how did the phrase “three sheets to the wind" come to refer to being drunk?

Dear Yahoo!:
How did the phrase “three sheets to the wind" come to refer to being drunk?
—Tippi

Dear Tippi:
Drink up, me hearties, yo ho! The sailing life gave us the intoxicating phrase “three sheets to the wind,” although “three sheets in the wind” came first.

Among nautical folks, a “sheet” refers to the rope used to secure a ship’s sail. On the square-rigged ships of yore, three sheets were needed to tie up the sails. So, if all three of the ship’s sheets were loose in the wind, the sail would flop about and the ship would go off course -- rather like a drunken sailor staggering around on shore.

“Three sheets in the wind” was first recorded in 1821 by Pierce Egan in his work “Real Life in London.” In those days, sailors had a rating system for their inebriation. “One sheet” was merely tipsy, and it went up to “four sheets,” meaning unconscious. Yo ho ho and a bottle of rum, indeed.