Abstract: A semisubmersible, stationary positioned vessel for offshore work, e.g. development of oil and gas fields and having a device for, in operational condition, increasing stability and dampen motion. The vessel has at least one submerged body as well as a number of legs supported thereby for carrying a work deck at a secure level above the operational water line. The waterline area of the vessel is increased at at least some of the legs. The vessel also comprises a device for rigidly connecting at least one horizontal plate below the submerged body. The area of the plate and the vertical distance from the body determining the volume of the added mass of water vacillating well below the water line following the elastic movements of the vessel.