Container ships are designed to transport containers only, and range in size from the small coasting container ships up to the large and fast ocean-going container ships. Container ships’ holds are cellular i.e. container ships’ holds fitted with vertical frames or guides into which the containers are slotted.
Container ships can handle containers of International Standards Organisation (ISO) dimensions, frequently 20 or 40 feet in length. Container ship sizes are expressed by the number of TEU (Twenty-Foot Equivalent Units) that the container ship able to carry.
Many small and medium-sized container ships are self-sustained (geared) i.e. they have cargo gear on board with which they can load and discharge their containers. All large container ships transport refrigerator-containers by supplying electric power outlets to which may be connected the container’s integral refrigeration compressor. Highly specialized container ships for trades where there is a high demand for chilled cargo are equipped with central refrigeration machinery which delivers cooled air to insulated containers through ‘portholes’ in the units although this system is now being phased out. A feature of container ships is the arrangement of their holds.
Container ships are completely open hold ships which means that the hatches give access to the whole of the cargo hold area so that there is no need for any stowage work and as the cell guides are erected in the holds no lashings are required below decks. Container ships’ hatch covers of the holds are either slab or pontoon type and are fitted out to carry containers up to six or seven tiers high. Below deck, the boxes are secured by the cellular arrangement but on the hatch covers, they must be lashed to prevent movement.
Modern deep-sea gearless container ships can carry up to about 23,000 TEU with a service speed of between 22 and 26 knots. Post-Panamax container ships can transit from the New Panama Canal.
Some container shipowners have introduced hatchless type container ships. In one type of design, the cell guides are extended above the main deck level so that on-deck lashing is also unnecessary. In another type of container ship, there is also a heightened and ‘streamlined’ foc’sle (fore-castle) with a ‘wave breaking’ device intended to keep water away from the main deck of the container ship. In both cases, the aim is to bypass the additional labor and delay involved in removing and replacing hatch covers as well as the tiresome securing of the containers carried on deck.
General Cargo and the Container Trades:
The largest percentage of cargo by sea is general cargo, which amounts to 60 percent of goods shipped by sea. Currently, most of the general cargo is moved in containers. One of the most important achievements of containerization is the efficiency of cargo operations and the achievement of scale economies by drastically reducing the cost of handling and
There are two main trades in the container shipping market: EastWest and North-South. China has the biggest volume in TEU lifts annually. Main trade routes include Shanghai to the West Coast of the United States (Transpacific), Shanghai-Mediterranean and Shanghai-North Europe (Far East-Europe), and North-South trades such as China (Shanghai) to Australia/New Zealand and South Africa. Other Intra-Asian trade routes include Shanghai-Singapore, Shanghai-East Japan and, Shanghai-Hong-Kong.
TEU (Twenty-Foot Equivalent Units):
Whilst the size of almost all other merchant ships is normally described in tons (or the metric counterpart – tonnes), the capacity of container ships is usually expressed in terms of the number of containers it is designed to carry. Traditionally, standard container sizes are either 20 feet or 40 feet long, 20 TEU (Twenty-Foot Equivalent Units), or 40 FEU (Forty-Foot Equivalent Units). Container ship sizes can range from about 100 TEU to over 23,000 TEU.
20 TEU (Twenty-Foot Equivalent Units) is used to present a rough indication of the container ship’s container carrying capacity, each container space being called a slot. Nevertheless when trading a container ship transport a mixture of 20 TEU and 40 FEU containers, some of the stowage positions may only be suitable for the smaller size, so that a more specific description of the vessel will indicate the number of 20-foot slots available (TEU) as well as the number of 40-foot slots (FEU); because the ships deadweight cargo capacity is also relevant the maximum average weight of the containers will also be stated.
Smaller container ships are used as feeder ships, feeding the hinterland around major container terminals with loaded containers inbound from abroad, before feeding containers for export back to the container terminal on the return route. Feeder container ships serve less sophisticated container ports. Hence, feeder container ships may well be geared (gantry cranes), enabling feeder container ships to load and to discharge containers with their shipboard equipment.