Introduction to the Ro/Ro Ships

The introduction of the roll-on/roll-off system to major trade routes of the world has added new dimensions to the modern cargo handling techniques offered to shippers. The roll-on/roll-off system was first introduced about the same time as the containership and has only recently gained wide acceptance. While there has been a rapid buildup of terminal areas, berths, and handling equipment for containerization at many ports, the roll-on/roll-off system has proved that it complements and supplements rather than competes with the containership and container handling methods.

More important for developing trade, it is a system that does not require massive specialized terminal facilities and shore-based equipment. Many operators conclude that the го/го method combines the best features of containerization, unitization, and breakbulk techniques. However, these ships also have unsatisfactory features such as wasted space and lashing problems. Recent ro/ro ships have been designed as almost full containerships where the containers are loaded and unloaded ro/ro fashion with forklift trucks.

Examples of cargo that have been literally rolled aboard ro/ro ships are heavy earth-moving machinery, automobiles farm equipment, large pieces of lumber, wood pulp, newsprint, sheet steel, piping, and other similar commodities. Rolling stock is ready for delivery upon arrival at the discharge port, and loading, stowing, and discharge operations are simplified.

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Barge Carrying Vessels (Cont.)

Let us talk a bit more about the barge carrying vessels, playing a very important role in the maritime shipping industry of today, and particularly in transportation of the heavy cargoes. See the previous article for the main discussion. Here we will mainly focus on the SEABEE type of vessel, i.e. the second one.

For the SEABEE type of vessel to empty a full vessel or load a full cargo of barges, giving a theoretical loading or discharge time of 13 hours, it will actually require a theoretical cargo handling total of 64 hours for each round trip, although allowing a 50 percent margin for unforeseen delays, the total cargo handling time is expected to be about four days.

Each barge deck of the SEABEE can accommodate two barge widths, with the upper deck having a capacity for 14 barges while the main and lower decks are each suitable for twelve units, with each hold stowage area measuring 11.1 m (36.54 ft) wide by 5.9 m (19,30 ft) high. As the upper deck is free of obstructions, except in the forward area, it is possible to carry double-width barges or up to ten open-type barges with cargoes of unlimited height, i.e. restricted only by the barge stability limit. It is also possible to carry containers on the top of the upper deck standard type barges.

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Barge Carrying Vessels

There are two existing types of barge carriers utilized today - the LASH system whereby the barge, or lighter, is hoisted on board the ship by a large gantry crane, and the SEABEE type where the barge is floated onto a synchrolift platform, elevated to the proper level, and then rolled along that deck into its stowed position. In a float-on concept the ship itself sinks similar to a floating drydock.

The barge carrier is best suited to trades where the barge can be utilized at both ends for distribution by river or other inland waterways. Although a point of debate, it would appear that the barge carrier is best suited to high grade bulk shipments in small quantities. Finished products would seem to be better shipped in containerships and large quantities of bulk would be most efficiently shipped in a bulk carrier.

LASH System

Although there are many variations in LASH ships with regard to barge and/or container capacity, we will concentrate on the barge aspect. In referring to the LASH arrangement, it can be seen that the LASH ship is arranged along the lines of a bulk carrier with a single deck and all accommodations forward. Machinery is located just aft of midships with port and starboard stacks to allow the crane access all the way to the cantilevered crane supports on the stern.

The lighters are brought in between these cantilevered arms and hoisted vertically by a gantry crane of 500 tons capacity. The crane legs are equipped with guides that line up with the stern and cargo hold guides. These guides ensure that the lighter does not sway while the crane is traveling along the deck. Traveling speed of the crane is 1.02 m/s (200 ft/min).

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Introduction to Containers

The containership carries the improvement of the general cargo ship one step further by unitizing all of its cargo within containers. The containership system is most suited for finished goods shipment as:

• the individual containers are suited in size to relatively small shipments which are to be expected in the finished goods trade;

• door to door, i.e. shipper to consigner, shipping is possible without the integrity of the container being broached. This protects valuable finished goods from the elements, handling damage, and pilferage without expensive crating;

• the time and cost of shipment door to door is reduced which is a requirement of some finished, for example perishable, goods.

The containership represents one of the types of ships in which the total shipping system must be carefully engineered before operations can start. Thus, this section will attempt to explain the total operation as it applies to the cargo itself.

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