Ray, an old retired sailor, puts on his old uniform and heads for the
Plymouth docks once more, just for old time's sake.

He engages a young expensive prostitute and takes her up to a room at the
local Pub.
He's soon going at it , as well as he can for an old salt of his age,
But needing some reassurance, he asks, "How am I doing?"
The prostitute replies, "Well Ray, you old sailor you, you're doing about
three knots."
"Three knots?" he asks. "What the Hell is that supposed to mean??"

She says, "You're knot hard, you're knot in, and you're knot getting your
money back!