Beam (nautical)

The beam of a ship is its width at its widest point. The maximum beam (B_MAX) is the distance between planes passing through the outer sides of the ship, beam of the hull (B_H) only includes permanently fixed parts of the hull, and beam at waterline (B_WL) is the maximum width where the hull intersects the surface of the water.^[1]

Generally speaking, the wider the beam of a ship (or boat), the more initial stability it has, at the expense of secondary stability in the event of a capsize, where more energy is required to right the vessel from its inverted position. A ship that heels on her beam ends has her deck beams nearly vertical.^[2]