Practicality:

* Knots: A knot is a unit of speed specifically designed for nautical use. It represents one nautical mile per hour. Nautical miles are based on the circumference of the Earth, making them more accurate for navigation than statute miles.

* Fathoms: Fathoms are a unit of depth, ideally suited for measuring water depths. One fathom is equal to six feet, which aligns with the reach of a sailor's outstretched arms.

Historical Context:

* Knots: The term "knot" originated from the practice of measuring a ship's speed using a log line. This line was marked with knots at specific intervals, and the number of knots that passed over the side in a given time determined the speed.

* Fathoms: Historically, sailors used their arms to measure the depth of the water. One fathom was the distance a sailor could reach with both arms outstretched.

Standardization and Safety:

* Consistent measurements: Using knots and fathoms ensured consistent measurement across different ships and crews, reducing errors and ensuring accurate navigation.

* Safety: Precise depth measurements were critical for avoiding hazards, ensuring safe passage through shallow waters, and anchoring safely.

Modern Usage:

While the methods of measuring speed and depth have evolved, knots and fathoms remain standard units in maritime navigation and nautical charts.

Why not mph or feet/meters?

* MPH: Statute miles are based on land measurements and are less accurate for navigating the Earth's curved surface.

* Feet/Meters: While these units are useful for everyday purposes, they are less practical for the specific needs of seafaring.

In summary, knots and fathoms were developed specifically for the unique demands of navigation and maritime operations. Their historical origins, practicality, and standardization contribute to their continued relevance in the maritime world.