Boom (sailing)

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In sailing, a boom is a spar (pole), along the foot (bottom) 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 an attachement point for more sophisticated control lines. Because of the improved sail control it is rare to find a non headsail without a boom.

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 (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. There the forward end of the boom is attached to the same stay 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 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. 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 larger 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 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 which 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 boomvang, 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.

Other lines that may 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 aluminum became available, it was adopted for sailboat spars. Aluminum spars are lighter and stronger than their wooden counterpart, require less maintenance and generally hold up better to marine conditions. Aluminum spars are usually associated with fiberglass boats, although you will still find a few early fiberglass hulled yachts that were equiped 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 fiber.

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 aluminum 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 fo the boom into which fittings on the foot of the sail are slid.

Other boom uses

On an open cockpit sailboat at a mooring, a tarp 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.

The final use of the boom is for remedial action on inattentive sailors. During certain sailing manoeuvres, the boom moves rapidly from one side of the boat to the other. Sailors must take care not to obstuct this movement with their head. Failure to do so can give one insight into the origins of the name boom.

See also

• Wishbone boom
• Yardarm
• Gaff

External Links

• [Nautical terms for parts of sailing boats]

 

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