I know this ain't the Anoraky thread but can't resisit getting one of me other Eskimo coats out.
That push-tow of post '65 AZAMs is 'blue flagging', that means he is, in effect, driving on the wrong side of the road - boats normally pass port to port i.e. they drive on the right. Vessels going with the stream are generaly less manoverable than those going against it and in certain places, usually on bends, they are permitted to go the 'wrong' side in order to maintain control more easily. When they are doing this they must show a blue flag, like this bloke is doing. Nowadays, this is usually a square blue board mounted on a horizontal spindal, normally the board is flat and only its thin edge visible, when 'flagging' they turn it vertical. Better than a flag coz those can stream edge on to the viewer and vanish.

Summertime