[1]3 2 2 6 3 @ 9 6 5 United States Patent Office .,.nted August 2,1966 3,263,965 DUAL-SPEED, DUAL-LOAD HOIST ARRANGEMENT Robert D. Mutch, Baie d'Urfe, Quebec, Canada, assignor to Dominion Brid-,e Company, Limited, Montreal, Quebec, Cai3ada Filed Aug. 31, 1964, Ser. No. 393,116 13 Claims. (Cl. 254-144) This invention relates to hoist,arrangements for cranes, 10 and partioularly to an improved hoist arrangement for overhea d cranes in which dual-speed and dual-load characte ristics are obtained by using two hook blocks reeved into@ one hoist rope system anct operated by a single hoist drum with one motor and one set of hoist 15 ,gearing . In a well known dual-speed, dual-hoist for overhead cranes, a single hook block is separated into two parts, an upper part and a lower part which, contains the hook, with both parts having a common rope reeving there- 20 between . An arrangement of locks allows the block to be used as a main hoist in one iinit, with both upper ,and lower parts locked together, giving a ratio of hig-h load capacity and slow speed, and also to be used as an 25 - auxiliary hoist with the upper part automatically looked to the overhead -trolley frame and the lower part free to be used as the @auxiliary hoist. In the latter auxiliary hoist arrangement the rope reeving in the fixed upper part of the block becomes part of the static system and 30 thus the block is effectively re-reeved and the mechanical @advan tage altered to provide t-he lower part of the block only with a ratio of low load capacity and high speed. A disadvantage with this arrangemetit is that although t-he upper part of the block is automatically locked to the 35 4overhe ad trolley frame for!auxiliary hoist operation, the locks connecting the upper and lower parts together for main hoist opera-tion require manual operation. For example, to separate the upper and lower parts of the block it is necessary to lower t@he block to t@he floor as a unit, 40 for an operator to manually disenga@.-e the connecting locks, and then to raise both paiu once again, whereupon the upper part is automatically locked to the overhead trolley frame aild the lower part is free to be lowered and used separately as an auxiliary hoist. This opera- 45 tion not only requires additional manual labour, but also takes more time due to t-he extra operating sequence of lowerin g the block for manual disengagement of the upper ;and IoNver block parts. T'he important factors in determining the heights of 50 building s, where -overhead cranes of the well known type are installed, are the maximum required distance from floor to crane hook, plus the distance from crane hook to t,he uppermost portion of the crane mechanism, pl@us the require d clearance between the crane mechanism and the 55 building roof. Thus, -anodier disadvantage in the well known arrangement lies in the fact that the upper and lower parts of the block are nested together, one on top of the other, therefore adding to the distance from the crane hook to the uppermost pgrtion of the crane mech- C)o ,anism and consequently adding to the overall building costs. The present invention overcomes the disadvantages outlined for the well known :arr-angement by providing two separate hook blocks positioned substantially on the 65 same horizontal plane and reeved into one hoist rope system, one block serving as the main hoist and the other block serving as the auxiliary hoist. A single hoist drum oper@at es the common hoist rope system and is driven by a single motor and a single set of hoist gea-ring. The 70 separate hook iblocks are each supported by beams built into the overhead trolley frame and each block, in its 2 uppermost position, nests against the underside of its respective beam, t-hus reducing the distance from crane hook to the uppermost portion of the crane mech@anism by the height of one hook block, @as compared with the well known arrangement. A system of locks automatically clamps one of the hook blocks to the underside of its respective support beam and frees the other hook block for operation when the crane operator selects the appropriate control lever, an automatic s-afety feature of the lock system ensuring that neither hook block will be released for operation until the other hook block is securely clamped t-o the underside of its support beam. As the rope system is common to both main and auxiliary hoist blocks, the rope reeving in the block clamped tD the underside of its beam will effectively become part of the static portion of the rope system and so, by providing each hook block with a different rope reeving arrangement, two hoists, eac,h having a different mechanical advanta@.-e, may be operated as main and auxiliary hoists from a single hoist drum and driving app@aratus. The ratio of the n-umber -of rope sheaves in earh block determines the relative load capacities @of the blocks, the hoisting speeds being inversely proportional to the load capacities, assuming the load on the hoist rope to remain substantially @onstant. Thus a 100 ton main hook block with 10 sheaves (20 parts of rdpe) could be combined with a 10 ton single sheave (2 parts of rope), a 20 -ton two sheave (4 piarts of rope),,or a 40 ton fo-ur sheave (8 parts of rope) auxiliary hook block. Therefore, if the speed of the main !hook block is 5 feet per minute, the corresponding speeds of the auxiliary hook blocks in the above examples will be 5@ feet per minute, 25 feet per minute, or 121/2 feet per minute respectively, that is @the ptoduct of load X speed is constant for all combinations. In the following description, three executions of block sheave combinations are shc>wn, the preferred example being an 8:1 combination iand the -alternative executions being 6:1 and 3:1 combina@tions. These executions cover two conditions of operation, the 8: 1 and 6: 1 combinations catering for the situati(>n where the;auxiliary hoist has a greater distance tD. travel than the m-ain hoist, or where higher hoisting speeds are required, such as w-here the auxiliary @hoist is required to travel down to a basement level or down a sunken shaft, and t-he 3: 1 combination catering for general situations where main and auxiliary hoists travel similar distances @and where higher auxiliary hoist lo-ad capacity is more essential than higher auxiliary hoisting speeds. It is, therefore, @the main object Df -this invention to provide an improved hoist arr-angemet for cranes w in the characteristics of high load capacity, slow speed and low load capacity, high speed are both combined in a single hoist arrangement. Another object of this invention is to provide an improved hoist arrangement for overhead cranes in which dual-load, dual-speed cbaracteristies are obtained by prDviding two hook blocks of different mechanical advantage ratios, which are reeved into one hoist rope system and operated by a single hoist drum with one motor and one set 6f hoist gearing. Another object of t-his invention is to provide an improved hoist artangemen@t which may be converted to either high load capacity, slow speed or low load capacity, high speed operation without the need for any manual operations. Another object of this invention is to provide an improved hoist arrangement for overhead cranes in which dual-load, dual-speed characteristics are obtained by providing two hook blocks of different mechanical ad-
[2]3 vantage ratios and incorporating a sys-tem of clamps to secure one hook block in its upper most and inoperative position when the ot@,her hook block is in operation, thus ensuring that only one hook block is in operation at any one time. A further object of this invention is to provide an improved hoist arrangement wherein the characteristics of dual-load and dual-speed are obtained without increasing the overall height of the apparatus. T-hese and other objects and ad@vant@ages of this invention will be apparent by reference to the following detailed specification and dra-wings in which: ,FIG. I is a schematic represent-a-tion of the 6:1 execution of this invention; IFIG. 2 is a schematic representation of the 3:1 execution of this invention; FIG. 3 is a plan view of the preferred 8: 1 execution of this invention, w-ith the hoist ropes omitted for clarity; FIG. 4 is a side elevation looking in the direction of arrow 4 in FIG. 3; FIG. 5 is an end elevation looking in the direetion of arrow 5 in FIG. 3; F,IG. 6 is a plan view of the operating linkage mechanism for the m@ain and auxiliary hoist clamps, taken approximately at 6-6 i@n FIG. 4 and omitting all other details for clarity; FIG. 7 is a section taken on 7-7 in FIG. 6 and shows further details of the operating linkage mechanism for the hoist clamps; FIG. 8 is a section taken on 8-8 in FIG. 6, showinfurther details of the linkage mechanism and a,-ain omitting all other details for clarity; ,FIG. 9 is a sectioia taken on 9-9 in FIG. 8; FIG. 10 is a section taken on 10-10 in FIG. 8; FIG. 11 is a section taken on 11-11 in F@IG. 8; FIG. 12 is an enlarged detail taken at 12 in FIG. 11; and FIG. 13 is an enlarged detail taken in the direction of arrow 1)3 in FIG. 12. Re-fer now to the figures, wherein like numerals repre. se,nt like parts throughout. All executions of th@is invention are assembled on a crane trolley frame. l@n the usual application of this invention the crane trolley frame will be mounted on rollers to travel transversely across the building width on transverse bridge girders, the bridge girders being mounted at each end on common end trucks which are mounted on rollers to travel lengthwise along the building on girders positioned lengthwise along each side of the building and close to the roof. Thus the trolley may be positioned, over any area of the building. F,IG. I shows a schematic representation of the 6:1 ratio execution of this invention, the main hook block having t@welve parts of rope and the auxiliary hook ,Plock having two parts of rope, providiing relatively low load capacity and high speed auxiliary hoist characteristics. In this execution hoist drtim 21, which has left and right-hand rope grooving (not shown), is rotatably mounted on the crane trolley frame (not shown) and suitably driven. Hoist rope 22 is anchored at each end near flanges 23 on hoist drum 21 and travels around hoist drum 21 in the lef-t and right-hand grooves to the two inner sheaves of the main hook block sheaves 24 in mai-n hook block 25. Hoist rope 22 is then reeved around the six rnain hook block sheaves 24 and the four fixed centre head sheaves 26, then travels upwards and around the fixed cent-re guide sheaves 27 and 28 and then the rope loop passes down and around the auxiliary hook block sheave 29 in aux-iliary hook blook 30. Auxiliary hook block sheave 29 acts as an equalizer when the main hook block 25 is in use and as its own equalizer when the auxiliary hook block 30 is in use. An equalizer bar may be substituted for sheave 29. Head sheaves 26 are journalled on common fixed shaft 3,263,965 4 31 and are supported on m-ain hook block beam 32 which is built into the trolley frame. Main hook block sheaves 24 are journ@alled on common shaft 33 to which double main hook 34 is attached. 5 Therefore, main hook block sheaves 24 travel up and down with main hook 34, the upward travel being lim-ited by main stop fr@ame 35 which comes to rest contacting the underside of main hook bloek beam 32. Guide sheaves 27. and 28 are joumalled on fixed 10 centres and supported by the trolley frame. Auxiliary sheave 29 is joumalled in auxiliary hook block frame 36 to which auxiliary hook 37 is attached. Therefore, a@@iliary sheave 29 travels up and down with auxiliary hook 37, the upward travel being limited 15 by auxiliary stop fra@me 38 which comes to rest contacting the underside of auxiliary beam 39, which is also built into the trolley frame. Stop frames 35 and 38 are integral with the hook block frames and act as stiffeners to withstand the rope 20 loads when the hook blocks are in contact with the undersides of their respective support beams. Clamping devices 40 and 41 are attached to the lower surfaces of main beani, 32 and auxiliary beam 39 respectively. The clamps are provided with tapered faces 25 arranged to grip corresponding tapered sur@faces on the hook blocks so that the clamps, when engaged, will force the hook blooks upwards against stop surfaces on the undersides of the support beams. Clampin.@ force is -Irovided by a !ever system with an o-ver-centre 30 counterweight, the position of which is controlled by a reversible electric motor with liniit switches to de-energize the motor as the counterweight approaches either end of its travel. The clamps are interlocked so that when one set is engaged, the other set is open. A 35 further interlock ensures t-hat neither set of clamps can be operated until both hook blocks are in their highest positions. This further interlock is operated in conjunction with the overhdisting Eniit switch. ioverhoisting protection is provided by a single limit 40 switch which cuts out the main motor in the hoist direction whenever either hook block reaches its uppermost position. The clanip motor circuit is then completed, allowing the clamps to be operated. in operation, one hook block is always cla@mped in 45 its uppermost position. This is carried out before the crane is, put into service and, thereafter, only one hook block can be operated at a-ny time. During the crane assembly both main hook block 25 and auxiliary hook block 30 will be on the ground. The hoist drum 21 5 0 is then rotated and the auxiliary hook block 30 will rise first and travel upwards to stop and be automatically clamped in its uppermost posi-tion. The crane control lever is then moved to "main" position and with continued hoist drum rotation t-he main hook block 25 55 will. rise to its uppermost position. Thereafter, moveMejat of the crane con@trol lever to either "maiw' or ,auxiliary" positions will release the respective set of clamps and free the hook block for operation as follows: With m@ain hook bloek 25 free and on the ground, 60 the control lever i@n "maiif' pos-ition and the auxiliary block 30 clamped in its upper@most position, rotation 6f hoist drum 21 in the hoist direction will cause the rope 22 to exert an upward load on the auxieary block 30 aga-inst the underside of its support beam 39 and 65 start to raise the main hook block 25, with or without a load. The rope system, now being taut but free to equalize around the sheave 29 of the auxieary hook block, will now raise the main hook block 25 as required. Reversal of hoist drum 21 will slacken the 70 rope system, thus removing the upward rope load on the aux-iliary block 30, causing the weight of the auoiary blidck to be supported bY its clamps 41 and allowing the main hook block 25 to be lowered. With the main hook block 25 in its uppermost position, 75 movement of the control lever to 11 atixiliary" position
[3]9 will engage the main hook block clamps 40 and reilease the auxiliary hook block clamps 41. The auxiliary hook block 30 is then free to b.- lowered and raised with or without a load, the main hook block 25 being pulled up against its support beain 32, by clamps 40, while the rope 22 runs freely through the main block sheaves 24 and head sheaves 26. FIG. 2 shows a schematic representation of the 3:1 ratio execution of this invention, the main hook block 25 having twelve parts of rope and the auxi-Eary hook block 30 having four parts of rope, providing relatively high load capacity and slow speed auxiliary hoist characteristics. This execution is basically the same as the execution shown in FIG. I except that there are two additional guide sheaves 42, two equalizer sheaves 43, the auxiliary hook block 30 has two auxiliary sheaves 29 and the hoist rope 22 is reeved around the sheaves as follows: Hoist rope 22 is anchored at each end near flanges 23 on hoist drum 21 and travels around hoist drum 211 in the left and right-hand grooves to the two inner sheaves of the main hook block sheaves 24 and then up and around the two guide sheaves 27, over the two guide sheaves 28 and down and around the two auxiliary sheaves 29. Hoist rope 22 then travels up and around the two guide sheaves 42 to the two inner head sheaves 26 and then is reeved around head sheaves 26 and the remainin.- main hook block sheaves 24, leaving the outer sheaves 24 to travel up and loop around equalizer sheaves 43 to complete the reeving. Equalizer sheaves 43 act as equalizers for both the main hook block 25 and the auxiliary hook block 30. By using a modified reeving a single equalizer sheave can be used in place of the two sheaves 43 shown in FIG. 2. The operation of this execution is the same as for the 6: 1 ratio execution shown in FIG. 1. Refer now to FIGS. 3, 4 and 5 which show the preferred execution of this invention and in which hoist rope 22 is omitted for clarity. Crane trolley frame 44 is mounted for movement transversely across the building on rollers 45, which roll on tracks 46 mounted on transverse bridge girders 47. Bridge girders 47 are mounted at each end on common end trucks (not shown) which are also mounted on rollers to traverse -the building lengthnvise on girders positioned lengthwise along ea:ch side of the building and close to the roof. Rollers 45 are coupled together by shafts 48 which are reversably rotated by driving motor 49 through gearbox 50. Hoist drum 21 is rotatably mounted in bearings 51 mounted on crane trolley frame 44, and is reversably rotated by driving motor 52 through brake 53, main gearbox 54 (shown in section in FIG. 3), driving shaft 55, pinion gear 56 and main gear 57. Main hook block 25 is positioned under main hook block supoprt beam 32 which is built integral with crane trolley frame 44. Eight main hook block rope sheaves 24 are rotatably mounted on concentric fixed shafts which are fixed in the frame of main hook block 25. Main hook 34 is mounted on main hook block 25 by a pin 59 fixed in a clevis 60, which is rotatably mounted in main hook block 25. Main clamp arms 40 are pivotally mounted in bearings 61 mounted on crane trolley frame 44, and are positioned such that when in the vertical position, as shown in FIG. 4, clamp jaws 62 engage main clamp ledges 63, fixed to main hook block 25, to clamp main hook block 25 to the underside of its suppor-t beam 32. Main clamp ledges 63 are positioned to present a sloping surface to enable clamp jaws 62 to pull main hook block 25 upwards against the underside of its support bearn 32. Six head rope sheaves 26 are rotatably mounted on shafts which are fixed between brackets 64 and mounted on the upper surface of crane trolley frame 44. Sheaves 26 are positioned directly above main hook block sheaves 3,263,966 6 24, the six sheaves 26 being positioned above the six outer spaces between main hook block sheaves 24. Auxiliary hook block 30 is positioned under auxi@liary hook block support beam 39, which is built integral with .5 crane trolley frame 44. Auxiliary rope sheave 29 is rotatably mounted on shaft 65, which is fixed in auxiliary hook block 30. Auxiliary clamps 41 are pivotally mounted to clamp auxiliary hook block 30 in its uppermost position by rotating from the 10 open position shown in FIG. 5, to the engaged position, as shown in broken line, where auxiliaryclamps 41 contact the auxiliary clamp ledges 66. Two guide rope sheaves 27 are rotatably joumalled between support brackets 67 and mounted separately on 15 the upper surf ace of crane trolley frame 44 and on the same horizontal plane as the six head rope sheaves 26. Cut-outs 68 and 69 are provided through the upper surface of crane trolley frame 44 for the passage of hoist rope 22 between head sheaves 26, main hook block 20 sheaves 24 and guide sheaves 27, and cut-outs 70 and 71 are provided for the passage of hoist rope 22 between guide sheaves 27 and auxiliary hook block sheave 29. The reeving of hoist rope 22 around the preferred execution of this invention is simi-lar to the reeving shown 25 in FIG. 1, but simplified as follows: Hoist rope 22 is anchored at each end to hoist drum 21 and travels around lefthand and right-hand grooves 72 and 73 respectively (shown in broken iline in FIG. 3), leaving hoist drum 21 and passing down to the two inner 30 sheaves of the eight main hook block sheaves 24. Hoist rope 22 is then reeved around the eight sheaves 24 and the sheaves 26, then travels upwards and around the two guide sheaves 27. The loop of hoist rope 22 then passes down and around sheave 29, which acts as an equalizer 35 sheave. When one hook block is clamped to the underside of its support beam and the other hook block is raised and trips the overhoisting limit switch to cut out the hoist drum motor there may, in rare instances, be a slight time lag 40 before the hoist motor actually stops. This is because the hoist motor is braked frictionally and there is the.@possibility that moisture on the brake drum may slightly retard the braking effect. To prevent any excessive strain on hoist rope 22, if this circumstance should occur, cush45 ioning springs have been incorporated into the auxiliary hook stop-plate 74 located close to the underside of support beam 39. Reference to FIGS. 3, 5, 6 and 9 show stop-plate 74 with shafts 75 extending upwardly from each corner and projecting into individual spring cham50 bers 76. Collars 77 are fixed to each shaft 75 and positioned within each spring chamber 76 to compress springs 78 when stop-plate 74 is forced upwardly. Thus, any overload on hoist rope 22 will be relieved by the cushioning springs 78, which are designed to be 55 compressed when a predetermined overload is imposed upon them. Refer now to FIGS. 6 to 13 which show details of the operating linkage mechanism for the main and auxiliary hoist clamps and in which all details not pertaining to the 6o linkage mechanism have been omitted for clarity. Reversible worm-drive motor reducer 79 is started when the crane control lever is moved to either "main" or "auxiliary" hoist position by the crane operator, the direction of rotation of motor 79 depending upon whether 65 main or auxiliary hoist is selected. The worm-drive of motor 79 is operably connected to move one end of arm 80 horizontally, the other end of arm 80 being positioned in slot 81 in counterweight 82. Counterweight 82 is non-rotatably mounted on cross-shaft 70 83, such that operation of motor 79 will result in rotation of cross-shaft 83, which is joumalled in bearings 84 mounted on !crane trolley frame 44. Lever 85 is nonrotatably mounted on one end of cross-shaft 83 and is pivotally connected to one end of link 86, the other end 75 of link 86 being pivotally connected to one arm of bell-
[4]7 crank 87. The other arin of bell-crank 87. is.pivotally connected to one end of link 88, the other end of link 88 being pivotally connected to the outer end of lever 89 which is pivotally mounted at 89a on crane trolley frame 44. The inner ends of links 90 and 91 are pivotally connected to lever 89 at positions equi-distant from the pivot point 89a, the other ends of links 90 and 91 being pivotally attached to the outer main hook block clamp arms 40. Inner and outer clamp arms 40 are non-rotatably mounted in pairs on cross-shafts 92 and connected in pairs, at the lower ends thereof, by clamp jaws 62. Crossshafts 92 are joumalled in bearings 61, mounted on the upper surface of crane trolley frame 44. Also, non-rotatably mounted on the other end of crossshaft 83 is lever 93, wh@'.ch is connected to lever 94 through link mecbanism 95. Reference to FIGS. 1 1 to 13 show details of link mechanism 95 and specifically spherical joints 96, which permit rotation of cross-shaft 83 to produce rotation of cross-shaft 97,. through levers 93 and 94 and link mechanism 95. Cross-shaft 97 is journalled in bearings 98, mounted on crane trolley frame 44. A first pair of auxiliary clamps 41 are non-rotatably mounted on the end of cross-shaft 97 opposite to the end on which lever 94 isconnected, and a second pair of opposed auxiliary clamps 41 are non-rotatably mounted on cross-shaft 99, which is journalled in bearin.-s 100 also mounted on crane trolley frame 44. Particular reference to FIG. 10 will show lever 101 non-rotatably mounted oncross-shaft 97 and lever 102 inon-rotatably mounted on cross-shaft 99, with links 103 interconnecting the ends thereof. Thus rotation of cross-shaft 97 will cause the first pair of auxiliary claraps 41 to rotate in the same direction of rotation and the second pair of auxiliary clamps 41, through levers 101 and 102 and links 103, to rotate in the opposite direction of rotation. The first and second pairs of aiixiliary clamps 4]L arepositioned to grip auxiliary clamp ledges 66 of auxiliary hook blcfck 30 when rotated to the engaged position (as shown in broken line in FIGS. 5 and 9), and to be disengaged from auxiliary clamp ledges 66 when in the open position (as shown in FIGS. 5 and 9). A counterweight 104 is non-rotatably mounted on crossshaft 97 and positioned to be in a balanced st-,tte when both pairs of auxiliary clamps 41 are in the open position, and to rotate with cross-shaft 97 to exert a bias force, to assist the clamping force, when auxiliary clamps 41 are in the engaged position. Also mounted on cross-shaft 83 is a cbain sprocket 105 which drives a smaller chain sprocket 106 by means of chain 107. Chain sprocket 106 drives a 2-way ratchet assembly 108 which, in @combination with solenoid operated pawls 109 and 110, provides one-way directional n-iovement for the operating linkage mechanism, see FIG. 4. Pawls 109 and 110 are alternatively operated when the crane control lever is moved to either "main" or "auxiliary" hoist positions, to permit rotation of crossshaft 83 in the required direction only and to lock the clamps in the engaged positions. The operating sequence of the preferred execution of this invention is as follows: Assume that main hook block 25 is latched and auxiliary hook block 30 is in the latching zone. To put main hook bl6ck 25 into operation the crane control lever is placed in "main" hoist position. Reversible worm-drive motor reducer 79 automatically starts and its worm-drive rotates to move arm 80 which lifts counterweight 82 and rotates cross-shaft 83 in an anti-clockwise direction. Anti-clockwise rotation of cross-shaft 83 produces anticlockwise rotation of bell-crank 87 and, through link 88, a corresponding anti-clockwise rotation of lever 89. Anticlockwise rotatiori of lever 89, through links 90 and 911, causes main hook block @clamp arms 40 to be rotated outwardly, thus releasing clamp jaws 62 from main clamp ledges 63 and freeing the main hook block 25 for operation. In this position counterweight 82 bas passed over the vertical position and is now exerting a downward bias 3,263,965 force to assist in maintaining clam arms 40 in the open position. Anti-clockwise rotation of cross-shaft 83. also simultaneously rotates lever 93 in an anti-cloekwise direction, thus lifting link mechanism 95 and rotating cross-shaft 97 in a clockwise direction, as shown in FIG. II. Clockwise rotation ofcross-shaft 97 causes counter-weight 104 to be moved away from its vertical balanced position to exert a bias force urging cross-shaft 97 to further clock10 wise rotation. In FIGS. 9 and 10 it is seen that the lifting of link mechanism 95 produces an anti-clockwise rotat,.on of cross-shaft 97 and, through links 103, a clockwise rotation of cross-shaft 99. Specific reference to FIG. 9 shows that this causes auxiliary clamps 41 to be securely 15 clamped to auxiliary clamp ledges 66, with counterweight 104 acting to retain auxiliary clarrps 41 in the engaged p,osition. Thus, releasing main hook block 25 for operation automatically clamps auxiliary hook block 30 in the non9,0 operative position, and rotation of hoist drum 21 in the required direction of rotation will now permit main hook block 25 to be lowered for operation. In the same manner, movement of the crane control lever to "auxiliary" hoist position will reverse the above 25 procedure, releasing atixiliary hook block 30 and securely clamping main hook block 25. In this case counterweight 82 will act to exert a bias force to assist the clamping force holding clamping arms 40 in their engaged positions. 30 A further execution of this invention, not illustrated, 'caters for a situation requiring an auxiliary hoist with a relatively high load capacity and where hoist speed is not of major importance. This further execution is similar to the execution shown in FIG. 2, except that auxiliary 35 hook block 30 has four auxiliary sheaves 29 and two additional head sheaves are mounted on the crane trolley franic above auxiliary sheaves 29 and the hoist rope 22, after reeving around auxiliary sheaves 29 and the two additional head sheaves, passes to the main head sheaves 40 26. Guide sheaves 27 and 28 may be used or omitted, as determined by the physical requirements of the hoist installation. What I
