with nodes will become as clear as the usual kilometers.