Abstract: There is provided a sea going barge train or modular tanker vessel for ocean transportation of cargo, such as oil or other dry or liquid materials, consisting of a forward traction unit, a rear powered caboose unit and a series of modular units or barges interposed therebetween wherein the units are serially and flexibly interconnected by means of a universal type coupling which permits relative limited yaw, pitch and roll movement between units. The hull of each barge unit is substantially semi-cylindrically shaped so that the hull immersed section is circular and the barge units are detachably coupled to each other fore and aft and to the traction and caboose units at the circle center of the circle segment defined by the hull cross section so that hull continuity of the barge train is maintained as the barge units roll relative to each other.