What unit is commonly used to express the measurement of speed in nautical navigation?

The unit commonly used to express the measurement of speed in nautical navigation is the knot. A knot is defined as one nautical mile per hour, and is specifically designed for maritime and air navigation. This unit is critical because it takes into account the curvature of the Earth, as nautical miles are based on degrees of latitude. Since the Earth is not a perfect sphere, using knots aligns navigational speeds with distances traveled over the globe, making it particularly suited for maritime purposes where distances are measured in nautical miles.

Other units such as mile per hour, kilometer per hour, or foot per second are typically used in land-based contexts, making them less relevant for nautical navigation. Thus, using knots enhances clarity and precision in maritime navigation, ensuring that all mariners are on the same page regarding speed and distance when plotting courses at sea.