Beam

Beam is the maximum width of a vessel, measured at its widest point perpendicular to the centerline. Beam directly affects interior space, deck area, stability, and the size of slip needed to dock the vessel.

For charters, beam is important for comfort: on two vessels of similar length, the beamier boat typically has more usable deck space, more cabin volume, and better stability at anchor. Catamarans, by design, have exceptionally wide beams relative to length and therefore far more living space than a monohull of comparable length.

Beam also constrains trailering, transiting locks, and docking at older marinas that were designed around narrower average vessels.