Commerce

Tankers

Tankers merit their own section because of its current importance in commerce and they are the biggest ships afloat today. A tanker is a large vessel that carries liquids. Early vessels used tanks and barrels within the hull, but by the end of the 19th century, tankers took on their present form: a hollow hull that is a tank. Cargo capacity is often measured in deadweight tons, about 1.016 times a metric ton. Very early oil tankers held only several hundred tons, increasing steadily to a maximum of 500000 tons today. Chemical carriers are smaller, most averaging more than 20000 tons. Ore-bulk-oil (OBO) tankers are multipurpose ships that carry a variety of cargoes, and average about 200,000 tons. Another type, the liquified-gas carriers, carry gases in a less voluminous liquid form. These and chemical tankers have rose steadily in recent years.

Other Cargo Ships

Other cargo ships include bulk-cargo ships, containerships, and Ro-Ro ships. Bulk-cargo ships are ships which carry bulk cargo like coal and grain. They have large compartments separated by bulkheads that carry bulk cargoes. Coal-carriers are called colliers. Some ships are hybrids that carry both bulk cargoes and manufactured goods. A containership is one that holds containers in its cargo hold. These ships carry a wide variety of products, most importantly manufactured goods. Ro-Ro ships are those with extendable ramps so that vehicles can be rolled right inside. They are mainly used to transport motor vehicles.

Ocean Liners

Ocean liners are oceangoing passenger transports running on fixed schedules. There are three fundamental types: superliner, express liner, and passenger-cargo liner. Superliners were the largest and most luxurious kind, averaging speeds of around 30 knots and held thousands of passengers. Superliners have been withdrawn from service in recent years because of the dominance of air travel. Express liners were smaller ships that operated more flexibly, but holding less passengers. Passenger-cargo combination ships hold under a thousand passengers, but also holds several thousand tons of cargo. Ocean liners in general have almost dissapeared from the oceans. The liners that remain serve as cruise ships, its travel function being replaced by much faster airplanes.