For a self-powered marine lifting vessel or catamaran having static buoyancy, a working deck is forcibly raised or lowered by flexing or extending each of a plurality of articulated pairs of fixedly mounted support beams connecting each hull and the deck. One version uses locally applied forces at the joints from adjacent hydraulic cylinders, incidentally causing the hulls to rotate about their axes. Another version forces the hulls to rotate axially from a non-rotating aft inter-hull linkage. Applications include routine harbor maintenance and hull cleaning, then emergency marine pollution including oil cleanup at a polluted site.