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RO-RO [ Roll-On / Roll-Off ]

A Roll-On/Roll-Off [RO/RO] ship is specifically designed to carry wheeled and tracked vehicles as all or most of its cargo. Vehicles are driven or towed on and off the ship by means of either the ship's own ramps or shore-based ramps. Because it is designed to accommodate cargoes which cannot be stacked but which vary in height, below-deck space and volume utilization is generally less efficient than on a containership. RO/RO ships are thus commercially viable only in certain specialized trades. However, the RO/RO is the preferred ship type for deployment of military unit equipment.

Analysis of the RoRo fleet is complex due to the diversity of the fleet and as a result it is a difficult sector to define. One sector is the deep sea Ro Ro sector, serviced by specialist players on long haul routes operating liner like services. These are generally with a dwt above 20,000 dwt, lane metre capacity of around 2,500 and container capacity over 1,000 teu. A second sector consists of smaller vessels operating on ferry / liner type services on short haul routes such as Baltic, Mediterranean, US Gulf and Japan. It is difficult to make a clear distinction between Ro Ro passenger ships and the Ro Ros operating in these trades. A third sector is more spot or short term charter orientated. In this sector, military demand demand can have a certain impact for some owners. And purpose built vehicle carriers have multiple decks (4-10+), high speed, roll on roll off discharging / loading facilities and internal decks and ramps carefully designed to reduce damage and speed up loading / discharge.

The military advantages of RO/RO ships include the capability for rapid loading and discharge of military vehicles and non-self-deployable aircraft, and open deck areas well suited to the carriage of outsized military cargo. Their military disadvantages include their relative unsuitability for carriage of sustaining supplies and ammunition (in comparison with general cargo and containerships) and their limited availability, because their market sector is much reduced compared with containerships.

In the 1960s the volume of vehicle transportation by ship started to expand to the extent that a special ship type was developed for this purpose, the basic concept whereof being still in use. In the beginning, it was for the most part passenger cars and vans that were transported on these ships (PCC--Pure Car Carrier type), on an average, the number thereof being several thousand vehicles (about 2000-4000) at a time. The ships returned empty. In the past few years a multipurpose ship type (PCTC--Pure Car & Truck Carrier with a payload of 4000 . . . >6500 passenger cars) has been gaining ground and in which about 20% of the deck area has been dimensioned to receive heavier wheeled or general cargo. When the heavy-load decks are filled with heavy cargo, the cargo carrying capacity of the remaining light decks is decreased significantly. The free space between heavy-load decks is considerably higher than that of normal car decks.

Ro/Ro vessels are ships in which the cargo is loaded and unloaded by means of vehicles that drive onto the ship and haul cargo to and from the vessel. No predetermined on-board location is assigned to the cargo as Ro/Ro vessels are equipped with ballast-adjusting mechanisms. Roll-on/roll-off (ro-ro) cargo handling systems refer to systems used when the cargo can be rolled onto the vessel, such as cases where a trailer is dropped with chassis on-deck by a tractor-trailer rig. Another type of ro-ro system uses fork lifts to load cargo (the fork lifts roll the cargo on and off the deck). These systems reduce costs associated with cargo loading (expensive crane systems and skilled crane operators are not required). This reduced cost and complexity of loading operations allows ro-ro vessels to call on smaller and less-developed ports.

Vessels employing this type of cargo handling equipment typically carry trailers, chassis- or trailer-mounted containers, cars, rail cars, and other rolling machinery, and other cargo (such as containers) driven on to the vessel by use of a fork lift or other rolling machinery. These vessels sometimes use a "drive-through" system with access both forward and aft, which speeds the loading and unloading process. The capacity of ro-ro vessels can be less than one-half that of a lo-lo vessel of similar size, as cargo cannot be stacked (due to wheels) and significant space is needed for on-load and off-load ramps. The reduced capacity of ro-ro ships is at least partially offset by the reduced cargo handling and port costs accrued by these vessels.

Roll-On/Roll-Off(Ro-Ro) shipping system involves the direct driving-on and driving-off of cargo. The Ro-Ro method enables shippers to load cargo on the chassis, trailer and "low-boy" at the plant or warehouse site, transport the vehicles to embarkation points and have them loaded directly onto the vessel. By rolling cargo on board these vessels and rolling it off at its destination, shippers can reduce the number of times their cargo is handled.

The inherent disadvantage of Ro-Ro is the waste of cargo carrying capacity due to undercarriage and all-around clearance requirements. Although the degree of packing may be reduced for Ro-Ro shipments, keep in mind that the cargo will travel aboard an oceangoing vessel and will be subjected to all the hazards of an ocean voyage.

These special ships usually have 10 to 12 cargo decks, and two of these are mainly reserved for transportation of heavier cargo. The heavy-load decks have to be placed relatively high on the level of the deck above the machinery space if it is located in the afterbody, and thus relatively high, which is not a good solution as regards the stability of the ship. On the heavy-load decks or on some parts thereof containers may also be placed which have to be brought aboard the ship either on wheeled pallets, in which case the pallets remain on the ship, or by special trucks. The containers are placed in stacks of 1 to 2 layers on the decks.

For functional loading and unloading, space is required for drive lanes, openings in transverse bulkheads, sides and decks. The ship has to be equipped with a heavy stern ramp, stern gates, and in general with 1 to 2 side ports. The transverse bulkheads must be provided with openings, and they have to be specially reinforced and equipped with remote controlled actuators. The cargo decks must have openings and be equipped with hoistable drive-lane ramps, of which some are fixed, some hinged or hoistable. In most cases there are also a few lift platforms of articulated type for handling cargo between two decks. The highest decks can be divided by means of hoistable car decks.

There are also car decks which are hinged to the side bulkheads and which can be turned by means of actuators into the operating position. All in all, the structures must have a great number of openings and they must be reinforced, there is a lot of bulky equipment, fixed or moveable, in these areas, and space has to be reserved for drive lanes. There are generally 2 to 3 longitudinal pillar rows on the decks, to reduce the hull weight, but at the same time to create restrictions as to the positioning of vehicles and cargo. The vehicles are driven within the ship using their own engine power. Because of exhaust gases the ventilation system of the ship must be exceptionally effective. A large number of ventilation ducts also splits the deck areas.

The total weight of vehicle carrying ships is also relatively heavy. The vehicles themselves are homogeneous, light transport goods, the stowage factor being on an average four to five times higher compared with container and general cargo. In a pure car carrier the weight of car cargo represents about 40 to 50% of the dead weight of the ship, while in PCTC-type ships it is only about 20 to 25% of the dead weight. In all circumstances, a considerable quantity of ballast water has to be transported to ensure the stability of the ship, in the most unfavourable cases the amount thereof exceeding the weight of the vehicle cargo. As a result, more engine power is needed, unnecessary fuel is consumed; besides, the shipping company does not gain anything from transporting "dead water ballast". The deck houses are located on the uppermost deck, and so are the life-boat stations.

The vertical center of gravity of the ship structure being high has been a limiting factor in utilizing the space vertically. In conventional techniques the construction design in the cargo spaces is based on steel plate deck reinforced with stiffening girders. The total thickness of such a local construction may be 200 . . . >450 mm and the plate thicknesses of fixed light-weight car decks are 5 to 6 mm at the minimum, exceeding considerably the local-strength thickness required by the cargo. In a plate field of a deck there are lower beams in each frame space and high frame girders at sparser intervals. On the edges of deck openings and drive ramps there are high, strong stiffening beams. Hoistable or turnable platforms are of lighter construction, shipyard specific, and constructed in accordance with generally known concepts. Such structures also require space either in the roof or on the walls; in addition, actuators need space.

Ships adapted to transport wheeled vehicles are usually provided with a single deck only, as in a Ferry. Occasionally there is more than one deck, but the ship will then have to be equipped with lifts or internal ramps for moving the vehicle from one deck to another. Ships for the transportation of new passenger cars have been designed with multiple decks and internal ramps permitting the stowing of the cars about in the same manner as in a parking house. The manoevering of these comparatively light cars is much easier than the manoevering of heavy loaded vehicles or container transporting trucks, so it is acceptable that a car performs sharp turns inside the shipe. With heavy loads that must be avoided.

To facilitate a rapid loading and unloading it is desirable that the ship be provided with at least two ramps located at about the same level, so the operations in any part of the ship will not be influenced by differences in height between the ship and the quay. The cargo carrying portion of the ship, which is provided with at least two decks, is subdivided into fully separated cargo volumes, formed as straight, blind alleys emanating from lobbies arranged inside the ramps. To permit access to the individual decks a longitudinal section through the ship, between two lobbies, will show that one deck is inclined upwards while the other deck is inclined downwards from the opposite lobby.

Out of consideration for the ship's safety it is desirable that the cargo carrying portion of the ship be subdivided into separate compartments, which is difficult to attain if the ship is provided with internal ramps, permitting communication between different decks.

To facilitate loading and unloading short travelling distances within the ship should be endeavoured, and as the loaded units usually are very heavy, sharp turns should be avoided. To permit rapid handling the ship should have at least two access ports, each with a communication ramp, and it is essentail that these are located at about the same level, so they may be simultaneously served from the same quay.

The current ship types have weaknesses in loading flexibility. Placing different kinds of customer-specific batches of different sizes on a number of fixed decks and partly on hoistable decks or drive ramps prolongs the loading phase and does not always succeed satisfactorily. The control of batches to be unloaded at a particular port may also lead to new intermediate loadings there. These problems are hard to eliminate using the current basic concept. Such ship types exert global sea traffic on all sea routes.

To facilitate firm fastening of wheeled cargo, the fixed structures of a ship have to be appropriately constructed; separate fastening equipment and plenty of manual work aboard are also needed. The basic decks of the ships are dimensioned for shaft and wheel loads of heavy wheeled cargo, whereby the local strength of the decks is on an average 8 to 20 times higher than is required by a load of passenger cars and vans.

Units moving on wheels are secured on a horizontally loaded vessel, in particular semitrailers, rolltrailers and cassettes are secured on a ro-ro vessel, by using different chains, webbings and wires, by means of which each cargo unit is fastened to the deck of the vessel. One problem in using chains, webbings and wires for lashing the cargo unit to the deck of the vessel is that, when these are used, the unit lashed to the deck together with lashings and the deck structure does not necessarily always form a continuous structure of sufficient strength, which might result in the shifting of cargo in the cargo space in case the number or the quality of lashings is inadequate. A problem with these known lashings is also that the lashing is done by hand, which is in itself rather expensive and time-consuming.

The vessel and the cargo unit are usually parallel, in which connection the forces which are caused by the movements of the vessel and which are directed at the cargo are greatest in the transverse direction, which means that transverse securing is very important when cargo units are lashed to the vessel. Safety factors are also important, and when chains, webbings, wires, etc. known from prior art are used, one problem is that it is possible to fit them in a wrong manner, in which connection the lashing does not necessarily fulfil the function set for it.

In addition to chains, webbings, etc., a trestle, or a trailer horse, is used in connection with securing of semitrailers, the wheelless end of the semitrailer being supported by means of the trestle for the time of transport on the vessel. Semitrailers are conventionally provided with their own legs, by means of which the wheelless end can be supported ashore, but these legs do not alone sustain the load which is directed at them from the unit and its cargo during sea transport as a result of the movements of the vessel, and thus said trestle or equivalent is needed for support of the semitrailer during sea transport. The trestle is usually made of steel and it is placed manually under the wheelless end of the semitrailer.

Hitherto known modes of installation of gas turbine engine powerplants in such vessels have involved use of the superstructure to support exhaust silencers, air intakes and their associated ducting at a high level, producing funnel-like structures which add top weight to the ship and increase wind resistance. This approach has also required intrusion of engine air intake ducts and exhaust ducts into otherwise revenue-earning deckspace above the two hulls. Further problems have been that there have been large pressure losses in the ducting associated with high level intakes, together with aerodynamic disturbance of the air flow into the compressor of the gas turbine engine.

The shape of conventional car carriers makes them very susceptible to wind pressure, which causes leeway, that is, sideways drift of a vessel. In 2003 a new wind resistance-reducing design for pure car carriers (PCCs) was registered with the Japanese Patent Office. The technology, applied to vessels since March 2003, was developed in cooperation with Universal Shipbuilding Corp. The vessel's bow is aerodynamically rounded and beveled along the bow line to help reduce pressure from headwinds. The upper deck has cargo space (called the garage deck) to maximize load capacity. The vessel also has different levels, with square cut corner sections, all along the sides of the vessel at the top of the garage deck, which help reduce pressure from sidewinds. The design effectively reduces leeway caused by wind pressure. As a result, the design improves both fuel efficiency, which in turn reduces emissions of CO2, NOx, and SOx in vessel engine exhaust, and speed. More than a year of voyages by PCCs of the new design proved, as expected, that the design reduces leeway, improves speed, and results in an annual fuel efficiency improvement exceeding 5% over similar PCCs of conventional design.

In March 2011 the Wilh. Wilhelmsen group launched its 150th anniversary vessel, MV Tnsberg, into operation. The Mark V vessel is the largest of its kind, with a length of 265 metres offering a cargo volume of 138 000 cubic meters over six fixed and three hoistable decks. The pioneering roll-on roll-off vessel is built at Mitsubishi Heavy Industries in Nagasaki, Japan. Four Mark V vessels will be delivered to Wilh. Wilhelmsen ASA and its partner Wallenius Lines. The second vessel will be delivered in August and two in 2012. The Mark V class is the most sophisticated vessel ever built in the roll-on roll-off segment.We expect that Mark V will strengthen our position as the global market leader within deep sea roll-on roll-off transport, said Jan Eyvin Wang, president and CEO of Wilh. Wilhelmsen ASA, representing the owner of the vessel. The Mark V class is the most sophisticated ro-ro vessels ever built, with major innovative design criteria such as high ramp capacity, deck strength and height, low fuel consumption, good transportation economy and safe cargo handling. Together with Mitsubishi Heavy Industries, we have constructed a class of environmentally friendly vessels with several unique features.

The ship has a Deadweight design of 31,824 tons, scantling 41,554 tons; and Gross tonnage 76,500 gt. With a Length overall 265 meters and a width of 12 meters and safe working load of 505 tonnes, the vessels stern ramp offers customers the possibility to ship larger units than ever before. With 50,335 square meters in deck area, of which 31,250 square meters is reserved for high and heavy cargo, and despite the increased capacity, the Mark V will use 15 to 20 percent less fuel per unit transported than the Mark IV, thanks to a streamlined hull and an advanced turbo generator. The clear height of the main deck, 7.1 metres, is also unprecedented for this kind of vessel. Cargo can even be loaded on the weather deck, which has a ramp from the deck below. Three decks can be hoisted by electric winches to provide maximum flexibility and utilisation.

The E/S Orcelle is Wallenius Wilhelmsens vision for the future of an environmentally friendly ocean transport industry. This 250 meter long concept vessel does not release any emissions into the atmosphere or into the ocean. It uses renewable energy sources and fuel cells to generate the energy required to power the vessel. Lightweight of vessel is 21,000 tons, and the maximum deadweight capacity is 13,000 tons. The vehicle capacity is 10,000 cars (Based on today's standard units), and the design cargo deck area is 85,000 m2 [compared to 50,335 m2 on the MV Tnsberg]. The E/S Orcelle is powered by the sensible utilisation of energy from renewable sources. These energy sources will include solar energy, wind energy and wave energy, and will be used in combination with a fuel cell system powered by hydrogen.

Wind energy will mainly be utilised for propulsion directly through three sails constructed of lightweight composite material. The E/S Orcelle will have an optimum cargo capacity of 85,000 m2 of cargo deck stowage area, roughly equivalent to 14 football fields. This is up to 50% more space than todays modern car carriers, which are capable of transporting 6,500 vehicles. The E/S Orcelle will be capable of transporting up to 10,000 cars on eight cargo decks. Three of the decks will be adjustable to accommodate cargo of different heights and weights. Compared to todays vessels, the pentamaran hull shape of the E/S Orcelle and its utilisation of energy from renewable sources will help optimise the cargocarrying capacity of the vessel. The E/S Orcelle will have a maximum deadweight capacity of 13,000 tons and weigh 21,000 tons much like todays car carriers. Yet the E/S Orcelle will be capable of carrying approximately 3,000 more tons of cargo, thanks to the use of lightweight materials and the elimination of ballast water. The E/S Orcelle is named after the Irrawaddy dolphin, or Orcelle in French. WWF, the global conservation organisation includes the dolphin, which resembles the beluga whale, among the world's critically endangered species.

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Page last modified: 18-05-2013 18:57:48 ZULU