The forestay is a wire that secures the mast to the front of the boat. With a fractional rig, rather than being attached to the top of the mast, the forestay is attached between about 1/8 and 1/4 of the length of the mast lower down. The foresail (jib or genoa) is then rigged to this stay. The mast is farther forward on the boat than on a masthead rig and so it has a larger mainsail. Masthead rigs are most common on larger keelboats or cruisers. A fractional rig is typically used on sailing dinghies and racing oriented keelboats, such as the J/24.
Fractional rigs were introduced on race boats in order to allow more controllability of the surface of the mainsail and also less drag when sailing upwind. According to one manufacturer, "a key to making fast boats easier to sail than slow boats is the 'fractional rig'".[1]
Fractional rigs tend to have a larger mainsail and a smaller headsail which is often a non-overlapping jib. This configuration is optimized for upwind sailing efficiency. For downwind sailing without a spinnaker, the larger mainsail of a fractional rig has a significant advantage over a masthead rig but a disadvantage when spinnakers are flown. Many newer high-performance fractional rig sailboats, fly the spinnaker or the gennaker from the masthead. On many modern skiffs and race dinghies, the jib is relatively small compared to the size of the main and it is normally left in place when the spinnaker or gennaker is used due to this type of jib's minimal aerodynamic interference.
Another major advantage of the fractional rig, especially the '3/4' rig (where the fore stay goes 3/4 the way up the mast), is that the jib can be taken in without inducing excessive weather helm which could cause the boat to lose control and “round up” into the wind. With the masthead sloop, both the main and the jib must be reduced in size evenly when shortening sail. This is typically accomplished by reefing the main and either rolling up a portion of the headsail on a furler, or changing to a smaller headsail.
Since jibs need considerable forestay tension to set properly and the amount of tension needed increases with wind speed, being able to drop the jib altogether in windy conditions puts less strain on the rig and hull. Fractional rigs are used on lightly built multihulls for this reason.
History
Throughout the 20th century, most sloops of less than 20 feet in length had fractional rigs.
Many (perhaps most) sailing sloops from the first part of the 20th century were fractional rigged. The increased prevalence of fractional rigs on sloops in the early 20th century probably coincided roughly with the disappearance of the gaff rig. One possibility for its increased prevalence during this era is that, relative to a masthead rig, it allows the designer to provide the boat with more sail area without using a bowsprit or a boom that extends beyond the stern, and without demanding that the sails be of a very high aspect ratio. This was important because the sailcloth available in those days made it difficult to construct high-aspect sails.
As sailcloth improved in the second half of the 20th century, it became possible to construct sails of a higher aspect ratio. It therefore became more practical for sloops to be designed with the simpler masthead-rigged mast. Most production sailboats from the '60s and '70s were masthead-rigged sloops. Masthead-rigged sloops typically carry a larger spinnaker than fractional-rigged sloops, and therefore enjoy a speed advantage when racing downwind.
Fractional rigged sloops are starting to become popular again, especially for high-performance racing boats. A fractional rig allows the mast to bend more easily, which in turn allows more adjustment to the shape of the mainsail, especially when sailing upwind. Many people believe that a fractional-rigged sloop is faster upwind than a similar masthead-rigged sloop, especially as the wind strength increases. Most of the newest generation of fractional-rigged sloops fly their spinnakers from the top of the mast. These boats are said to have "masthead spinnakers" and this development gives the boat very good performance both upwind and downwind in all wind strengths.
Maintaining forestay tension
An inherent problem of a fractional rig is its inability to exert as much tension on the forestay as a similar masthead rig. The reason for this is because the attachment point of the forestay is not directly opposite to the backstay. Under certain conditions, the moment arm that results from these offset attachment points can be used to advantage as this is an effective method of inducing bend in the mast which in turn flattens the mainsail. If the distance between the attachment points is too great, a mast of average stiffness will be unable to apply optimum forestay tension, unless one of the following mast-stiffening design features is used:
Jumper stays — These additional stays and their associated jumper struts limit the amount that the upper portion of the mast can bend and thereby enable tension to be effectively transferred from the backstay to the forestay. Jumper stays were common in the first part of the 20th century. Their biggest disadvantage is weight and windage aloft.
Running backstays — These are supplemental temporary backstays (one on each side) that attach opposite of the forestay. They are very effective at generating forestay tension, but make the boat more difficult to tack because one running backstay needs to be released and the other one applied each time the boat tacks.
Swept back spreaders — Swept back spreaders (or rather their associated shrouds, which attach to the deck significantly aft of the mast) provide significant fore-and-aft support to the mast and thereby increase tension in the forestay. The biggest disadvantage of this scheme is that it makes it difficult to deliberately slacken the forestay for the purpose of making the jib fuller in light winds.
A sloop is a sailboat with a single mast typically having only one headsail in front of the mast and one mainsail aft of (behind) the mast. Such an arrangement is called a fore-and-aft rig, and can be rigged as a Bermuda rig with triangular sails fore and aft, or as a gaff-rig with triangular foresail(s) and a gaff rigged mainsail. Sailboats can be classified according to type of rig, and so a sailboat may be a sloop, catboat, cutter, ketch, yawl, or schooner. A sloop usually has only one headsail, although an exception is the Friendship sloop, which is usually gaff-rigged with a bowsprit and multiple headsails. If the vessel has two or more headsails, the term cutter may be used, especially if the mast is stepped further towards the back of the boat.
A sailboat or sailing boat is a boat propelled partly or entirely by sails and is smaller than a sailing ship. Distinctions in what constitutes a sailing boat and ship vary by region and maritime culture.
A sail plan is a description of the specific ways that a sailing craft is rigged. Also, the term "sail plan" is a graphic depiction of the arrangement of the sails for a given sailing craft.
A jib is a triangular sail that sets ahead of the foremast of a sailing vessel. Its tack is fixed to the bowsprit, to the bows, or to the deck between the bowsprit and the foremost mast. Jibs and spinnakers are the two main types of headsails on a modern boat.
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. For square-rigged ships, this maneuver is called wearing ship.
On a sailing vessel, a forestay, sometimes just called a stay, is a piece of standing rigging which keeps a mast from falling backwards. It is attached either at the very top of the mast, or in fractional rigs between about 1/8 and 1/4 from the top of the mast. The other end of the forestay is attached to the bow of the boat.
A backstay is a piece of standing rigging on a sailing vessel that runs from the mast to either its transom or rear quarter, counteracting the forestay and jib. It is an important sail trim control and has a direct effect on the shape of the mainsail and the headsail. Backstays are generally adjusted by block and tackle, hydraulic adjusters, or lines leading to winches.
A staysail ("stays'l") is a fore-and-aft rigged sail whose luff can be affixed to a stay running forward from a mast to the deck, the bowsprit, or to another mast.
A genoa sail is a type of large jib or staysail that extends past the mast and so overlaps the main sail when viewed from the side, sometimes eliminating it. It was originally called an "overlapping jib" and later a genoa jib. It is used on single-masted sloops and twin-masted boats such as yawls and ketches. Its larger surface area increases the speed of the craft in light to moderate winds; in high wind, a smaller jib is usually substituted, and downwind a spinnaker may be used.
A spinnaker is a sail designed specifically for sailing off the wind from a reaching course to a downwind, i.e. with the wind 90–180° off bow. The spinnaker fills with wind and balloons out in front of the boat when it is deployed, called flying. It is constructed of lightweight fabric, usually nylon, and is often brightly colored. It may be optimised for a particular range of wind angles, as either a reaching or a running spinnaker, by the shaping of the panels and seams.
A mainsail is a sail rigged on the main mast of a sailing vessel.
A cutter is a type of watercraft. The term has several meanings. It can apply to the rig of a sailing vessel, to a governmental enforcement agency vessel, to a type of ship's boat which can be used under sail or oars, or, historically, to a type of fast-sailing vessel introduced in the 18th century, some of which were used as small warships.
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.
A Bermuda rig, Bermudian rig, or Marconi rig is a configuration of mast and rigging for a type of sailboat and is the typical configuration for most modern sailboats. This configuration was developed in Bermuda in the 1600s; the term Marconi, a reference to the inventor of the radio, Guglielmo Marconi, became associated with this configuration in the early 1900s because the wires that stabilize the mast of a Bermuda rig reminded observers of the wires on early radio masts.
Running backstays support the headstay in a fractionally rigged boat. A masthead rig has the advantage of not needing them. A running backstay runs from each lateral corner of the stern to the mast at the level where the forestay begins in the fractional rig. Together with other rigging, it supports the mast. Because they are attached low on mast, they can present a significant problem in an accidental gybe, as the boom hits the stay, with the possibility of breaking the boom, mast, or both.
A mast-aft rig is a sailboat sail-plan that uses a single mast set in the aft half of the hull. The mast supports fore-sails that may consist of a single jib, multiple staysails, or a crab claw sail. The mainsail is either small or completely absent. Mast-aft rigs are uncommon, but are found on a few custom, and production sailboats.
The Esse 850 is an 8.5 metre long racing sportboat designed by Umberto Felci and built by Josef Schuchter Sportboats of Stafa, Switzerland. The first hull was sold in 2004 and the Esse 850 International Class Association was begun in 2005 in Europe.
A masthead rig on a sailing vessel consists of a forestay and backstay both attached at the top of the mast.
The San Juan 33S is an American sailboat that was designed by David Pedrick as racer and first built in 1981.
A solent refers to a sail and rigging system on sailboats, typically sloops. Sailors, particularly French sailors, often refer to a 100% jib as a Solent, because its smaller size is preferable when sailing in the strong winds found in the Solent between the Isle of Wight and Britain. The common use of roller-furling headsails, or genoas, on modern cruising yachts allows the jib to be reduced in size, but partially-furled sails lack the efficiency of a sail that is actually cut to a smaller size. Accordingly, it is preferable to fly a separate, smaller jib—the solent—instead.
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