In
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, Windsurfing, windsurfer, or Kitesurfing, kitesurfer), on ''ice'' (iceboat) or on ''land'' (Land sa ...
, a boom is a
spar (pole), along the of a
fore and aft rigged
sail
A sail is a tensile structure, which is made from fabric or other membrane materials, that uses wind power to propel sailing craft, including sailing ships, sailboats, windsurfers, ice boats, and even sail-powered land vehicles. Sails may b ...
, 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 drawing of a sailing craft, viewed from the side, depicting its sails, the spars that carry them and some of the rigging that supports the rig. By extension, "sail plan" describes the arrangement of sails on a craft. A sailing c ...
without a boom, but
lateen sails, for instance, are loose-footed. In some modern applications, the sail is rolled up into the boom for storage or
reefing (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 drawing of a sailing craft, viewed from the side, depicting its sails, the spars that carry them and some of the rigging that supports the rig. By extension, "sail plan" describes the arrangement of sails on a craft. A sailing c ...
. 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 tr ...
as the sail's
luff (forward edge).
Lines on the boom
The control lines (ropes) on the boom act in conjunction with the
halyard and
leech line to ensure that the sail is trimmed most effectively.
Two primary sail control lines are attached to every boom:
* The
outhaul runs from 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 ...
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 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 may be used to control luff tension.
* The
boom vang, 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, 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 holds up the free end of the boom when the sail is lowered.
*
Lazy jacks guide the sail onto the top of the boom for
furling 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 (or aluminum in North American English) is a chemical element; it has chemical symbol, symbol Al and atomic number 13. It has a density lower than that of other common metals, about one-third that of steel. Aluminium has ...
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 comp ...
.
Various hardware is found attached to the boom. The hardware could include
fairleads,
blocks, block tracks, and
cleats. For attachment, screws are used on wooden booms and screws or
rivets 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 Corporation, Lockheed (now Lockheed Martin). Capable of using unprepared runways for takeoffs and landings, the C-130 w ...
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 jackets, 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 barycenter or balance point) is the unique point at any given time where the weighted relative position of the distributed mass sums to zero. For ...
and increase the chances of
capsizing 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 plan, sail and rigging arrangement in which a sailing ship, sailing vessel's primary driving sails are carried on horizontal spar (sailing), spars that are perpendicular (or wikt:square#Adjective, square) to t ...
or the
standing lugsail have always worked without booms. Modern alternatives without a boom are the
mast aft rig.
Other boom uses
On an open
cockpit
A cockpit or flight deck is the area, on the front part of an aircraft, spacecraft, or submersible, from which a pilot controls the vehicle.
The cockpit of an aircraft contains flight instruments on an instrument panel, and the controls th ...
sailboat at a
mooring
A mooring is any permanent structure to which a seaborne vessel (such as a boat, ship, or amphibious aircraft) may be secured. Examples include quays, wharfs, jetties, piers, anchor buoys, and mooring buoys. A ship is secured to a mooring to ...
, 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 reinf ...
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 aboard heavy items like a
dinghy
A dinghy is a type of small boat, often carried or Towing, towed by a Watercraft, larger vessel for use as a Ship's tender, tender. Utility dinghies are usually rowboats or have an outboard motor. Some are rigged for sailing but they diffe ...
.
Other boom types
Flexible boom
When the foot of a sail is attached along its whole length to a boom, the stiffness of the boom tends to hold the lower part of the sail flat.
[Dear 2004, p.67][Vanderbilt 1931, p.162] However, the greatest aerodynamic efficiency of the sail is created when the sail is allowed to curve into an
airfoil
An airfoil (American English) or aerofoil (British English) is a streamlined body that is capable of generating significantly more Lift (force), lift than Drag (physics), drag. Wings, sails and propeller blades are examples of airfoils. Foil (fl ...
-like shape.
A flexible boom bends with the sail to create this greater efficiency.
Park Avenue boom
A "Park Avenue" boom allows for the same aerodynamic curvature as a flexible boom, but is a rigid construction with a flat surface on top.
[Vanderbilt 1931, p.163] Instead of being fastened directly to the boom, the foot of the sail is fastened to fittings that slot into grooves that run transversely across the boom.
As these fittings move within their grooves, the foot of the sail is free to curve.
It takes its name from the great width of such a boom fitted to the yacht ''
Enterprise
Enterprise (or the archaic spelling Enterprize) may refer to:
Business and economics
Brands and enterprises
* Enterprise GP Holdings, an energy holding company
* Enterprise plc, a UK civil engineering and maintenance company
* Enterpris ...
'' for the
1930 America's Cup competition, a hyperbolic comparison to the width of
Park Avenue
Park Avenue is a boulevard in New York City that carries north and southbound traffic in the borough (New York City), boroughs of Manhattan and the Bronx. For most of the road's length in Manhattan, it runs parallel to Madison Avenue to the wes ...
.
[Dear 2004, p.67][Vanderbilt 1931, p.164]
See also
*
Wishbone boom
Bibliography
*
*
References
Further reading
*
{{Sail Types
Sailboat components
Sailing rigs and rigging
Nautical terminology