The boom is a spar usually made of aluminum or wood which provides support to the foot of the mail sail. The boom attaches to the mast at a joint called the gooseneck. The gooseneck pivots allowing the boom to be easily adjusted by the main sheet. Four lines are attached to the boom:

1. The outhaul runs along the boom and pulls the back corner of the sail (the clew) aftward.

2. The main sheet is attached midway along the boom and allows the skipper to pull in and let out the mainsail. In a close haul point of sail, the mainsheet can pull the boom downwards and, in turn, increase leach tension.

3. The traveler increases boom control during tacking and up-wind sailing.

4. The boomvang is an intricate set of pulleys running diagonally between the boom and the lower portion of the mast. The boomvang pulls the boom downwards and, in turn, increases leach tension and decreases leach twist.

Various fairleads and cleats are attached by screws and rivets in wooden and aluminum spars respcetively. Aluminum booms are lighter and stronger than their woooden counterpart and are used more often in competitive racing. They are usually associated with fiberglass boats. The wooden boom is found most often on older sailboats and handmade dinghies.