Shipping on the Oceans

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Shipping on the Oceans

Throughout recorded history, humans have relied on the oceans to ship goods quickly and efficiently. Historically, shipping on the oceans had several advantages over shipping over land. Shipping over land required moving bulky and heavy goods over mountains, across deserts, or through forests. The location of roads often dictated where goods could be shipped. Before vehicles, land travelers also had to carry enough food and water to keep their pack animals alive, adding to the weight of their loads.

Two thousand years ago, the power of the Roman Empire was founded on the economic benefit that Rome gained from its control of trade on the Mediterranean Sea. Most of Rome's empire lay on the shores of the Mediterranean Sea, which served as a highway for the trade of wine, food, timber, spices, and other valuable materials. Rome's power stretched from Gaul (modern France) around the Mediterranean Sea to the Middle East and to North Africa. Rome also had territory in modern Britain. Rome typically imported raw materials from its faraway territory and exported finished goods back to its territory.

The expansion of European nations into lands fueled trade with their colonies over vast expanses of oceans. British trade with India and Southeast Asia under the British East India Company in the sixteenth through eighteenth centuries delivered spices and teas to Britain via ships. Britain's colonies in North America also shipped raw materials such as timber, furs, and cotton across the Atlantic Ocean to Britain, who shipped finished goods back to the United States.

In the nineteenth century, ships made of iron and steel used steam power to transport goods across the oceans faster than ever before. The rise of diesel powered vessels in the twentieth century made shipping cheaper and faster. Goods could be shipped to ports on the other side of the world in days instead of weeks and months.

Shipping today

Today, merchant ships transport more than 90% of the world's cargo. There are several reasons that ships move more cargo than any other form of shipping. First, ships are the cheapest form of transportation. Second, in a world in which many countries have poor roads, boats are often the most efficient and reliable means of shipping. Third, boats can move greater amounts of cargo than any other form of shipping.

Despite the rise of shipping cargo by aircraft, the ocean shipping industry continued to grow throughout the twentieth century. From the early 1920s through the end of the century, the worldwide number of ships in the merchant shipping fleet increased from under 30,000 to nearly 90,000. Total tonnage increased at an even greater rate. The total tonnage of merchant ships increased from 59 million gross tons (a unit of measurement to describe the size of a ship) to over 500 million gross tons during the same period.

Types of merchant ships

Modern merchant ships serve a variety of purposes. Therefore, shipping vessels come in many different shapes. Some ships, called tankers, are designed to carry liquids. The most common type of tanker is the oil tanker. Over 3,500 oil tankers carry petroleum products to ports around the world. Oil tankers are among the largest ships in the world. Some oil tankers are over 1,300 feet long, or the length of about 4.5 football fields! Similar to oil tankers, chemical tankers carry various liquids such as vegetable oil, acids, and liquid fertilizers. Many of the chemicals carried by chemical tankers are hazardous. Chemical tankers carry smaller loads than oil tankers due to the increased danger of the cargo, and because consumers require greater amounts of oil.

Most merchant ships carry dry cargo. Over the last fifty years, container ships have become one of the most important ship designs. Container ships carry sealed cargo containers that can be unloaded directly onto trains or trucks, thus becoming a railway car or a truck trailer. This allows the container to be loaded only once upon departure and unloaded once upon delivery to its final destination. New designs for cargo ships will soon carry up to 15,000 containers that are each 20 feet in length.

Bulk carriers, another type of dry cargo ship, carry large quantities of raw material such as iron ore, steel, coal, or wheat. Bulk carriers transport their goods in large cargo holds without the use of containers. A cargo hold is a section of a ship that is divided from the rest of the ship for the transport of a single type of cargo. Shipping in bulk decreases transportation cost by reducing loading and unloading costs. For example, with modern loading methods, more than 15,000 tons of iron ore can be loaded onto a bulk carrier in one hour. Bulk carriers can carry more than 250,000 tons of goods and may have over 10 individual cargo holds.

Problems with shipping

Shipping on the oceans poses a variety of possible problems, including harm to the environment, loss of cargo, and loss of lives. The major causes of shipping accidents are human mistakes, poor equipment maintenance, and natural disasters. Most accidents are avoidable, and the last 100 years have seen a dramatic decrease in the number of shipping accidents. Increased training and safety regulations have lessened the number of accidents caused by human error and poor maintenance. Weather forecasting has improved greatly in the last century, leading to fewer accidents from natural disasters such as hurricanes.

Oil and chemical tankers pose a serious threat to the environment if they lose their cargo. Oil and chemical spills can poison fish and marine mammals. A well-known oil spill, although not the largest, was the Exxon Valdez accident in 1989, when the tanker Exxon Valdez ran aground on rocks in Prince William Sound, Alaska. Nearly 11 million gallons of oil spilled out into the natural environment, killing fish, birds, and marine mammals. The resulting cleanup of the waters and shore cost about $2 billion.

Bulk container ships are involved in more accidents than any other form of cargo ship. Bulk container ships have large hatches that stretch across most of the width of the ship. This decreases the overall strength of the ship, especially in rough seas. About thirteen bulk container ships sink each year. On average, about 70 people lose their lives every year in accidents involving bulk container ships.

Although shipping by ocean is far less expensive than shipping by aircraft, it is also slower. Because the large amount of cargo that modern merchant ships can carry means that less than one percent of the purchase price of a product goes towards ocean shipping, many merchants and consumers choose to wait the extra time for the goods.

Adrienne Wilmoth Lerner

For More Information


Bone, Kevin, et al. The New York Waterfront: Evolution and Building Culture of the Port and Harbor. New York: Monacelli Press, 2003.

Gardiner, Robert. The Shipping Revolution: The Modern Merchant Ship. New York: Book Sales, 2000.


"Marine Navigation." NOAA National Ocean Service, National Oceanic and Atmospheric Administration. (accessed on August 27, 2004).