What Is A Knot, And How Many Knots Are In A Mile?

Distance at sea is measured differently than distance on the Earth.

Definition

A nautical mile is defined as a unit of length based on the earth鈥檚 circumference that is equal to a single minute of latitude. A nautical mile is not a statute mile (a mile measured over land.) Nautical miles are most commonly used in navigating and charting, especially over water. Compared to the statute mile, a nautical mile is slightly larger. Previously, there was no internationally defined and recognized conversion between a nautical mile and a statute mile. During that time, the UK and the US used different definitions. However, since the 20^th century, one nautical mile is internationally defined as equal to 1.1508 statute miles. Compared to meters, one internationally defined nautical mile is equal to 1,852 meters.

A knot is a unit of speed based on the nautical mile. One knot is the same as one nautical mile per hour. Therefore, one knot is equal to 1.1508 statute miles per hour (1.1508 mph). The internationally recognized symbol for the knot by the ISO and the Institute of Electrical and Electronics Engineers is kn. Some people use another common symbol of the knot which is denoted as kt. The knot is most commonly used in maritime and air navigation as well as in meteorology. A liner at sea travelling at a speed of 1 kn along a path marked by a meridian is said to be travelling at least a minute of geographic latitude in an hour.

What Is The Origin Of Knots?

The term 鈥渒nots鈥� has a maritime origin. In times past, sailors did not have the modern technologies for navigation and measuring speed while at sea. Instead, they used a simple tool called a common log in order to approximate the speed of vessels at sea. The common log was simply a coil of rope with knots tied at uniformly spaced distances. The rope was then joined to a piece of wood with the shape of a slice of pie. The wooden end was then dropped into the sea so that it could float. The rest of the coil unrolled gradually as the ship sailed. The coil was allowed to unroll for a specific amount of time which was determined by an hourglass. After the specified time was exhausted, the rope was reeled back into the ship. Sailors would then tally the number of knots between the piece of wood and the ship. The speed of the ship was the number of knots counted. Based on the current knowledge of a knot, it is safe to conclude that the distance of intervals between the knots was close to one nautical mile. The reason for this conclusion is that, by then, the nautical mile had not been internationally defined and accepted.

Most professionals do not use knots among non-professionals because it is not a widely understood unit. Instead, professionals would usually convert the measurements.