Abstract:
A system and method for automated handling, transferring and storing conventional cargo storage containers on a cargo ship wherein the containers are stored in a multi-tier cell system and are manipulated by powered transfer units which are selectively moveable along an intersecting overhead track system such that containers may be simultaneously retrieved from, moved or placed within any of the cells of the ship. The transfer units are equipped both with hoists, which control spreader beams which are selectively secured to the cargo containers, and guide stabilizers, which prevent undesirable movement of the cargo containers when they are elevated above the cell structures such that the containers may be manipulated even during rough sea conditions such that the system is essentially continuously operable as a floating supply distribution system.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention is generally directed to methods and devices utilized with container ships for loading and discharging standardized cargo shipping containers and more particularly to an automated multi-directional material handling system which may be used to selectively retrieve and discharge containers while a ship is at sea. 
   2. Brief Description of the Related Art 
   The most efficient and economical manner of shipping goods over waterways is the use of standardized cargo containers. The containers are designated in standard sizes which are generally twenty or forty feet in length. The containers are specifically designed so that they may be loaded into the holds and on the decks of ocean going vessels and off loaded from the vessels at a port by use of either on-board or on-shore cranes which place the containers directly onto land transport vehicles including railway cars and trucks. Container ships are specialized vessels which are specifically designed to maximize the storage capacity of international storage and shipping containers. Conventional container ships include one or more hold areas extending from the bow to the stern of the ship with each hold area being divided into a plurality of vertically tiered cells. The cells are defined by vertical steel beams which act as guides for the corners of the containers such that the containers may be stacked one upon another within each cell. Typical cells may retain as many as six or seven stacked containers. 
   With conventional container ships, the cells are covered by hatch covers or plate which are removed in order to allow a crane to access the uppermost container in each cell. Typically, a container ship will include one or a plurality of either fixed or mobile bridge cranes which have hoists for selectively elevating the containers from the cells and for lowering the containers into the cells. When fixed cranes are provided sufficient cranes must be positioned at various areas spaced along the deck in order to allow access to each cell. The use of overhead bridge cranes permits a single crane to be moved on parallel guide rails. The bridge cranes, are moveable laterally from side to side along the bridge structure such that the cranes are moveable in a horizontal plane. 
   There are several drawbacks with respect to current container ship load handling or transfer systems. Utilizing conventional systems it is not possible to easily retrieve a specified container which may be located at a bottom of a cell without requiring the removal and temporary placement of other containers along the deck of the ship. During rough sea conditions, such retrieval is not possible. Further, the manner in which the containers are loaded and off-loaded requires the ship to be stabilized and thus either be at a dock or be in an offshore area with quiet seas which permit loads to be elevated safely from the cell structures. 
   A further drawback of current container ship material handling systems which utilize bridge cranes for elevating and lowering the shipping containers is that only a single bridge crane can operate over a given area of the ship at any one time, thus slowing the rate at which containers can be retrieved or stowed relative to the cells of the container ship. 
   In view of the foregoing, it would be beneficial to have a material retrieval and handling system which could be used on container ships whereby selected containers may be rapidly and easily retrieved regardless of their position within a cell of the ship and regardless of sea conditions. Further, it would be beneficial to have such a system wherein multiple container handling units could operate over a common grid structure so that a plurality of containers may be simultaneously moved with respect to the cells of the various holds of the container ship. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to an automated material retrieval handling and storage system for use in manipulating standardized cargo containers within cells of a container ship wherein the system includes a grid track structure which is securely mounted above the cells of the container ship and which defines intersecting and generally perpendicularly oriented tracks on which are guided container transfer units. Each transfer unit is mounted by a plurality of carriages which are mounted within the tracks such that the transfer units are suspended from the tracks and are moveable both from fore to aft and from port to starboard relative to the cells of a container ship. Each transfer unit includes hoists which are connected to a spreader beam structure which is formed as a frame for engaging and locking on to a standardized cargo container. In order to stabilize cargo containers as they are elevated above the cell structures toward the transfer units, each transfer unit includes an extendable stabilizer mechanism which prevents swinging of the container even under rough sea conditions as they are removed from the cells. 
   The transfer units are powered, in a preferred embodiment, by motors which power drive gear systems which are selectively engageable with fixed gear racks mounted to the grid track system. The drive motors have anti-backdrive features such that when they are not powered, with the gears in engagement with the racks mounted to the grid system, the motors act as locks to prevent movement of the transfer units. 
   The system is designed to provide a space above the upper tier of each cell which is large enough for the transfer units to maneuver while suspending a spreader beam therefrom such that the containers may be manipulated throughout the grid system and moved from one cell area to another beneath a raised deck of a ship. This not only enables movement of containers without placing the containers to the upper deck of the ship but also allows containers to be moved without having to remove the hatch covers above a cell in order to retrieve a specific cargo container from a predetermined area. 
   Using the system of the present invention, it is possible to utilize a single crane which may be in a fixed position along the deck of a container ship and move the cargo containers to specified discharge areas wherein one or more hatch covers may be removed while maintaining the other hatch covers closed during either loading or off-loading of the storage containers. The system thereby reduces the amount of effort and manual labor which is necessary to access the storage containers, permits movement of multiple containers within an area below the deck but above the cell structures such that the container may be interchangeably manipulated from space to space and further permits the area of the hold to be protected by being substantially covered by the removable hatch plates except in an area designated for loading and off-loading. 
   It is a primary object of the present invention to provide an automated material handling, retrieval and storage system for container ships which allows the ships to function as moveable supply sources such that supplies from containers may be manipulated while at sea, even during poor weather conditions, by providing a systems which enables cargo containers to be selectively retrieved and manipulated below deck for above deck transfer when and as necessary. 
   It is yet another object of the invention to provide a material handling system for use on container ships which facilitates the efficient maneuvering, loading and off-loading of standardized cargo containers wherein a plurality of transfer units move the containers simultaneously along a grid track system so that a plurality of containers may be moved simultaneously without interfering with one another. 
   It is a further object of the present invention to provide an automated material handling system for use on container ships wherein the cargo stowage cells of the ship may be placed in an unconventional orientation, such as an L-shaped configuration, which would not other wise be possible utilizing bridge crane structures which operate in a predetermined rectangular plan, as the grid structure of the present invention allows movement of transfer units throughout the total surface area of a hold of a ship regardless of its configuration. 
   It is also an object of the present invention to provide a material handling, retrieval and storage system for standardized international cargo containers which enables specific containers to be retrieved from any level of a multi-tiered cell structure of a hold without requiring that containers be elevated above the deck level thus making the system safer not only for the materials but also for personnel handling the cargo containers. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A better understanding of the invention will be had with respect to the accompanying drawings wherein: 
       FIG. 1  is a perspective illustrational view, in cross section having portions broken away, of a hold of a cargo container ship showing hatch plates covering a number of cells at the base of a crane and wherein hatch plates have been removed from a plurality of cells in which cargo storage containers are selectively stowed; 
       FIG. 2  is a top plan view of a section of the grid track system of the present invention which is mounted to a superstructure which supports the hatch covers of the container ship and which shows four carriages which suspend one of the transfer units of the present invention from the grid track system; 
       FIG. 3  is a top plan view of one of the transfer units of the present invention; 
       FIG. 4  is a side view of the transfer unit shown in  FIG. 2  and showing a cargo container secured to a spreader frame which is suspended from the hoist system of the transfer unit of the present invention; 
       FIG. 5  is a view similar to  FIG. 4 , on a smaller scale, showing the transfer unit elevating a cargo container from a lower tier of a cell of the cargo hold of the container ship; 
       FIG. 6  is a cross sectional view of one of the drive motors and the drive gears of the transfer unit of the present invention engaging the gear rack associated with the grid system of the invention; 
       FIG. 7  is a front plan view of the drive motor and gear drive assembly of  FIG. 6  in a driving position; 
       FIG. 8  is a view of the drive motor and drive gear arrangement of  FIG. 6  shown in a disengaged position; 
       FIG. 9  is a front elevational view of the drive gear of  FIG. 8 ; 
       FIG. 10 . is an enlarged view of the stabilizer assembly associated with the transfer units of the present invention shown in a fully raised position; 
       FIG. 11  is a cross sectional view of the stabilizer assembly of  FIG. 10  shown in an extended position ready to mate with a probe extending from the spreader frame of a transfer unit of the present invention; 
       FIG. 12  is a cross sectional view taken along line  12 - 12  of  FIG. 10 ; 
       FIG. 13  is a cross sectional view showing one of the carriage assemblies for mounting a transfer unit to one of the grid tracks of the invention; 
       FIG. 14  is a cross sectional view taken along line  14 - 14  of  FIG. 13 ; 
       FIG. 15  is a view taken along line  15 - 15  of  FIG. 13 ; 
       FIG. 16  is an enlarged view of the carriage member shown in  FIG. 13 ; 
       FIG. 17  is a cross sectional illustrational view of the system of the present invention shown in a container ship having four hold areas and showing one of the transfer units moveable along the grid system within the third hold area for purposes of illustrating an environment of the invention; and 
       FIG. 18  is an enlarged cross sectional view taken along line  18 - 18  of  FIG. 17 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   With specific reference to  FIG. 17  of the drawing figures, the system of the present invention will be described in association of a container ship  20 . It should be noted that the system may be used in other non-shipping environments such as mini-warehouses, distribution warehouses, garages and the like. The container ship is shown in cross section at the central portion so as to illustrate four hold areas  21 ,  22 ,  23  and  24  each of which is divided into a plurality of vertically tiered cells  25 . The cells are defined by vertically and horizontally extending steel beams which are generally of a size to allow a conventional standardized cargo container to be restrained within each cell in a conventional manner well know to those in the art. With the invention, however, the upper portion or upper tier of cells shown at T 7 , as opposed to being situated on the deck  26  of the vessel, are actually seated on top of each tier of cells within an enclosure  28  defined by steel plates which are secured to an enclosure which is formed as steel framing secured to the superstructure of the ship and which extends upwardly from the conventional deck a height sufficient to allow for at least a single tier of storage containers “C” to be stowed. Above that, a grid track system which is used to support vehicle transfer units in accordance with the teachings of the present invention is provided. The space above the normal cell height is shown generally at 30 in  FIG. 17  and may be, for example, 16 feet in height. 
   With specific reference to  FIG. 1 , a partial cross sectional perspective view of hold  22  of the container ship  20  is shown in greater detail. The enclosure  28  is shown as being reinforced by a plurality of fore and aft extending steel beams  31  and starboard to port extending beams  32  each of which is constructed to coincide with the cells over which the enclosure  28  is positioned. This grid structure is sealed utilizing conventional hatch plates  34  which are removably mounted in a conventional manner to the structure. As further shown in  FIG. 1  and in  FIG. 18 , there are seven storage tiers T 1  through T 7  in each cell  25  of the hold area and, further, there are shown, seven cells in width between the starboard and port side of the ships hull. 
   The system of the present invention allows the first six tier levels to be completely filled with storage containers “C” as is illustrated in  FIGS. 1 and 18 , however, approximately half of the seventh tier “T 7 ” of each of the cells are left vacant or empty upon the initial loading of the vessel in order to allow for storage containers to be shuffled within the seventh tier in order to retrieve containers from the lower tiers “T 1 -T 6 ” of the vessel. Utilizing the invention, a container located on the sixth tier may be elevated and placed in the seventh tier of one of the cells and, in like manner, the underlying container in the fifth tier may also be raised and placed in an empty seventh tier of another cell. In this manner, access can be obtained to any of the containers within a cell without requiring that the containers be elevated out of the hold area of the ship. Once a desired container such as shown at C′ in  FIG. 1  is exposed, the container may be elevated by use of a ships crane  35  utilizing conventional hoist line equipment  36 . In  FIG. 17 , four such cranes  35  are shown for purposes of facilitating the loading and off-loading of containers from the various holds of a cargo ship. As opposed to using the ship&#39;s crane  35  to elevated container C′ from the cell, the container may be elevated by one of the transfer units, to be described hereinafter, and moved to an area for off-loading by the crane  35 . 
   One of the benefits of the present material and article handling system is that the hatch plates  34  need not be removed from each of the tiered cell structures because the cargo containers “C” may be moved to any selected open cell area. Therefore, cargo containers which are stored in the cells beneath the hatch plates  34  shown at  FIG. 1  can be moved to an opening by the transfer units which are used with the invention and which operates within the upper open area  30  of the enclosure  28  above the tiered cells. Thereafter, the cargo container C′ may be raised by the crane. This means that, with the present invention, it is not necessary to remove all the hatch covers to obtain access to underlying cargo storage containers as the storage containers may be elevated to the open space  30  within the enclosure  28  and thereafter maneuvered to any predetermined area for retrieval by the ship&#39;s crane  35 . 
   As previously described, the present invention utilizes powered transfer units  40  which are only roughly illustrated in  FIGS. 1 ,  17  and  18  which are moveably supported on a grid track system  42 , which system is illustrated in  FIG. 2 . 
   The grid track structure  42  includes a plurality of intersecting generally C-shaped steel tubing members  44  which are fixedly secured, such as by welding, bolting or other attachment means to the underside of each of the fore and aft extending structural girders or beams  31  which openly intersect with similar C-shaped hollow steel tubing members  45  which are fixedly mounted, such as by welding, to the underside of each of the port to starboard extending structural members or beams  32  of each of the cell structures of the invention. The grid system  42  is shown in  FIG. 2  in cross section such that the upper or back wall of each of the hollow beams is not shown, however, lower flanges  46  and  47  of each beam are shown as being spaced from one another to define an open channel  48  for passage of pilot shafts associated with roller carriages which serve to mount the transfer units  40  to the grid system, as will be described in greater detail. The transfer unit  40  shown in top view in  FIG. 2  is supported within the grid system by four separate carriages  50 A,  50 B,  50 C and  50 D. 
   With specific reference to  FIGS. 13 through 16 , one of the transport carriages  50 A is shown in greater detail. The carriage is shown as including a plurality of ball rollers  51  which are designed to track on an upper surface  52  of each of the lower flanges  46  and  47  of one of the track segments  44  or  45 . The track segment  45  is shown in the drawing Figures. The carriage includes a main body portion  53  which supports a central pilot shaft  54  which extends through the open slot  48  in the guide track. With specific reference to  FIG. 14 , each carriage includes opposite sets of guide rollers  56  and  57  which extend upwardly from the body  53  so as to engage opposing sidewalls  59  and  60  of the track  45 . Each carriage also includes oppositely oriented guide rollers  61  and  62  provided on opposite sides of the body which are used to guide the carriage when moving along a perpendicular guide track  44 . In this manner, and as shown at  FIG. 2 , when the transfer unit  40  reaches an intersection of the track segments  44  and  45 , the direction of the transfer vehicle may change so that the transfer unit moves either fore and aft relative to the ship or athwartship from port to starboard or visa versa relative to the ship. The carriages will be guided by the sets of rollers  56 ,  57  and  61 ,  62  depending upon which track segment the transfer unit is traveling at a particular time. 
   Each carriage further includes a guide roller  65  mounted to the pilot shaft  54  so as to track between a pair of gear racks  66  and  67  which are welded or otherwise secured to the lower surface of each of the flanges  46  and  47  respectively of the guide track  45 . Similar gear racks are provided in spaced relationship to the track segments  44 . The guide rollers  65  engage the inner surfaces of the each of the guide racks to stabilize the movement of the carriage relative to the guide tracks  44  and  45  of the grid system  42 . The shaft  54  extends down and is engaged within a mounting member  68  which is designed to be securely connected to the transfer unit  40  in order to support the transfer unit relative to the carriages, generally as shown at  68  in  FIG. 3 , at one of the corners of the transfer unit  40 . The teeth of each gear rack  66  and  67  are bidirectional at each intersection. 
   With specific reference to  FIG. 16 , each carriage roller member  51  is mounted within a housing  70  mounted by a stub shaft  72  to the base  53  of the carriage. The stub shafts  72  are secured by snap rings  74  to the body  53 . Disk springs  75  are shown as being provided between each roller ball housing  70  and a lower surface of the body  53  of the carriage to provide a shock absorbing effect for each of the roller assemblies. 
   As described, each transfer unit  40  is supported by at least four carriages which are mounted generally adjacent the corners of the transfer unit as shown in  FIG. 3 . 
   With reference to  FIGS. 2 through 12 , one of the transfer units  40  of the present invention will be described in greater detail. It should be remembered that a plurality of transfer units will operate within the system of present invention. Because of the intersecting grid tracks of the system  42 , the plurality of transfer units will move independently of one another moving cargo containers within the open area  30  above the top tier T 7  of the cells within each hold with transfer units being able to maneuver about one another because of the intersecting grid system. 
   Each transfer unit  40  includes a main body  80  which is defined having upper and lower surfaces  81  and  82 . Generally, the body is defined by a steel frame covered by steel sheet metal along the upper and side surfaces. Mounting brackets  83  are provided at each of the corners extending from the upper surface of the transfer unit and connect with the mounting member  68  associated with each carriage. The mountings members may be connected utilizing conventional bolts or may be connected by welding. In order to drive the transfer units relative to the grid track system  42 , the present invention provides four separate motors  90 A,  90 B,  90 C and  90 D each of which drives pinion gears which are pivotally mounted as will be explained in greater detail so as to be selectively brought into meshed engagement with the spaced gear racks  66  and  67  mounted to the grid track segments  44  and  45 . The motors  90 A through  90 D are specifically designed to provide power for moving the transfer unit  40  along the grid track segments  45  between starboard and port with respect to the container ship. Four additional motors  94 A through  94 D are provided for providing power to similar pinion drive gears associated therewith which are selectively moveable into engagement with the gear racks  66  and  67  secured to the grid track segments  44  so as to move the transfer unit fore and aft relative to the container ship. As the manner in which the motors  90 A-D and  94 A-D are used to power the drive pinions is the same, only one drive assembly associated with motor  90 A will be described in greater detail and is shown in  FIGS. 6-9 . The motor  90 A is fixedly mounted to a support frame  96  which is secured to the upper surface of the transfer unit. 
   As shown in  FIGS. 3 and 6 , each of the motors  90  and  94  are mounted to similar brackets  96  which are secured to the upper surface of the transfer unit. Each motor has an output drive shaft  97  to which is fixedly secured a pair of spaced driving pinion gears  98  which are disposed within a pivot housing  100 . A pair of driven gears  102  are mounted in spaced relationship to a stub shaft  103  which is secured to the housing  100 . Teeth of the driven pinion gears  102  mesh with the teeth of the drive gears  98 . In the position of the housing  100  shown in  FIGS. 6 and 7 , the driven pinion gears  102  are shown as being in driving engagement with respect to the gear racks  66  and  67  which extend along the grid track system. 
   To insure proper alignment of the driven gears  102  with the gear racks  66  and  67 , the housing  100  also supports a guide wheel  105  mounted to a shaft  106 . The guide wheel is of a size to cooperatively be seated between the gear racks  66  and  67  as shown in  FIG. 7 . When it is desired to disengage the motors and thus the driven gears  102  from the gear racks  66  and  67 , a hydraulic or pneumatic cylinder  108  is activated to pivot the housing  101  to a retracted position, as shown in  FIGS. 8 and 9 . The cylinder  108  has a ram arm  109  pivotally connected at  110  to the housing  100 . 
   To lock the housing  100  in a position to ensure that the driven gears  102  engage and are maintained in engagement with the gear racks  66  and  67 , a second hydraulic or pneumatic cylinder  112  is provided which is connected at its base to a locking pin  114  which is moveable guided within a cylinder  115  which is mounted below the housing  100 . In a position shown in  FIGS. 8 and 9 , the locking pin  114  is extended within a receiver  116  provided in a base of the housing  100  thereby preventing rotation of the housing and insuring engagement of the drive gears  98  with the driven gears  102 . In the event of power failure, this pin remains in the locked position. The cylinder  112  is connected through ram arm  118  to a pivot attachment  120  along the upper surface of the transfer unit. 
   When it is desired to disengage the gears  102  from the gear racks  66  and  67 , the locking pin  115  is withdrawn from the receiver  116  of the housing  100  thereby allowing the hydraulic or pneumatic cylinder  108  to pivot the housing  100  to the disengaged position for the driven gears  102  as shown in  FIGS. 8 and 9 . 
   As previously noted, the motors  90 A,  90 B,  90 C and  90 D are all connected to similar drive gear assemblies which function to move the transfer unit along the tracks or track segments  45  whereas the drive motors  90 A,  90 B,  90 C and  90 D include similar drive gear arrangements which are used to power or move the transfer unit along the guide track segments  44 . 
   Although power to the motors  90  and  94  may be provided by onboard batteries carried by each transfer unit, AC power may also be supplied to the transfer units through an inductive power transfer raceway system  130 . The raceway extends parallel and outside each of the guide tracks of the grid system of the present invention. Power is supplied in a conventional manner to the raceway and the raceway can be insulated both electrically and from atmospheric conditions. Similar systems are currently used on bridge cranes used on container ships. One such raceway system is referred to as an “Inductive Power Transfer” (IPT) provided by Wampfler, Inc. of Florence, Ky. To receive power, each motor includes an electrical collector shoe  132  which extends outwardly in opposing relationship with respect to the conductor raceway system as is shown in  FIG. 4  of the drawings. 
   With specific reference to  FIGS. 4 and 5 , each of the transfer units of the present invention supports a generally conventional spreader beam  140  which has a frame type structure of a size to compatibly engage the shipping containers “C”. Each of the spreader beams includes lock mechanisms illustrated at  142  in drawing  FIG. 5  which are positioned at the four corners of the spreader beam and engage within lock boxes which are provided as a standard feature in all international shipping containers. As a frame is lowered into contact with the upper surface of the container “C”, the locks are activated and they rotate within the lock boxes to secure the spreader beam to the container. Thereafter, the containers are raised utilizing a hoist assembly carried by each of the transfer units  40 . Mounted to the upper surface of each of the transfer units are a pair of hoist assemblies  145  each of which is driven by a motor  146  which receives power from the raceway  130  as previously described. As an alternative, onboard batteries may also be provided to supply power to the motors  146 . The motors are connected through gearboxes  147  to pairs of winding drums  148  about which cables  150  are selectively wound. The remote end of each cable is secured at  151  to the frame of the transfer unit. Each of the cables extends about pulleys  155 , four which are provided on the spreader beam. 
   As shown in  FIG. 5 , each of the tiered cells is defined at the corners by structural beams  160  and  161  which intersect at approximately 90° and form four guide channels for guiding the container “C” and the spreader beam  140  as they are raised or lowered with respect to the cells. In the present invention, however, means are provided for securing the spreader beam and the container so that they do not sway as they are lifted into the open space  30  above the upper tier T 7  of the cells. This is an important feature of the transfer units of the present invention as it allows the transfer units to control movement of the cargo containers even during rough seas thereby allowing the containers to be manipulated when it is not possible to do so with conventional material handling systems currently used on container ships. 
   As shown in  FIG. 5 , each of the spreader beams include a central guide pin or probe  165  which is mounted to a base  166  secured to the spreader beam frame. As the spreader beam is raised, the pin engages within an extensible guide tube  168  which is telescopically mounted with respect to a support housing  170  by way of an intermediate tube  172 . The housing  170  is mounted by supports  174  to the upper surface of the transfer unit  40 . 
   The container guide assembly is shown in more detail in  FIGS. 10 through 12 . As shown, the guide tube  168  is generally square in configuration so as to cooperatively receive the pin which is also generally square in cross sectional configuration. Because of the cooperating engagement of the pin within the tube  168 , it is not possible for the spreader beam to rotate relative to the transfer unit when the spreader beam and the cargo container “C” are elevated into the open area  30  above the upper tier level T 7  of the cells to control the spreader beam when a container is not attached to the spreader beam. 
   The guide tube  168  further includes a pair of outwardly extending guide flanges  175  which are guided by spaced rollers  176  mounted to the intermediate tube  172 . As shown in  FIG. 12 , the lower extent of the guide tube  168  is limited by the upper set of rollers  176  as an upper flange  178  of the tube engages the upper rollers  176  in a fully extended position. 
   As the spreader beam is raised utilizing the hoist assemblies of the present application, when the pin  176  engages within the tube  168 , the tube will begin to elevate within the intermediate guide tube  172 . Supplemental rollers  180  are also mounted to the intermediate tube  172  and are oriented to engage the outer edge of each of the flanges  175  of the guide tube  168 . These rollers also engage the inner surface  182  of the primary support housing  170  of the guide assembly as the guide tube  168  and intermediate tube  172  are elevated as the container is raised by the hoist assemblies associated with the transfer unit. The guide assembly is shown in its fully elevated position in  FIG. 10  wherein the telescoping guide tube  168  and the intermediate guide tube  172  are fully received with the primary support housing  170 . Although not shown in the drawings, any appropriate locking mechanism may also be used to secure the guide assembly in its fully raised position as shown in  FIG. 10 . 
   To further guide and control the movement of the container “C” relative to the transfer unit when in a fully raised position as illustrated in dotted line in  FIG. 5 , four corner guide arms  200  which are slightly flared outwardly at their lower edges  201  are provided. Each guide arm has two guide wall portions which intersect at approximately 90° with respect to one another so as to cooperatively engage the corners of the spreader beam  140  which is secured to a container as is illustrated in the drawing figure when the container is raised relative to the transfer unit as is illustrated in  FIG. 4 . 
   As previously described, in accordance with the teachings of the invention, plural transfer units may operate within the grid track system of the present invention thereby enabling containers to be shuffled simultaneously within the open area  30  defined above the upper tier T 7  level of the cells within a hold. 
   With the present invention, a number of spaces in the T 7  level of each hold are vacant when the container ship is fully loaded. This permits containers from lower tier levels (T 1 -T 6 ) to be moved into the open spaces so as to retrieve containers at lower tier levels. After a desired container is retrieved utilizing a transfer unit of the present invention, the containers which have been moved can be replaced within a particular cell from which they were originally taken. 
   When a transfer unit is to be moved, the drive pinion associated either with the motors  90  which are used to drive the drive gears to move the transfer unit laterally between the starboard and port are operated or the motors  94  which are used to power the transfer unit between the fore and aft direction are operated. At each intersection a change in direction may be made as is illustrated in  FIG. 2 . When a change in direction is desired, the transfer unit automatically stops at the intersection and a change is made in the drive gears which are powered. The arrangement of the grid system is such that the transfer unit is centered over each cell at each intersection of the grid system to thereby facilitate the extraction or insertion of containers out of or into the cell. When a change of direction is required, the driven pinions for the new direction engage the rack gear teeth at which time the driven pinions that were driving the transfer unit disengage from the rack gear teeth. This provides constant control of the transfer unit and insures that it is under direct drive in which ever direction it is traveling at all times. 
   Whenever the transfer unit is extraction or inserting a container out of or into a cell, both sets of driven pinions powered by the motors  90  and  94  are set to engage the rack gear teeth in a stopped mode. This securely locks the transfer unit in position. 
   By way of example, it is contemplated that the motors used to power the drive gears are anti-backdrive motors and will enable the transfer units to operate at approximately 60 feet per minute when fully loaded and at approximately 90 feet per minute with no load. The hoist motors may include two 75 horse power AC motors which obtain their power as previously described from the power raceway. The hoists will lift fully loaded containers at a rate of approximately 75 feet per minute and may operate at up to 112 feet per minute with no load. 
   The system of the present invention may be fully automated and interfaced with an inventory control system so that each transfer unit is directed to a given cell and to a given container location within the hold by multiplexing a command signal from the inventory control system through the power raceway grid wiring. Digital input from the drive motor rotations and counting rack teeth and registration at digitized check points along the grid system or at each cell location will provide guidance for the transfer units within the system. The hoist motors will also have digitized features for determining the exact elevation and relationship of the transfer beam to each transfer unit when raising and lowering a container. 
   Utilizing such a system, a designated container may be automatically located and containers above the designated container may be moved appropriately and, thereafter, relocated once the designated container has been retrieved utilizing the transfer units and their hoist mechanisms. 
   Once a designated container is located it may selectively elevated and positioned for retrieval from the hold utilizing the ships crane as previously described. Loading of the hold can also be fully automatic with each container being placed at a predetermined location within the hold. 
   The foregoing description of the preferred embodiment of the invention has been presented to illustrate the principles of the invention and not to limit the invention to the particular embodiment illustrated. It is intended that the scope of the invention be defined by all of the embodiments encompassed within the following claims and their equivalents.