Nautical miles differ from land miles because air, land and water are three different elements. Each has its own distinctive features and characteristics. One of these features is that the nautical mile is longer than the land mile. Why has it happened so historically?
Back in the days of the ancient Romans, one land mile was equal to 1000 steps. Later, a specific figure was established - 1609 meters. The length of the nautical mile was 1852 meters. Where does this difference come from?
A bit of history …
In order to measure the speed of a ship, it was inconvenient for sailors to use land miles. Especially, there were unjustified risks during emergency work. From the raging elements during the storm, the life of the sailors was in great danger. Under such conditions, it was not possible to use land measurements.
Therefore, we found a more suitable option. They took a heavy log on a rope and threw it overboard. Then they counted how many knots would pass through the sailor's hands in a certain period of time before the rope was pulled.
Empirically determined the distance between the nodes and the time interval. There are different versions about the exact definition. One of them was when the distance between nodes averaged 15 meters. It took 30 seconds.
It was practical and rational. The countdown was measured with an hourglass. All that remained was to count the knots and look at the sand in the clock. Even an illiterate sailor could complete the task.
Summed up these studies and found out. The length from one knot to another until the rope is pulled is 15 meters, in time it takes 30 seconds. The average speed of the ship was calculated by simple arithmetic operations. Thus, one nautical mile was 1852 meters in one hour.
With the development of navigation, even greater convenience was introduced. One nautical mile became equal to one minute along the meridian. 1 degree equals 60 minutes. On the map, this would be 60 nautical miles. The nautical mile has become convenient for calculating navigation problems.
Therefore, the navigators began to measure the distance on the map with a compass. Applying it to the degree scale, they recognized the distance in nautical miles. For example, to find out a distance of 30 miles, it is enough to measure out 30 arc minutes with a compass on any meridian plotted on the map.
Now, of course, all equipment is computerized. There is no need to use outdated methods, but the nautical mile, as a unit of measure for distance, remained unchanged at 1852 meters. It is called navigational or geographic.
The knot is used in shipping as the basic unit of speed. Nautical miles and knots are the same understandable and familiar measurements at sea as kilometers and meters on land.