@Kendall 22 Nov 13 - 07:31 PM
A ship at anchor will always have left itself searoom before anchoring, which will still be there when weighing: there's time enough to weigh anchor and then set sail, particularly as the only thing making way on the ship at that point is the current. Many ships could be worked by a mere fistful of very exhausted men, which is how the prize crew system worked. And if you haven't left yourself searoom, either don't sail until the tide, currents and winds change, or crab your way out using sprung anchors and boats - which isn't what the song describes.
Sheets and halyards will normally be secured so they can be left to their own devices at that point. If it's really necessary to use the wind, a minimum sail can be set first, but the same applies.