The term to square a yard is used when sailing a square-rigged ship.
To "square a yard" is to lay the yards at right angles to the line of the keel by trimming with the braces.
"Squaring a yard" adjusts the position of the square sails so that they are perpendicular to the keel of the ship. This is done in order to "run before the wind', i.e., sail with the wind directly behind the vessel rather than tacking.
When a square-rigger is running downwind, and the yards are positioned perpendicular to the line of the keel, both sheets that control the yard (braces) are tied off aft (i.e., straight back), leading to the figurative phrase "Both sheets aft."
"Both sheets aft, The situation of a square-rigged ship that sails before the wind, or with the wind right astern. It is said also of a half-drunken sailor rolling along with his hands in his pockets and elbows square." [1]
"Square ... A term peculiarly appropriated to the yards and their sails. Thus, when the yards hang at right angles with the mast they are said to be 'square by the lifts;' when perpendicular to the ship's length, they are 'square by the braces;' but when they lie in a direction perpendicular to the plane of the keel, they are 'square by the lifts and braces.' The yards are said to be very square when they are of extraordinary length, and the same epithet is applied to their sails with respect to their breadth." [1]
Sailing employs the wind—acting on sails, wingsails or kites—to propel a craft on the surface of the water, on ice (iceboat) or on land over a chosen course, which is often part of a larger plan of navigation.
Rigging comprises the system of ropes, cables and chains, which support a sailing ship or sail boat's masts—standing rigging, including shrouds and stays—and which adjust the position of the vessel's sails and spars to which they are attached—the running rigging, including halyards, braces, sheets and vangs.
A sailing ship is a sea-going vessel that uses sails mounted on masts to harness the power of wind and propel the vessel. There is a variety of sail plans that propel sailing ships, employing square-rigged or fore-and-aft sails. Some ships carry square sails on each mast—the brig and full-rigged ship, said to be "ship-rigged" when there are three or more masts. Others carry only fore-and-aft sails on each mast, for instance some schooners. Still others employ a combination of square and fore-and-aft sails, including the barque, barquentine, and brigantine.
Sailing rigs describe the arrangement of sailing vessels' rig components, including their spars, rigging, and sails. Examples include a schooner rig, cutter rig, junk rig, etc. Rigs may be broadly categorized as fore-and-aft and square-rigged. They may incorporate a mixture of both categories. Within the fore-and-aft category there is a variety of triangular and quadrilateral sail shapes. Spars or battens may be used to help shape a given kind of sail. Each rig may be described with a sail plan—formally, a drawing of a vessel, viewed from the side.
A point of sail is a sailing craft's direction of travel under sail in relation to the true wind direction over the surface.
A jibe (US) or gybe (Britain) is a sailing maneuver whereby a sailing vessel reaching downwind turns its stern through the wind, which then exerts its force from the opposite side of the vessel. Because the mainsail boom can swing across the cockpit quickly, jibes are potentially dangerous to person and rigging compared to tacking. Therefore accidental jibes are to be avoided while the proper technique must be applied so as to control the maneuver. For square-rigged ships, this maneuver is called wearing ship.
A spinnaker is a sail designed specifically for sailing off the wind on courses between a reach to downwind. Spinnakers are constructed of lightweight fabric, usually nylon, and are often brightly colored. They may be designed to perform best as either a reaching or a running spinnaker, by the shaping of the panels and seams. They are attached at only three points and said to be flown.
Gaff rig is a sailing rig in which the sail is four-cornered, fore-and-aft rigged, controlled at its peak and, usually, its entire head by a spar (pole) called the gaff. Because of the size and shape of the sail, a gaff rig will have running backstays rather than permanent backstays.
Running rigging is the rigging of a sailing vessel that is used for raising, lowering, shaping and controlling the sails on a sailing vessel—as opposed to the standing rigging, which supports the mast and bowsprit. Running rigging varies between vessels that are rigged fore and aft and those that are square-rigged.
A yard is a spar on a mast from which sails are set. It may be constructed of timber or steel or from more modern materials such as aluminium or carbon fibre. Although some types of fore and aft rigs have yards, the term is usually used to describe the horizontal spars used on square rigged sails. In addition, for some decades after square sails were generally dispensed with, some yards were retained for deploying wireless (radio) aerials and signal flags.
This glossary of nautical terms is an alphabetical listing of terms and expressions connected with ships, shipping, seamanship and navigation on water. Some remain current, while many date from the 17th to 19th centuries. The word nautical derives from the Latin nauticus, from Greek nautikos, from nautēs: "sailor", from naus: "ship".
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 and its shape,. 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.
A full-rigged ship or fully rigged ship is a sailing vessel with a sail plan of three or more masts, all of them square-rigged. Such a vessel is said to have a ship rig or be ship-rigged, with each mast stepped in three segments: lower, top, and topgallant.
In sailing, a sheet is a line used to control the movable corner(s) (clews) of a sail.
Tacking or coming about is a sailing maneuver by which a sailing craft, whose next destination is into the wind, turns its bow toward and through the wind so that the direction from which the wind blows changes from one side of the boat to the other, allowing progress in the desired direction. Sailing vessels are unable to sail higher than a certain angle towards the wind, so "beating to windward" in a zig-zag fashion with a series of tacking maneuvers, allows a vessel to sail towards a destination that is closer to the wind that the vessel can sail directly.
The junk rig, also known as the Chinese lugsail, Chinese balanced lug sail, or sampan rig, is a type of sail rig in which rigid members, called battens, span the full width of the sail and extend the sail forward of the mast.
Weather helm is the tendency of sailing vessels to turn towards the source of wind, creating an unbalanced helm that requires pulling the tiller to windward in order to counteract the effect.
Forces on sails result from movement of air that interacts with sails and gives them motive power for sailing craft, including sailing ships, sailboats, windsurfers, ice boats, and sail-powered land vehicles. Similar principles in a rotating frame of reference apply to windmill sails and wind turbine blades, which are also wind-driven. They are differentiated from forces on wings, and propeller blades, the actions of which are not adjusted to the wind. Kites also power certain sailing craft, but do not employ a mast to support the airfoil and are beyond the scope of this article.
A sail is a tensile structure—which is made from fabric or other membrane materials—that uses wind power to propel sailing craft, including sailing ships, sailboats, windsurfers, ice boats, and even sail-powered land vehicles. Sails may be made from a combination of woven materials—including canvas or polyester cloth, laminated membranes or bonded filaments—usually in a three- or four-sided shape.
This glossary of nautical terms is an alphabetical listing of terms and expressions connected with ships, shipping, seamanship and navigation on water. Some remain current, while many date from the 17th to 19th centuries. The word nautical derives from the Latin nauticus, from Greek nautikos, from nautēs: "sailor", from naus: "ship".