A knot is the unit of sailing speed, and the voyage of a ship 1 nautical mile/hour is 1 knot, which is denoted by the code name "kn". The internationally recognized standard nautical mile is1852m, and China also recognizes this standard. The code name in the sea is "M". A chain is a unit for measuring short distances in navigation. A chain 1 is equal to110 nautical mile, which is indicated by the code "Cab". In addition, this section is also the length unit mark for the manufacture and use of ship anchor chain links. Generally speaking, the length of 27.5m anchor chain is 1 knot, while the ship anchor chain length sign in China is 1 knot with 20m.

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The sea is an international unit of measurement. 1 nautical mile =1.852km (km) (China standard). Standard symbol n miles. The symbol used in People's Republic of China (PRC)'s legal unit of measurement is n miles. It is equal to the arc length corresponding to 1 minute latitude on the earth's elliptical meridian (once equal to 60 minutes, a circle is 360 degrees).

Because the meridian circle of the earth is an ellipse with different curvatures at different latitudes, the corresponding arc lengths of latitude 1 are not equal.

As early as16th century, maritime navigation was quite developed, but there were no clocks or nautical recorders at that time, so it was difficult to accurately determine the sailing speed of the ship. However, a clever sailor came up with a wonderful method. When the ship is sailing, he throws a floating body with a rope into the sea, and then calculates the speed of the ship according to the length of the rope pulled out in a certain period of time. The time at that time was still measured by quicksand timer.

In order to calculate the speed of the ship more accurately, sometimes the rope is very long, so many knots are tied at the equal distance of the rope, so that the whole speed measuring rope is divided into several sections. As long as the number of knots dragged by the rope in the same unit time is measured, the corresponding speed can naturally be measured. As a result, "knot" has become a unit of measurement for the speed of seagoing ships; Correspondingly, the speed measuring units of underwater weapons such as seawater velocity, offshore wind speed and torpedo are widely used in the world.

The speedometers of modern seagoing ships are very advanced, and some of them can be displayed digitally at any time. "Throwing knots" has long been history, but knots are still used as the speed unit of seagoing ships.

References:

Baidu Encyclopedia-Li Hai