What is Anchor Watch?

Legal Definition
A watch, consisting of a small number of men, (from one to four,) kept constantly on deck while the vessel is riding at single anchor, to see that the stoppers, painters, cables, and buoy-ropes are ready for immediate use. The Lady Franklin, 2 Lowell, 220, Fed. Cas. No. 7,984.
-- Black's Law Dictionary
Legal Definition
The lookout maintained while a vessel is at anchor.
-- Ballentine's Law Dictionary