A floating and maneuverable hull washing and cleaning plant for ships, includes cleaning and washing means submerged below the water level and operating against the hull, propulsion members for moving the plant in the engagement and washing against the hull in its length, members for controlling and changing the buoyancy displacement of the plant with control of the immersion level; a basin with side walls within which the cleaning and washing means are positioned, the cleaning and washing means being arranged in said basin and brought into contact with the hull during the cleaning with the control of the plant floating and of the position of the support members of the cleaning and washing means with respect to the basin itself; and guiding members for engaging and positioning the ship during the treatment.