Width determines where a ship can go and how it behaves. Beam is the maximum breadth of a vessel measured at its widest point, usually amidships.

Beam affects stability, cargo capacity, and the ability to transit canals and locks. A wider beam generally improves initial stability but can increase resistance and limit access to narrow waterways. Designers balance beam against length, draft, and operational requirements.

Canal authorities publish maximum allowable beam for transit. The Panama Canal’s original locks, for example, constrained ship design for decades. On the bridge, officers use beam when calculating under-keel clearance in tight turns and when planning berth approaches.

• Maximum width of a ship
• Influences stability, capacity, and route access
• Constrained by canals, locks, and berths
• Key dimension in ship design and maneuvering