Bulk cargoes can vary considerably in their stowing properties – e.g. iron ore stows around 12 cubic feet for every tonne, whereas coke may stow as high as 90 cubic feet per tonne. Obviously, in the cases of iron ore, full deadweight will be reached with cargo holds little more than a third full, whilst a cargo of coke will fill cargo holds to capacity and the vessel may theoretically be losing potential revenue earnings because of lack of space in cargo compartments. (Unlike free-flowing bulk barley, coke cannot be loaded in upper wing tanks, because it would not only be extremely difficult and time-consuming, if not impossible, to load it through the restricted deck openings to the wing tanks, it would probably continually block the ‘bleeding’ apertures when it came to discharge). For heavy cargoes of iron ore, it is important that bulkcarriers be loaded so they do not become too ‘stiff’ and dangerous in their handling at sea. Consequently, cargo is normally loaded in adjacent holds – say Holds 2, 4, 6 and 8 of a 9-hold bulkcarrier – the vessel being especially ‘hold-strengthened‘ during the building process to facilitate the demands of this trade. The facility of carrying cargo in adjacent holds with others empty is particularly useful for loading or discharging at more than one port when carrying commodities other than heavy ores. Whether this practice has contributed significantly to the poor loss record of bulkers is currently under review along with the changes mentioned earlier. Some bulkcarriers are fitted with ‘self-discharging‘ facilities. These may be a simple arrangement by which the vessel carries its own cargo-grabs which can be fitted to the ship’s derricks or cranes and used to discharge or perhaps even to load cargo. Some vessels have a ‘gantry’ arrangement, by which a ‘travelling’ crane moves longitudinally the  length  of  a  bulkcarrier  along  a  gantry  rail  and  is  thus  able to  operate over any particular hatchway.