Old Murphy spent 40-plus years in the Merchant Marines before retiring. One night he wondered whether he could still do the wild thing, and went down the shipyard.
He found a working girl who fit his price range and nearby to an economical hotel room. They got in bed and started going to it. After a while, Murphy asked, “How am I doing?”
She said, “Well sailor, you’re doing about three knots.”
“Three knots?” said Murphy, “What do you mean?”
She explained, “You’re not in, you’re not hard, and you’re not getting your money back.”