Sail components include the features that define asail'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 awing placed vertically on the vessel—and are beyond the scope of this article.
Sails may be classified as eithertriangular, 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, orquadrilateral, which includes sails that are attached to a spar at the top and have three other sides, or assquare. They also may be classified assymmetrical (square sails and symmetricspinnakers) orasymmetrical (most other sails). Typically, asymmetrical sails perform better onpoints of sail closer to the wind than symmetrical sails and are designed forfore-and-aft rigs. Symmetrical sails perform best on points of sail that are further from the wind direction.[1][2]
Triangular sails have names for each of three edges and three corners,explained below. Rigs with such sails includeBermuda,cutter,lateen and vessels with mixed sail plans that includejibs and otherstaysails. Most triangular sails are classified asasymmetrical andfore and aft; symmetricspinnakers aresymmetrical triangular sails that are designed for off-the-wind use.[3]
Gaff,gunter,lug,junk and somesprit sails have four sides and are setfore and aft so that one edge is leading into the wind, forming anasymmetric quadrilateral shape. Naming conventions are consistent with triangular sails, except for the top edge and corners, asexplained below.[4]
Asquare rig is a type ofsail and rigging arrangement in which the primary driving sails are carried on horizontalspars which are perpendicular, orsquare, to thekeel of the vessel and to the masts—the sails themselves are not square but aresymmetrically quadrilateral. These spars are calledyards and their tips, beyond the last stay, are called theyardarms[5]. A ship mainly so rigged is called asquare-rigger.[6]
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 ordraft.
The top of all sails is called thehead, the leading edge is called theluff, the trailing edge is theleech, and the bottom edge is thefoot.
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 theroach, 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 ofbattens.[1] Offshore cruising mainsails sometimes have ahollow leech (the inverse of a roach) to obviate the need for battens and their ensuing likelihood ofchafing the sail.[12]
Roach is a term also applied to square sail design—it is the arc of a circle above a straight line from clew to clew at the foot of a square sail, from which sail material is omitted. The greater the departure from the straight line, the greater the "hollow" in the roach.[13][14] The roach allows the foot of the sail to clear stays coming up the mast, as the sails are rotated from side to side.[15]
The names of corners of sails vary, depending on shape and symmetry.
Those triangular sails that are attached to both a mast along the luff and a boom along the foot have depth, known asdraft 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 efficientairfoil shape for the sail. Draft can also be induced in triangularstaysails by adjustment of the sheets and the angle from which they reach the sails.[23]
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.
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:[1][3]
Traditionally, sails were made fromflax orcottoncanvas.[3] Materials used in sails, as of the 21st Century, includenylon for spinnakers—where light weight and elastic resistance to shock load are valued—and a range of fibers, used for triangular sails, that includesDacron,aramid fibers—includingKevlar, and otherliquid crystal polymer fibers—includingVectran.[3][1]
Woven materials, like Dacron,[24] may be specified as either high or lowtenacity, as indicated, in part by theirdenier count (a unit of measure for thelinear 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 ofmelamine. Such cloth is typically specified by deniers forwarp and fill (weft), e.g. 220/570.[25]
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Conventional sails comprise panels, which are most often stitched together, at other times adhered. There are two basic configurations,cross-cut andradial.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 thebias) 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.[26]
Radial sails have panels that "radiate" from corners in order to efficiently transmit stress and are typically higher-performance than cross-cut sails. Abi-radial sail has panels radiating from two of three corners; atri-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.[3]
Higher-performance sails may be laminated, constructed directly from multiple plies offilaments,fibers,taffetas, andfilms—instead of woven textiles—and adhered together.Molded sails are laminated sails formed over a curved mold and adhered together into a shape that does not lie flat.[3]
Where a sail may rub against a spreader on the mast, aspreader patch may be placed on a jib, when it overlaps with the mast,[27] or on the mainsail, where it may interfere whenfurled[28] or when the sail is backwinded against themast.[29]
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.[3] Measures for seam structural attributes—shown with a typical value for a sewn seam—include:[30]
Whereas textiles are typically sewn together, other sail materials may beultrasonically welded—a technique whereby high-frequencyultrasonicacousticvibrations are locally applied to workpieces being held together under pressure to create a solid-stateweld. It is commonly used forplastics, and especially for joining dissimilarmaterials.[30]
Sails have a variety of treatments at their edges, either to attach the sail to a stay, spar or mast or to prevent a free edge from fluttering or fraying.
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 ashackle, attached to a line or spar—thehalyard at the head, a shackle at the tack, and theouthaul at the clew. The connecting shackle runs through agrommet at each of these points. There are additional points where reinforcing and grommets may occur: at thecunningham, adownhaul used to flatten a mainsail (jibs may have a similar feature), and along the foot of aGenoa jib to allow a line to lift it out of the waves. The head of a triangular sail may have a rigidheadboard riveted to it in order to transfer load from the sail to the halyard.[26]
Square sails and gaff-rigged sails also have grommets at corners. Only the clews on a square sail take a comparatively large amount of stress, because the head is supported along the spar. Three sides of gaff-rigged sails are attached to a mast or spar.[20]
Asail batten is a flexible insert in a fore-and-aft sail that provides added stiffness and definition to the sail's airfoil cross-section.[1] The most common use of sail battens is in theroach of a mainsail. The batten extends the leech past the line that runs from the head and the clew of the sail to create a wider sail towards the top. Cruising sailboats may have four to six battens. Racing sailboats may have full-length battens, as well, that allow for better sail shape.[1] Battens are also found in jibs ofbeach-cat catamarans.[32] Most battens are fiberglasspultrusions with a thin, rectangular cross section.[1]
Junk rigs feature full-length battens that facilitate short-handed sail handling, including reefing. The battens are attached loosely to the mast with lines calledbatten parrels that allow fore-and-aft motion as the sail is controlled by individual sheets leading to multiple battens.[33]
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 includetell-tales, windows—used on dinghy sails[34]—and lettering and other graphics that include sail numbers and manufacturers logos, etc.
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.:
Other hardware includescam cleats, used to tension luff and foot lines.[12]
Different categories of sails arereefed (reduced in size) in different manners and therefore have different fixtures that achieve shortening of sail. Traditional canvas square and gaff-rigged sails have one or more rows ofreefing lines that pass through the sail, which reach around the sail that has been gathered in to reduce its size and secure the remaining unreefed sail to the spar (square rig) or boom (gaff rig).[35] Gaff-rigged sails require an extra set of lines to secure the part of the leech that becomes the new clew. These are calledreef pendents that drop through acomb on the boom, where they are secured, as needed.[4]
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.[35]
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 leach 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).[1]
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