Illustration of movement 447 in the book “507 mechanical movements”, 1908

“This method of passing a boat from one shore of a river to the other is common on the Rhine and elsewhere, and is affected by the action of the stream on the rudder, which is carries the boat across the stream an the arc of a circle, the center of which is the anchor which is holds the boat from floating down the stream.”

The big arrow shows the flow direction.
The small arrow shows the direction of the flow’s force that applies to the rudder and pushes the boat.