Roll-on/roll-off (also called "RoRo") are transport ships or vessels that use a ramp to load and unload cargo using wheels or tracks. Self-propelled cargo (such as automobiles) can be loaded or unloaded by driving directly onto the ship.
Cargo that is not self-propelled can be loaded or unloaded using handling equipment with wheels or tracks.
The advantages of RoRo ships compared to other types of vessels stems from their lack of dependence on lifting equipment, such as cranes, to load and unload cargo. Because RoRo ships do not require the use of lifting equipment, loading and unloading operations can be completed faster and safer compared to other types of ships, and are not subject to delays based on weather conditions. Additionally, because cargo on RoRo ships does not require additional preparation for loading and unloading (such as containering), this creates additional efficiencies, leading to faster delivery times and associated cost savings.
The main criticisms of RoRo ships are related to their seaworthiness. As one example, because RoRo ships are designed to carry as many vehicles as possible, they lack transverse bulkheads to create maneuvering space within the ship, leading to lower watertight integrity, which causes greater risk of loss at sea when water ingress or flooding occurs. Additionally, the lack of bulkheads also hinders fire fighting efforts, as fires are able to spread more rapidly.
In January 2017, the International Maritime Organization (IMO) reported that accidents aboard RoRo vessels accounted for almost two-thirds of lives lost at sea, even though RoRo vessels represent a small percentage of the total tonnage of merchant vessels.
RoRo ships are particularly useful for the military because they are capable of moving large amounts of military equipment on a short timeline.
In the United States, more than 90 percent of military cargo is carried by ship. A 2018 U.S. Department of Defense Mobility Capabilities and Requirements Study states that “Since the early 1990s, Pentagon mobility studies have consistently identified a requirement for about 20 million square feet of roll-on/roll-off capacity to quickly transport material in support of a contingency.”
To support these needs, the Military Sealift Command maintains the Ready Reserve Force, a reserve fleet of inactive cargo ships on standby at various ports, and available for short-notice military deployment. These vessels are mostly roll-on/roll-off ships.
In 2021, it was reported that the People's Republic of China was converting civilian RoRo ferries for use in military amphibious operations, potentially enabling increased surge amphibious assault capabilities. Some commentators have speculated that these preparations are in anticipation of a potential military operation in Taiwan.
Commercial uses of RoRo include transporting automobiles, trucks, agricultural equipment, railroad cars, and trailers, among other types of cargo.
According to the United Nations Conference Trade and Development (UNCTAD) report on COVID-19 and Maritime Transport: "The COVID-19 pandemic has significantly impacted on Ro/Ro services. Since March 2020, port calls by Ro/Ro ships worldwide declined by 22.8 percent compared with the same period in 2019. One in four ship calls has been suspended. Total calls by Ro/Ro ships since the beginning of 2020 declined by 13.8 percent as compared with the same period in 2019.”
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