Boom

The horizontal spar attached to the mast that supports the foot of the mainsail.

How to sign

Use Dominant flat-B, palm down. The base or passive hand is Non-dominant upright 1-hand: mast; boat locus established. Set mast at the boat’s center. Place the flat-B at the mast’s lower middle. Extend horizontally aft from the mast in one level line. Hold the flat-B behind the mast as the boom. Place the mast first. From its lower middle, extend a flat-B hand horizontally aft, palm down, to show the boom.