withstand stacking and motion at sea. Containers are of standard size, the largest ones weighing up to about 30 metric tons when loaded. The use of standard containers facilitates ship-board stowage land or waterway transportation, and rental or lease A large container ship may be loaded or unloaded completely in about half a day, compared to veral days for the same amount of cargo in break-bulk cargo ship. Generally, the shipper places the cargo in the container and, except for custom inspection, it is delivered unopened to the consignee. Highway trailers(most commonly), railroad cars, or barges transport containers to and from their land destination and are therefore apart of the same transportation system. For a given payload cargo capacity, container ships are larger and more costly to build than the traditional cargo ship, but both the cargo handling cost and the idle ship time in port are reduced cons Although in some ships containers are moved horizontally for loading and unloading, the predominant arrangement is that illustrated in Fig. I where containers are stowed in vertical cells and moved vertically in and out of the vessel Roll-on/Roll-off ships With a broad interpretation all ships that are designed to handle cargo by rolling it on wheels can be considered under this heading. This would include trailer ships; sea trains( carrying railroad cars or entire carriers: ships carrying pallets handled by forklift trucks from and to shore; and so on, the following is a description of a ship of this type, which is intended primarily to operate as a trailer ship, although it may handle several types of wheeled vehicles Roll-on/ Roll-off ships require a high proportion of cubic capacity relative to the amount of cargo and are particularly suited to services with short runs and frequent loading and unloading They need even shorter port time than container ships but their building cost is higher Because fully loaded toll-on/roll-off ships can not carry enough cargo to immerse them deeply their large freeboard allows the fitting of side ports above the waterline for handling of cargo on heels by means of ramps. Usually, ships of this type have a transom stern(a square-shaped stern like that of a motorboat) fitted with doors for handling wheeled vehicles on an aft ramp Roll-on/Roll-off ships have several decks, and the cargo is handled on wheels from the loading deck to other decks by elevators or sloping ramps. Both internal elevators and ramps occupy substantial volume in the ship. The need for clear decks, without interruption by transverse bulkheads, and tween decks for vehicle parking results in a unique structural arrangement Barge-carrying This type of ship represents a hold step in the trend toward cargo containerization and port time ductions. Cargo is carried in barges or lighters each weighing up to 1000 metric tons when loaded. The lighters are carried below and above deck and handled by gantry cranes or elevator platforms These are among the fastest, largest, and costest ships for the carriage of general cargo. For their size, their payload capacity is less than that of the conventional break-bulk cargo ship. However they can be loaded and unloaded much faster and with a considerable saving in man-hours Because the lighters can be waterborne and operated as regular barges, these large ships can erve undeveloped ports advantageously Using portable fixtures that can be erected quickly, barge-carrying ships can be adapted for the transport of varying amounts of standard containers in addition to or in plane of lighters Bulk cargo shipswithstand stacking and motion at sea. Containers are of standard size, the largest ones weighing up to about 30 metric tons when loaded. The use of standard containers facilitates ship-board stowage, land or waterway transportation, and rental or lease. A large container ship may be loaded or unloaded completely in about half a day, compared to several days for the same amount of cargo in break-bulk cargo ship. Generally, the shipper places the cargo in the container and，except for custom inspection, it is delivered unopened to the consignee. Highway trailers (most commonly), railroad cars, or barges transport containers to and from their land destination and are therefore apart of the same transportation system. For a given payload cargo capacity, container ships are larger and more costly to build than the traditional cargo ship, but both the cargo handling cost and the idle ship time in port are reduced considerably. Although in some ships containers are moved horizontally for loading and unloading, the predominant arrangement is that illustrated in Fig.1 where containers are stowed in vertical cells and moved vertically in and out of the vessel. Roll-on/Roll-off ships With a broad interpretation all ships that are designed to handle cargo by rolling it on wheels can be considered under this heading. This would include trailer ships; sea trains(carrying railroad cars or entire carriers: ships carrying pallets handled by forklift trucks from and to shore; and so on, the following is a description of a ship of this type, which is intended primarily to operate as a trailer ship, although it may handle several types of wheeled vehicles. Roll-on/Roll-off ships require a high proportion of cubic capacity relative to the amount of cargo and are particularly suited to services with short runs and frequent loading and unloading. They need even shorter port time than container ships but their building cost is higher. Because fully loaded toll-on/roll-off ships can not carry enough cargo to immerse them deeply, their large freeboard allows the fitting of side ports above the waterline for handling of cargo on wheels by means of ramps. Usually, ships of this type have a transom stern (a square-shaped stern like that of a motorboat) fitted with doors for handling wheeled vehicles on an aft ramp. Roll-on/Roll-off ships have several decks, and the cargo is handled on wheels from the loading deck to other decks by elevators or sloping ramps. Both internal elevators and ramps occupy substantial volume in the ship. The need for clear decks, without interruption by transverse bulkheads, and tween decks for vehicle parking results in a unique structural arrangement. Barge-carrying ships This type of ship represents a hold step in the trend toward cargo containerization and port time reductions. Cargo is carried in barges or lighters each weighing up to 1000 metric tons when loaded. The lighters are carried below and above deck and handled by gantry cranes or elevator platforms. These are among the fastest, largest, and costest ships for the carriage of general cargo. For their size, their payload capacity is less than that of the conventional break-bulk cargo ship. However, they can be loaded and unloaded much faster and with a considerable saving in man-hours. Because the lighters can be waterborne and operated as regular barges, these large ships can serve undeveloped ports advantageously. Using portable fixtures that can be erected quickly, barge-carrying ships can be adapted for the transport of varying amounts of standard containers in addition to or in plane of lighters. Bulk cargo ships