A brail, or brail line, is a nautical term referring to a small rope attached horizontally across a sail and used to pull the sail toward the mast, reducing the area of the sail. Several brails are usually attached to a sail for this purpose and are part of a sailing ship's rigging, meaning its configuration of masts, sails, and ropes. Each brail runs through a grommet from the luff, the leading vertical edge of the sail closest to the wind, across the main body of the sail, through another grommet, and back to the luff. Toward the mast, the brails are attached to a longer rope that runs down almost the entire length of the mast and which is used to pull the brails and gather up the sail. Brail lines are used only on certain types of sails in certain sailing rigs, most commonly the sails called coursers, usually the foresail, mainsail, and mizzen sail.
There are various ways of reducing the area of a sail, or stowing it, and if the sail has brails, they are used to do this. A sail can be furled, which means it is either folded, called flaking in nautical terms, or packed, meaning it is stuffed into a container. For example, a spinnaker is often packed into a bag called a turtle. A sail can also be reefed, which is often done to increase control of the ship in stormy conditions. Reefing can involve lowering and tying down the sail, wrapping it around a boom or spar, or folding it in sections.
In the process of furling or reefing a sail, the brail lines can be used to gather in the sides and corners of the sail before it is further stowed. These sides and corners are referred to by specific sailing terms. The luff is the vertical edge of the sail closest to the wind; the leech is the aft, vertical edge farthest from the wind; and the foot is the bottom, horizontal edge of the sail. The nautical command to use the brails to furl or reef a sail is "brail up the sails" or "hale up the brails."
To reef or furl a sail using brail lines, one must pull on the single vertical rope running down the mast that the brails are attached to. This pulls the sail in toward the mast. The vertical rope is then secured and the sail can be further stowed if needed.