They are designed in such a manner that no space is wasted. Their capacity is measured in TEU (Twenty-foot Equivalent Units). This is the number of 20 ft containers that it can carry. The majority of containers used today are 40 ft in length. Above a certain size, container ships do not carry their own loading gear. Hence loading and unloading can only be done at ports with the necessary cranes. However, smaller ships with capacities up to 2 900 TEUs are often equipped with their own cranes.
Informally known as "box boats," they carry the majority of the world's dry cargo, meaning manufactured goods. Cargoes like metal ores or coal or wheat are carried in bulkcarriers. There are large main line vessels that ply the deep sea routes, then many small "feeder" ships that supply the large ships at centralized hub ports. Most container ships are propelled by diesel engines, and have crews of between 20 and 40 people. They generally have a large accommodation block at the stern, directly above the engine room. Container ships now carry up to 10,000 containers on a voyage.
The first container ships were converted tankers, built up from surplus tanker Liberty ships after World War II. Container ships are by now, all purpose-built and, as a class, they are the biggest cargo ships on the oceans, right after crude oil tankers.
Shipyards
Large container ships (over 7000 TEU) have been built in the following shipyards:
- Odense Steel Shipyard, Denmark
- Hyundai Heavy Industries, South Korea
- Samsung Heavy Industries, South Korea
- Daewoo Heavy Industries, South Korea
- IHI. Kure. Japan
- Mitsubishi Heavy Industries, Nagasaki. Japan
