An old retired sailor puts on his old uniform and heads for the docks once more, for old times sake. He engages a prostitute and takes her up to a room. He's soon going at it as well as he can for a guy his age, but needing some reassurance, he asks, 'How am I doing ?' The prostitute replies, 'Well, old sailor, you're doing about three knots.' 'Three knots ? he asks. 'What's that supposed to mean ?' She says, "You're knot hard, you're knot in, and your knot getting your money back.