An old retired sailor puts on his uniform and heads to 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 3 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.