This reminds me of an occasion when cruising the Union Canal near Ratho. A wide beam hire boat was coming towards us with a woman waving both arms standing at the bow, in an agitated action, firstly in one direction and then the other. Not knowing what was required of us, we simply stopped. The instructions continued and they kept moving towards us.
It was only when we could hear was also being shouted did we appreciate that her husband who steering couldn't see over or along the boat and she was shouting "left a bit" followed by "right a bit" coordinated with her hand movements.
We let them pass us before we moved.