Roller furling is a mechanized method of stowing a sail that involves rolling it evenly onto a cylindrical spar or beam. Mechanized furling is most often used on foresails and jibs although it is possible to install roller furling mechanisms on mainsails. The average roller mechanism consists of a spar, beam, or spool to which the leading edge or luff of the sail is attached. This spar is rotated by a motor, hand crank, or a coiled line mechanism which wraps or furls the sail around it. A similar method is used to reef sails or reduce their bearing surface.
Furling a sail is the practice of rolling up the sail so that it no longer catches the wind and is out of the way. This is generally done when mooring the craft after a trip or when very high winds make the use of the sail dangerous. Furling may be achieved in a number of ways including manually or mechanically rolling the sail around a spar or simply lowering it to the deck and folding it up. Manual methods are fairly simple to achieve on smaller craft but become difficult as the sail area increases, particularly if the vessel is being sailed single handed. Mechanical roller furling can greatly reduce the time and effort required to furl or set sails of all sizes.
The mechanisms behind roller furling are generally fairly simple, particularly in the case of jibs and foresails. A rotating spar or beam driven by an electric motor, hand operated crank, or a rope coil is placed in front of the sail's luff or leading edge. The sail luff is attached to this spar; when it rotates, it simply winds the sail around it. When the sail is to be set again, the sheet or adjustment line at the rear lower corner of the sail is generally used to unroll it again. To achieve this action successfully, the sail should be flexible enough to be rolled around a small radius, as flat as possible, and free of any battens, braces, or other obstructions.
Mainsails are difficult to roller furl due to the mast attachments common in these sails. There are, however, mechanisms which furl the sail into the mast itself although flaking or folding the sail is generally considered to be a more practical solution. A mechanism similar to roller furling is also used to reef sails or partially reduce their area in high winds. These mechanisms allow the total area of the sail exposed to the wind to be reduced incrementally depending on prevailing conditions.