Catamaran

A catamaran is a twin-hull craft, two slender demihulls joined by a cross-structure or bridging deck, that carries its stability in the wide hull spacing rather than in beam of a single hull. Because the transverse waterplane inertia scales with the square of the demihull separation, a catamaran has very high transverse metacentric height and stiff, short-period roll, with large deck area for its displacement. The slender demihulls run at high length-displacement ratio, which lowers wave-making resistance at speed, the reason most fast ferries are catamarans. The trade-offs are higher wetted surface, cross-deck loads from out-of-phase wave forces on the two hulls, and stiff motions, often managed with ride-control foils or interceptors.