sailing Sailing employs the wind—acting on sails, wingsails or kites—to propel a craft on the surface of the ''water'' (sailing ship, sailboat, raft, windsurfer, or kitesurfer), on ''ice'' (iceboat) or on ''land'' (land yacht) over a chosen cou ...

, a boom is a

spar SPAR, originally DESPAR, styled as DE SPAR, is a Dutch multinational that provides branding, supplies and support services for independently owned and operated food retail stores. It was founded in the Netherlands in 1932, by Adriaan van Well, ...

(pole), along the of a

fore and aft A fore-and-aft rig is a sailing vessel rigged mainly with sails set along the line of the keel, rather than perpendicular to it as on a square rigged vessel. Description Fore-and-aft rigged sails include staysails, Bermuda rigged sails, ga ...

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'' flatter when the sail angle is away from the centerline of the boat. The boom also serves as an attachment point for more sophisticated control lines. Because of the improved sail control it is rare to find a non-

headsail 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.> In the English language, ships were usually describe ...

without a boom, but

lateen sail A lateen (from French ''latine'', meaning "Latin") or latin-rig is a triangular sail set on a long yard mounted at an angle on the mast, and running in a fore-and-aft direction. The settee can be considered to be an associated type of the same ...

s, for instance, are loose-footed. In some modern applications, the sail is rolled up into the boom for storage or

reefing Reefing reduces the area of a sail, usually by folding or rolling one edge of the canvas in on itself and attaching the unused portion to a spar or a stay, as the primary measure to preserve a sailing vessel's stability in strong winds. Restoring ...

(shortening sail).

Boom attachment

The forward end of the boom attaches to a mast just below the sail, with a joint called the gooseneck. The gooseneck pivots allowing the other end of the boom to move freely. The

clew Sail components include the features that define a sail's shape and function, plus its constituent parts from which it is manufactured. A sail may be classified in a variety of ways, including by its orientation to the vessel (e.g. ''fore-and-a ...

(back corner) of the sail attaches to the free end of the boom. The entire ''foot'' of the sail may be attached to the boom or just the clew. If the ''foot'' is not attached to the boom, the rig is known as loose footed. A boom may be found on small

headsails 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.> In the English language, ships were usually describe ...

. There the forward end of the boom is attached to the same

stay Stay may refer to: Places * Stay, Kentucky, an unincorporated community in the US Law * Stay of execution, a ruling to temporarily suspend the enforcement of a court judgment * Stay of proceedings, a ruling halting further legal process in a tri ...

as the sail's luff (forward edge).

Lines on the boom

The control lines (ropes) on the boom act in conjunction with the

halyard In sailing, a halyard or halliard is a line (rope) that is used to hoist a ladder, sail, flag or yard. The term ''halyard'' comes from the phrase "to haul yards". Halyards, like most other parts of the running rigging, were classically made of ...

and leech line to ensure that the sail is trimmed most effectively. Two primary sail control lines are attached to every boom: * The

outhaul An outhaul is a control line found on a sailboat. It is an element of the running rigging, used to attach the mainsail clew to the boom and tensions the foot of the sail. It commonly uses a block at the boom end and a cleat on the boom, closer ...

runs from the

of the sail to the free end of the boom. Hauling in on (tightening) the outhaul increases ''foot'' tension in the main sail. Modern loose footed sails are cut so that the outhaul is also able to pull the clew downwards towards the boom. * The sheet is attached midway along the boom or at the free end, typically by means of a

block Block or blocked may refer to: Arts, entertainment and media Broadcasting * Block programming, the result of a programming strategy in broadcasting * W242BX, a radio station licensed to Greenville, South Carolina, United States known as ''96.3 ...

. The block is typically attached to the boom by means of a bail, which is a U-shaped piece of metal, flattened at the ends to allow attachment with screws or rivets. In smaller boats such as dinghies it is used to control the angle of the sail to the wind on each point of sail. On largest boats this function is largely assumed by the traveller and the main sheet is used to adjust the twist of the sail to present the luff of the sail to the wind all of the way up the mast. Easing the main sheet increases twist and the twist is usually adjusted so that the aft end of the top

batten A batten is most commonly a strip of solid material, historically wood but can also be of plastic, metal, or fiberglass. Battens are variously used in construction, sailing, and other fields. In the lighting industry, battens refer to linea ...

in the main sail runs parallel to the boom. The traveller is a track running from one side of the boat to the other upon which sits a car to which the other end of the sheet is attached. Moving the car from side to side alters the angle of the boom to the centreline of the boat while minimising the effect on the twist of the sail. A boom will frequently have these additional sail control lines attached: * A

downhaul The downhaul is a line which is part of the rigging on a sailboat; it applies downward force on a spar or sail. The most common downhaul on a modern sailboat is attached to the spinnaker pole, though this may be referred to as the foreguy in some r ...

may be attached to the boom near the gooseneck to pull the boom down and increase tension on the luff (forward edge) of the sail. If no downhaul is present, the gooseneck is usually fixed vertically to the mast and a

cunningham Cunningham is a surname of Scottish origin, see Clan Cunningham. Notable people sharing this surname A–C * Aaron Cunningham (born 1986), American baseball player *Abe Cunningham, American drummer * Adrian Cunningham (born 1960), Australian ...

may be used to control luff tension. * The

boom vang A boom vang (US) or kicking strap (UK) (often shortened to "vang" or "kicker") is a line or piston system on a sailboat used to exert downward force on the boom and thus control the shape of the sail. The Collins English Dictionary defines it ...

, kicking strap or kicker is an intricate set of pulleys (and, on yachts, a hydraulic ram) running diagonally between the boom and the lower portion of the mast. The kicker pulls the boom downwards. When the boat is running away from the wind the sheet will be fully eased and so the kicker becomes the primary means of controlling sail twist. * The

Preventer A gybe preventer, preventer, or jibe-guard, is a mechanical device on a sailing vessel which limits the boom's ability to swing unexpectedly across the boat due to an unplanned accidental jibe. During an unplanned accidental jibe (or ''gybe'' ...

, prevents the boom from jibing. This line is run from a point on the boom to a point forward such as a deck cleat or the base of a stanchion. Ideally, the preventer should run from the aft end of the boom to a turning block at or very close to the bow and then back to a cleat convenient to the cockpit. The line does not take tremendous force if used properly, but it prevents the boom from starting a jibe if the wind shifts or the boat rolls. Sophisticated form of preventer is a

Boom Brake A boom brake is a device designed to control the swing of the boom on a sailboat. The boom brake acts as a preventer A gybe preventer, preventer, or jibe-guard, is a mechanical device on a sailing vessel which limits the boom's ability to swin ...

, which not only prevents unwanted jibes, but allows a slow measured jibe by modulating the tension on the brake. * Reef Lines, are used to tie-off excess sail, when sails are reefed (shortened). Some modern systems known as "jiffy reefing" or "slab reefing" have permanent lines running through the boom for purposes of reefing. Pulling on these lines helps to gather the excess sail at the bottom of the boom, and to secure the reef points to the fore and aft of the boom. With a well designed system sailors can reef the sails without leaving the cockpit. Other lines that may be found on a boom include: * A

topping lift The topping lift (more rarely known as an uphaul) is a line which applies upward force on a boom on a sailboat. Part of the running rigging, topping lifts are primarily used to hold a boom up when the sail is lowered. This line would run from nea ...

, holds up the free end of the boom when the sail is lowered. *

Lazy jack Lazy jacks (or lazyjacks) are a type of rigging which can be applied to a fore-and-aft rigged sail to assist in sail handling during reefing and furling. They consist of a network of cordage which is rigged to a point on the mast and to a ser ...

s guide the sail onto the top of the boom for

furl Furl (from File Uniform Resource Locators) was a free social bookmarking website that allowed members to store searchable copies of webpages and share them with others. Every member received 5 gigabytes of storage space. The site was founded by ...

ing when the sail is lowered.

Boom material and hardware

Traditionally booms, and other spars, were made of wood. Classic wooden hulled sailboats, both old and new, will usually have wooden spars. When

aluminium Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...

became available, it was adopted for sailboat spars. Aluminium spars are lighter and stronger than their wooden counterpart, require less maintenance and generally hold up better to marine conditions. Aluminium spars are usually associated with fibreglass boats, although one can still find a few early fibreglass hulled yachts that were equipped with wooden spars. On very large sailing vessels, the spars may be steel. Modern, high performance, racing yachts may have spars constructed of more expensive materials, such as

carbon fibre Carbon fiber-reinforced polymers (American English), carbon-fibre-reinforced polymers (Commonwealth English), carbon-fiber-reinforced plastics, carbon-fiber reinforced-thermoplastic (CFRP, CRP, CFRTP), also known as carbon fiber, carbon compo ...

. Various hardware is found attached to the boom. The hardware could include

fairleads A fairlead is a device to guide a line, rope or cable around an object, out of the way or to stop it from moving laterally. Typically a fairlead will be a ring or hook. The fairlead may be a separate piece of hardware, or it could be a hole in ...

, blocks, block tracks, and cleats. For attachment, screws are used on wooden booms and screws or

rivets A rivet is a permanent mechanical fastener. Before being installed, a rivet consists of a smooth cylindrical shaft with a head on one end. The end opposite to the head is called the ''tail''. On installation, the rivet is placed in a punched o ...

on aluminium booms. If the foot of the sail is attached to the boom, there may be hoops from the foot of the sail, around the boom, or there may be a track on the top of the boom into which fittings on the foot of the sail are slid.

In-boom furling

There are quite a few variations of in-boom furling available. Generally the boom is hollow with a spindle in the center upon which the sail is rolled (furled). The techniques for turning the spindle vary, but frequently a line is used to spin the spindle and recover or reef the sail. In most cases the sail can be full battened and has virtually infinite reefing options. Some sailors consider this approach safer than in-mast furling, since the sail can be lowered and flaked in the traditional method, in the case of mechanical failure. In most applications, the sail can be lowered or reefed from the cockpit. Most designs will not accommodate a loose-footed mainsail.

Boom safety concerns

The second leading cause of death on sailboats is directly attributed to the use of booms. Booms can cause injuries directly, sweep people overboard, and their associated hardware and lines represent tripping hazards. On larger boats, sailors tend to stand on the boom to perform sail maintenance and install or take off sail covers. Falls from the boom onto the deck below occur. Even when stationary, booms represent a hazard since on most boats there is insufficient headroom to walk below them without ducking. According to a German study, "boom strikes were the most common cause of sailing injury overall". When boom injuries occur far from shore they can require expensive rescues. In 2010 the US Coast Guard and Air National Guard utilized a

Lockheed C-130 Hercules The Lockheed C-130 Hercules is an American four-engine turboprop military transport aircraft designed and built by Lockheed (now Lockheed Martin). Capable of using unprepared runways for takeoffs and landings, the C-130 was originally desig ...

aircraft to rescue a man from 1400 miles off the Mexican coast. Deaths and injuries can occur on boats operating upon lakes and coastal waters. As a precaution, any sailboat with a low boom should mandate use of

life jacket A personal flotation device (PFD; also referred to as a life jacket, life preserver, life belt, Mae West, life vest, life saver, cork jacket, buoyancy aid or flotation suit) is a flotation device in the form of a vest or suite that is worn by a ...

s, and ensure others know how to obtain assistance and operate the craft. In Boston a sailor knocked overboard by the boom died in full sight of the land and other boats and the person left aboard didn't know how to use the radio.

New boat designs to lower boom risks

To address the dangers associated with the boom, some designers have raised the boom higher off the deck or applied padding. However, these raise the

center of gravity In physics, the center of mass of a distribution of mass in space (sometimes referred to as the balance point) is the unique point where the weighted relative position of the distributed mass sums to zero. This is the point to which a force ma ...

and increase the chances of

capsizing Capsizing or keeling over occurs when a boat or ship is rolled on its side or further by wave action, instability or wind force beyond the angle of positive static stability or it is upside down in the water. The act of recovering a vessel fr ...

and turtling. Some designers have addressed the issue by eliminating the boom completely. Classic types of sail like the

square rig Square rig is a generic type of sail and rigging arrangement in which the primary driving sails are carried on horizontal spars which are perpendicular, or square, to the keel of the vessel and to the masts. These spars are called '' yards'' ...

or the standing lugsail have always worked without booms. Modern alternatives without a boom are the

mast aft rig 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 abs ...

Other boom uses

On an open cockpit sailboat at a

mooring A mooring is any permanent structure to which a vessel may be secured. Examples include quays, wharfs, jetties, piers, anchor buoys, and mooring buoys. A ship is secured to a mooring to forestall free movement of the ship on the water. An ''an ...

, a

tarpaulin A tarpaulin ( , ) or tarp is a large sheet of strong, flexible, water-resistant or waterproof material, often cloth such as canvas or polyester coated with polyurethane, or made of plastics such as polyethylene. Tarpaulins often have reinforce ...

may be run over the boom and tied to the rails to form a tent over the cockpit. In certain situations on larger boats, the boom can be used as a crane to help lift heavy items like a

Dinghy A dinghy is a type of small boat, often carried or towed by a larger vessel for use as a tender. Utility dinghies are usually rowboats or have an outboard motor. Some are rigged for sailing but they differ from sailing dinghies, which ...

aboard.