saddle-bottomed wagons are large-volume hoppers are exclusively unloaded by gravity and are therefore classed as self-discharging hoppers. unlike normal hopper wagons, however, their discharge cannot be controlled and the entire load must be dropped. to unload the flaps on the side swing out allowing the load to empty. this is aided by the floor which slopes downwards on both sides like a gable roof. the discharging chutes on either side are relatively high up. these wagons are frequently seen in unit trains for transporting bulk goods such as coal or mineral ore from mines or ports to steelworks or power stations.