Rotatable Container-hoisting Apparatus

Abstract

Hoisting apparatus for cargo containers that permits the containers to be oriented in any rotative position so that containers can be positioned as desired in container cells, on dock surfaces, and like locations. A cable guiding system in which the spacing between the several vertical cable runs in the system can be altered between a relative widely spaced, highly stable position and a relatively closely spaced position at which the cable guiding structure can enter into container cells without contacting the walls that define the cell. An auxiliary frame adapted to be mounted between the cable guiding structure and a conventional container-engaging spreader frame, which auxiliary frame is adapted to rotatively position a spreader frame and container engaged thereby. The auxiliary frame includes sensors to determine the degree of load imbalance, if any, of a container engaged thereby, and a counterweight and a drive system for the counterweight that positions the counterweight so as to compensate for any imbalance arising from an eccentrically loaded container.

Description

This invention relates to hoisting apparatus for hoisting cargo containers during transportation of such containers between a dock or like cargo storage area and a ship or like transport vessel.

A typical cargo container is of rectangular configuration in plan. Container ships and like vessels adapted for transporting cargo containers are provided with vertically extending walls that define cells which in the plan aspect have a shape similar to and slightly larger than the container so that the containers can be stacked one on top of another in the cells. In order to utilize most efficiently the volume in a ship's hold, a portion of the cells are oriented with their longest dimension longitudinal of the ship and another portion of the cells are oriented with their longest dimension athwartship, or transverse of the length of the ship. It is desirable to provide a single hoisting structure that can load containers into the cells irrespective of the orientation of a particular cell, and although copending commonly assigned Pat. application Ser. No. 643,993, discloses a rotatable device for achieving variable positioning of containers, such device cannot enter into all container cells. The apparatus of the present invention achieves improved operation over the subject matter of said copending patent application and provides a loading apparatus that is somewhat more versatile than such previously described apparatus, since the present invention provides apparatus capable of entry into cells irrespective of the orientation of the cells.

The environment in which the present invention finds particular utility includes a generally horizontally extending crane boom that extends outwardly from a tower into a position overlying a ship or like transport vessel. Mounted on the boom is a pair of parallel, spaced-apart track rails. A carriage is rollably supported on the rails and the carriage has supported thereon a plurality of cable guide sheaves to guide the cable downwardly to permit raising and lowering of a load. As described in U.S. Pat. No. 3,102,642, four separate cable runs between the carriage and the load are desirable to achieve load stability. Maximum spacing between the cables affords stability to the load.

The permissible spacing between the cables is limited, however, by the distance between the cell walls, because the cables cannot be so widely spaced apart that they contact or rub the cell walls. Moreover, the permissible spacing between the cables depends on whether a container supported by the cables is positioned for loading into a longitudinally extending cell or into a transversely extending cell.

According to the present invention, a carriage is provided that has means thereon for varying the spacing between the cables that depend from the carriage. Thus, the cables can be adjustably spaced apart to attain maximum possible stabilization without causing interference with the cell walls.

The lower ends of the hoisting cables engage a so-called quick-change headblock which includes sheaves through which the cables are trained as well as means for effecting engagement of the cargo container or like load to be hoisted.

The present invention provides a quick-change block that affords adjustment of the spacing between the cable sheaves thereon so that containers engaged thereby can be positioned for entry into either longitudinally or transversely elongate cells.

Because, as pointed out above, many ships have some container cells that are oriented longitudinally and some container cells that are oriented transversely, it is desirable to provide a container-engaging structure that can be rotatably or pivotally driven to position the container for entry into either a longitudinally elongated cell or a transversely elongated cell. Pat. application Ser. No. 643,993 referred to above discloses a rotatable structure for rotating or positioning containers for any orientational position on a dock or like flat surface. The present invention includes a rotatable device that is so sized that it can enter into cells irrespective of the orientation of the cell. To permit accomplishment of such mode of operation, the depending cables must be relatively closely spaced to one another since they must be no greater than the width, the shortest dimension, of the cell. Closely spaced cables do not afford optimum stability to containers, particularly when the containers are eccentrically loaded. According to the present invention, a counterweight is provided on the spreader frame that engages the containers, and a sensing system for sensing the differential tension in the cables is employed for controllably positioning the counterweight to compensate for any unbalanced condition in the container. Thus the relatively close spacing of the cables does not preclude efficient balanced operation of the apparatus.

The above, as well as other objects, features and advantages of the present invention will be more apparent after referring to the following specification and accompanying drawings in which:

FIG. 1 is a partially schematic elevation view showing a cargo-hoisting apparatus with the cables disposed at a widely spaced position;

FIG. 2 is a view similar to FIG. 1 with the cables closely spaced for entry into a transversely extending cell;

FIG. 3 is a plan view taken along line 3-3 and drawn at a somewhat enlarged scale;

FIG. 4 is a plan view of a rotatable intermediate spreader frame according to the present invention;

FIG. 5 is a side elevation view of the intermediate frame of FIG. 4;

FIG. 6 is an end elevation view of a frame of FIG. 4;

FIG. 7 is a fragmentary view at enlarged scale of the supporting structure of FIG. 6;

FIG. 8 is a side view of FIG. 7;

FIG. 9 is a diagrammatic view showing the load imbalance sensors; and

FIG. 10 is a schematic view of the load imbalance sensors and counterweight drive mechanism of this invention.

Referring more particularly to the drawings, reference numerals 12 and 14 indicate structural members of a crane boom that is held in elevated horizontal position by a tower structure, not shown, in a position overlying a ship or like transport vessel. The crane boom is typically supported so that it projects out from a wharf transversely or athwartship of a vessel situated alongside the wharf. Secured to members 12 and 14 are track rails 16 which are shown as I-beams in the drawing. Supported on track rails 16 for rolling movement thereon is a carriage 18 which has wheels 20 that are adapted to roll along the track rails. Carriage 18 pivotally supports yokes 22, each of which has paired sheaves 24 which sheaves guide horizontal cable runs (not shown) into plural vertically extending runs indicated at 26a, 26b, 26c, 26d, 27a, 27b, 27c, and 27d. The horizontal space between vertical runs 26a and 26b on the one hand, and 27a and 27b on the other hand, is governed by the spacing between paired sheaves 28 and paired sheaves 30. Sheaves 28 are carried on a subcarriage 32 which is transversely slidable along guide members 34 that are an integral part of frame 18. A similar undercarriage 36 supports sheaves 30. Guide members 34 are shown in the drawings as I-beams and undercarriages 32 and 36 are dimensioned so that they slide between the upper and lower flanges of the I-beam section. For moving the undercarriages 32 and 36 between the relatively widely spaced position shown in FIG. 1 and the relatively closely spaced position shown in FIG. 2 there is provided a motor 38 coupled to a drive sheave 40 through a speed-reducing gear 42. See FIG. 3. In engagement with drive sheave 40 are plural drivebelts 44 that are trained around double transfer sheaves 46. Idler sheave 48 at the extremities of carriage 18 support in cooperation with double transfer sheaves 46 drivebelts 50. One reach of each drive chain 50 is connected to a carriage 32, 36 by means of a connector 52. Thus it will be seen that energization of motor 38 will effect movement of undercarriages 32 and 36 toward and away from one another along guide members 34.

Cable runs 26a, 26b, 26c, 26d, 27a, 27b, 27c, and 27d support at their lower ends a pair of quick-change headblocks 54 and 56. Certain details of these blocks are disclosed in U.S. Pat. application Ser. No. 675,448. Block 56 is typical and includes an outboard sheave 58 and an inboard sheave 60 (see FIG. 6). The quick-change headblocks also include locking devices 62 that serve quickly to lock onto the headblock suitable load-engaging apparatus, a specific form of which will be described in more detail hereinafter. To illustrate the versatility of the apparatus of the present invention, headblocks 54 and 56 are shown in FIG. 1 in engagement with a conventional spreader frame 64 and in FIG. 2 in engagement with an improved rotatable auxiliary frame 66 made in accordance with the present invention.

Extending between quick-change headblocks 54 and 56 is an adjustable frame that includes lateral segments 68 adapted to telescope into a central frame 70. Headblocks 54 and 56 are shown in FIG. 1 in their extreme extended position and in FIG. 2 in their extreme retracted position. Carried on central frame 70 is a cable bucket 71 into which an electrical control cable 72 coils as the headblocks are raised and from which the electrical control cable pays out as the headblocks are lowered. Locking pins 73 (see FIG. 5) cooperate with suitably positioned holes in segments 68 and central frame 70 to lock the segments 68 in the extended position, the retracted position, or any desired intermediate position.

FIG. 1 shows a container C positioned between a forward cell wall 74f and an aft cell wall 74a. Container C is engaged by a spreader frame 64 which spreader frame has upstanding connector elements 64c for engagement by quick-change headblocks 54 and 56. The headblocks are widely spaced in FIG. 1 because the longest dimension of the cell, i.e., the distance between walls 74f and 74a, is oriented longitudinally of the vessel of which the cell is a part. In FIG. 2 a forward cell wall 75f is spaced from an aft cell wall 75a by a distance equal to the width of container C'. The cell residing between walls 75f and 75a is oriented with its longest dimension transversely of the longitudinal dimension of the vessel. Lateral segments 68 are telescoped into central frame 70 so that headblocks 54 and 56 are sufficiently close to one another to fit between cell walls 75f and 75a. Because the distance between connecting elements 64c on spreader frame 64 is fixed, an intermediate rotatable auxiliary frame 66 is provided for placement between headblocks 54 and 56 and spreader frame 64.

Intermediate rotatable auxiliary frame 66, as can be seen in FIG. 5, includes an upper frame element 76, a lower frame element 78, and a rotary drive apparatus 80 therebetween for joining the upper and lower elements together and for establishing the relative rotational position therebetween. Extending upwardly from frame element 76 are connector elements or plates 82 which are formed for engagement with quick-change headblocks 54 and 56 in order that the rotatable auxiliary frame 66 can be quickly removed from the hoisting apparatus when it is not needed. Depending from lower frame element 78 are quick-change connector elements 84 which engage with complementary elements 64c projecting upwardly from a spreader frame 64'. Spreader frame 64', although of a size different from spreader frame 64, is otherwise identical in structure and function. Rotating mechanism 80 is similar to the structure described in the above-mentioned Pat. application Ser. No. 643,993. More specifically, rotating mechanism 80 includes a motor 86 that powers a slewing drive formed by a pinion 88 enmeshed with a ring gear 90 which is rigid with lower frame element 78. Ring gear 90 is formed on the interior face of a bearing race 92 which is attached to lower frame element 78 by means of crossbeams 94. A second bearing race 96, which is secured to upper frame element 76, constrains antifriction balls 97 so that the upper and lower frame elements can be rotated relative one another. Thus when motor 86 is energized, lower frame element 78 is rotated with respect to upper frame element 76 so that a load attached to the lower frame element is rotated with respect to the hoisting cables, carriage 18, and rails 16.

Because quick-change headblocks 54 and 56 are spaced relatively closely when engaged with connector plates 82 of upper frame element 76, an unbalanced load condition in a container could, if not compensated for, cause the container to tilt to such a degree that it would not properly fit between the cell walls. For compensating for such unbalanced condition, a movable counterweight 98 is employed. The counterweight is disposed between side rails 100 of lower frame 78 and has flanged wheels 102 projecting laterally therefrom for rolling engagement on the side rails. The position of counterweight 98 along rails 100 is established by a motor 104 which drives a pair of cable drums 106 and 108 through a reducing gear or transmission 110. Cables 112 each have a bight wrapped around drums 106 and 108 and have their ends attached to opposite sides of the counterweight as indicated at 114 in FIG. 5. Each cable 112 is guided around opposed sheaves 116 and 118 so that as drums 106 and 108 are rotated, counterweight 98 is moved along side rails 100. An idler sheave 118 is provided for each cable 112 to guide the cable clear of rotary drive mechanism 80.

Motor 104 is actuated to move counterweight 98 only when an unbalanced load condition exists. For sensing the presence of such unbalanced condition, the sheaves in headblocks 54 and 56 are carried by yokes 120 that are mounted in the headblocks for pivotal movement around a pivot pin 122. Yokes 120 are pivotable about the axis of pivot pin 122 between an extended position shown in FIG. 6 and a retracted position shown in FIG. 8. Locking pins 124, 126, and 128 are provided for retaining the yokes in a desired position, locking pins 124 and 126 being provided for holding the yokes in the extended position, and locking pin 128 being provided for retaining the yokes in the retracted position. When the apparatus is being employed with an ordinary spreader frame, as shown in FIG. 1, unbalanced load conditions do not constitute a problem, and yokes 120 are moved to the retracted position shown in FIG. 8 in order to maximize the angle of convergence of the cables 26 and 27, thereby to maximize the degree of damping of swaying motion. When, however, the apparatus is being used for spreader frames and containers that can be rotated to the position shown in FIG. 2, yokes 120 are moved to the extended position shown in FIG. 6, thereby to maximize stability against the effects of an unbalanced load.

When undercarriages 32 and 36 are in the widely spaced position shown in FIG. 1, container C is reasonably stable because of the wide spacing of the cables in a direction longitudinally of the container. In such condition it is desirable to have the angle between cable runs 27a and 27b and cable runs 27c and 27d at a substantial magnitude as shown in FIG. 8. Such position is established by swinging the yokes 120 inwardly and locking them in such position by means of locking pins 128. A substantial angle between the cable runs is desirable in order to minimize swaying or oscillation of the container in a direction in and out of the paper as viewed in FIG. 1. When, however, the undercarriages 32 and 36 are moved to the relatively closely spaced position, as shown in FIG. 2, to adapt the system to handle containers at a 90.degree. position from that shown in FIG. 1, the maximum spacing between cable runs 27a and 27b and cable runs 27c and 27d that can be obtained is desirable to compensate as much as possible for load imbalance. To achieve such condition, yokes 120 are moved to the outer position of FIG. 6 and there retained by engagement of locking pins 124 and 126. At such position an abutment 120a of yoke 120 moves into operative connection with load cells 130 and 132. See FIG. 8. Thus the system for sensing container imbalance is made active.

The system for positioning counterweight 98 is activated by providing hydraulic load cells 130 and 132 at diagonally opposite yokes 120. Hydraulic load cells suitable for this purpose are available from the Martin Decker Company. The output of each load cell, a hydraulic fluid pressure, is transmitted through flexible hoses 134 and 136, respectively, to an electrohydraulic control circuit 138 for actuating motor 104. Thus the pressure existing in hydraulic line 134 is proportional to the load on cable runs 26a and 26b, and the pressure in line 136 is proportional to the load on cable runs 27c and 27d. The differential between the pressures in lines 134 and 136 is proportional to the degree of imbalance of the combined weight of the load, the apparatus for engaging the load, and the counterweight 98.

Differential pressure switches 140, 142, 144 and 146 respond in accordance with the magnitude and direction of differential pressures between lines 134 and 136. The differential pressure switches in one system designed according to the present invention are known by the trade name Melatron switches. Pressure switch 140 includes a hydraulic element 140h, which includes an electrical armature 140a movable between a normally closed fixed contact 140c, and a normally open fixed contact 140b. Pressure switch 140 is arranged so that when the pressure in hydraulic line 134 exceeds that in hydraulic line 136 by a preselected increment, armature 140a is moved out of contact with fixed contact 140c and into contact with fixed contact 140b. When the pressure in hydraulic line 136 exceeds the pressure in hydraulic line 134, however, the normally closed relationship between armature 140a and fixed contact 140c is not affected.

Differential pressure switch 142 includes a hydraulic element 142h to which is operatively connected an electrical armature 142a that is movable between a fixed normally closed contact 142c and a fixed normally open contact 142b. Differential pressure switch 142 is so arranged that when the pressure on hydraulic line 136 exceeds the pressure on hydraulic line 134, armature 142a is moved away from fixed contact 142c toward fixed contact 142b.

Conductors 148 and 150 are series connected through armature 140a, fixed contact 140c, armature 142a, and fixed contact 142c. It will be appreciated that the existence of a pressure differential between hydraulic lines 134 and 136 will open the series circuit between conductors 148 and 150. Such conductors form an interlock in association with the hoisting control apparatus (not shown) that raises and lowers cables 26 and 27. Consequently, the raising of cables 26 and 27 will be arrested when a severely unbalanced load condition is sensed, and raising will be resumed only after the unbalance is corrected by appropriate positioning of counterweight 98.

Differential pressure switches 144 and 146 are provided for effecting proper positioning of the counterweight. Differential pressure switch 144 includes a hydraulic element 144h that is connected to hydraulic lines 134 and 136 and that is adapted to operate an armature 144a when the pressure in hydraulic line 134 exceeds the pressure in hydraulic line 136. The armature is normally connected to a fixed contact 144c, but when such differential pressure is sensed the armature moves into connection with a fixed contact 144b. Differential pressure switch 146 includes a hydraulic element 146h that is connected to hydraulic lines 134 and 136 and which is adapted to operate an armature 146a from a normally closed contact 146c to a normally open contact 146b only when the pressure in hydraulic line 136 exceeds the pressure in hydraulic line 134. Thus, when the pressure in hydraulic line 134 exceeds the pressure in hydraulic line 136, a circuit is established by pressure switch 144 through armature 144a and fixed contact 144b; when pressure in hydraulic line 136 exceeds the pressure in hydraulic line 134, a circuit is established by pressure switch 146 through armature 146a and fixed contact 146b. A power source exemplified schematically in FIG. 10 at 152 is provided for connection through one or the other of such circuits. The circuit including armature 144a and fixed contact 144b is connected to a forward motor drive relay coil 154, and the circuit including armature 146a and fixed contact 146b is connected to a reverse motor drive relay coil 156. Operatively associated with forward motor drive relay coil 154 are normally closed contacts 154a and 154b, and normally open contact 154c and 154d. Operatively associated with reverse motor drive relay coil 156 are normally closed contacts 156a and 156b, and normally open contacts 156c and 156d. A power source 158 has a positive terminal connected to one side of contacts 154b and 154d, and a negative terminal connected to one side of contacts 154a and 154c. Counterweight drive motor 104 has one of its armature terminals connected to one side of contacts 156b and 156d, and the other of its armature terminals to one side of contacts 156a and 156c.

As will be appreciated from FIG. 10, when both relay coils 154 and 156 are in a deenergized or quiescent state, the circuit between power source 158 and counterweight drive motor 104 is open. When, however, either of the relays is energized in response to the presence of an unbalanced load condition, power source 158 is connected to counterweight 104. When relay 154 is activated in response to actuation of differential pressure switch 144 by an increase of hydraulic pressure in line 134 over that in line 136, a circuit from the positive terminal of power source 158 to the motor is established through contact 154d and contact 156b, and a circuit from the negative terminal of the power source to the motor is established through contacts 154c and 156a. This circuit condition causes counterweight 98 to be moved toward the right as viewed in FIG. 5. Contrariwise, when coil 156 is energized, a circuit from the positive terminal of power source 158 to the motor is established through contacts 154b and 156c, and from the negative terminal of the power source to the motor through contacts 154a and 156d. Such circuit condition causes the counterweight to be driven leftwardly as viewed in FIG. 5. Simultaneous actuation of relays 154 and 156, a condition that might arise through some instability in the hydraulic portions of the system, has no effect on the position of counterweight 98 because no circuit is established between power source 158 and motor 104 when both relays are energized.

Actuation of motor 104 as described above continues until the counterweight is positioned to compensate for the load unbalance and restore equal pressure in hydraulic lines 134 and 136. When equal pressure is restored, differential pressure switches 140, 142, 144, and 146 release with two consequences: counterweight drive motor 104 ceases operation and the interlock constituted by conductors 148 and 150 is reestablished to permit hoisting of the load.

In operation with a container vessel in which all container cells are elongate in a direction longitudinally of the vessel (transversely of structural members 12 and 14 and track rails 16), a conventional spreader frame 64 is attached directly to quick-change headblocks 54 and 56 as shown in FIG. 1. Undercarriages 32 and 36 are positioned at their outer or most widely spaced position, at which the space between cables 26 and 27 is sufficiently large to lift a container C in straight orientation even though the load in the container is unbalanced. This mode of operation of the apparatus of this invention demonstrates that the system is versatile.

In loading and unloading a vessel having transversely elongate container cells, it is necessary to bring cables 26 and 27 toward one another to clear cell walls 75f and 75a as seen in FIG. 2. For establishing such relatively close spacing between the cables, motor 38 is energized to bring undercarriages 32 and 36 to a position such that sheaves 28 and 30 will guide cables 26 and 27 along vertical paths that are spaced from one another by a distance less than the smaller dimension of the container cell. Additionally, the space between quick-change headblocks 54 and 56 is reduced by removing pins 73 and telescoping segments 68 into central frame 70. In the retracted position as can be seen in FIG. 2, the quick-change headblocks clear cell walls 75f and 75a. Because the connector elements on spreader frame 64 are fixed, quick-change blocks 54 and 56 are disengaged from such connector elements for permitting the inward movement of the headblocks. The connector elements on rotatable auxiliary frame 66 are spaced to engage headblocks 54 and 56 in their relatively closely spaced position and the auxiliary frame is attached to the headblocks when the headblocks are moved to the closely spaced position. Quick-change connector elements 84 on the lower element 78 of auxiliary frame 66 are joined to the connector elements 64c on spreader frame 64. By energization of motor 86, spreader frame 64 and a container C' engaged thereby can be positioned for handling containers in either longitudinally elongate cells or transversely elongate cells.

In lifting container C' in FIG. 2 into and out of a transversely elongate cell, the apparatus is sensitive to unbalanced loads within container C' because of the relatively close spacing between the vertical cable runs. If the load in the container is unbalanced, the tension in cable runs 26a and 26b is different from the tension in cable runs 27c and 27d. See FIG. 9. Such difference will be manifested at the outputs of hydraulic load cells 130 and 132. The difference in pressure arising from an unbalanced load is manifested while slack in the cables is being taken up and before the container actually moves. If it be assumed that the heaviest portion of the load in container C' is adjacent to load cell 130, the pressure in hydraulic fluid line 134 will exceed the pressure in hydraulic line 136 and differential pressure switches 140 and 144 will be actuated. Activation of differential pressure switch 140 interrupts the interlock circuits through conductors 148 and 150 which in turn interrupts power to the hoisting motors through conventional electrical circuitry, not shown. This system function is desirable to prevent abrasion between the container and the walls of a canted container cell, or to prevent, in extreme cases, binding or jamming of the container in the cell.

Actuation of pressure switch 144 moves armature 144a to fixed contact 144b so as to connect power source 152 to motor drive relay coil 154. Energization of coil 154 establishes a connection between power source 158 and counterweight drive motor 104, thereby driving the counterweight away from the relatively heavy side of the container and toward the relatively light side of the container. When the counterweight has moved to a position at which the load imbalance is compensated for, the tension in cables 26a, 26b, 27c, and 27d equalizes, and the fluid pressure in hydraulic lines 134 and 136 correspondingly equalizes. Pressure switches 140 and 144 consequently deactivate so that movement of counterweight 98 is terminated and the interlock circuit formed by conductors 148 and 150 is reestablished. Thus the container movement within the container cell can proceed.

It will be noted that the lower frame element 78, along which counterweight 98 is moved, rotates in unison with spreader frame 64 and any container engaged thereby. Consequently, balance, when once established for a given container, will not be upset by rotative movement of rotating mechanism 80.

Container C' can be deposited onto a pier surface or waiting railroad car or the like in any desired orientation. When the container is disengaged from spreader 64 the empty spreader will not be raised unless and until counterweight 98 is moved to the center of lower frame 78, because location of the counterweight 98 at an offcenter position will cause a pressure differential between lines 134 and 136 opposite from that assumed above.

One system designed according to the present invention employs a counterweight 98 weighing 41/2 tons; the length of side rails 100 available for supporting flanged wheels 102 is approximately 14 feet. Such system is satisfactory for handling containers having a length of 20 or more feet and for compensating for unbalanced load conditions in such containers.

Thus it will be seen that the present invention provides a system for loading and unloading containers from ships or like vessels that have longitudinally elongate cells, or transversely elongate cells, or a combination of both. Not only is the apparatus of the invention useful in newly constructed hoisting systems, but existing systems can be adapted to employ the novel apparatus without extensive modification.

Although one embodiment of the present invention has been shown and described, it will be obvious that other adaptations and modifications can be made without departing from the true spirit and scope of the invention.

Claims

We claim:

1. In combination with a generally rectangular spreader frame that includes thereon means for engaging a cargo container and means connected to the frame at at least two spaced-apart points thereon for raising and lowering the frame, the improvement that includes apparatus for counteracting such imbalance as may exist in a container engaged by the frame, said apparatus comprising a counterweight, means for mounting said counterweight on said spreader frame for movement along a path intermediate said spaced-apart points, means for comparing the force due to gravity at said two points, and means responsive to said force comparing means for moving said counterweight toward the one of said two points that has the least force applied thereto.

2. The invention of claim 1 in combination with first and second blocks attached to said frame, each said block including a yoke pivotally mounted therein, a sheave supported in each said yoke, said sheaves being positioned at said two spaced-apart points on said frame, means for limiting the degree of pivotal movement of said yokes so that the force on said limiting means is proportional to the tension on cables trained around said sheaves supported in said yokes, a hydraulic load cell mounted to each said limiting means, said load cells constituting an element of said force comparing means and having hydraulic outputs at a pressure proportional to the force applied thereon by said yokes, means including electrical contacts for closing said contacts in response to a pressure differential in said hydraulic outputs, and a motor connected in circuit with said contacts for driving said counterweight along said path.

3. The invention of claim 2 in combination with means including a normally closed contact for opening said contact when a differential pressure exists between said load cells, said normally closed contact constituting an interlock circuit which is opened when an unbalanced condition is sensed by the apparatus.

4. Container-hoisting apparatus for raising and lowering a container that has a relatively long length dimension and a relatively short width dimension into a vertically elongate open top stowage cell that has similar dimensions in a horizontal plane, said hoisting apparatus comprising a rectangular spreader frame having length and width dimensions approximately equal to the container and the cell, means on said spreader frame for engaging the container, means for hoisting the spreader frame, said hoisting means including at least two depending tension members attached to the spreader frame at at least two points that are spaced apart by a distance no greater than the width of the cell so that said spreader can be lowered into the cell without interference, said hoisting means further including first and second means for guiding said tension members into at least two depending runs at the upper end of said two depending tension members; and means for positioning said first and second means towards and away from one another to adjust the space between said depending tension members at their upper end to a distance that is no greater than the width of the cell, and a counterweight movable relative said frame for compensating for unbalanced loads in said container.

5. Container-hoisting apparatus for raising and lowering a container that has a relatively long length dimension and a relatively short width dimension into a vertically elongate open top stowage cell that has similar dimensions in a horizontal plane, said hoisting apparatus comprising a rectangular spreader frame having length and width dimensions approximately equal to the container and the cell, means on said spreader frame for engaging the container, means for hoisting the spreader frame, said hoisting means including at least two depending tension members attached to the spreader frame at at least two points that are spaced apart by a distance no greater than the width of the cell so that said spreader can be lowered into the cell without interference, and a counterweight movable relative said frame for compensating for unbalanced loads in said container, and means operably connected to at least a plurality of said depending tension members for detecting the difference in tension at said plurality of tension members and means responsive to said detected tension differences for positioning said counterweight.