The meaning of the expression "three sheets in the wind" is universally appreciated: not to put too fine a point on it or beat around the bush, a person so described is drunk. But where the expression might have come from is nothing like as clear.
Some experts on these matters believe it had its origin in windmills. The old Dutch-style windmill has four wooden vanes to which are attached four "sails", or more properly, apparently, "sheets".
If one of the sheets is missing or severely damaged, then only three sheets are presented to the wind: the whole machine is then severely out of balance, and in a fresh breeze the entire structure of the mill goes into a violent and potentially destructive shudder - evoking the image of a staggering drunk.
More commonly, however, it is thought that "three sheets in the wind" can be traced to that strange custom aboard sailing ships of never calling a rope a rope but esoterically naming it something else entirely. Thus a "halyard", according to my interpretation of what the experts tell me, holds things - usually sails - vertically; a "sheet" holds things horizontally; and a "line" holds things more or less rigidly in place. Most importantly, the "main sheet" controls the mainsail, and two others - the "windward sheet" and the "leeward sheet" - control something called the headsail.
Now seasoned mariners will no doubt reach immediately for their quills and Quink at this shallow, and perhaps erroneous, exposition of the technicalities, but the metaphor is plain enough: if one sheet is loose, a sail flaps in the wind and a ship's progress is unsteady; two sheets "in the wind" and control becomes extremely difficult; and with "three sheets in the wind", a ship reels erratically in the manner of a drunken sailor.
Some, however, believe the nautical derivation of the term "three sheets in the wind" is even more imaginative. In olden times, if a sheet broke under strain, it was necessary for a sailor to secure both it and the wildly flailing canvas as soon as possible, before the massive sail would flap itself to pieces.
It was a dangerous task: one touch by a wire sheet, and a hapless sailor might find himself swept overboard to almost certain death. The story goes that a volunteer who successfully secured a sheet that was "in the wind" was given a generous tot of rum as a reward. A sailor, therefore, who had secured "three sheets in the wind", and lived to drink his just deserts, was likely to end up very happy - but extremely drunk.