Lighter Aboard Ship (LASH) Ships
The Lighter Aboard Ship (LASH) is a single-decked vessel with large hatches, wing tank arrangements, and a clear access to the stern. The LASH has a gantry crane with a cargo handling capacity of approximately 450 LT. The function of this crane is to convey barges or lighterage from the stowed location aboard the ship to the stern region and to lower the barges or lighterage into the water. Some LASH ships are equipped with container gantry cranes for the handling of the onboard complement of containers. Different classes of LASH ships have capacities ranging from 64 to 89 barges or a mixture of LASH barges and military lighterage.
LASH ships stow their lighters vertically in cells and on top of the hatch covers. Each LASH ship is equipped with a 500-LTON (480-MTON) gantry crane to lift the lighters at the stern of the ship and stow them athwartships throughout the ship. A 35-LTON (31-MTON) gantry crane located forward is used to load containers and stow them athwartships. Three to four lighters normally can be loaded onto or discharged from the ship in one hour. A LASH ship can normally load or discharge its lighters in about 20 hours. The container crane is capable of handling approximately sixteen 20-foot (6-m) containers an hour.
LASH lighters are thin-skinned boxes with water-tight hatch covers. The lighter can carry up to 371 LTON (340 MTON) of cargo at a maximum draft of just over 8 feet (2.4 m). Some lighters are equipped for easy ventilation and provide for smoke detection and fire extinguishing. The lighters are not ac- cessible during transit in the mother ship. The LASH lighter, with covers installed, floats at a draft of just less than 2 feet (61 cm). Each of the hatch covers weighs approximately 6,000 pounds (2,722 kg). The shallow draft allows the barge to be drawn by deck winches very close to the unprepared river bank. By keeping the mooring cables taut, the "drift" caused by strong river current is eliminated. As the barge is loaded, the shoreside edge of the hull will settle firmly its full length on the river bank. The settling will add stability to the barge and aid in loading. Should high and low tidal conditions be expected along coastlines, it is necessary to prevent the lighter from settling on shore.
Ships of the type with open stern walls are in common usage for transporting cargo lighters from one location to another. These ships are generally of a dual hull design that includes a system of ballast tanks that permit the ship to operate in a partially submerged or a fully floating mode. A first layer of lighters can be loaded on such ships by initially partially submerging the ship, floating the lighters into the cargo hold through the open stern wall, securing the lighters in place and then raising the ship to its floating position by evacuating the ballast tanks. The lighters are subsequently unloaded in the reverse manner when the ship reaches its destination. The lighters used in connection with such ships generally have a cargo carrying capacity of up to about 350 tons and a combined maximum weight including cargo of up to about 500 tons. Ships of this type typically carry about twenty or thirty lighters and are commonly used in inland waterways, but not generally used as ocean-going vessels.
The desirability of providing lateral support for lighters on the decks of lighter-transport ships has been recognized. A conventional technique for providing such lateral support includes providing the bottom of the lighters with guide rails or keels which are supported against trestles fixed such as by welding to the deck of the lighter-transport ship and which project upwardly therefrom. The bottom keel of the lighter and the trestle thereby support the lighter in the lateral direction on the deck of the ship. Moreover, the sides of the lighter are fastened to the deck of the ship by means of diagonal rigging screws as is well known in the art.
However, since the trestles project upwardly from the deck of the lighter-transport ship, the use of wheeled loading vehicles on the deck constituting the load space of the ship is severely restricted. Furthermore, it is well known that lighter-transport ships are frequently used to carry containers and/or other loads on cargo platforms. Since the trestles would otherwise constitute an obstruction to the loading of the deck, special detachable adapters have been designed which are fitted on the trestles so that a plane base is provided for the containers or cargo platforms. It will be appreciated, however, that the use of such adapters is inconvenient and time-consuming. Moreover, such adapter structures are cumbersome so that their handling and storage create problems.
In order to laterally support lighters provided with rails on their bottoms, the loading deck of a lighter-transport ship can be provided with channels situated beneath and opening onto the upper surface of the deck which are adapted to receive the rails of the lighters, and cover plates associated with the channels for selectively closing the same. The cover plates are removed from the channels to open the same when lighters are supported on the deck so that the rails are received within the channel. The cover plates are shifted over the channels to close the same when wheeled loading vehicles are moved on the deck.
Ocean-going transport systems have been provided wherein cargo is loaded in lighters which are floated to a ship. The lighters are lifted from the water and deposited in the cargo hold of the ship by a crane carried on the ship and subsequently unloaded in the reverse manner when the ship reaches its destination. The ocean-going cargo ships employed with such systems generally have a cargo handling capacity of about 90 to about 100 lighters and are of conventional hull design with entirely enclosed cargo holds and hatch covers for sealing such cargo holds.
For example, U.S. Pat. No. 3,390,657 describes a gantry crane adapted for operation on a vessel to lift lighters and transport them from an outboard loading position astern the vessel to and through a hatch and into a cargo hold, the crane being located for travel on spaced rails extending longitudinally along opposite sides of the ship. The ship is disclosed as having spaced cantilevered stern beams which provide a platform on which the crane may travel to an outboard position for lifting a floating lighter from the water. The crane is used to lift the lighter out of the water vertically upward to a position above the cargo hatches of the ship and to transport the lighter to a particular cargo hatch and lower it into the cargo hold for storage. U.S. Pat. Nos. 3,469,716 and 3,515,086 describe a sea-going transport system that includes in combination with a gantry crane mounted on the deck of a ship a guide system for restraining swinging movement of lighters being transported from a floating position adjacent the stern of the ship to a storage position in the cargo hold of the ship. The guide system described in these patents includes a pair of lead-in stern guides pivotally depending from a pair of parallel spaced cantilevered stern beams which project horizontally from the stern of the ship, and a guide-rail-guide-carriage arrangement mounted on the legs of the gantry crane and adapted for restraining swinging movement U.S. Pat. No. 3,515,085 describes a load frame assembly for use with a sea-going transport system which includes a collapsible member for each ropefall of the hoisting system to maintain tension in the ropefalls when the lighter is tossed by sea swells. U.S. Pat. No. 3,536,204 describes an anchoring device for securing a traveling ship-board crane to the deck of the ship.
It would be advantageous to provide a system for transporting lighters from a floating position adjacent the stern of a ship to a storage location aboard said ship or for transporting such lighters from said storage location to said floating position that would be suitable for use with ships of the open stern wall type. Such a system would necessarily include guide members for restraining the swinging movement of the lighters when loading and unloading such lighters using the crane of the systems. However, such guide members would have to be designed in such a manner so as to also permit the loading and unloading of lighters by floating such lighters into or out of the cargo hold. It would be advantageous if such a system were of a simplified design and construction relative to the transport systems designed for use with conventional ocean-going cargo vessels.
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