Roller furling is a method of furling

Furl (sailing)

Furling refers to stowing or dousing a boat's sail by flaking , packing , roller furling or just lowering it onto the deck. Nowadays, it is becoming more common to use the term "furling" to refer to reefing a sail that is part of a roller furling system....

 or reefing

Reefing

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...

 wherein a sail

Sail

A sail is any type of surface intended to move a vessel, vehicle or rotor by being placed in a wind—in essence a propulsion wing. Sails are used in sailing.-History of sails:...

 is rolled around a stay

Stays (nautical)

Stays are the heavy ropes, wires, or rods on sailing vessels that run from the masts to the hull, usually fore-and-aft along the centerline of the vessel...

 or rotating spar

Spar

In sailing, a spar is a pole of wood, metal or lightweight materials such as carbon fiber used on a sailing vessel. Spars of all types In sailing, a spar is a pole of wood, metal or lightweight materials such as carbon fiber used on a sailing vessel. Spars of all types In sailing, a spar is a...

. Roller furling is most commonly encountered on foresail

Foresail

A foresail is one of a few different types of sail set on the foremost mast of a sailing vessel:* A fore and aft sail set on the foremast of a schooner or similar vessel....

s, such as jib

Jib

A jib is a triangular staysail set ahead of the foremast of a sailing vessel. Its tack is fixed to the bowsprit, to the bow, or to the deck between the bowsprit and the foremost mast...

s, with mainsail

Mainsail

A mainsail is a sail located behind the main mast of a sailing vessel.On a square rigged vessel, it is the lowest and largest sail on the main mast....

s a distant second.

Furling methods

The furling system itself is very simple in concept. The edge of the sail to be furled is stiffened in some way, such as by attaching it to a length of plastic pipe or by sewing in a stiff material. This stiffened edge serves to spread the force of the furler along the edge of the sail, so that the sail will furl along its full length. This stiffened edge is then attached to the source of energy for furling, which may be a handle that is turned, a spool containing a line that is pulled, or a motor.

Murray Scheiner, a sailor and professional rigging designer from Great Neck, New York, first invented the furling jib in the late 1960s. His inspiration came from observing a disabled sailor friend who required several crew members to hoist the jib, preventing him from sailing independently. This invention greatly changed sailing for professionals and leisure sailors alike.
Since the Wykeham Martin furling gear (http://www.davey.co.uk/pdf/wykeham_martin_gear.pdf) has been in continuous production in Britain for approximately 100 years it is possible that someone else thought of this system before Mr Scheiner, but that it took some time before the idea came to America independently.

The simplest and most common furling systems are for jibs and other headsails. These generally consist of either a plastic pipe or a specially stiffened jib, and a spool to hold the furling line. The jib is attached to the furler, and the line is wound around the spool. When the line is pulled, the furler turns, rolling up the jib; when the furling line is released, the jibsheet may be used to unfurl the jib.

The other common type of furling system is for the mainsail. The mainsail may be furled into the mast

Mast (sailing)

The mast of a sailing vessel is a tall, vertical, or near vertical, spar, or arrangement of spars, which supports the sails. Large ships have several masts, with the size and configuration depending on the style of ship...

 or the boom

Boom (sailing)

In sailing, a boom is a spar , along the foot of a fore and aft rigged sail, that greatly improves control of the angle and shape of the sail. The primary action of the boom is to keep the foot of the sail flatter when the sail angle is away from the centerline of the boat. The boom also serves...

, with boom furling systems being simpler and more common. The simplest boom furling system consists of a boom that can rotate along its axis, with a latch to lock it in place. Provision must be made to allow the mainsail to wrap around the boom without interfering with the mainsheet, such as end-boom sheeting or a bridle. To furl the mainsail, the boom is unlocked, and then rotated to take up the desired amount of mainsail, and then locked in place. More advanced boom furling systems will wrap the furling mechanism in a slotted cover, so the sail furls inside the cover; this also makes sheeting easier, since the sheet may be attached to the outer portion of the boom. These systems use either a line, a hand operated crank, or a hydraulic or electric powered furler.

Sail requirements

To be successfully furled, a sail must be flexible enough to wrap around a tight radius. Sail stiffening devices such as batten

Batten

A batten is a thin strip of solid material, typically made from wood, plastic or metal. Battens are used in building construction and various other fields as both structural and purely cosmetic elements...

s are commonly used on mainsails, and roller furling systems must either stop furling at the point the lowest batten is reached, or the battens must be removed to continue furling the sail. It is possible to use battens that lie parallel to the roller, so a sail designed to be roller furled can use appropriate battens.

The sail must also have a fairly straight edge to lie along the furling roller, and be flat enough to form a neat, compact roll. If the sail meets these conditions, then it may be suitable for use with a roller furling system; if the sail is not, then it may be possible to replace the sail with one of a design more conducive to furling. Jibs and genoas, for example, are generally suitable for furling, as they are relatively flat, while a gennaker

Gennaker

A gennaker is a sail that was developed around 1990. Used when sailing downwind, it is a cross between a genoa and a spinnaker. It is asymmetric like a genoa, but the gennaker is not attached to the forestay like a jib or genoa. The gennaker is rigged like a spinnaker but the tack is fastened to...

, with its larger degree of camber, is probably not suitable for furling.

Boom furling mainsails also must deal with the issue of the leading edge. Most sails attach to the mast with sliders or a rope supported edge that rides in a track in the mast, and this adds bulk to the leading edge of the sail as it rolls. This is also an issue when unfurling, as the edge of the sail must be fed smoothly into the mast's track when unfurling. The weight of the sail and furling equipment also increases the boom's mass, which can increase the danger of injury to a crewmember if they are hit by the swinging boom.

Mast furling systems avoid the issues of boom furling, but add their own issues. Mast furling systems essentially eliminate the possibility of battens, as vertical battens are not practical. Without battens, the mainsail must be cut with a hollow leech, like the typical jib, which reduces the sail area. Mast furlers also add mass all along the length of the mast, raising the center of mass

Center of mass

In physics, the center of mass or barycenter of a system is the average location of all of its mass. In the case of a rigid body, the position of the center of mass is fixed in relation to the body...

 of the boat, which decreases stability.

External references

• Instructions for building a small boat jib furler, using primarily PVC
  PVC
  Polyvinyl chloride is a plastic.PVC may also refer to:*Param Vir Chakra, India's highest military honor*Peripheral venous catheter, a small, flexible tube placed into a peripheral vein in order to administer medication or fluids...
  
  pipe and fittings