US3845865A

US3845865A - Marine cargo handling crane

Info

Publication number: US3845865A
Application number: US00232644A
Authority: US
Inventors: G Campbell; T Kasuga
Original assignee: Algoship International Ltd
Current assignee: Algoship International Ltd
Priority date: 1968-12-27
Filing date: 1972-03-07
Publication date: 1974-11-05
Anticipated expiration: 1991-11-05

Abstract

A crane particularly for assembly on the deck of a vessel, including a post having a fixed first section and a second section rotatable on the first section and a pair of jib booms pivotally mounted on the post for rotation in a horizontal plane and means for topping the boom, and a traversing trolley on each jib boom from which the cargo hoisting hook is suspended, and independent means for slewing and topping each jib boom and for raising and lowering the cargo hoisting hook in any traversed location of the trolley on its respective jib boom.

Description

United States Patent [1 Campbell et al.

MARINE CARGO HANDLING CRANE Inventors: George Thomas Richardson Campbell; Toshishige Kasuga, both of Tokyo, Japan Algoship International Limited, Nassau, Bahamas Filed: Mar. 7, 1972 Appl. No.: 232,644

Related U.S. Application Data Division of Ser. No. 883,002, Dec. 8, 1969, Pat. No. 3,658,787.

Assignee:

Foreign Application Priority Data Dec. 27, 1968 Japan 43-96323 Apr. 10, 1969 Japan..; i 44-27949 Aug.26, 1969 Japan 44-81151 References Cited UNITED STATES PATENTS 6/1904, Van Driessche 212/47 1 NOV. 5, 1974 2,370,661 3/1945 Hayes i 212/145 2,867,333 1/1959 De Shano 212/56 3,365,077 1/1968 MOrk i 212/57 3,486,635 12/1969 Thomson 212/3 3,610,432 10/1971 Kuribaynshi 212/3 FOREIGN PATENTS OR APPLICATIONS 1,120,050 7/1968 Great Britain 212/3 212,660 5/1968 U.S.S.R 212/47 Primary Examiner-Evon C. Blunk Assistant Examiner.leffrey V. Nase Attorney, Agent, or Firm-Fetherstonhaugh & Co.

[57] ABSTRACT A crane particularly for assembly on the deck of a vessel, including a post having a fixed first section and a second section rotatable on the first section and a pair of jib booms pivotally mounted on the post for rotation in a horizontal plane and means for topping the boom, and a traversing trolley on each jib boom from which the cargo hoisting hook is suspended, and independent means for slewing and topping each jib boom and for raising and lowering the cargo hoisting hook in any traversed location of the trolley on its respective jib boom. r

9 Claims, 16 Drawing Figures- MARINE CARGO HANDLING CRANE This is a division, of application Ser. No. 883,002

filed Dec. 8, I969 now U.S. Pat. No. 3,658,787.

cargo hook, to a desirable location, was poor as it is done by a combination of operations, i.e., topping, slewing and hoisting. In the topping operation, as the angle of the boom is increased, the center of gravity of the boom and the cargo will rise resulting in greater power requirements.

In some cases spotting ability was reduced to such an extent that the topping operation was almost impossible. a

b. In the Burtoning system, lifting and slewing are effected with two derricks held in fixed position and two whips. The ends of the whips are fastened to a single cargo hook. Because of the complexity and rigidity of the system spotting ability is extremely reduced. Deck Crane r c. The length of hoisting rope between a cargo hook and jib top sheaves varies greatly with the slewing radius. At the minimum slewing radius position, the length of rope can be so long that swaying motion can hinder cargo operation to great extent. (I. When a cargo has to be luffed in-board toward the heel of the jib, jib angleshas tobe increased and this can be a very difficult operation when the cargo load is great. e. In general, the cost is higher than other equipment.

The present invention has for its object toprovide a marine cargo handling equipment which has an im proved cargo handling efficiency. The invention incorporates a topping slewing and traversing trolley system. The topping and slewing apparatus (goose-neck) is located on a pair of booms in the mid-section on a rotatable post section mounted on a. fixed post section erected on the deck. The post has a fixed first section and a rotatable second section rotatable on the first section, the second section including a pair of booms, each of which includes a traversing trolley with a cargo hook suspended therefrom for travel therealong.

Reference is made to the accompanying drawings in which:

FIG. 1 is a general arrangement of one form of cargo handling crane according to the present invention,

I SYSTEM A.

FIG. 2 is a plan of the crane system shown in FIG. 1.

FIG. 3 illustrates the relation between traversing trolley rope and cargo hook hoisting rope in the system shown in FIGS. 1 and 2.

FIG. 4 illustrates the relation between trolley and boom of the system shown in FIGS. 1 and 2.

FIG. 5 is a schematic view illustrating the slewing system shown in FIGS. 1 and 2.

FIG. 6 is a general arrangement of a modified crane system B.

FIG. 7 is an enlarged'vertical section of the gooseneck arrangement shown in FIG. 6.

FIG. 8 is a general arrangement of a modified crane system C.

FIG. 9 is a plan of the crane system C" shown in FIG. 8.

FIG. 10 is a general arrangement of a modified crane system D."

FIG. 11 is an enlarged side elevation of the goose neck arrangement shown in FIG. 10.

FIG. 12 is a horizontal section taken on the line C on FIG. 11.

FIG. 13 is a schematic view illustrating a modified crane system H.

FIG. 14 is a schematic view of the hydraulic system for the cylinders in FIG. 13.

FIG. 15 is a schematic view illustrating a modified crane system I.

FIG. 16 is a plan view showing the slewing operations of the crane in FIG. 15.

As shown on FIGS. 1 and 2, in system A a fixed post (9) is erected vertically on the deck above the longitudinal centre of a ship. A boom supporting structure (gooseneck) (30) is located in the mid-position of the post (9). On the I section main structure of the boom (1), a boom outrigger (l8) and a strength member (19) are constructed to form a diamond shaped parallelo gram. On the gooseneck (30), for slewing purpose a vertical spindle (l3) and for topping purpose a horizontal pin (12) are fitted. In order to fix the boom (1) in horizontal position or to top it, sheaves (17) (17') and (17") and topping winch (14) are installed as shown. Bypulling in the rope (8), the boom can be topped or lowered. For slewing purpose an outrigger (31) is built on the fixed post (9). Sheaves(22) (22) (21) and (21) are arranged as shown on FIG. 5. One end of each of the ropes (20) and (20') is anchored on to the outrigger (31) and another end is lead to the slewing winch (23) via sheaves (21) (22) and (21') (22) respectively. However ropes (20) and (20) are reeled onto the split drum of slewing winch- (23) in such a way that they reel in an opposite direction. To

pick up any slack inthe rope, an adjusting weight (27) is suspended by rope (20'). Depending on the rotation of drum of the winch (23), the boom can be slewed in or outboard along the boom (1). The cargo hook is suspended by rope (6) which has one end'fixed to the end of the I section boom and another end lead to the drum of hoisting winch (15), via sheaves (4) (4') (5) and (11) as shownon FIGS. 1 and 3.'Sheaves (4) and 3 operating the hoisting winch while trolley is traversing. In this system cargo handling is mainly done by combination of slewing, hoisting and traversing of trolley (2).

As shown on FIG. 5, slewing operation can be illustrated as follows:

An operation of slewing winch (23) in the direction of arrow will reel in rope and pay out rope (20), this will slew the boom (1) to the right around the spindle (13). In this system, maximum slewing angle of the boom is about 150.

As shown on FIG. 3, traversing mechanism can be illustrated as follows:

An operation of traversing winch (16) in the direction of arrow will reel in rope (7) and payout rope (7) rope (7) will pull the trolley (2) along the boom (1). The traversing of trolley will in no way alter the height of cargo hook, as the relation between sheaves (4) (4') and (5) is not altered.

As it is known that the centre of gravity of cargo handling equipment cannot rise too high above the deck, this will immediately put a limit on the vertical position of the gooseneck. If a circumstance arises where the cargo height requirement for handling is about the height obtained with the boom in horizontal position, it is necessary to top the boom. The trolley is designed so that it may be locked into position at the tip of the boom by a shackle or any other appropriate means. This enables the cargo to be luffed by reeling in rope (8) with the topping winch (14).

In order to stow the boom when not in use, just simply pay out rope (8) by the topping winch (l4) and the boom can be lowered onto the deck with the heel supported by pin (12). This automatically lowers the center of gravity of the equipment and increases the stability of the ship.

The advantages accrued from the invention can be listed as follows:

a. Traversing of cargo is simple and smooth operation with reduced power requirements. With comparison to the conventional system, the spotting ability is increased considerably. Less power will mean less cost.

b. Unlike conventional equipment, the cable length between a cargo hook and boom tip sheaves is not unnecessarily long and this will prevent cargo from swaying excessively.

c. The problem ofjib lifting is eliminated while luffing the cargo inboard toward the heel of the jib.

d. Because of its simple operation, cost can be reduced considerably and yet it will be much more efficient. Its design lends itself readily to hatchcover handling equipment.

The system so far described consists of a fixed post (9) with an outrigger (31) and wire ropes. However slewing of the boom can be done by many other mechamsms.

As shown on FIGS. 6 and 7, in system B other mechanism will be described below:

The hoisting, topping and traversing operation in this system are exactly the same as previous system. However the topping sheave (17) is fixed to an outrigger (54) as shown on FIG. 6. A long protruding gooseneck (30) is located in the mid-position of the fixed post (9). This gooseneck (30) incorporates a vertical spindle (40) for center of slewing and at the bottom of this spindle (40) is a cross-member (43) which in turn has two horizontal pins (12) attached under it. The pins (12) are for topping purpose. A drive motor (41) with a brake (46) on the top and a reduction gear (45) with extending pinion (44) on the bottom is mounted on the gooseneck (30). Power supplied by the drive motor (42) is transmitted to a gear (42) from the pinion 44) and this swivels the boom (1) around the spindle (40) which is located on the ships center.

In this system, maximum slewing angle covered is approximately 300 and this is due to the elimination of an outrigger (31). A conventional derrick system can serve one hold aft or forward of its post, whereas the system described above can handle cargo in any direction except an area of approximately 50 on the side where the post (9) is located. In other words, this one crane can handle almost two holds. In this invention as the trolley is capable of traversing near to the slewing center, spotting ability is considerably higher. Navigation from the bridge is made easier as the fixed post is located off-center of ship and it provides clear visibility. The gear arrangement described above can be easily replaced by wire rope arrangement.

As shown on FIGS. 8 and 9, in system C in order to cover even a larger handling area, swivelling support (54) (for instance incorporating roller) is mounted on top of a fixed post which is erected on the centerline of a ship.

At the bottom part of this fixed post, a reduction gear unit (55) is installed. This reduction gear unit (55) is geared to a turning table (58) which rotates the swivelling post (51) on the swivelling support (54). Guide rollers (53) are made to follow the outer circumference of the fixed post (52) while swivelling post (51) is rotating. A drive-motor (57) with a built in brake (56) is mounted on the turn table (58). The pinion (59) of the drive-motor (57) meshes with the gear (55) of the fixed post (52) and rotate the swivelling post (51). Two booms of the type shown on FIGS. 6 and 7 are mounted on a swivelling post (51). The construction of the booms (l) and its relation to the swivelling post (51) are identical to the previous system described. The relations between trolley (2), cargo hook (5) and topping lift (8) are identical to previous system except that the winches (14) (15) and (16) are mounted on the turn table (58) so that their relative positions with the swivelling post (51) do not alter. With this arrangement each boom (1) (1) can cover approximately 180 slewing area. With two booms operating simultaneously, the crane can cover almost 360 working area.

As shown on FIGS. 10, 11 and 12 in system D for easy stowing purpose of the boom, a T section guide (60) is welded vertically onto the fixed post (9) along its length up to mid-position of the post. An inverted V-shaped top guide (61) is built on the top of the T" section guide (60). Pin holes (62) (62) and (62") are made as shown on FIG. 12. Sliding gooseneck guide (63) has a vertical spindle (64) and on the top part of this spindle, a horizontal pin (12) which supports the boom (1) is incorporated. One end of the gooseneck hoisting rope (65) is anchored to the lower end of the boom (1) and another end is lead to a topping unit (14) via sheave as shown on FIG. 10. To set up the system for cargo handling, one reels in rope (65) by topping unit (58) to lift the boom (1) into position. By utilizing the ram (67) built on to the bracket (69) locking pin (66) is pushed through holes (62) (62) and (62") and this locks the sliding gooseneck guide (63) into fixed position. Once the gooseneck is in position, the boom (1) can be lifted to a fixed horizontal position by means of rope (8) and topping winch (14). Any one of those slewing methods mentioned before can be employed in this system. To stow the boom (1) on the deck, use the ram (67) and pull out the locking pin (66), this enables the gooseneck guide (63) to slide along the T section guide. Byoperating the topping unit (68) and topping winch (14) simultaneously, the boom can be lowered down onto the deck and can be stowed. This lowers the center of gravity of the equipment and consequently contributes to the stability of the ship.

With the increase in size of a ship recently, especially beam-wise, an increase in slewing radius in order to reach outboard has become a problem.

As shown on FIGS. 13 and 14 in system H for the purpose of easy slewing of the boom, a fixed post (9) is erected vertically on the deck and has an outrigger (31).A boom supporting structure (gooseneck) (30) is located in the mid-position of the post (9). On the gooseneck (30), for slewing purposes a vertical spindle (l3) and for topping purposes of the boom (ll) horizontal pins (l2) are fitted. Sheaves (22) (22') are suspended from an outrigger (31). Sheaves (87) (87) are fitted on post (9) and also hydraulic cylinders (90)( 90') are fitted at the side of post (9), sheaves (88) (88') are equipped on the end of the cylinders rods (89) (89'). One end of the ropes and (20') are anchored on to the boom outrigger (18) and another end is fitted on post(9) via sheaves (22) (22'), (87) (87') and (88) (88) after passing a couple of folds between sheaves (88) (88) and (87) (87'). This arrangement reduces the pistons stroke on the cylinders (90) (90'). (8) in FIG. 20 indicates topping rope.

FIG. 14 illustrates a hydraulic circuit for slewing cylinders (90) (90), pressurized oil flows from the oil pump (93) to the hydraulic cylinders (90) (90') via the manually operated changing valve (91) and the throttle check valves (92) (92). Therefore by operation of the hydraulic cylinders (90) (90) which pulls ropes (20) (20) via the sheaves (88) (88') fitted on the cylinder rods (89) (89) and the boom (1) can be slewed accordingly. In FIG. 20, ifthe pressurized oil is led to the cylinder (90) which slews the boom (1) to direction 0, the cylinder rod (89) is pulled by rope (20) which is anchored at the boom outrigger (18) according to the booms slewing motion.

Oil in the cylinder (90) flows to the oil tank (94) passing through the throttle valve (92'). If the pressurized oil is .led to the cylinder (90) which slews the boom 1) to direction p, oil in the cylinder (90) flows to the oil tank (94) through the throttle valve (92). i

In FIG. 14, (95) indicates a pressure adjusting valve, (93) indicates an oil pump, (96) indicates an electric motor for an oil pump (93), (97) indicates a check valve.

Whenthe boom (1) is slewed using hydraulic cylinders (90) (90') the boom (1) is slewing in circular motion around the revolving center of the boom (1) and sheaves (22) (22') are not situated at the revolvingv vided a length adjusting device for rope on the starboard side and the port side.

In system H, when the boom (1) is operating by ropes (2(1) (20 and hydraulic cylinders (90) (90) each stroke of the cylinder rods can be separately moved at the different proportion, therefore ropes (20) (20') do not slacken during slewing movement of the boom (1). When the pressurized oil flow to the hydraulic cylinders (90) or (90') which pull ropes (20) or (20') and slew the boom in the direction of O or P, oil flows from the pulled hydraulic cylinders (90') or (90) to the oil tank (94) through the throttle check valves (92') upper deck due to the boom is operated by two hydraucenter of the boom (1), therefore payout length of rope (92) which restrain the oil flow and hydraulic pressures occur at the pulled hydraulic cylinder or (90) when boom (1) is slewed in the direction of O, the

- hydraulic cylinder (90') is pulled by rope (20) slightly,

b. In comparison with conventional single winch driven slewing, it is cheaper in cost.

c. There is less wire trouble such as slipping off, and cutting of wire ropes at the drum.

d. The smaller winch platform necessary on the main (31). A boom supporting structure (gooseneck) (30) is located in the mid-position of the post (9). On the gooseneck (30), for purposes of slewing of the boom (l).horizontal pins 12) are fitted. The rope length adjusting arms (98)(98') which have sheaves (99a)(- 99a')(99b)(99b') at the end and pin hinge parts are fitted at both ends of an outrigger(3l) in such a way that it can be slewed.

Stoppers (100) (100) are provided in inner positions of the aforesaid adjusting arms at its both ends. When the adjusting arms (98) (98') move towards the direction indicated by (m) (m') from the position of Him at the outrigger at certain degrees, (a) (the arms will stop at the stopper (101))(100').

Each one end of the ropes (20) and (20) is anchored on to the boom outrigger (18) and the other end of them is led to the slewing winch' (102) installed at the lower part of post (9) in such a way that when rope (20) is paid off, the other rope (20) is wound in, and vice versa, via sheaves (99:1)(99a'), (99b)(99b') and sheaves (101)(101) installed on outrigger (31).

(8) in FIG. 15 indicates topping rope. When the boom (1) is slewed by the slewing winch (102) from the position of "C to the position of "D rope (20) does not turn aforesaid adjusting arm (98) at first, however, rope (20) is guided by sheave (99b) from a certain position. As theadjustingarm (98) is stopped at angle a by stopper (100'), rope (20) cannot turn the adjusting arm (98) more than angle a toward arrow m. When the boom (1) is situated at the position of C, ropes (20)(20) the length between the positions of CO and the positions of 5.8 are V, ropes (20)(20) the length between s,s' and R,R at the adjusting arms (98)(98) are x, when the boom (1) is situated at the position of D in H6. 16, rope the length between the position Q and the position of R at sheaves (99a) is W, rope (20) the length between the position Q, and the position at sheaves (99b) is y. Therefore the following Equality" can be obtained.

x can be decided from the above an equality. There fore, if ropes (20) and (20') are wound by one drum (102) in such a way that when rope (20) is paid off, the other ropes (20') is wound in and vice versa, the ropes (20) and (20) do not slacken always according to the slewing motion of the boom (1) without special rope length adjusting device. When the boom is slewed from the position of C to the opposite way, the above equality" can be used conversely. The system so far described consists of a fixed post (9) on the main deck. However the rotating post or travelling post are available instead of a fixed post (9).

The advantages accrued from the invention can be listed as follows.

a. Special slewing ropes length adjusting device is not required due to this invention and adjustment of slewing ropes can be automatically done only to select suitable length of the adjusting arms.

b. ln comparison with a conventional slewing system for the boom, it is cheaper in cost and also makes for a simpler slewing system.

While the above description relates to a crane particularly adapted for erection on the deck of a marine vessel for optimum efficiency in loading and unloading the holds of the vessel, it is to be understood that the crane, per se, can be used for many other uses on land where spotting of the load is of the utmost importance.

What we claim is:

l. A cargo handling crane comprising a main two section post, a first section of which is fixed and a second section of which is mounted on a turntable rotatable about said first section of the post, a main outrigger on said second section of the post, said main outrigger extending on opposite sides of the post in a plane normal to the axis of the post, a pair of booms mounted one at each end of the said main outrigger, means to pivot each of said booms (a) for slewing of the booms and (b) for topping the booms, a hoisting trolley on each of said booms, the said trolleys adapted for travel along the length of their respective booms, means for separately slewing each boom, individual rope means for separately topping each boom, for transversing each of said hoisting trolleys on its respective boom and for hoisting loads via said hoisting trolleys winch means on the said turntable for individually paying-in and payingout said rope means,

said slewing means on each boom comprising a slewing rope means passing over pulleys mounted on a further outrigger extending from said post on either side of the said main outrigger, a boom outrigger extending at right angles on either side of the centerline of the boom and to which one end of the pairs of slewing ropes are secured, an adjusting arm pivotally mounted on opposite ends of the said further outrigger on said second section of the post, each of said adjusting arms including a pair of sheaves mounted at each end thereof, stop means on each of said adjusting arms limiting the movement of the arms in the direction of said second section of the post, the said slewing ropes being laid about said sheaves, the said adjusting arms taking up a position during paying-out and paying-in to automatically take up slack in the slewing ropes.

2. A cargo handling crane as set forth in claim 1 in which means are provided for locking each said hoisting trolley in a selected position on its respective boom.

3. A cargo handling crane asset forth in claim 1 in which the said post is mounted on the deck of a vessel on the longitudinal centerline thereof.

4. A cargo handling crane as set forth in claim 1 in which the each boom has a pair of guide surfaces extending along the length thereof and the said hoisting trolley is provided with rollers adapted to run on said guide surfaces, the said rope means include a pair of ropes, one adapted to pull the trolley in one direction along the boom and the other adapted to pull the trolley in the opposite direction and a two barrel winch over which the pair of ropes are laid, and the hoisting rope means include a pair of pulleys suspended from said hoisting trolley, a hoisting rope laid over said pulleys and attached at one end to the extreme end of the boom, a hoisting hook pulley suspended on said hoisting rope between said pair of pulleys, and a hoisting winch for said hoisting rope.

5. A cargo handling crane as set forth in claim 1 in which the means to pivot each of the said booms include a vertically disposed pivot pin permitting slewing of the attached boom and a horizontally disposed pivot pin on the said vertically disposed pivot pin permitting topping of the attached boom, said pivot pins attached to an outer end of the said main outrigger.

6. A cargo handling crane as set forth in claim 1 in which each said boom is in the form of a diamondshaped truss member whose major axis is lengthwise of the boom and where the minor axis is formed by said boom outrigger which is located midway along the length thereof and is disposed in a horizontal plane.

7. A cargo handling crane as set forth in claim 1 including a pair of hydraulic cylinders located adjacent the said second section of the post, a sheave on the external end of the piston rod of each of said hydraulic cylinders, the said slewing ropes passing over the said sheaves for simultaneous paying-out and paying-in to slew the said boom about its pivot mounting controlled by the operation of the said hydraulic cylinders.

8. A cargo handling crane as set forth in claim 1, in which the said second section of the post includes a guide member disposed parallel with the axis of the post and the said main outrigger is slidably mounted on the said guide member and means to lock the said main outrigger on said guide member in a pre-selected position.

9. A cargo handling crane comprising a main two section post, a first section of which is fixed and a second section of which is mounted on a turntable rotatable about said first section of the post, a main outrigger on said second section of the post, said main outrigger extending on opposite sides of the post in a plane normal to the axis of the post, a pair of booms mounted one at each end of the said main outrigger, means to pivot each of said booms (a) for slewing of the booms and (b) for topping the booms, a hoisting trolley on each of said booms, the said trolleys adapted for travel along disposed pivot pin on the said vertically disposed pivot pin permitting topping of the attached boom, said pivot pins attached to and an outer end of the said main outrigger, and said slewing means comprising a power driven motor drivingly engaged with each vertically disposed pivot pin for turning the said vertically disposed pivot pin to slew its respective boom.

Claims

1. A cargo handling crane comprising a main two section post, a first section of which is fixed and a second section of which is mounted on a turntable rotatable about said first section of the post, a main outrigger on said second section of the post, said mAin outrigger extending on opposite sides of the post in a plane normal to the axis of the post, a pair of booms mounted one at each end of the said main outrigger, means to pivot each of said booms (a) for slewing of the booms and (b) for topping the booms, a hoisting trolley on each of said booms, the said trolleys adapted for travel along the length of their respective booms, means for separately slewing each boom, individual rope means for separately topping each boom, for transversing each of said hoisting trolleys on its respective boom and for hoisting loads via said hoisting trolleys winch means on the said turntable for individually paying-in and paying-out said rope means, said slewing means on each boom comprising a slewing rope means passing over pulleys mounted on a further outrigger extending from said post on either side of the said main outrigger, a boom outrigger extending at right angles on either side of the centerline of the boom and to which one end of the pairs of slewing ropes are secured, an adjusting arm pivotally mounted on opposite ends of the said further outrigger on said second section of the post, each of said adjusting arms including a pair of sheaves mounted at each end thereof, stop means on each of said adjusting arms limiting the movement of the arms in the direction of said second section of the post, the said slewing ropes being laid about said sheaves, the said adjusting arms taking up a position during paying-out and paying-in to automatically take up slack in the slewing ropes.

3. A cargo handling crane as set forth in claim 1 in which the said post is mounted on the deck of a vessel on the longitudinal centerline thereof.

6. A cargo handling crane as set forth in claim 1 in which each said boom is in the form of a diamond-shaped truss member whose major axis is lengthwise of the boom and where the minor axis is formed by said boom outrigger which is located midway along the length thereof and is disposed in a horizontal plane.

9. A cargo handling crane comprising a main two section post, a first section of which is fixed and a second section of which is mounted on a turntable rotatable about said first section of the post, a main outrigger on said second section of the post, said main outrigger extending on opposite sides of the post in a plane normal to the axis of the post, a pair of booms mounted one at each end of the said main outrigger, means to pivot each of said booms (a) for slewing of the booms and (b) for topping the booms, a hoisting trolley on each of said booms, the said trolleys adapted for travel along the length of their respective booms, means for separately slewing each boom, individual rope means for separately topping each boom, for transversing each of said hoisting trolleys on its respective boom and for hoisting loads via said hoisting trolley winch means on the said turntable for individually paying-in and paying-out said rope means, said means for pivoting each of the said booms including a vertically disposed pivot pin permitting slewing of the attached boom and a horizontally disposed pivot pin on the said vertically disposed pivot pin permitting topping of the attached boom, said pivot pins attached to and an outer end of the said main outrigger, and said slewing means comprising a power driven motor drivingly engaged with each vertically disposed pivot pin for turning the said vertically disposed pivot pin to slew its respective boom.