Sailing ships needed tall spars; modern ships still need height for sensors and lights. A mast is a vertical or near-vertical spar on a ship that supports sails, signal equipment, radar antennas, lights, and other gear.

On sailing vessels the mast is a primary structure carrying the rig. On powered ships, masts are lighter structures for navigation lights, antennas, and sometimes cargo gear. Height and placement affect radar horizon, light visibility, and clearance under bridges.

Masts must withstand wind loads and the motion of the ship. Climbing a mast for maintenance requires safety gear and procedures. The arrangement of lights on the mast helps other vessels identify the ship’s type and aspect at night.

• Vertical spar supporting sails or equipment
• Carries lights, antennas, and signal gear on modern ships
• Subject to wind and motion loads
• Affects radar range and bridge clearance