Source: Port of New Orleans.
Prior to containerization, break-bulk cargo had to be manually loaded and unloaded. Several systems were put in place to do so, depending on the type of cargo and how it was packaged. Cargo could be in barrels, crates, or bags, but the maximum size of these load units remained to the level that crews could carry using various means. Piers were usually made out of wood because of lower construction costs, particularly since the loads transiting were not particularly heavy (loads of half to one ton). In the above photo, longshoremen are using a system of pulleys and slides to lift bagged cargo onto a ship from a hand cart that traveled a short distance from the adjacent on-dock transit shed. Such warehouses were prevalent in ports at that time to ensure that break-bulk cargo spent the least amount of time exposed outdoor. Still, the cargo was prone to damage and presented the opportunity for cargo theft.
The cargo being handled in the above photo appears to be flour, particularly since New Orleans has historically been a major export gateway for American agricultural goods shipped through the Mississippi system. The disks on the mooring lines were to prevent rodents from climbing into the ship as the bagged foodstuff was particularly vulnerable. The typical productivity level of a longshoremen crew was 5 to 10 tons per hour (a modern gantry crane is capable of handling 500 tons per hour), implying that ships spent a large share of their commercial life at ports being loaded or unloaded. At a later time, further attempts at unitization involving pallets and larger bags were made. Still, the system changed little until containerization in the late 1950s.