In England a gangplank is a gangboard, though both here and there the same thing is also called a gangway.
In any case, whether plank, board, or way, it’s a means of “going” aboard or off a ship.
And that, in Old English, is what a gang was, a “going.”
In later times gang began to mean also a set or group of things that “go” together, thus giving us the sense of a band of persons who go or act co-operatively.
