Roll-on/roll-off (RORO or ro-ro) ships are vessels designed to carry wheeled cargo such as automobiles, trucks, semi-trailer trucks, trailers or railroad cars that are driven on and off the ship on their own wheels. 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 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.
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Various types of RORO vessels include ferries, cruiseferries, cargo ships, and barges. New automobiles that are transported by ship are often moved on a large type of RORO called a Pure Car Carrier (PCC) or Pure Car Truck Carrier (PCTC).
Elsewhere in the shipping industry cargo is normally measured by the metric tonne, but RORO cargo is typically measured in units 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 several 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 MS Color Magic, a 75,100 GT cruise ferry that entered service in September 2007 for Color Line. Built in Finland by Aker Finnyards, it is 223.70 m (733 ft 11 in) long, 35 m (114 ft 10 in) wide and can carry 550 cars as well as 1270 lane meters of cargo.[2]
The RORO passenger ferry with the greatest car-carrying capacity is the Ulysses (named after a novel by James Joyce) which is owned by Irish Ferries. The Ulysses entered service on 25 March 2001 and operates between Dublin and Holyhead. The 50,938 GT ship is 209.02 m (685 ft 9 in) long and 31.84 m (104 ft 6 in) wide, and can carry 1342 cars and 4101 lane meters of cargo.[3]
At first, wheeled vehicles carried as cargo on oceangoing ships were treated like any other cargo. Automobiles had their fuel tanks emptied and their batteries disconnected before being hoisted into the ship’s hold, where they were chocked and secured. This process was tedious and difficult, vehicles were subject to damage, and could not be used for routine travel.
The world's first roll-on/roll-off service was a railway ferry, started in 1833 by the Monkland and Kirkintilloch Railway which operated a wagon ferry on the Forth and Clyde Canal in Scotland.[4]
During WWII, Landing Ships were among the first seagoing 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 sped up dramatically. Comet also had an adjustable chocking system for locking cars onto the decks, and a ventilation system to remove exhaust gases that accumulate during vehicle loading.
During the 1982 Falklands War the SS Atlantic Conveyor was requisitioned as an emergency aircraft and helicopter transport for British Hawker Siddeley Harrier STOVL fighter planes; one Harrier was kept fueled, armed, and ready to VTOL launch for emergency air protection against long range Argentine aircraft. She was sunk by Argentine Exocet missiles after offloading the Harriers to proper aircraft carriers but the vehicles and helicopters still aboard were destroyed.[5] After the war a modular concept called SCADS, "shipborne containerized air-defense system" proposed a modular system to quickly convert a large Ro-Ro into an emergency aircraft carrier with ski jump, fueling systems, radar, defensive missiles, munitions, crew quarters, and work spaces. The entire system could be installed in about forty eight hours on a container ship or ro-ro when needed for operations up to a month unsupplied. The system would quickly be removed and stored again when the conflict was over.[6] The Soviets flying Yakovlev Yak-38 fighters also tested operations using the civilian Ro-Ro ships Agostinio Neto and Nikolai Cherkasov.[7]
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 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 the cargo. They typically have a stern ramp and a side ramp for dual loading of thousands of vehicles, and 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 short tons (136 t; 134 long tons) with liftable panels to increase clearance from 1.7 to 6.7 m (5 ft 7 in to 21 ft 10 in) 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 Faust, out of Stockholm, in June 2007 the car carriers entered a new era called the large car and truck carrier (LCTC).[8]
The car carrier, Auriga Leader, built in 2008 with a capacity of 6,200 cars, is the world's first partially solar powered ship.[9]
The seagoing RORO car ferry, with large external doors close to the waterline and open vehicle decks with few internal bulkheads, has a reputation for being a high risk design (to the point where the acronym is sometimes derisively expanded "Roll On/Roll Over"[10]). An improperly-secured loading door can cause a ship to take on water and sink, as happened for example in 1987 with the MS Herald of Free Enterprise. Water sloshing on the vehicle deck can set up a free surface effect making the ship unstable and causing it to capsize. Free surface water on the vehicle deck was determined by the Court of Inquiry to be the immediate cause of the 1968 capsize of the TEV Wahine in New Zealand.[11]
Despite these inherent risks, the very high freeboard raises the seaworthiness of these vessels. For example, the car carrier MV Cougar Ace listed 80 degrees to its port side in 2006, but did not sink, since its high enclosed sides prevented water from entering.
The acronym ROPAX (roll on/roll off passenger) describes a RORO vessel built for freight vehicle transport along with passenger accommodation. Technically this encompasses all ferries with both a roll on/roll off car deck and passenger-carrying capacities, but in practice ships with facilities for more than 500 passengers are often referred to as cruiseferries.
The ConRo vessel is a hybrid between a RORO and a container ship. This type of vessel has a below-decks area used for vehicle storage while stacking containerized freight on the top decks. Examples of ConRo ships such as those in the fleet of Atlantic Container Line can carry a combination of 1,900 twenty-foot equivalent units (TEUs) of containers, up to 1,000 TEUs of heavy equipment, as well as project and oversized cargo on three decks and up to 2,000 automobiles on five decks. Separate internal ramp systems within the vessel segregate automobiles from other vehicles, mafi trailers and breakbulk cargo.
A RoLo (roll-on lift-off) vessel is another hybrid vessel type with ramps serving vehicle decks but with other cargo decks accessible only by crane.
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