Boom (sailing)

In sailing, a boom is a spar (pole), along the foot (bottom edge) 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 as an attachment point for more sophisticated control lines. Because of the improved sail control it is rare to find a non headsail without a boom. In some modern applications, the sail is rolled up into the boom for storage or reefing (shortening sail).

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).

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:

A boom will frequently have these additional sail control lines attached:

Other lines that may be found on a boom include:

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

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Wikipedia