Earlier this year we anchored in a North/South oriented channel between two islands in the Andaman Sea. Good holding in 10m, 1 to 2 kt tidal current
. Dead calm night.
There were other boats anchored, we dropped the hook toward the North of the channel and left a decent distance between us and the nearest boat to the South even after stretching our chain with plenty of scope
. All boats oriented bow to North into the current
Dived and checked anchor well set and made sure we were nowhere near the nearest boat's anchor/chain; it was a boat doing charters. Set anchor alarm to very small radius, had dinner, relaxed in cockpit
and waited for tide to reverse, which it duly did. Now all the boats oriented with bows to South.
Suddenly, in the dark, we hear voices nearby and see the boat that was to our South still pointing south but right next to our starboard side. We shouted "are you dragging?" Interestingly, their reply was "no, you are dragging".
Two points I find interesting from the human performance point of view:
1. The very first assumption we both made was that the other boat was dragging.
2. It is possible that neither boat was dragging.
What is really not possible is for one boat to drag the anchor up-current, which was the other skipper's assumption. If you are seeing someone in your stern get closer to you at anchor, it is most likely you that is dragging, or you have so much more scope
than the other boat that you get closer when the current reverses.
That said, and to answer the OPs question, keeping some form of watch at night is of the utmost importance, even if it is just the anchor alarm. In our case that didn't help because we didn't move, but we could have. If we had been more alert we could have called the other boat earlier and alert them.