A Tale of Two Tugboats

Two Mississippi tugboat captains, who had been friends for years, would always cry "Aye!" and blow their whistles whenever they passed each other.

A new crewman asked his boat's mate, "Why do they do that?"

The mate looked surprised and replied, "You mean that you've never heard of:

"An 'Aye' for an 'Aye' and a 'Toot' for a 'Toot'?"

*Thanks, SalTCBug