Most modern merchant ships can be placed in one of a few categories, such as: Bulk carriers are cargo ships used to transport bulk cargo items such as ore or food staples (rice, grain, etc.) and similar cargo. A bulk carrier can be recognized by the large box-like hatches on its deck, designed to slide outboard for loading. Bulk cargo can be either dry or wet. Container ships are cargo ships that carry their entire load in truck-size containers, in a technique called containerization. They form a common means of commercial intermodal freight transport. Informally known as “box boats,” they carry the majority of the world’s dry cargo. Most container ships are propelled by diesel engines, and have crews of between 20 and 40 people. They generally have a large accommodation block at the stern, directly above the engine room. Tankers are cargo ships for the transport of fluids, such as crude oil, petroleum products, liquefied petroleum gas, liquefied natural gas and chemicals, also vegetable oils, wine and other food. The tanker sector comprises one third of the world tonnage. Reefer ships are cargo ships typically used to transport perishable commodities which require temperature-controlled fruits, meat, fish, vegetables, dairy products and other foodstuffs. Roll-on/roll-off ships are cargo ships designed to carry wheeled cargo such as automobiles, trailers or railway carriages. RORO (or ro/ro) vessels have built-in ramps which allow the cargo to be efficiently “rolled on” and “rolled off” the vessel when in port. While smaller ferries that operate across rivers and other short distances still often have built-in ramps, the term RORO is generally reserved for larger ocean-going vessels.
Ferries are a form of transport, carrying (or ferrying) passengers and sometimes their vehicles. Ferries are also used to transport freight (in lorries or freight containers) and even railroad cars. Most ferries operate on regular, frequent, return services. A foot-passenger ferry with many stops, such as in Venice, is sometimes called a water bus or water taxi. Ferries form a part of the public transport systems of many waterside cities and islands, allowing direct transit between points at much lower cost than bridges or tunnels. Many of the ferries operating in Northern European waters are ro/ro ships. Cruise ships are passenger ships used for pleasure voyages, where the voyage itself and the ship’s amenities are considered an essential part of the experience. Cruising has become a major part of the tourism industry, with millions of passengers each year. Cable layer is a deep-sea vessel designed and used to lay underwater cables for telecommunications, electricity and such. A tugboat is a boat used to maneuvre, primarily by towing or pushing other vessels in harbours, over the open sea or through rivers and canals. They are also used to tow barges, disabled ships, or other equipment like towboats. A dredger (sometimes also called a dredge) is a ship used to excavate in shallow seas or fresh water areas with the purpose of gathering up bottom sediments. A barge is a flat-bottomed boat, built mainly for river and canal transport of heavy goods. Most barges are not self-propelled and need to be moved by tugboats towing or towboats pushing them. Barges on canals (towed by draft animals on an adjacent towpath) contended with the railway in the early industrial revolution but were outcompeted in the carriage of high value items due to the higher speed, falling costs, and route flexibility of rail transport. Coastal trading vessels, also known as coasters, are shallow-hulled ships used for trade between locations on the same island or continent. Their shallow hulls mean that they can get through reefs where sea-going ships usually cannot (sea-going ships have a very deep hull for supplies and trade etc.