Container ships are ocean going ships which are specifically designed to handle shipping containers, giant metal boxes which usually measure 40 feet (12 meters) long. Shipping containers can contain a wide variety of dry goods items to be shipped all over the world including foods, textiles, and electronics. The idea of containerizing products for shipping was conceived in the twentieth century, when shipping companies realized that shipping products in giant containers was more efficient. In the 1950s, the technique was perfected, and by the end of the century, these ships were moving millions of tons of goods all over the planet.
Early container ships were designed to be loaded with railway boxcars. The boxcars could be moved directly into the shipping yard on wheels, and then lifted onto the ship with cranes. At the other end, the boxcars could be put back onto the tracks and moved to their final destination. In the 1950s, Malcolm McLean, who founded McLean Trucking and later moved into shipping, refined the technique, moving just the container onto the ship, rather than the container and the wheeled chassis used to support it. This eliminated wasted space on ships, and also paved the way to the development of these ships, which are designed to have maximum space efficiency for containers of a uniform size.
Usually, the storage space of container ships is measured in terms of Twenty-foot (6 meters) Equivalent Units (TEUs). Most shipping containers come in lengths of either 20 or 40 feet, meaning that the ship can be efficiently packed to capacity with a collection of shipping containers. On small ships, rigging equipment is attached to the ship so that it can be loaded or unloaded anywhere. On larger ships, the ship has no rigging equipment, and must be docked in specific ports with cranes that are capable of working with the very large ship.
When preparing goods for transportation on container ships, the packaging company clearly labels its shipping containers, often attaching electronic tags to track them with. The contents of a container are listed on a manifest, and containers are loaded so that containers going to different destinations are stacked together on the ship, allowing for rapid unloading at the end destination. The shipping containers can be placed on railway flatcars or onto specially designed trucks to get to and from the shipping yard, and to their ultimate destinations.
Like other very large ships, container ships carry a certain amount of risk for their owners. The highly valuable cargo is usually insured against loss of the ship to weather or piracy. These ships are very slow and difficult to maneuver, requiring special skills on the part of the crews that run them to make efficient time from port to port. In addition, the contents of shipping containers can be damaged, and it is important for crane operators to be well trained and conscientious about the products that they are handling. These ships also have environmental impacts, especially on smaller harbors that must be dredged to accommodate them. Dredging is damaging to the marine environment, and this has been raised as a concern by environmental organizations which are worried about the proliferation of container shipping.