Feeder container ship.

Container ship with own unloading gear.

Medium size purpose built container ship.
Today, most small size general cargo will be on a containership, also known as "box" ships. The "boxes" they carry are containers that generally are found in twenty and forty foot lengths. The market power of the United States was influential in determining the imperial dimensions of today's containers. Initial ISO external container dimensions, standardised in the early 1960's, are still for the most part intact today.  The twenty-foot equivalent (TEU) is the standard by which container volume is measured.  This refers to a container with external dimensions of 8'x8'x20'. Volume is sometimes measured by FEU's, forty-foot equivalents, 8'x8'x40', as well. Since the 1960's, numerous other container sizes have emerged.  Over 20 recognized ISO container sizes are in use today. Fortunately the most important container dimension, width, has been resistant to change. ISO container widths have stayed constant for two reasons. First, widths wider than eight feet cause navigational problems in regions of the world where narrow roads are common, such as Europe.  Second, a standardised container width enables containerships to use cells more efficiently to stack containers. They can be filled with just about any type of cargo, from televisions sets to fruit or meat. 


Large purpose built container ship.

The capacity of a container ship is measured in TEU. Container ships come in all sizes up to 8,000 TEU, with vessels in build of up to 9,200 TEU, and projected up to 12,000 TEU. Many vessels have a number of container slots that will accept refrigerated containers. The smaller ships engaged on coastal and short sea routes are known as feeders. Containers preloaded with goods for export can be locked and sealed before they are loaded onto the ship. With the use of shore based independent moving gantry cranes, the loading and unloading work is extremely fast. In line with the fast cargo handling work, container ships are usually built for speed, so that cargo can arrive at their destinations fast. The general arrangement of a pure container ship has changed over the years, with the first vessels being general cargo ships modified to carry containers, and usually had their own cargo gear in the form of derricks or cranes, but the holds were not specially designed with cell guides. Some of the medium sized modern vessels are geared, and call at ports that have no infrastructure for unloading containers.

Typical modern medium size feeder container ship of 900 TEU. Usually ungeared like this one, but sometimes fitted with cranes so they can load from ports with limited infrastructure.
Comparatively high speeds and swift turn arounds in port are vital in maintaining the liner schedules of container ships. Cargo handling efficiency is sought from large dockside gantry cranes at the terminals serving large long haul ships which are generically non-geared (without their own cranes). Feeder container ships, however, are often geared, their deck cranes, commonly of the slim-line type to maximise container stowage spacefacilitating cargo handling in ports with limited infrastructure. To facilitate loading, some ships have stacking guides arranged in rows along the deck.

All the cargo holds contain guides for the containers so that it is easy to slide them in place. The containers are made so that the corners can be locked in place very easily. Because the containers are lowered in place precisely and the corners are matched for interlocking, it is important to keep the ship at even keel during the cargo work. For this purpose, container ships have remotely controlled ballast pumps and valves that can be controlled by deck officers.

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