Knots are a unit of speed used in maritime and aviation, equal to one nautical mile per hour. But how does this compare to miles per hour, the more common speed unit used on land? Understanding the difference between knots and miles per hour requires understanding the nautical mile.
The NOAA Ship Pisces, a research vessel, utilizes knots for speed measurement due to their relevance to nautical miles.
Nautical Miles vs. Statute Miles: The Foundation of the Difference
A nautical mile is slightly longer than a statute mile (the mile used on land). One nautical mile equals approximately 1.1508 statute miles. This difference stems from the nautical mile’s origin: it’s based on the Earth’s circumference and is defined as one minute of latitude. This makes it incredibly useful for navigation using latitude and longitude coordinates, especially over long distances where the Earth’s curvature is significant.
Knots: Speed on the Water and in the Air
One knot is equivalent to one nautical mile per hour. Therefore, a speed of one knot is roughly 1.15 miles per hour. This measurement is deeply rooted in maritime history. Before modern technology, sailors used a device called a “common log” to measure speed.
Sailors historically used a “common log” to measure knots, dropping a knotted rope into the water and counting the knots passing in a given time.
This tool consisted of a rope with knots tied at uniform intervals, attached to a wooden board. The board was thrown overboard, and the number of knots that passed through a sailor’s hands in a specific timeframe indicated the ship’s speed in knots.
Why Use Knots Instead of Miles Per Hour?
The use of knots and nautical miles simplifies navigation based on charts using latitude and longitude. Since one minute of latitude equals one nautical mile, calculating distances and speeds becomes straightforward. This is essential for both maritime and aviation navigation, where precise calculations are crucial for safety and efficiency. While seemingly complex, the relationship between knots and miles per hour is a fundamental aspect of travel on water and in the air. Understanding this connection allows for a clearer comprehension of speed in these contexts.
