Container ships are vessels designed around the exclusive carriage of cargo containers. Provision is typically made for the electrical powering of refrigerated reefer containers. As opposed to deadweight, capacity is measured in twenty-foot equivalency units (TEU's). As containers are relatively light (by marine cargo standards - they are limited to the structural capacity of the container itself, as well as other transportation means in an intermodal system), the vessels carriage ability is limited more by volume than displacement (a volume-limited design).
Feeders are small container ships, and may have the ability self-unload (particularly if the ship also or previously operates as a general cargo ship). Their TEU capacities range from about 175 TEU to a few hundred. A normal operational profile for a feeder is to redistribute containers from large, international container ports to smaller ports (or vis-versa) which are incapable of handling the size or volume of cargo of a larger containership.
As containers generally contain consumer goods, and may include perishables, speed is a particular concern to the value of transport. Large container ships generally operate long distances between continents. In the past, they were often built to canal sizes; however, with speeds in the mid-20 knot range, very large container ships can make up for extended routes with speed and volume. Large container ships are almost exclusively unloaded by shore-based facilities. Cell guides are generally fitted to stabilize container tiers, generally with a significant number of containers on deck and thus high superstructures (to maintain line of sight regulatory requirements).
Larger container ships will not be geared, that is are not fitted with cranes. Large container ports will be equipped with gantry cranes fitted with spreaders suitable for rapidly lifting and moving containers. When designing container ships, the primary consideration is the number of TEU's the vessel can economically fit. Care must be taken to ensure sightlines, particularly over the bow, are achieved as this may limit stack height. The stabilizing arrangement must be considered, with sufficient space, coamings, guides, lashing points, cones, etc. fitted. The arrangement of hatches should be sorted out fairly early. A class of container ships, hatchless designs, fore-go hatches & store containers in holds which are open to the environment. In these vessels, additional pump capacity is provided to deal with rain and green water.