The sail is a structure above the main hull of a submarine that serves mainly as a streamlined fairing around the masts and antennas. On top of the sail is the bridge which is only used when the submarine is surfaced. If the submarine has a conning tower, the structure is known as a fairwater. In the UK the sail is known as the fin.

The terms conning tower, fairwater, and sail are often (incorrectly) used interchangeably.
                         |   |
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                      |  (Bridge) |
                      |           | < Sail
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(based on original ASCII art by bigmouth_strikes)
sagan = S = salescritter

SAIL /sayl/, not /S-A-I-L/ n.

1. The Stanford Artificial Intelligence Lab. An important site in the early development of LISP; with the MIT AI Lab, BBN, CMU, XEROX PARC, and the Unix community, one of the major wellsprings of technical innovation and hacker-culture traditions (see the WAITS entry for details). The SAIL machines were shut down in late May 1990, scant weeks after the MIT AI Lab's ITS cluster was officially decommissioned. 2. The Stanford Artificial Intelligence Language used at SAIL (sense 1). It was an Algol-60 derivative with a coroutining facility and some new data types intended for building search trees and association lists.

--The Jargon File version 4.3.1, ed. ESR, autonoded by rescdsk.

A modern windsurfing sail is made of monofilm, dacron and mylar. Sensitive parts are reinforced with kevlar mesh.

Currently, two desingns of a sail are predominant: camber induced and RAF (Rotating Asymmetric Foil). Cambered sails are more stable and powerful, but are more difficult to handle during manoeuvres. The current trend is that only the large race sails have camber inducers. The rigidity of the sail is also determined by a number of battens.

The leading edge of a sail is called the luff. The mast is in the luff tube. The rear edge is called the leech. The front bottom corner of the sail, where the mast foot protrudes, is called the the tack, and the rear corner, to which the boom is atached, is called the clew. The bottom edge, between the clew ant the tack, is called the foot.

A windsurfing sail is tensioned at two points: at the tack (by downhaul), and at the clew (by outhaul). There is a set of pulleys for downhauling at the tack and there's a grommet at the clew. Most shape is given to the sail by a very strong downhaul, bending the mast in the luff tube. The outhaul tension is relatively weak, mostly just to keep the sail from flapping.

The sail is tuned by adjusting the downhaul and the outhaul. Generally, the sail has to be trimmed more for stronger winds. More downhaul tension loosens the upper part of the leech, "spilling" the wind at the gusts and shifting the center of effort of the sail down. In contrary, releasing the downhaul tension shifts the CoE up. More outhaul makes the sail flatter, easier to control, but less powerful, and less outhaul brings more camber, more low-end power, shifts the CoE to the front, and limits the speed by increasing the aerodynamic resistance.

There are different kinds of sails for different kinds of windsurfing: wave, freestyle, freeride, race.

The size of the sail is measured in square metres and it can be anything from 3 m2 to 6.5 m2 for wave sails and from 6 m2 to 12 m2 for racing sails, with ranges for freestyle and freeride sails spanning somewhere between these extremes.

Sail: transportation: watercraft

A sail is used to propel a sailboat or assist a motorboat, or may be used to steady a working vessel. It is generally made of reinforced mylar or fabric, but sails have been made of aluminum, plywood, hide, leaves, and other materials. The sail is rigged to develop lift from the wind, and transfer the force to the hull.

The two primary methods of sails for getting lift from the wind are to block the wind or to bend the wind. The traditional square-rigged boat efficiently blocks the wind, giving it excellent downwind speed. Fore-and-aft sailing rigs are more efficient at bending the wind, allowing them to sail well at an angle upwind. Blocking the wind allows the sail to develop force based on the velocity of the wind, its density, and the surface area of the sail. There is not consensus on the exact mechanism by which force is developed from bending the wind, but the force is based on the apparent velocity, and the aerodynamics of the sail (including the angle of attack of the chord of the sail, depth and position of maximum camber, and the induced drag.)

Most sails are designed to use both methods of gaining lift, but a boat's rig will tend to focus on one or the other depending on it's designed use, and its sails will be more efficient in one method or the other. In example, an America's Cup boat is very efficient going upwind (bending), while a full-rigged Ship is the extreme downwind rig (blocking).

When describing a triangular sail, the corners are all reinforced with patches, as they carry the strain of the forces on the sail. Each has a hole of some type, called a cringle, to which lines or shackles are connected to attach and control the sail. Their names are as follows:

  • Tack
    The lower, forwardmost corner. It is usually attached to the boat using a shackle or tack hook fitting. Bermudan mainsails are tacked to the boom or gooseneck, while staysails (including jibs) are usually shackled to a deck fitting or the stemhead, sometimes using a tether.
  • Head
    The uppermost corner is generally called the head. The halyard is attached here, which is used to hoist the sail up and to tension the leading edge of the sail. On Bermudan mains, a large and stiff headboard is usually attached, which supports additional sail area like a gaff or other yard does.
  • Clew
    The lower, aftermost corner. On unboomed sails, the sheets attached directly to the clew and both trim and spread the sail. On boomed sails there is usually an outhaul line or car which is used to tension the sail, and the sheet is attached to the boom to adjust the trim.

Each edge of the sail also has a number of elements, and of course even more specialized language. Around each edge is a tape called the tabling which is carefully matched to the sail material so it will not deform the sail's shape as it stretches in the wind.

  • Luff
    The leading edge of the sail cuts the wind and indicates when the sail is stalling, such as when the pointing too close to the wind. The luff is often attached to a stay or mast using shackles, boltrope or slug in a slot, a lacing, hoops or parrels, or slides in or on a track. A sail downhaul may be added to an attached sail luff to make it easier to dowse the sail. For many staysails, however, the luff is just a smooth edge tensioned by the halyard and possibly a tack downhaul.
  • Foot
    The lower edge of the sail is called the foot, and may include a rounded portion called foot roach if the sail is not attached to a boom. Boomed sails may be attached by the same methods as the luff, or the sail might be loose-footed and attached only at the tack and clew. The outhaul controls the tension of this edge.
  • Leech
    The aftermost edge is responsible for releasing the wind smoothly to avoid causing turbulence and, thereby, induced drag. A leech cord inside the tape can help with the shape of the edge, as will a vang and the sheet lead. On Bermudan mainsails especially, but also other triangular sails occasionally, additional sail area may be added as a rounded bulge of the leech called roach. Roach is usually supported by battens, either short ones sewn into pockets or full-length yards attached to cars at the mast like a junk rig. (But unlike the junk, the battens cannot vang the leech for trim.) Traditionally a yacht's ensign is hoist 2/3 up the leech, or might be sewn there.

A four-sided bending sail adds an upper edge called the head. If the upper edge is attached to a spar it will have some form of outhaul but will most likely be laced to the yard. Otherwise the head will be a smooth tape, probably acting at least in part as an extension of the luff. The extra corner, at the juncture of the head and the luff, is called the throat, while the corner of head and leech is called the peak.

On the other hand, four-sided blocking sails, commonly called square-sails, have a different use of the jargon.

  • Head
    The head is generally laced to the yard. The tabling includes a head rope and head holes for lacing, and large earings at each end.
  • Leech
    The square sail has two leeches, and the edge cutting into the wind like the luff of the bending sails will be called the weather leech (or just the luff on non-archaic boats.) Each leech will include cringles for the reef-tackle, and ends in a clew cringle. The leech liner is a patch added to take the chafe from the reef tackle.
  • Foot
    The foot is concave, with the clews sometimes much lower than the middle of the sail. The footrope is a strong element of this edge, to prevent the stretching which might split the sail.

A sail is sized to a boat based on how much wind can be expected where the boat sails, how much the boat masses (displaces), and what the underwater shape of the hull might be. The most common issue is not enough wind, so a larger sail than is seamanly is usually flown. And reefing is how a sail is made smaller to deal with more wind than the boat can use. On traditional triangular sails, the sail is partially lowered and a portion of the foot is tied in a reef using reef nettles or sail ties, the tack and clew may be held down to the boom using a reefing line, a tack hook, or lashing. Roller reefing is hardly a new technology, and may be found on staysails rolling in the luff, and on mainsails rolling in either the luff or the foot of the sail. Some bending sails are brailed to reef them, such as on large sprit rigs and certain gaff rigs like the Brixton Trawler. On a square sail the clews and foot are hauled up toward the yard using the reef-tackle to haul in on the buntlines, with the reef tied in using the nettles on the reef band.

  • Edwards, Fred; Sailing as a Second Language; International Marine Publishing Company; © 1988 Highmark Publishing Ltd.; ISBN 0-87742-965-0
  • Marino, Emiliano; The Sailmaker's Apprentice: A guide for the self-reliant sailor; International Marine/Ragged Mountain Press; © 1994 International Marine; ISBN 0-07-157980-X
  • rootbeer277; Fabulousness: Editing On-The-Fly; (requested ms not provided but is currently owed favours-of-choice)
  • Rousmaniere, John; The Annapolis Book of Seamanship; Simon & Schuster; © 1983, 1989 John Rousmaniere; ISBN 0-671-67447-1

Sail (?), n. [OE. seil, AS. segel, segl; akin to D. zeil, OHG. segal, G. & Sw. segel, Icel. segl, Dan. seil. &root; 153.]


An extent of canvas or other fabric by means of which the wind is made serviceable as a power for propelling vessels through the water.

Behoves him now both sail and oar. Milton.


Anything resembling a sail, or regarded as a sail.


A wing; a van.


Like an eagle soaring To weather his broad sails. Spenser


the extended surface of the arm of a windmill.


A sailing vessel; a vessel of any kind; a craft.

⇒ In this sense, the plural has usually the same forms as the singular; as, twenty sail were in sight.


A passage by a sailing vessel; a journey or excursion upon the water.

⇒ Sails are of two general kinds, fore-and-aft sails, and square sails. Square sails are always bent to yards, with their foot lying across the line of the vessel. Fore-and-aft sails are set upon stays or gaffs with their foot in line with the keel. A fore-and-aft sail is triangular, or quadrilateral with the after leech longer than the fore leech. Square sails are quardrilateral, but not necessarily square. See Phrases under Fore, a., and Square, a.; also, Bark, Brig, Schooner, Ship, Stay.

Sail burton Naut., a purchase for hoisting sails aloft for bending. -- Sail fluke Zool., the whiff. -- Sail hook, a small hook used in making sails, to hold the seams square. -- Sail loft, a loft or room where sails are cut out and made. -- Sail room Naut., a room in a vessel where sails are stowed when not in use. -- Sail yard Naut., the yard or spar on which a sail is extended. -- Shoulder-of-mutton sail Naut., a triangular sail of peculiar form. It is chiefly used to set on a boat's mast. -- To crowd sail. Naut. See under Crowd. -- To loose sails Naut., to unfurl or spread sails. -- To make sail Naut., to extend an additional quantity of sail. -- To set a sail Naut., to extend or spread a sail to the wind. -- To set sail Naut., to unfurl or spread the sails; hence, to begin a voyage. -- To shorten sail Naut., to reduce the extent of sail, or take in a part. -- To strike sail Naut., to lower the sails suddenly, as in saluting, or in sudden gusts of wind; hence, to acknowledge inferiority; to abate pretension. -- Under sail, having the sails spread.


© Webster 1913.

Sail (?), v. i. [imp. & p. p. Sailed (?); p. pr. & vb. n. Sailing.] [AS. segelian, seglian. See Sail, n.]


To be impelled or driven forward by the action of wind upon sails, as a ship on water; to be impelled on a body of water by the action of steam or other power.


To move through or on the water; to swim, as a fish or a water fowl.


To be conveyed in a vessel on water; to pass by water; as, they sailed from London to Canton.


To set sail; to begin a voyage.


To move smoothly through the air; to glide through the air without apparent exertion, as a bird.

As is a winged messenger of heaven, . . . When he bestrides the lazy pacing clouds, And sails upon the bosom of the air. Shak.


© Webster 1913.

Sail, v. t.


To pass or move upon, as in a ship, by means of sails; hence, to move or journey upon(the water) by means of steam or other force.

A thousand ships were manned to sail the sea. Dryden.


To fly through; to glide or move smoothly through.

Sublime she sails The aerial space, and mounts the winged gales. Pope.


To direct or manage the motion of, as a vessel; as, to sail one's own ship.



© Webster 1913.

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