What is a “Knot”? The term “knot” refers to a measurement of speed equal to one nautical mile per hour. A nautical mile is slightly longer than a standard mile.
- 1 nautical mile = 1.15 miles = 1.85 kilometers
- 1 knot = 1.15 miles per hour = 1.85 kilometers per hour
- 1 knot = 20.251969 inches per second = 51.44 centimeters per second
The Origin of “Knots”
The term “knot” dates back to the 17th century when sailors measured the speed of their ships using a device called a “log.” This device consisted of a spool of rope with evenly spaced knots, attached to a piece of wood shaped like a pie slice.
The wood piece was thrown overboard from the back of the ship and floated behind it. As the ship moved forward, the rope was allowed to unwind freely from the spool. After a specified amount of time, the rope was pulled back in, and the sailors counted the number of knots that had passed overboard between the ship and the piece of wood. This count was used to estimate the ship’s speed.
Why Use Knots?
- Historical Methods: The method of using a log with knots was practical and reliable for sailors navigating the seas. The use of knots provided a standardized measurement system that was crucial for accurate navigation.
- Nautical Relevance: Nautical miles are used instead of regular miles because they correspond more directly with the Earth’s geography. One nautical mile is based on the circumference of the Earth and is equal to one minute of latitude.
- Consistency and Tradition: The measurement of speed in knots has remained consistent over centuries, maintaining tradition and consistency in maritime practices.
Understanding why ship speed is measured in knots gives insight into the history of navigation and the practical needs of early sailors that have carried through to modern maritime practices.