Boom

A horizontal spar used to extend the foot of a sail and control its angle to the wind. 

A boom is an essential part of a sailing vessel’s rigging, typically attached to the mast and extending along the bottom edge (foot) of a sail, most commonly the mainsail. Its primary function is to hold the sail in place and control its shape, allowing the sailor to adjust the sail’s angle to the wind, which is critical for optimising the boat’s speed and direction. The boom pivots horizontally from the mast and can be moved side to side (a process known as “trimming”) to catch the wind more effectively. This movement is controlled by lines such as the mainsheet, which is attached to the boom and allows for fine adjustments. 

The boom also helps to keep the sail taut, preventing it from flapping or “luffing” when sailing upwind. Without a boom, the sail would be much less efficient, as it would not maintain the correct shape to harness wind power effectively. Additionally, the boom plays a role in manoeuvres such as tacking and jibing, where the sail and boom must swing from one side of the boat to the other. Sailors must be cautious during these manoeuvres, as the boom can move quickly and forcefully, posing a risk of injury. 

In some cases, smaller boats or certain rigs may not use a boom, but for most modern sailing yachts, it is a critical component for controlling the mainsail and achieving optimal sailing performance.