Sail components include the features that define a sail's shape and function, plus its constituent parts from which it is manufactured. A sail may be classified in a variety of ways, including by its orientation to the vessel (e.g. fore-and-aft) and its shape, (e.g. (a)symmetrical, triangular, quadrilateral, etc.). Sails are typically constructed out of flexible material that is shaped by various means, while in use, to offer an appropriate airfoil, according to the strength and apparent direction of the wind. A variety of features and fittings allow the sail to be attached to lines and spars.

Whereas conventional sails form an airfoil with one layer of fabric, wingsails comprise a structure that has material on both sides to form an airfoil—much like a wing placed vertically on the vessel—and are beyond the scope of this article.

Classifications

Sails may be classified as either triangular, which describes sails that either come to one point of suspension at the top or where the sail comes to a point at the forward end, or quadrilateral, which includes sails that are attached to a spar at the top and have three other sides, or as square. They also may be classified as symmetrical (square sails and symmetric spinnakers) or asymmetrical (most other sails). Typically, asymmetrical sails perform better on points of sail closer to the wind than symmetrical sails and are designed for fore-and-aft rigs. Symmetrical sails perform best on points of sail that are further from the wind direction.

Triangular

Triangular sails have names for each of three edges and three corners, explained below. Rigs with such sails include Bermuda, cutter, lateen and vessels with mixed sail plans that include jibs and other staysails. Most triangular sails are classified as asymmetrical and fore and aft; symmetric spinnakers are symmetrical triangular sails that are designed for off-the-wind use.. A ship mainly so rigged is called a square-rigger.

Shape

thumb|Square sail edges and corners (top), [[running rigging (bottom)]]

The shape of a sail is defined by its edges and corners in the plane of the sail, laid out on a flat surface. The edges may be curved, either to extend the sail's shape as an airfoil or to define its shape in use. In use, the sail becomes a curved shape, adding the dimension of depth or draft.

Edges

The top of all sails is called the head, the leading edge is called the luff, the trailing edge is the leech, and the bottom edge is the foot.

;Head

:The head is the upper edge of the sail, and is attached at the throat and peak to a gaff, yard, or sprit. For a triangular sail the head refers to the topmost corner.

;Leech

:The aft (back) edge of a fore-and-aft sail is called the leech (also spelled leach). However, once a symmetrical sail has wind blowing along its surface, whether on a reach or close-hauled, the windward leech may be called a luff (see below).

;Luff

:The forward (leading) edge of a fore-and-aft sail is called the luff, and may be attached along a mast or a stay. and, when on a reach or close-hauled, the windward leech of a square sail may be called the luff or the weather leech.

;Foot

:The foot of a sail is its bottom edge. On a fore-and-aft mainsail, the foot is often attached, at the tack and clew, to a boom; on a square sail to a spar by clews on both ends; if no boom or spar is present, the sail is said to be "loose-footed".

Roach

A fore-and-aft triangular mainsail achieves a better approximation of a wing form by extending the leech aft, beyond the line between the head and clew in an arc called the roach, rather than having a triangular shape. This added area would flutter in the wind and not contribute to the efficient airfoil shape of the sail without the presence of battens. The roach allows the foot of the sail to clear stays coming up the mast, as the sails are rotated from side to side.

;Peak

:On a quadrilateral sail, the peak is the upper aft corner of the sail, at the top end of a gaff, a sprit or other spar.

;Throat

:On a quadrilateral sail, the throat is the upper forward corner of the sail, at the bottom end of a gaff or other spar. Gaff-rigged sails, and certain similar rigs, employ two halyards to raise the sails: the throat halyard raises the forward, throat end of the gaff, while the peak halyard raises the aft, peak end.

;Clew

:The corner where the leech and foot connect is called the clew on a fore-and-aft sail. On a jib, the sheet is connected to the clew; on a mainsail, the sheet is connected to the boom (if present) near the clew. On a square sail underway, the tack is the windward clew and also the line holding down that corner.

Draft

Those triangular sails that are attached to both a mast along the luff and a boom along the foot have depth, known as draft or draught, which results from the luff and foot being curved, rather than straight as they are attached to those spars. Draft creates a more efficient airfoil shape for the sail. Draft can also be induced in triangular staysails by adjustment of the sheets and the angle from which they reach the sails.

Construction

thumb|Laminated sail with Kevlar and Carbon fibers.

thumb|[[Catamaran with full-length battens in a laminated sail.]]

Sails are constructed of fabrics that may be woven or manufactured as films. The sail are often assembled of multiple panels that are arrayed in a manner that transfers the load from the wind to the sail's attachment points—a combination of corners and edges—that transmits the load into the mast and powers the boat. Construction of such sails requires stitching, bonding, reinforcements and other features to achieve this. Other sails are constructed directly from fibers, filaments and films.

Materials

The characteristics of a sail are due to design, construction and the attributes of the fibers, which are woven together to make the sail cloth. There are several key factors in evaluating a fiber for suitability in weaving a sail-cloth:

  • Initial modulus – The ability to resist stretching. Higher resistance is better for upwind sails.
  • Breaking strength (tenacity) – Measured as a force per cross sectional area of fiber. Higher is better for sails.
  • Creep – Describes the long term stretch of a fiber or fabric. A material with creep may have a superior modulus, but lose its shape over time.
  • Resistance to ultraviolet light – Strength loss from exposure to the Sun’s UV rays measured by a standardized exposure test.
  • Flex strength – Strength lost due to bending, folding, or flogging, which is frequently measured with an industry standard 50 fold test.
  • Cost-effectiveness – Both the initial cost and its durability of the material define its cost-effectiveness over time.

Traditionally, sails were made from flax or cotton canvas. may be specified as either high or low tenacity, as indicated, in part by their denier count (a unit of measure for the linear mass density of fibers). High-tenacity Dacron comes in multiples of 220, 350 and 570 deniers, whereas low-tenacity Dacron comes in multiples of 150, 250, and 400 deniers. Sailcloth is typically heat-shrunk to tighten the weave and then receives a chemical bonding finish of melamine. Such cloth is typically specified by deniers for warp and fill (weft), e.g. 220/570.

Panels and laminations

thumb|Sail detail at the tack of a mainsail, showing various types of seam stitches where panels join, bolt ropes in the luff and foot, and two [[cringles.]]

Conventional sails comprise panels, which are most often stitched together, at other times adhered. There are two basic configurations, cross-cut and radial. Cross-cut sails have the panels sewn parallel to one another, often parallel to the foot of the sail, and are the less expensive of the two sail constructions. Triangular cross-cut sail panels are designed to meet the mast and stay at an angle from either the warp or the weft (on the bias) to allow stretching along the luff, but minimize strutting on the luff and foot, where the fibers are aligned with the edges of the sail.

Radial sails have panels that "radiate" from corners in order to efficiently transmit stress and are typically higher-performance than cross-cut sails. A bi-radial sail has panels radiating from two of three corners; a tri-radial sail has panels radiating from all three corners. Mainsails are more likely to be bi-radial, since there is very little stress at the tack, whereas head sails (spinnakers and jibs) are more likely to be tri-radial, because they are tensioned at their corners. or on the mainsail, where it may interfere when furled or when the sail is backwinded against the mast.

<gallery>

Zagiel horyzont.svg|Cross-cut panels

Zagiel birad.svg|Bi-radial panels

Zagiel gwiazda.svg|Tri-radial panels

</gallery>

Stitching and bonding

Conventional sail panels are sewn together. Sails are tensile structures, so the role of a seam is to transmit a tensile load from panel to panel. For a sewn, textile sail this is done through thread and is limited by the strength of the thread and the strength of the hole in the textile through which it passes. Sail seams are often overlapped between panels and sewn with zig-zag stitches that create many connections per unit of seam length.

  • Breaking force (newtons) –
  • Elongation (percent) – 22%
  • Strength (newtons/millimetre) –
  • Modulus of elasticity (newtons/millimetre) –

Whereas textiles are typically sewn together, other sail materials may be ultrasonically welded—a technique whereby high-frequency ultrasonic acoustic vibrations are locally applied to workpieces being held together under pressure to create a solid-state weld. It is commonly used for plastics, and especially for joining dissimilar materials.

  • Leech lines are found on mainsails and large jibs to tighten the leech and prevent fluttering. They run through a sleeve on the leech from the head to the clew, where there is usually a clam cleat to tighten it. Occasionally, foot lines perform an analogous function on a loose-footed sail.
  • UV protection panels are usually affixed to the leech and foot of roller furling jibs to prevent ultraviolet rays from reaching the sailcloth while the sail is not in use. These are typically a dark color to absorb the harmful rays.

Reinforcements at attachment points

thumb|Headboard on a mainsail.

The corners of triangular sails are typically areas of high stress and consequently often have reinforced layers and tape radiating from, whether cross-cut or radial in construction. Their corners are always attached to a shackle, attached to a line or spar—the halyard at the head, a shackle at the tack, and the outhaul at the clew. The connecting shackle runs through a grommet at each of these points. There are additional points where reinforcing and grommets may occur: at the cunningham, a downhaul used to flatten a mainsail (jibs may have a similar feature), and along the foot of a Genoa jib to allow a line to lift it out of the waves. The head of a triangular sail may have a rigid headboard riveted to it in order to transfer load from the sail to the halyard. Most battens are fiberglass pultrusions with a thin, rectangular cross section.

Fittings

Sails usually have fittings attached to them that transmit force through a small area. These include grommets, which reinforce fabric at an attachment points and connections to lines; hoops and slides, which attach sails to spars; and reefing features, which may include reefing lines attached to the sail or grommets that have reefing lines running through them. Additional features include tell-tales, windows—used on dinghy sails—and lettering and other graphics that include sail numbers and manufacturers logos, etc.

Hardware

Where sails are attached to a mast, spar, or stay there is some kind of connection—often it's the bolt rope running through a groove in the mast, boom, or head foil—otherwise, there is a piece of hardware involved, e.g.:

  • Gaff sails usually have hoops that slide up and down the mast.

Mainsails on Bermuda rigs typically have paired grommets that secure the luff and leech to the boom, as the sail is lowered to reduce its area. These become the new tack and clew. A reefing line typically runs through the reef point on the luff to quickly secure the new clew. The grommet that becomes the new tack is typically hooked onto the boom. There may be grommets along the line between the new tack and clew that allow ties to pass through around the boom.

Tell-tales

Tell-tales are pieces of yarn, thread or tape that are affixed to sails to help visualize airflow over their surfaces. Typically, they are mounted near the luff of sails, but they are also found on the leech on some sails. To windward, a sagging tell-tale indicates still air, either from stalling (indicated on the leeward side, when the sail is sheeted in too far, compared to the apparent wind) or pinching (indicated on the windward side, when the sail isn't sheeted in far enough, compared to the apparent wind).