Abbreviation for a vessel designed to carry vehicles, so arranged that the vehicles may be loaded and unloaded by being rolled on or off on their own and/or auxiliary wheels, via ramps fitted in the sides, bow or stern of the vessel. A ro-ro vessel has one or more decks either closed or open, not normally subdivided and generally running along the entire length of the ship. In this type of vessel, damage stability becomes critical when large portions of the vessel, such as garages and holds are flooded.
Roll-on/roll-off system was first introduced in 1950s and the first modern oceangoing roro vessel was the twin-screw USNS COMET built in 1958 to carry military vehicles. Ro-ro vessels transport wheel-based cargo or cargo that is loaded with wheel-based equipment, and available cargo space is expressed in lane meters. Typical cargo are vehicles, roll trailers and cassettes with forest products or with single or double stacked containers.
Cargo is literally rolled on board ro-ro ships. Sometimes roll trailers and cassettes loaded with cargo are stowed by forklift directly on the ro-ro deck. This is called Sto-Ro handling (Stowable Ro-Ro).
As the efficient cargo handling is most important for ro-ro vessels, these ships have large unrestricted cargo decks without transverse bulkheads. Usually ,the ro-ro cargo is loaded and unloaded over the stern ramp, sometimes as wide as the entire cargo space. Internal ramps or elevators are used to reach the upper and lower cargo decks. For really fast cargo handling, two level ramps can be used. Special ramps on the quay are required to facilitate this.
Many ro-ro vessels operate on short trades with frequent port calls. Most of them are equipped with both thrusters and some have also stern thrusters. Usually, they are fitted with high lift rudders in order to ensure good manoeuvring characteristics also at low speeds.
The location of the accommodation varies and can be either in the stern, amidships or at the forward end. All versions exist, but the forward location has become popular in recent deliveries. The forward accommodation does not disturb the cargo flow and provide protection from green water for the cargo on the upper deck.