Final answer:
For proper anchoring, the recommended amount of line, known as scope, is about 8 times the width and 15 times the depth of the water. These measurements ensure adequate holding power for the anchor and prevent dragging, similar to how historical sailors used knotted ropes to measure water depth for anchoring.
Step-by-step explanation:
When anchoring a boat, the amount of line (also known as 'scope') let out in comparison to the water depth can determine the anchor's holding power and the boat's swinging radius. An older "rule of thumb" for anchoring was to use a scope of 5 to 7 times the water depth; however, newer guidelines recommend using a scope of approximately 8 diameters wide and 15 diameters deep. This means that for every foot of water depth, one should let out 8 feet of line side-to-side and 15 feet of line vertically to ensure sufficient holding power for the anchor and to prevent dragging.
The importance of these measurements is highlighted by the fact that historical sailors measured depths using a fathom, a six-foot measure on a knotted rope. They considered the depths and the necessary line to ensure their anchors did not drag, just as modern boaters must consider their scope today.