What is a "fathom"?

A fathom is defined as a unit of measurement for determining water depth, specifically equivalent to six feet. This measurement is crucial for various maritime activities, such as navigation and anchoring, as it allows mariners to ensure that their vessels can safely operate in waters of adequate depth. This understanding of depth is essential for preventing groundings and ensuring safe passage in areas with varying undersea topography.

The other options represent different concepts in maritime practice: vessel speed measurement typically involves knots or other units; cargo capacity is assessed in tons or cubic feet; wind speed is measured in knots or miles per hour. Each of these metrics serves important functions, but they do not pertain to fathoms or its specific role in measuring water depth.