The biggest ship ever built proved too big to pay its way
The supertanker Seawise Giant, later renamed Knock Nevis, stretched about 458 metres and could carry 565,000 tonnes. Yet ships that size rarely sailed full, which made them money-losers, and builders stopped making supertankers altogether. Even the huge TI-class tankers that followed seldom use more than 70 percent of their capacity.
Any vessel that carries cargo or paying passengers counts as a merchant ship, and the range is startling. It includes six-metre inflatable dive boats in Hawaii, Mississippi River casino boats holding 5,000 or more gamblers, New York Harbor tugs, 300-metre container ships and even tourist submarines in the Caribbean. In wartime these civilian vessels may be pressed into service ferrying troops and supplies for their navies.
Many sail under a flag of convenience, registered in places such as Liberia or Panama whose maritime laws owners find friendlier than those at home. Greece controls the largest single merchant fleet, around 16 percent of world tonnage. In English, Merchant Navy on its own means Britain's fleet, while the American equivalent is the Merchant Marine. Name prefixes reveal a vessel's job, such as LNG for a liquefied natural gas carrier or SV for a sailing vessel.
Bulk carriers, recognisable by big box-shaped hatches that slide or fold open, haul iron ore, bauxite, coal, cement and grain, and their width is often set by the Panama Canal. Lake freighters have worked the Great Lakes and Saint Lawrence Seaway for more than a century. Tankers run from a few hundred tons for small coastal harbours to several hundred thousand for long hauls, carrying oil and gas but also ammonia, chlorine and styrene. Aside from pipelines, they are the only way to shift oil in bulk, and wrecks such as the Exxon Valdez and Torrey Canyon caused major spills.
Passenger vessels once doubled as freighters. Ocean liners long carried mail and parcels in holds served by derricks, and cargo ships commonly took up to twelve paying passengers. Modern cruiseferries carry lorries and cars, and train ferries load entire railway wagons, while most cruise ships have dropped cargo space entirely.
Source: Merchant ship
