Reefing is a sailing manoeuvre intended to reduce the area of a sail on a sailboat or sailing ship, which can improve the ship's stability and reduce the risk of capsizing, broaching, or damaging sails or boat hardware in a strong wind. Modern sailboats often combine reefing and furling of sails, as shown in fully furled Genoa headsail of the Bavaria 36 in the image at right.
There are three common methods of reefing: conventional, roller, and jiffy. The latter two make sail-handling easier and allow reefing to be done with fewer crew members.
Sails may have built-in alternate attachment points that allow their area to be reduced. In a mainsail, one to four horizontal rows of cringles, called reef points, may be placed above the foot of the sail. Tying the sail to the boom at these reef points forms a new tack and clew and reduces the sail's area. More than one row of reef points increases options for possible sail area. To perform the reef, a crewman must pull the reefing line as another crewman is lowering the sail. Reefing is used mostly when the winds are too strong and are overpowering the boat and the steering.
Roller reefing involves rolling or wrapping the sail around a wire, foil, or spar
to reduce the sail's exposure to the wind. The mainsail is wrapped around the boom
, which contains a mechanism in the gooseneck
that rolls in the sail--or special hardware inside the boom or mast is used to reef the sail by winding it around a rotating foil. These latter systems are known as mainsail furling systems. Conventional roller reefing on a rotating boom can be difficult and time-consuming, typically requiring a crew member to work at the mast in heavy weather. By comparison, furling systems operate easily through control lines led to the cockpit. Roller reefing allows a more gradual and controllable method of reefing than conventional or jiffy reefing.
Jiffy reefing, also called slab reefing or single line reefing, is quicker and easier than conventional reefing or conventional roller reefing and involves folding the sail in sections, or slabs, along the boom. One or two reefing lines placed through the reef cringles at the sail's luff and leach edges are used to pull those points down tight to the boom, creating a new tack and clew for the sail. Reefing lines can be led back to the cockpit, and crew members can perform reefing without going on deck in heavy weather. In jiffy reefing there is no need to tie to the boom at the reef cringles on the sail. The equipment for jiffy reefing is often integrated with Dutchman flaking, a furling
technology that flakes (or folds up) the sail on alternate sides of the boom rather than on a messy pile on one side of the boom.