The beam of a ship is its width at the widest point, or a point alongside the ship at the mid-point of its length. Generally speaking, the wider a ship (or boat)'s beam, the more initial stability she will have, at the expense of reserve stability in the event of a capsize, where more energy is required to right the vessel from its inverted position. Typical length:beam ratios for small sailboats are from 2:1(dinghies to trailerable sailboats around 20') to 5:1(racing sailboats over 30'). Large ships have widely varying beam ratios, some as large as 20:1.

Nautical terms