ro-ro (roll-on roll-off) ship

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A vessel, both military and civilian, where vehicles are loaded on by means of a bow ramp and are offloaded by a similar ramp at the stern or by side ports. Commercial ships are connected to land by Linkspans, a ramp designed to alter in height and slope depending on the state of the tide or loading of the ships. Many ro-ros have mezzanine, or portable, decks which can be taken to deck head height when handling large commercial vehicles, but lowered to half height allowing twice the deck area to be made available for cars. Unlike the old-fashioned cargo ship, the cargo space is open from bow to stern without any transverse bulkheads.

Ro-ro ships are nothing new as they were being built in the 19th century to transport trains across rivers too wide for bridges, and Linkspans were first produced by the Glasgow shipbuilder Robert Napier around 1850. An early example of a ro-ro is the Firth of Forth ferry which started operations in 1851. The ships were equipped with rails which could be connected to the ones on land, and a train simply rolled onto the ship and then off it again at the other end. In its heyday the overnight Golden Arrow service from London to Paris was transported in exactly the same way.

During the Second World War (1939–45) the same principle was used to transport tanks and other equipment in landing craft for amphibious assaults. However, after the war anyone wanting to take his car across any stretch of water had to have it loaded and unloaded by crane, an expensive and time-consuming business. Statistics issued by the port of Dover showed that it handled about 10,000 cars annually in this way before the introduction in 1953 of ro-ro passenger ferries with terminals to service them. Within a year the numbers of cars handled by the port rose to 100,000 and by 1994 it was handling 4.5 million. By 1994 the world's ro-ro fleet of 4,600 vessels could be divided into several types, two-thirds of them dedicated to carrying cargo.

The US Navy's Military Sealift Command also runs a type of ro-ro ship with a slewing stern ramp which services two side ports. Designated a Large, Medium-speed, Roll-on Roll-off ship, or LMSR, these ships, of 55,000 displacement tonnes, have a carrying capacity of 35,000 square metres (380,000 sq. ft.), and are used to sealift the equipment of large combat forces.

However, the most widely known type of ro-ro is the car/passenger ferry where vehicles, both private and commercial, drive on at one end and drive off at the other. They are extremely popular with holidaymakers and hauliers because of the speed with which they can be loaded and offloaded. Nevertheless, ro-ro ferries do have problems. Constructed with cargo doors at both ends, especially vulnerable to wear and tear when used as vehicle ramps, and without internal transverse bulkheads, they are vulnerable if an accident occurs. When flooding happens, either through the cargo doors or through the hull being pierced, there is nothing to stop water flowing rapidly onto the car deck. This can cause the ro-ro to list, the cargo shifts, and the ro-ro quickly capsizes. As a safeguard against this, modern ro-ros have bows which hinge upwards and a secondary door inside. This acts as both a collision bulkhead and a ramp which is attached to a Linkspan.


Subjects: Maritime History.

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