The modern roll-on/roll-off ship can trace its origins back more than one hundred years to the early days of the steam train. Ships were specially designed to take trains across rivers which were too wide for bridges: the ships were equipped with rails, and the trains simply rolled straight on to the ship, which sailed across the river to another rail berth where the train would roll off again. An example is the Firth of Forth ferry in Scotland which began operations in 1851.
It was not until the Second World War, however, that the idea of applying the ro-ro principle of road transport became practicable – and was used in constructing the tank landing craft used at D-Day and in other battles. The principle was applied to merchant ships in the late 1940s and early 1950s. It proved to be extremely popular, especially on short-sea ferry routes, encouraged by technical developments on land as well as sea, notably the increase in road transport. For the shipper, the ro-ro ship offered a number of advantages over traditional ships, notably speed. As the name of the system implies, cars and lorries can drive straight on to a ro-ro ship at one port and off at the port on the other side of the sea within a few minutes of the ship docking.
Roll-on/roll-off (RORO or ro-ro) ships are vessels designed to carry wheeled cargo, such as cars, trucks, semi-trailer trucks, trailers, and railroad cars, that are driven on and off the ship on their own wheels or using a platform vehicle, such as a self-propelled modular transporter. This is in contrast to lift-on/lift-off (LoLo) vessels, which use a crane to load and unload cargo. RoRo shipping is typically the least expensive shipping method, even when compared with different container shipping methods.
RORO vessels have either built-in or shore-based ramps that allow the cargo to be efficiently rolled on and 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 large oceangoing vessels. The ramps and doors may be located in stern, bow or sides, or any combination thereof.
There are various types of Roro ships:
- Pure Car Carriers and Pure Car Truck Carrier are peculiar types having a box-like framework. Its superstructure feature runs the whole hulls’ breadth and length, entirely enclosing and insulating the cargo. The PCC or Pure Car Carriers carry only cars while the PCTC transports a different variety of four-wheeled vehicles; cars, trucks, and more. Unlike other Ro-Ro ships, PCC and PCTC are quite broader in size and thus, are quite discernible. Such are primarily used for delivering newer automobiles to their required exporting locations.
- The ConRo is essentially a synthesis of a container ship and a Ro-Ro. A ConRo has both top and below decks. Below-decks area is substantially used for storing vehicles. On the other hand, the top deck portion is utilised for stacking containerised goods or freight. What’s more distinct about ConRo is that its interior framework is designed to make its loads equally distributed and stabilised. The maximum capacity of ConRo can be over a fifty thousand deadweight tonnes.
- RoPax ship is, in essence, laid out to transport not only cargo but passengers or travelers as well. The term RoPax literally means, Ro for Roll-on and Pax for people or passenger aboard. Such type of ship is the one that is actually known as ferries, which carry both automobiles and passengers over river docks.
- Large, Medium-Speed Roll-on/Roll-off (LMSR) refers to several classes of Military Sealift Command (MSC) roll-on/roll-off type cargo ships. Some are purpose-built to carry military cargo, while others are converted.
- A RoLo (roll-on/lift-off) vessel is another hybrid vessel type, with ramps serving vehicle decks but with other cargo decks only accessible when the tides change or by the use of a crane.
References: Wikipedia, netwavesystems.com, globalsecurity.org
Sea News Feature, May 8