Roll-on/roll-off (RORO or ro-ro) ships are ferries designed to carry wheeled cargo such as automobiles, trucks, semi-trailer trucks, trailers or railroad cars. This is in contrast to lo-lo (lift on-lift off) vessels which use a crane to load and unload cargo.
RORO 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. The ramps and doors may be stern-only, or bow and stern for quick loading.
Various types of RORO vessels include ferries, cruiseferries, cargo ships, and barges. A true RORO's ramps can serve all of the vessel’s decks; otherwise it is a hybrid type. New automobiles that are transported by ship around the world are often moved on a large type of RORO called a Pure Car Carrier (PCC) or Pure Car Truck Carrier (PCTC).
Unlike elsewhere in the shipping industry where cargo is normally measured by the metric tonne, RORO cargo will typically be measured in the more convenient unit of lanes in meters (LIMs). This is calculated by multiplying cargo length in meters by the number of decks and by its width in lanes (lane width differs from vessel to vessel and there are a number of industry standards). Aboard PCCs cargo capacity is often measured in RT or RT43 units which is based on a 1966 Toyota or by car equivalent units (CEU).
The largest RORO passenger ferry is , a 75,100 GT cruiseferry that entered service in September 2007 for Color Line. Built in Finland by Aker Finnyards, she is long, wide and can carry 550 cars as well as 1270 lane meters of cargo.
The RORO with the greatest car-carrying capacity is the Ulysses (named after a novel by James Joyce) which is owned by Irish Ferries. She entered service on 25 March 2001 and operates between Dublin and Holyhead. The 50,938 GT ship is long and wide, and can carry 1342 cars and 4101 lane meters of cargo.
The first RoRo ships were ferries carrying steam trains across rivers. One of the earliest was Firth of Forth ferry in Scotland which started in 1851 and operated for nearly forty years, until the completion of the Forth Bridge.
Ferries hauling rail cars were used after the US Civil war in New York harbor, the Great Lakes and the St. Clair River in Detroit. By the latter quarter of the century, car ferries were a common sight in San Francisco and Puget Sound. A car ferry worked the Columbia River for many years at Kalama for the Northern Pacific Railway. By the turn of the century, car ferries became important adjuncts to railway systems particularly those which were discontinuous due to geography. Montreal, Newfoundland and Labrador, Prince Edward Island, and the Islands of Japan were all cut by water, and thus needed ferries. Russians used car ferries on Lake Baikal to move rail cars while the line was finished.
The first automobile roll-on roll-off ship was the Suhulet and her 3 sisters Sahilbend, Saadabad and Sultanahmet. They were commissioned in the Ottoman Empire during 1871 in Istanbul to enable Trans-Bosphorus automobile and horse-car crossings.
During WWII, landing craft were also among the first ships enabling road vehicles to roll directly on and off. Post war, the idea was adopted for merchant ships and short ferry crossings. The first RoRo service crossing the English channel began from Dover in 1953.
In 1957 the US military issued a contract to the Sun Shipbuilding and Dry Dock Company in Chester, PA for the construction of a new type of motorized vehicle carrier. The ship, Comet, had a stern ramp as well as interior ramps which allowed cars to drive directly from the dock, onto the ship, and into place. Loading and unloading was speeded dramatically. Comet also had an adjustable chocking system for locking cars onto the decks, and a ventilation system to remove any exhaust gases that accumulated during vehicle loading.
The Atlantic Conveyor was requisitioned during the Falklands War to ferry Helicopters and STOVL Harrier fighters which flew to their assigned fleet carriers before it was sunk after being hit by two Argentine Exocet missiles. In September 1983 Soviet Yakovlev Yak-38 pilots operated from the civilian ‘Ro-Ro’ vessel Agostinio Neto, they conducted further tests from another ‘Ro-Ro’, Nikolai Cherkasov. ‘Ro-Ro’ and other types of container ships have been suggested as emergency STOVL escort carriers with pre-fab ski jump, air control tower, and defensive systems.
Since 1970 the market for exporting and importing cars has increased dramatically and the number and type of RO/ROs has increased also. In 1973, Japan’s K Line built the European Highway, the first Pure Car Carrier (PCC), which carried 4,200 automobiles. Today’s pure car carriers and their close cousins, the Pure Car/Truck Carrier (PCTC) are distinctive ships with a box-like superstructure running the entire length and breadth of the hull, fully enclosing and protecting the cargo. They typically have a stern ramp and a side ramp for dual loading of many thousands of vehicles, as well as extensive automatic fire control systems.
The PCTC has liftable decks to increase vertical clearance as well as heavier decks for "high and heavy" cargo. A 6500 unit car ship with 12 decks can have three decks which can take cargo up to 150 tons with liftable "panels" to increase clearance from 1.7 meters to 6.7 meters on some decks. Lifting decks to accommodate higher cargo reduces the total capacity.
With the building of the Wallenius Wilhelmsen Logistics's 8000 CEU car carrier Stockholm Faust in June 2007 the car carriers entered a new era called the LCTC (Large Car & Truck Carrier).