The Riddle of the Sands (movie, 1979)

In the early years of the 20th Century, two British yachtsmen (Michael York and Simon MacCorkindale) stumble upon a German plot to invade the east coast of England in a flotilla of specially designed barges. They set out to thwart this terrible scheme, but must outwit not only the cream of the German Navy, but the feared Kaiser Wilhelm himself.