Cargo Ship | Research & Encyclopedia Articles

Cargo Ship

Cargo ships are necessary for world commerce. There are two basic kinds of cargo ships: freighters and tankers. Freighters come in all shapes and sizes in order to accommodate various loads. Dry cargo vessels comprise one category and are used to transport coal, grain, iron ore, and similar products that can be loaded in bulk. The first of these hauled iron ore on the Great Lakes during the late 1800s; it resembled a long steel box, with crew quarters at the front and engine at the back. Modern freighters, by contrast, have a double hull for strength and safety, and include storage areas for fuel oil, water ballast, or fresh water. The largest of these in use today, with the bridge and engine room near the tail, can haul over 100,000 tons of cargo. Barges are smaller forms of these bulk carriers. Formerly powered by sail, they now have diesel engines or are towed by tugboats. There are also general cargo ships used for hauling packaged items. Around the turn of the century these ships had three islands, or three structures, that stood out above the main deck: the crew quarters at the front, the bridge near the middle, and the cabins for officers and passengers at the stern. Cargo was loaded between these three structures. One-island vessels eventually replaced these early designs because they provided room for additional and larger hatches, thus simplifying loading and unloading. During World War II the United States built many of these one-island vessels, called Liberty and Victory ships, which transported troops and supplies throughout the world. Modern cargo ships house powerful, electrically driven cranes and derricks. These ships can be loaded from the side and stern as well as from the hatches and they feature automatic engine and navigational controls. The need to improve efficiency has led to at least three specialized cargo ship designs: containers, roll on/roll off, and LASH (Lighter Aboard Ship). Container vessels reduce the time that is spent in port and are filled with prepackaged aluminum boxes of various sizes. Money is saved because there is less loading and unloading time as well as less breakage and theft. Some of these ships can hold around 1,000 containers; each one equals the cargo-carrying capacity of 17 standard World War II freighters. Roll on/roll off ships also utilize containers, but these boxes have wheels on them which allow them to be hauled like truck trailers both on and off the ship. A LASH is a huge freighter which can stow small loaded barges (lighters). The second kind of cargo ship is the tanker.

In 1878 Ludwig Nobel revolutionized the way oil was carried. Previous to his time, all liquids were transported in barrels or tanks, yet Nobel launched a ship that was one huge tank itself. The early tankers were 300 feet long with a capacity of 2,300 tons of oil. Today, there are tankers 1,000 feet long that can carry 300,000 tons of oil. Their hulls are divided into tanks, which are loaded or unloaded by pump s. Because of recent well-known oil spills from some of these vessels, there are plans for double-hulled construction to prevent such disasters. Other tankers can carry liquefied natural gases in specially designed tanks. Space between the gas tanks and the hull is filled with an inert gas to prevent oxygen in the air and any leak of gas from combining to produce an explosive mixture. Finally, there are multipurpose ships that combine the features of a freighter and a tanker. Some have refrigerated space for foods that spoil easily, tank space to haul liquids, and a deck for roll on/roll off containers. In 1968, the United States launched its first multipurpose vessel with the capability of carrying containers, roll on/roll off cargo, various general cargo, and refrigerated items.

Rising fuel prices during the 1970s prompted the development of a new technology that used sails shaped like aircraft wings turned on end to take some of the burden off the engines and save fuel. Slightly curved to form a wing shape, these sails were attached to a mast that could pivot and locate the best angle for the sail to catch the wind. Once the computers set the mast at the best angle to the wind, the sail created the same "lifting" force that an airplane's wing generates, except that the force pushed the ship along the water. However, this system did not always prove to be efficient for extremely large vessels.

By the late 1990s, the trend was toward building even larger vessels for container freight, and in 1997, the largest such ship was the 1,043-foot long Dutch ship, Regina Maersk. Capable of handling about 6,000 steel or aluminum containers (each 20-feet long), it requires a crew of only 15. One of the most revolutionary designs for cargo ships is the planned waterjet-propelled cargo vessel proposed to travel between the United States and Europe. Called the FastShip Atlantic, it is designed to cruise at 42 knots (48 mph). Since this is twice the speed of conventional freighters, it will cut transatlantic travel time in half -- to three and a half days. Powered by six to eight gas turbine engines which drive five water jets (which use no moving parts and operate on the same principle as a jet ski), the new freighter will range between 560 to 860 feet long. The key to attaining such high speed with such a huge vessel is the ship's radically new "semi-planing" hull. Flatter and wider than a conventional hull at the stern (front), it allows the vessel to skim over the water rather than push through it. This means it need not slow at all for waves as high as 50 feet. Once it reaches port with its cargo, transfer is accomplished rapidly by gliding them off or onto the ship using large metal pallets buoyed by a cushion of air. FastShip promises to transform all aspects of transatlantic delivery since it will not only shorten door-to-door delivery from the traditional 14-35 days to an astounding 5 days, but will make cargo ships dependable, on time freight delivery systems since they will no longer be subject to heavy seas.