Barge Carrier Ships
Transport ships for carrying floating cargo are known and are referred to as LASH ships and as barge carriers. For reasons that are not apparent, the US Navy designates the SEABEE type barger carrier as a T-AKR Vehicle Cargo Ship, while the Lighter Aboard Ship (LASH) vessels are designated T-AK Cargo Ship.
The loading and discharging of floating containers or vessels with such ships is as a rule done on free water by shipborne lifting devices which pick up the floating vessels from the water for transfer to the ship and vice versa. Such expensive shipborne lifting devices have the common disadvantage that they require an assembly of a large number of individual parts with a relatively low degree of reliability and in most cases the loading and unloading operations are impaired by the sea water conditions and the atmospheric environment of the ship. A further disadvantage is that such vessels usually have to be operated by shore side personnel because of the prevailing agreements between ship owners and longshoremen unions. Such personnel are normally unable to operate such gear as carefully and safely as a trained crew of the ship. In addition with the use of travelling ship cranes for the handling of floating vessels, the cranes sensitivity to the ship's inclination is a further disadvantage.
Barge ships are designed to carry specially designed barges (lighters) or a combination of such barges and containers. Thus, they are necessarily large ships with a large heavy lift capability. Their design was intended to combine the flexibility and self-sustained cargo handling capability of the general cargo ship with the rapid port turnaround time of the RO/RO and containership. This combination, however, has not proved commercially viable in most trades.
The search for more economic modes of cargo transportation has led to the introduction of designs of sea-going transport ships with facility for taking a number of loaded barges on board. Such systems of transportation afford a number of advantages, notably in simplifying the transfer of cargo from inland sites to an ocean transport ship via inland waterways and the eventual transport of the cargo to coastal or inland delivery points. By eliminating the off-loading of cargo from the barges into the transport ship and vice versa, important labour and energy cost savings are achieved and the speed and general convenience of the water-borne transportation exercise is enhanced.
In the transport of cargo throughout the world, cargo must often be transported in various types of vessels depending on the depth of the water in which the vessel travels. For example, when grain from the Midwest is harvested for transport to foreign countries, the grain must be placed in relatively shallow vessels such as barges or the like and moved down river, such as the Mississippi River, to grain elevators where the grain is then unloaded from the barges, into the grain elevators. Subsequently a deep draft vessel, such as a cargo ship, is then loaded with the grain so that the ship may then transport the grain cargo to foreign ports. Most grain elevators would be located for example, between New Orleans and Baton Rouge, since any travel north of Baton Rouge by a deep draft vessel is impossible because of the shallow depth of the Mississippi River. Even on the occasion where the deep draft vessel can receive the cargo of grain directly from the shallow draft barge, again time and effort and expenses are incurred when this transfer is undertaken.
It is trite that many harbours without deep water docking facilities are either completely excluded from participating in the revenue capable of being generated by bulk material loading, or if not completely excluded, are confronted with diverse costly logistical and environmental concerns. The logistical concerns may include the establishment of deep sea berths, conveyors with offshore tressels and frequent dredging, all with concomitant environmental and noise pollution, disruptions, and installation and maintenance costs.
One solution has been to load cargo onto a shallow draft barge which then travels out to deep water, is moored alongside the cargo ship and then off-loaded. Many barges however lack self off-loading capabilities. Generally, even those barges with self off-loading capabilities have no, or limited means to discharge the material into the cargo holds of a cargo vessel at deep sea.
Many problems, often related to the high cost of labor, have changed the economic and technical natures of shipping. For example, for many centuries materials have been transported by barges on rivers, lakes, canals, and inland waterway systems to ports near the river mouth, unloaded there from the barges, loaded onto ocean-going vessels, sent to other ports across the sea, unloaded there, and reloaded in many instances onto other barges to be shipped up another river system. In recent years, however, the costs of loading and unloading cargo have risen higher at an ever-increasing rate. Containerizing of cargoes has helped somewhat, but even then, as well as in bulk-loaded barges, there has remained the necessity of unloading the barges at one port, placing the container and other cargo on a pier, and then loading from the pier into an ocean-going vessel, only to require the reverse procedure in the ports to which the cargo is carried by that vessel. All this adds considerably to the ultimate cost of the product concerned, and the time required for transportation.
An apparent answer to the problem is to ship the barges themselves. Since they cannot undergo an ocean voyage directly in the water, this would require loading the barges aboard an ocean-going vessel. However, few vessels are capable of carrying a series of barges aboard, and the problem of loading barges on the vessels must be confronted. The barges are often very large and heavy; cranes or elevators to lift them would be very expensive. In fact, large river barges cannot be lifted by cranes or elevators.
Inventions such as U.S. Pat. No. 3,913,512, issued Oct. 21, 1975, and co-pending application, Ser. No. 105,414, now abandoned, filed Dec. 19, 1979 have proposed flotation loading of barges and other cargo-carrying containers into barge-carrying ships. Since the barges are already in the water, flotation loading can be employed with a specially constructed ship that has a suitable hold and a gate through which the barge may be floated into the hold.
However, barges are not as easily handled as are smaller cargo-carrying containers; so particular provisions have had to be made for them. Many barge types are long relative to their beam. The barges used on the Mississippi and Rhine rivers, for example, are very long compared to their width; the Mississippi barges are more than 60 meters long and more than 10 meters wide. For a barge-carrying system to be practical, the ocean-going, barge-transporting vessel must be able to carry many barges. A ship able to accommodate only a single line of barges would, of necessity be extraordinarily long and narrow to be profitable. This general problem was solved in our U.S. Pat. Nos. 3,978,806, issued Sept. 7, 1976; and 4,135,468, issued Jan. 23, 1979. Those patents relate to a vessel having a plurality of longitudinal holds, side by side, either two or three parallel holds, each of which can take the full width of a barge and each of which can accommodate several barges in line or tandem. Also, the problem of loading and unloading the vessel with barges was alleviated by mechanisms shown, for example, in our U.S. Pat. No. 4,147,123, which issued Apr. 3, 1979.
A problem that arises as soon as one attempts to load two or more tiers of barges in a single vessel, is the problem of draft. A few ports can accommodate drafts up to 75 or 80 feet, drafts that exceed those of most vessels, so that their depths would accommodate a ship loading two or more tiers of barges. However, most ports have depths less than 40 feet. A system restricted to voyages between deep-draft ports would not be econimically practical. For this reason, the preferred form of these barge-carrying vessels has a lock disposed at one end, for hydraulically elevating barges to the various tier levels in floatation loading. This broadens the range of barges on which the system can operate; not requiring any special roller mechanisms for dry loading and unloading. It also increases the number of ports which may be serviced.
The economic feasibility of this mode of transportation depends on being able to load and carry the maximum amount of cargo in a minimum of space. Each unused or unusable area in the vessel detracts from its profitability. It is, therefore, desirable to maximize a vessel's efficiency by using as much potential cargo-carrying space as possible.
To that end, a problem has arisen. The space occupied by the loading lock has been generally unusable for the transportation of cargo. At best, it had been possible to store and transport one barge on the bottom of a lock. Since the lock typically extends from the lowest tier to the upper deck of such vessels, space which could otherwise be used to store at least one extra barge for each tier of longitudinal barge holds serviced by the lock has remained unused. This was primarily because of an inability to securely support barges at multiple levels of a loading lock without interfering with the operation of the lock when loading.
In one known type of barge-carrying system, loaded barges are lifted from the water by lifting equipment at the stern of the transport ship and conveyed along the cargo decks by a conveyor (see e.g. the article entitled "Doctor Lykes" in Shipping World and Shipbuilder, September 1972, page 1045).
In order to permit a greater number of barges to be carried proposals have been made to make the transport ship of double-deck form and enable it to be immersed to the draft required for docking barges onto the upper as well as the lower deck. It has also been proposed to provide for storage of barges in superimposed tiers for providing a transport ship with an internal hydraulic water-lift whereby barges floated into the ship at a given level can be raised within the ship and suspended from the overlying deck. Further barges can then be stowed in an underlying tier. This proposal avoids the need for a second deck and avoids the need for the docking draught of the transport ship to be increased for taking on the upper tier of barges.
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