Which of the following is a method to determine if an anchor is dragging?

A reliable method for determining if an anchor is dragging involves feeling vibrations from the anchor line. These vibrations can occur if the anchor is not holding properly in the seabed and the boat begins to move relative to the anchor. If you are feeling a consistent vibration or increase in tension along the anchor line, this is a strong indication that the anchor has become dislodged and the vessel may be drifting.

The other options do not provide accurate or reliable methods for assessing anchor drag. For example, noticing a change in the boat's speed might not directly correlate to the anchor's holding; other factors such as wind or current could also affect speed. While crew movement could suggest an issue, it is not a definitive sign of dragging, as crew may move for various reasons unrelated to anchor status. Checking for clear skies above is unrelated to anchoring and would not provide any insight into whether the anchor is dragging.