A plant (1;20) for transferring cargo (23) to and from a ship (24), said plant comprising an elevated rail structure (2) and a crane unit (3) where the elevated rail structure (2) is arranged on one side of the ship (24) and comprises a longitudinal rail (6) which extends essentially parallel to the longitudinal axis of the ship and where the crane unit is arranged to transfer a load or a group of loads to and from said ship, is supported by said longitudinal rail and is displaceable along said longitudinal rail. The crane unit furthermore comprises a boom (10) and a trolley (21) where the boom of said crane unit extends essentially perpendicular to the longitudinal rail such that one end of the boom extends over the ship; and where the boom of said crane unit comprises a transverse rail (13) which extends in a direction which is essentially transverse to the longitudinal rail and essentially parallel to the centre line of the boom. The trolley is displaceably connected to said transverse rail of said boom and the trolley of said crane unit comprises a lifting device (22) for lifting said load or said group of loads. Furthermore, the transverse rail (13) of said boom (10) is arranged underneath said longitudinal rail (6) of said elevated rail structure (2). In this way, the trolley can move back and forth along the transverse rail without any hindrances.