Boom

The boom is the horizontal spar attached to the foot of the mainsail at the gooseneck on the mast. It holds the foot taut and lets the crew control the sail’s angle to the wind with the mainsheet and its leech tension and twist with the vang or kicker. On most modern rigs the boom also carries the reefing points used to reduce mainsail area in a blow. A swinging boom in a gybe is the most common cause of head injury aboard.