What unit is used to measure the speed of a ship?

The unit used to measure the speed of a ship is a knot. One knot is defined as one nautical mile per hour, which is approximately 1.15 statute miles per hour or 1.85 kilometers per hour. This unit is particularly suited for maritime navigation because it is based on nautical miles, which take into account the curvature of the Earth, making it more relevant and practical for navigation on water compared to standard land measurements.

Nautical miles, and consequently knots, are more useful for sailors because they directly relate to geographic coordinates on charts, enabling effective calculation of distances traveled over water. Thus, using knots allows for more precise navigation, particularly in relation to latitude and longitude.

The other options represent different units of speed that are not typically used in maritime contexts, making them less suitable for measuring the speed of a ship.