An old retired sailor puts on his old uniform and heads for the docks once more, for old time’s sake.
He engages a "dock lady" 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 lady 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 you're knot getting your money back.'