The Collaborative International Dictionary
Luff \Luff\ (l[u^]f), v. i. [imp. & p. p. Luffed (l[u^]ft); p. pr. & vb. n. Luffing.]
(Naut.) To turn the head of a vessel toward the wind; to sail nearer the wind; to turn the tiller so as to make the vessel sail nearer the wind.
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(Naut.) To flutter or shake from being aligned close to the direction of the wind; -- said of a sail.
To luff round, or To luff alee, to make the extreme of this movement, for the purpose of throwing the ship's head into the wind.
Wiktionary
vb. (present participle of luff English)
Wikipedia
In sailing, luffing refers to when a sailing vessel is steered far enough toward the direction of the wind (" windward"), or the sheet controlling a sail is eased so far past optimal trim, that airflow over the surfaces of the sail is disrupted and the sail begins to "flap" or "luff" (the luff of the sail is usually where this first becomes evident). This is not always done in error; for example, the sails will luff when the bow of the boat passes through the direction of the wind as the sailboat is tacked.
A sailboat can also be "luffed" slightly without completely de-powering the sails. Often this occurs on the point of sail known as close hauled, this is sometimes referred to as pinching or "feathering" and is sometimes done deliberately in order to make a more direct course toward an upwind destination (see: " beating to windward"), or to "de-power" a sail on a windy day to maintain control of the sailboat. "Luffing" can also be used to slow or stop a sailboat in a controlled manner.
Luffing is also a process of power kites when they stall and the front (or leading) edge falls downwards.
Usage examples of "luffing".
Dead and injured men were scattered everywhere, and the luffing sails were torn and spattered with blood, and the weather-darkened wood of mast and gunwales was ploughed up in many places to show the bright, fresh wood underneath.
Short-short-short and the deck crew broke out the long sweeps to spider-walk the ship out into open water, six strokes and the poles were run inboard and the northing wind caught at the jibsails, luffing, thunder-cracks of rippling canvas.
Like an Admiral working his ship to windward, he had suddenly come about and, after a few moments’ luffing and disarray, was now on an altogether novel tack: “The lady used to be called Anne Hyde—a close relation of John Comstock.
The island rose steeply here, and _Birdwing_ ghosted with its sails luffing for lack of wind.
He glanced down at the heaving boat, the bowman poised with his hook, Bonden at the tiller gauging the scend of the sea, alternately filling a trifle and then luffing up, and at Stephen, looking meek in the stern-sheets, nursing his box: he sniffed, and went below without a word.
With the master, on the course to steer, luffing up the second they were past the island that made the near corner of the bay.