A nautical knot is an accepted unit for determining speed at which an object travels in one hour the distance corresponding to a nautical mile. Refers to non-systemic quantities, but can be used with SI units. According to generally accepted international standards, it is equal to 1852 m / h (nautical mile per hour) or 0.514 m / s.
The prevalence of nodes is explained by the great convenience of their use in navigation calculations - a ship moving at a speed of 1 node in the direction of any meridian in 60 minutes overcomes 1 arc minute of latitude.
The history of the appearance of the sea knot
At the dawn of shipbuilding and navigation, devices were still not invented to help navigate the vast expanses of the open sea. They didn’t know how to determine the location of the ship, therefore, in order not to “get lost” they preferred to walk along the coast - the Phoenicians and ancient Greeks often did this.
Over time, the location of the ship learned to calculate using geographic coordinates. If latitude (position relative to the equator) was determined by the polar star, then with longitude (position relative to the Greenwich meridian) much more problems arose. Sailors had to calculate the distance that they traveled from a point with a known longitude for a certain time interval. To this end, a device called a sector lag was created. The word lag comes from the Dutch log - distance.
Interesting fact: In order to transfer the speed value from knots to kilometers per hour we need to multiply the number of knots by 1.852 (mile value). For example, 12 * 1.852 = 22.2 km / h.
The principle of operation of the first lags
The earliest example of a lag is an ordinary log or board with an attached cable - a line (laglin). While the vessel was moving, the device was thrown overboard from the stern. It was held on the water surface using the processes of the laglin at several points, which made it possible to occupy a perpendicular position relative to the direction of travel of the ship.
Due to the deceleration of the sector by water, the line was fed at about the speed of the ship. The sailor determined the length of the line going overboard for a fixed time, most often 30 or 60 seconds. To do this, knots were knitted on the cable with the same interval, which were then counted. The distance between the nodules was set in advance so that the number of nodes reflected the speed of the craft. As a result, the new unit received the name node.
Give an example
If the lag is divided into sectors, the intervals between which are 50.7 feet (identical to 1/120 nautical miles) at an object moving speed of one knot, the device can be etched into two nodules (1/60 mile) in 60 seconds, and 30 seconds by 1 knot. It turns out that in the case of etching of ten knots in 30 seconds, the speed of the ship is 10 knots.
Interesting: Correct use of the term - the ship is in full swing thirteen knots, while it is incorrect to say thirteen knots per hour.
Modern lag
A lag is a device that determines the speed of a ship. There are several types of lags that measure by determining the pressure of water. Today, ships use devices based on flat blades rotating during movement. When they move, the blades rotate, setting in motion a mechanism that determines the actual speed of the craft. The following types of lags are also used:
- Induction;
- Hydrodynamic;
- Hydroacoustic - correlation and Doppler.
Interesting fact: Until 1965, knots were considered the most common unit of measurement in the UK, but then they received a new name - miles.
Offshore units serve as the main unit for determining the speed of a floating craft. This concept appeared during the heyday of sailing, when for the first time they began to use a special device for measuring speed - a lag that was equipped with a cable with knots tied to it.
