Roll On/Roll Off

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Loading a Ro Ro passenger car ferry
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Loading a Ro Ro passenger car ferry

RORO or ro-ro are acronyms for Roll On/Roll Off, describing a significant feature of a ship designed to carry wheeled cargo such as automobiles, trailers or railway carriages. 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.

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[edit] Types

A Canadian RORO Ferry
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A Canadian RORO Ferry
The Cetus Leader, a 6500 unit PCTC
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The Cetus Leader, a 6500 unit PCTC
The Pride of Burgundy, a P&O Ferries passenger car ferry on the Dover-Calais English Channel route which can carry 600 cars. [1]
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The Pride of Burgundy, a P&O Ferries passenger car ferry on the Dover-Calais English Channel route which can carry 600 cars. [1]

Various types of RORO vessels include ferries, cruiseferries, cargo ships, and barges. A true RORO's ramps can serve all of the vessel’s decks; otherwise it is a hybrid type. New automobiles that are transported by ship around the world are often moved on a large type of RORO called a Pure Car Carrier (PCC) or Pure Car Truck Carrier (PCTC).

Unlike elsewhere in the shipping industry where cargo is normally measured by the metric tonne, RORO cargo will typically be measured in the more convenient unit of lanes in meters (LIMs). This is calculated by multiplying cargo length in meters by its width in lanes (lane width differs from vessel to vessel and there are a number of 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 barges in the world operate between the United States and Puerto Rico carrying highway trailers, shipping containers on chassis, new and used cars, and oversized cargos on three decks. These barges are towed by ocean-going tugs and sail four times per week from Jacksonville, Florida to San Juan.

[edit] History

At first, wheeled vehicles carried as cargo on oceangoing ships were treated like any other cargo. Automobiles had their gas 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, and could not be used for routine travel.

The first RoRo ships were ferries carrying steam trains across rivers. One of the earliest was Firth of Forth ferry in Scotland which started in 1851 and operated for nearly forty years, until the completion of the Forth Bridge.

Ferries hauling rail cars were used after the US Civil war in New York harbor, the Great Lakes and the St. Clair River in Detroit. By the latter quarter of the century, car ferries were a common sight in San Francisco and Puget Sound. A car ferry worked the Columbia River for many years at Kalama for the Northern Pacific Railway. By the turn of the century, car ferries became important adjuncts to railway systems particularly those which were discontinuous due to geography. Montreal, Newfoundland, Prince Edward Island, and the Islands of Japan were all cut by water, and thus needed ferries. Russians used car ferries on Lake Baikal to move rail cars while the line was finished.

During WWII, landing craft were the first 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 speeded dramatically. Comet also had an adjustable chocking system for locking cars onto the decks, and a ventilation system to remove any exhaust gases that accumulated during vehicle loading.

[edit] Car Carriers

Skaugran Oslo
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Skaugran Oslo
A PCC ship's starboard side showing side ramp.
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A PCC ship's starboard side showing side ramp.

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 the European Highway, the first Pure Car Carrier, which carried 4,200 automobiles. Today’s pure car carriers and their close cousins, the Pure Car/Truck Carrier are distinctive looking ships with a box-like superstructure running the entire length and breadth of the hull, fully enclosing and protecting the cargo. They typically have a stern ramp and a side ramp for dual loading of many thousands of vehicles, as well as 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 tons with liftable "panels" to increase clearance from 1.7 meters to 6.7 meters on some decks. Lifting decks to accommodate higher cargo reduces the total capacity. The largest PCC currently in service is the MV Mignon, which can carry up to 7,200 cars.

[edit] Risks

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. An improperly-secured loading door can cause a ship to take on water and sink, as happened for example with the Herald of Free Enterprise in 1987. Also, water sloshing on the vehicle deck can set up a free surface effect making the ship unstable and causing it to capsize.

[edit] Benefits

While the characteristics of seagoing RORO car ferries have inherent risks, there are benefits to its seaworthiness. For example the car carrier Cougar Ace listed 80 degrees to its port side in 2006 but did not sink, since its high enclosed sides prevented water from entering.

[edit] Variations of RORO

The acronym ROPAX describes a RORO vessel equipped with cabins to accommodate passengers.

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.

A RoLo vessel is another hybrid vessel type with ramps serving vehicle decks but with other cargo decks accessible only by crane.

[edit] See also

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