I've briefly swum behind a boat that was anchored, but in a steady current (between some Danish islands). It's really like the boat is speeding away from you, e

I've briefly swum behind a boat that was anchored, but in a steady current (between some Danish islands). It's really like the boat is speeding away from you, even while anchored. (We had some safety measures which I mostly forgot, but it included a very long line behind the boat. Not sure if we were attached to that line.)