GB2040872A

GB2040872A - Sling engagement boss

Info

Publication number: GB2040872A
Application number: GB7900161A
Authority: GB
Original assignee: OCEANIC CONTRACTORS Inc
Current assignee: OCEANIC CONTRACTORS Inc
Priority date: 1979-01-03
Filing date: 1979-01-03
Publication date: 1980-09-03

Abstract

At least two horizontally spaced boss members 5 are secured in an upstanding condition to a unit or module which is to be lifted by slings 14 and loops of which engage over smoothly curved preferably cylindrical waist portions 13 of the respective boss members. Each boss member has a "U" or "C" shape flange 8 forming on its underside a smoothly curved guide surface against which the sling 14 reacts to be directed upwardly and outwardly from its respective boss member. The diameter of the waist portion 13 is large with respect to the diameter of the rope for the sling 14 and preferably the sling 14 is guided by the flange 8 so that the horizontal and vertical components of force applied from tension in the sling 14 intersect at a position which in plan view is in the central region of the boss member and which is adjacent to a plate 12 by which the boss member is intended to be secured in the unit to be lifted. <IMAGE>

Description

SPECIFICATION A unit to be carried by sling means and a boss member for use in such a unit This invention relates to a unit to be carried by sling means.

It is conventional practice in the carriage of unit packages or modules for lifting or lowering by hoist, derrick or crane to provide on the unit two or more horizontally spaced lifting points to which one or more slings can be coupled for attachment of the unit to a lifting hook. The types of sling used for this purpose are well known in the art and generally comprise a rope member with an eye formed at each end thereof, one eye being intended for attachment to a first lifting point while the other can be attached to the crane hook or to a second lifting point (while the crane hook is intended to connect with the rope at a position between the eyes) or the rope can be doubled so that both eyes are attached to the same lifting point (and again the crane hook engages with the mid part of the doubled rope).Alternatively both eyes can be attached to the crane hook while the lifting point is coupled between the doubled sling at the mid part length thereof. For particularly heavy units or large equipment packages cable laid slings of grommet form (a continuous length of rope spliced to form eyes at each end) or of single length form having each end thereof doubled and spliced to form the eyes is used.

A typical lifting point may be one or more plates which are attached to or integrally formed with the unit and extend upwardly therefrom. These plates are provided with holes to each of which a shackle is coupled by a pin with the slings attached to the shackles. With such shackle and sling couplings it has been determined that the efficiency of the sling varies in accordance with the relative diameters of the rope of the sling and that of the material of the bow of the shackle with which the rope sling engages. For efficient usage of the sling the diameter of the material of the shackle with which the rope sling engages should be as large as possible in comparison with the diameter of the rope in the sling to alleviate unnecessary strain in the material of the rope by such rope having a relatively small radius of curvature in extending around the bow of the shackle.With this in mind and in an attempt to use rope slings efficiently it has hitherto been proposed to incorporate in the eye of the sling a thimble which maintains the radius of curvature of the rope in the eye relatively large irrespective of the diameter of the material in the bow of the shackle to which the eye of the sling may be connected.

While the use of shackle and pin lifting points and thimbled eyed lifting slings have been found suitable for carriage by slings of relatively lightweight loads they have been found to be inefficient and undesirable for the carriage of heavier units such as, for example, may be encountered in the construction of offshore oil and gas platforms where a unit to be lifted on to the site may weigh in the region of 1,500 to 2,000 tonnes and often require cable laid slings having a diameter in the region of 200 millimetres to 300 millimetres. Even with such large diameter rope slings the efficiency of the sling is still dependent upon the relative diameter of the rope as compared with the diameter of the material in the bow of a shackle around which it engages and it is usually impractical to provide such large diameter ropes with thimbles.Furthermore, when using the shackle pin and lifting plate technique for very heavy units it is essential that the plates are accurately located at predetermined geometrical positions on the unit so that, when the unit is lifted through the slings from a central hook the plates are not subjected to excessive bending or torsional strains (which may damage the unit or even deform ortearthe plates therefrom).

In the lifting of very heavy units other than plate members which may be carried from two lifting points along an edge, at least three and usually four horizontally spaced lifting points are provided and where possible a matching set of slings is used to ensure that all the slings are of the same length. If there is a mis-match between the slings the load of the unit may not be evenly distributed between all of the slings and thereby some of the slings may be excessively strained and the unit can be subjected to torsional loads (with the result that the unit can be damaged or alternatively additional expense is incurred in its construction to provide sufficient rein forcementto resist such torsional loads to which it may be subjected during carriage).Bearing in mind the large diameter size slings which may be employed it frequently occurs that an allegedly matching set of slings includes slings which are, unintentionally, of different lengths and as a result compensation has to be built intQ the lifting system to accommodate the mis-match. Hitherto such compensation has been in the form of a link plate which is incorporated at one or more lifting points and is connected at one end by a swivel pin to the previously mentioned upstanding plates on the unit while its other end carries the shackle (which is coupled to the link plate by the shackle pin) to which is connected the .rope sling; although providing effective compensation for rope sling mis-match the provision of a link plate at a lifting point can often be an expensive and time consuming operation.

It is an object of the present invention to provide a unit to be carried by sling means and by which the aforementioned disadvantages of conventional shackle and pin lifting points can be alleviated.

According to the present invention there is provided a unit to be carried by sling means and having at least two horizontally spaced and upstanding bosses for engagement by said sling means; each said boss having a waist portion of substantially smoothly curved profile for receiving the sling means and guide surface means for retaining the sling means against upward movement from the waist portion, and wherein the guide surface means presents a substantially smoothly curved profile against which the sling means is intended to react to be directed upwardly and outwardly from its respective boss, said bosses and their guide surface means being arranged so that with sling means in engagement therewith and during lifting of the unit by the sling means, the sling means will extend from the bosses and converge to a common region which is located between and above the bosses and to which region they are substantially directed by the guide surface means.

Further according to the present invention there is provided a combination of a unit as specified in the immediately preceding paragraph and sling means which are received on the boses to extend, when the unit is carried by said sling means, outwardly and upwardly from the respective bosses and under the direction of the guide surface means to converge at a common region between and above the bosses at which common region the sling means can be coupled for carriage of the unit.

Still further according to the present invention there is provided a longitudinally extending boss member for use in a unit as specified in the penultimate paragraph and comprising a waist portion of substantially smoothly curved profile for receiving sling means and guide surface means for retaining the sling means longitudinally on the waist portion, said guide surface means having a substantially smoothly curved profile against which the sling means is intended to react when longitudinally retained thereby and wherein the profile of said guide surface means is arranged for directing the sling means laterally outwardly of the boss member and at an acute angle relative to the longitudinal extent of that member.

Although the present invention was primarily developed for the lifting and lowering by sling means of very heavy units as may be encountered in the construction of offshore platforms it is to be realised that it is not restricted to such use and can be applied to any size or weight of unit. The body of the unit will usually be a package or module which is intended to be lifted or lowered by the sling means; alternatively however the unit can be in the form of a spreader frame by which a package is intended to be carried. The upwardly extending bosses will usually be mounted as an integral prat of the unit although if required they can be removably secured to the unit.

In a unit of the present invention the boss can extend through the eye of a sling or alternatively a sling can be doubled around the boss so that such sling is located to extend around the waist portion.

The waist portion will have a smoothly curved profile to recieve the sling without unnecessary distortion along the run of the sling and is preferably substantially cylindrical. Furthermore, the waist portion can have an effective diameter which is large in comparison with the diameter of the material used in conventional shackles; for example it is envisaged that with cable laid rope slings having a diameter in the order of 300 millimetres the waist can have a diameter in the order of 1,000 millimetres so alleviating the need for the sling to be deformed around surfaces of small radii.

The guide surface against which the sling reacts on a boss will usually extend, in plan, part way only around the periphery of the boss and will generally be of substantially "C" or "U" shape. However, if required two guide surfaces can be provided on each boss which are located on opposite sides thereof to direct both protions of the sling which extend from the waist portion upwardly and outwardly of the boss at a predetermined angle. The smoothly curved profile of the guide surface will usually be of substantially part circular configuration in horizontal elevation.With this arrangement of the guide surfaces the slings will usually lie in face-to-face contact with the peripheral extent of the respective guide surfaces and thus be directed from the guide surfaces upwardly and outwardly of the boss at a predetermined angle; such predetermined angle of elevation for the sling means is not critical in relation to the bosses since a deviation from this angle of, for example, within the range + or -5" may be permissible without subjecting the bosses to unacceptable strain through the guide surfaces. This has the advantage that the selected lengths of the slings are not critical although it is still preferred that the slings are a matched set.Furthermore, the orientation of the guide surfaces of the bosses on the unit is not critical in so far as the direction at which the slings will extend, in horizontal plan view, outwardly from the respective bosses towards the common region to which they are intended to be attached to a hook.

It is envisaged that a tolerance of + or - 10 of the desired sling line can be achieved in plan view without subjecting the bosses to unacceptable strains since within these tolerances the slings can be permitted to swivel on their respective waist portions whilst still being directed upwardly and outwardly of the bosses by the guide surfaces thereon. Furthermore, the bosses can be mounted on the unit to be capable of rotation about respective upstanding axes thereby permitting the bosses themselves to swivel under the influence of their respective slings so that the guide surfaces centralise themselves during rotation of the bosses to direct the slings along optimum sling lines in plan view.This facility whereby the orientation of the bosses, especially the guide surfaces, on the units is not critical both in determining the angle of elevation at which the slings will extend outwardly and upwardly in side elevation from the respective bosses and also the direction in plan view at which the slings can converge towards the common region for lifting is particularly advantageous. This is because the centre of gravity of a unit is often not at the geometrical centre of that unit and as a result, in conventional structures having plate and shackle lifting points, the structure and orientation of the plates are usually unique as regards design and detail. By the present invention howeverthe above mentioned tolerances can permit the same design of boss to be used at each lifting point and the design of boss may be finalised before the centre of gravity of the unit is known.

Preferably each boss comprises an upstanding body member of tubular, usually cylindrical, structure which includes the waist portion and a saddle portion which carries the guide surface and can be secured, usually by welding, to the body member to extend outwardly therefrom. The saddle portion is conveniently in the form of a flange on the body member.

If, as frequently occurs, it is necessary to shorten the effective length of a sling (for example in the event of a mis-match in a set of slings) this can be achieved by providing a packing member which is removably located between the waist portion of a boss and below the guide surface to effectively increase the extent of the peripheral surface of the boss on which the sling is received. Such a packing member will usually straddle the waist portion of the boss to provide a smooth transition surface therewith and will usually be located on the side of the boss remote from that on which the sling extends outwardly and upwardly. The provision and fitting of such a packing memberto decrease the effective length of a sling is a relatively simple and inexpensive operation as compared to the previously discussed link plate technique as used with a shackle.

It may be desirable for safety reasons, particularly during initial lifting of the unit of the present invention by slings, to ensure that the sling cannot be dislodged from the waist portion or that the two part lengths of a sling which emerge from a common waist portion will not become misaligned during the initial lifting stage (that is while the slings are being lifted from the top of the unit to their final elevations). With this in mind the two part lengths of a common sling which emerge outwardly from the waist portion of a boss may be linked together by a light rope binding or a device such as a shackle with a relatively large bearing radius.Alternatively, or in addition, retaining means can be provided on the boss for retaining the sling means at a position in which it underlies the guide surface; such retaining means is preferably in the form of removable substantially vertically extending pins which are located adjacent to the guide surface and are spaced horizontallly from the waist portion so that the sling will extend over the waist portion captured between that portion, the pins and the guide surface.

A further advantage which may be derived from the present invention is that the eye or loop of the sling which engages with the waist portion can be located for transportation in a condition in which the eye or loop extends in a horizontal plane together with the remaining length of the sling (for example, with the sling resting on the flat top of a unit) so that when the sling is re-positioned for lifting; the eye or loop merely bends up into engagement with the guide surface. This compares with conventional shackled slings in which the eye or loop engaging with the shackle is retained, even when not in use, to extend in a substantially vertical plane while the remaining length of the sling will usually be positioned to extend in a horizontal plane so that when re-positioned for lifting, the sling can be subjected to undesirable deformation.

Although the boss member will usually be fabricated by welding it will be appreciated that alternative techniques of manufacture can be used such as forging, casting or machining from the solid.

The present invention will now be described, by way of example only, with reference to the accompanying illustrative drawings, in which: Figure 1 is a perspective view of a unit constructed in accordance with the invention and having four bosses by which it is lifted through slings from the hook; Figure 2 is a perspective view of a boss member incorporated in the unit of Figure 1; Figure 3 is a further perspective view of the boss member shown in Figure 2 with a sling attached thereto; Figure 4 is a plan view of part of the unit shown in Figure 1 and illustrates one of the bosses; Figure 5 is a part section through the unit of Figure 1 taken on the line A-A of Figure 4; Figure 6 is a similar view to that of Figure 4 and illustrates a modification in which the effective length of the sling means is shortened by a packing member;; Figure 7 is a similar section to that shown in Figure 5 and illustrates a modified form of boss which is adapted to receive a double sling arrangement, and Figure 8 is a plan view of the boss in Figure 7 and illustrates the use of a packing member with the double sling arrangement.

The unit in Figure 1 has a body in the form of a module 1 with a substantially flat upper surface 2.

The module 1 may be regarded as a structural unit for an offshore gas or oil platform formed of steel girders 3 and sheeting 4, and having a weight in the order of 2,000 tonnes. Extending upwardly from the surface 2 and in a substantially common horizontal plane are four horizontally spaced bosses 5 which are located one at each of the corners of a notional rectangle. The bosses 5 are secured in the unit integral with the girder framework and each boss 5 is formed as a boss member as shown in Figures 2 and 3.

Each boss member is of fabricated steel structure and comprises an upstanding cylindrical tubular body member 6 the upper end of which is closed by a cap 7 welded to the body member. Located beneath the rim of the cap member 7 and spaced therefrom is a flange 8 of generally "U" shaped configuration. This flange 8 is welded to the body member 6 and is reinforced against the rim of the cap 7 by webs 9 and box members 10 both of which are welded to the body member 6, the flange 8 and the rim of the cap 7. The underside of the flange 8 provides a guide surface 11 which surface extends throughout its peripheral extent around the body member 6 substantially perpendicularly relative to the longitudinal axis of the body member. The guide surface 11 is symmetrically disposed on the body member 6 and, as will be seen from Figure 5, presents a substantially smoothly curved profile.More particularly, the guide surface 11 extends in horizontal plan view as shown in Figure 4 part way only around the circumference of the body member 6 (preferably such circumferential extent is greater than 180 and in the present example is approximately 210 ) and in horizontal elevation as shown in Figure 5 each side portion of the guide surface 11 is of substantially part circular configuration. If required the lowermost portion of the flange 8 as shown in Figures 3 and 5 (that is the mid-region of the "U" shaped flange member) can be omitted so that the guide surface 11 is effectively formed by two smaller diametrically opposed flange portions on each side of the body member 6.

Located below the flange 8 and spaced therefrom and in the longitudinal mid-region of the body member 6 is a mounting plate 12 which extends in a plane perpendicular to the longitudinal axis of the body member 6 and is welded to that member. The part circumferential extent of the outer surface of the body member 6 located between the upper surface ofthe plate 12 and the guide surface 11 effectively constitutes a waist portion 13. The lowermost part length of the cylindrical member 6 below that plate 12 is located in the body of the module 1 and is secured by welding to the girders and plates of the module with the plate 12 located substantially in the plane of the surface 2 (the plate 12 is also welded to the framework of the module).In mounting the four boss members in the unit it is ensured that such members are orientated so that the guide surfaces 11, when extrapolated upwardly from their respective bosses, converge at a predetermined common region above and between the four bosses 5.

The unit 1 is lifted and carried by a matched set of four equal length single cable laid slings 14 which extend between a respective one of the bosses 5 and a hook 15 (which will usually be on a barge mounted derrick). Each sling 14 has an eye at each end thereof and is doubled so that both eyes engage with the hook 15 while the doubled end of the sling is looped over the respective boss 5 to engage the waist portion 13 beneath the guide surface 11 (as shown in Figures 3 and 5). With a module weight of approxi mately 2,000 tonnes each sling 14 may have a rope diameter of 300 millimetres and the diameter of the waist portion 13 will likely be in the order of 1,000 millimetres.

During initial lifting of the unit by the hook 15 the slings are tensioned and drawn upwardly over the waist portions 13 to react against the guide surfaces 11 by which they are retained on the bosses while the slings attain their angles of elevation a as determined by the lengths of the slings and the geometrical lay-out of the bosses 5. As will be seen from Figure 5 when the slings attain their predetermined angle of elevation a they each bear in substantially face-to-face contact against the whole or major part length of the respective guide surfaces 11 which surfaces therefore act to direct the slings upwardly and outwardly from their respective bosses towards the hook.By this arrangement it is preferred that each guide surface 11 is located at a position which minimises the bending stresses in the tubular body member 6 and it will be seen from Figure 5 that the tension along the line of each sling 14 (where it extends from the boss) and the horizontal component of force to which the body member 6 is subjected by the sling reacting against the waist portion intersect at a position (indicated at X) which is adjacent to the plate 12 and well within the confines of the tubular body, preferably in the central region of the boss (thus minimising the bending moment at this point).

It will be particularly noted from Figure 5 that the angle of elevation a is not critical since the sling 14 will mould itself to follow the profile of the guide surface 11 in accordance with the angle of elevation as may be determined by the length of the slings 14; in practice however the bosses 5 will be designed for use with predetermined loads and with predetermined angles of elevation a which provide optimum efficient usage of both the bosses and the slings and it is envisaged that the tolerance variation possible for the angle of elevation a will usually be within a range of + or - 5". Similarly the line along which the slings 14 will extend in horizontal plan view (as shown in Figure 4) from their respective bosses is not critical even though it is desirable for the bosses to be mounted to direct the slings along predetermined lines 16 for efficient usage of the slings and the guide surfaces, in practice the lines 16 can vary from a predetermined optimum direction (as indicated atp in Figure 4) by approximately + or - 10". During any such misalignment of the sling line 16 the bosses 5 will be subjected to lateral forces but provided the misalignment is within predetermined tolerances these forces can easily be carried by the tubular structure of the body member 6 and the reinforced flange 8. Furthermore, the tubular structure of the bosses renders them with considerable flexural and torsional strength to resist any unbalanced forces to which they may be subjected by friction and misalignment forces from the slings.

To ensure that the slings 14 are retained on their respective bosses during carriage of the unit, a pair of diametrically opposed retaining pins 17 can be provided. These are removably mounted adjacent to the guide surface 11 and extend upwardly over the waist portion 13. The loop of the sling 14 is retained beneath the guide surface 11 by the two pins 17 (see Figures 4 and 5) which latter are conveniently housed in and extend upwardly from sockets formed in the plate 12 or carried by brackets 17a on the body member 6.

In the event that is is required to shorten the effective length of a sling 14 a packing member 18 in the form of a saddle can be mounted on the waist portion 13 to straddle the tubular member 6 as shown in Figure 6. The packing member 18 is interposed between the waist portion and the loop of the sling 14 and provides a smooth transition surface with the waist portion over which the sling extends. The packing member effectively increases the peripheral extent of the waist portion and thereby reduces the effective length of the sling. It will be noted from Figure 6 that in horizontal plan view the packing member 18 is proud of the flange 8 and so the sling is unsupported by the flange overthis partofthe packing member (although the flange does serve to retain the packing member 18 against longitudinal displacement upwardly overthe body member 6).

When determining the requirements for lifting a particular unit it may be necessary to provide two slings which extend from a or each boss 5 to the hook 15. Such an arrangement is illustrated in Fig ures 7 and 8 where the eye of a first sling 14 is engaged overthe waist portion 13 of a boss 5 to bear against and be retained by the guide surface 11 in a similar manner to that previously described. Also engaging around the waist portion of the boss 5 immediately below the sling 14 is an eye of a second sling 14a.The two eyes of the slings 14 and 14a remote from the boss 5 are attached to the hook 15 and upon lifiting of the unit the or each pair of slings are elevated to a position indicated in Figure 7 whereby the upper sling 14 reacts against, and is guided by, the surface 11 while the lower sling 14a bears against the underside of the sling 14 to follow the profile of that sling and extend upwardly and outwardly from the boss in parallel with the sling 14.

If the slings 14 and 14a are matched to be the same length it will be apparent from Figure 7 that, since the radius of curvature over which the sling 14a extends in engaging with the waist portion 13 of the boss is greater than the radius of curvature over which the sling 14 extends on the waist portion, the effective length of the sling 14 is greater than that of the sling 14a and so in use the slings 14 and 14a would be subjected to different tensions (or the sling 14 may be without practical effect).To alleviate this latter possibility a packing member 18 as previously described with reference to Figure 6 is seated on the waist portion interposed between the sling 14 and the waist portion; the effect of the packing member 18 is to decrease the effective length of the sling 14 and the size of the packing member is appropriately selected to ensure that both slings 14 and 14a have the same effective length.

If required, a stop plate 19 can be provided which is welded to the waist portion 13 at a position which is below and adjacent to the upper sling 14 and beneath which stop plate 19 the extremity of the eye of the sling 14a is located to abut against that plate.

The stop plate 19 conveniently serves to reduce some of the vertical loading on the flange 8 and to spread that loading overthe length of the body member 6. Similarly to the previously described examples, both sling members 14 and 14a can be retained during lifting of the unit by removable pins 17. In the event that a single sling is doubled so that both eyes thereof are located on the same boss 5 in a similar manner to the arrangement shown in Figure 7 and the loop of the doubled sling is engaged with the hook 15, the packing member 18 can be omitted since the parallel part lengths of the sling will (neglecting friction) adjust automatically to provide the same tension throughout the sling. Desirably the underside surface of the stop plate 19 is shaped to present a smoothly curved profile to the lower sling member 14a so that that sling member is guided from beneath the stop plate upwardly and outwardly of the boss smoothly into abutment with the upper sling member 14.

Claims

1. A unit to be carried by sling means and having at least two horizontally spaced and upstanding bosses for engagement by said sling means; each said boss having a waist portion of substantially smoothly curved profile for receiving the sling means and guide surface means for retaining the sling means against upward movement from the waist portion, and wherein the guide surface means presents a substantially smoothly curved profile against which the sling means is intended to react to be directed upwardly and outwardly from its respective boss, said bosses and their guide surface means being arranged so that with sling means in engage menttherewith and during lifting of the unit by the sling means, the sling means will extend from the bosses and converge to a common region which is located between and above the bosses and to which region they are substantially directed by the guide surface means.

2. A unit as claimed in claim 1 in which the waist portion is substantially cylindrical.

3. A unit as claimed in either claim 1 or claim 2 in which the guide surface means of at least one boss is carried by at least one flange of that boss.

4. A unit as claimed in any one of the preceding claims in which at least one of the bosses comprises an upstanding body member having the waist portion and at least one further member which carries the guide surface means and which is secured to and extends outwardly from the body member.

5. A unit as claimed in claim 4 in which the body member is tubular.

6. A unit as claimed in any one of the preceding claims in which at least one of the bosses has an upstanding axis and the guide surface means extends, throughout its extent, substantially perpendicularly relative to that axis.

7. A unit as claimed in any one of the preceding claims in which the guide surface means extends, in horizontal plan view, part way only around the peripheral extent of its respective boss.

8. A unit as claimed in claim 7 when appendant to claim 2 in which the guide surface means extends peripherally, in horizontal plan view, over at least 180or of the cylindrical surface of the waist portion.

9. A unit as claimed in any one of the preceding claims in which the guide surface means is of substantially part-circular configuration in horizontal elevation.

10. A unit as claimed in any one of the preceding claims in which the guide surface means of at least one boss is a single substantially "U" or "C" shaped guide surface of smoothly curved profile.

11. A unit as claimed in any one of the preceding claims in which at least one boss is mounted as an integral part of the unit.

12. A unit as claimed in any one of the preceding claims in which at least one boss has a horizontally extending mounting plate from which boss extends upwardly and which mounting plate is secured to or in an upper surface of the body of the unit.

13. A unit as claimed in any one of the preceding claims in which at least one boss has a downwardly extending portion which is secured within the body ofthe unit.

14. A unit as claimed in claims 12 and 13 when appendantto claim 4 in which the mounting plate extends outwardly from the body member at a position above the lower end of that member and below the waist portion, and the lower end portion of the body member below the mounting plate is secured within the body of the unit.

15. A unit as claimed in any one of the preceding claims in which at least one boss is secured as part of the unit by welding.

16. A unit as claimed in any one of the preceding claims in which at least one boss has on its waist portion stop means spaced from and below said guide surface means and between which guide surface means and stop means first sling means is intended to be received on the waist portion and wherein said stop means is intended to locate second sling means when received on the waist portion to underlie the stop means.

17. A unit as claimed in claim 16 wherein said stop means has a peripheral extent around the boss which is less than that of the guide surface means so that, in use, the second sling means can bear in part against the first sling means to follow the profile of the first sling means and be directed thereby upwardly and outwardly of the boss in substantially parallel relationship with the first sling means.

18. A unit as claimed in either claim 16 or claim 17 when appendantto claim 3 in which the stop means comprises a flange plate which extends outwardly of the boss and underlies the flange or flanges which carry the guide surface means.

19. A unit as claimed in any one of claims 16 to 18 in which the stop means has an undesirable surface of substantially smoothly curved profile against which the second sling means is intended to react to be directed upwardly and outwardly of its respective boss.

20. A unit as claimed in any one of the preceding claims in which retaining means is provided for retaining the sling means at a position in which it underlies the guide surface means.

21. A unit as claimed in claim 29 in which the retaining means comprises pin means removably located adjacent to the guide surface means and spaced horizontally from the waist portion, said pin means being arranged so that the sling means when received on the waist portion will be captured between that portion, the pin means and the guide surface means.

22. A unit as claimed in any one of the preceding claims in which at least one removable packing member is located or locatable between the waist portion of a boss and below the guide surface means, said packing member effectively increasing the smoothly curved extent of the peripheral surface of the boss over which the sling means is received.

23. A unit as claimed in claim 22 in which the or each packing member straddles the waist portion of the boss and provides a substantially smooth transition surface therewith.

24. A unit as claimed in any one of the preceding claims in which at least one boss is mounted in the unit to be capable of rotation about an upstanding axis.

25. A unit as claimed in any one of the preceding claims in which the unit has a body comprising a package or module to be lifted or lowered by sling means.

26. A unit as claimed in any one of claims 1 to 24 in which the unit has a body comprising a spreader frame intended for carrying a package or module for lifting or lowering by sling means.

27. A unit as claimed in any one of the preceding claims in which four bosses are provided which are disposed in a substantially horizontal plane and extend upwardly at positions which, in horizontal plan view, are located substantially at the corners of a notional rectangle.

28. A unit as claimed in claim 1 and substantially as herein described with reference to the accompanying illustrative drawings.

29. The combination of a unit as claimed in any one of the preceding claims and sling means which are received on the bosses to extend, when the unit is carried by said sling means, outwardly and upwardly from the respective bosses and under the direction of the guide surface means to converge at a common region between and above the bosses at which common region the sling means can be coupled for carriage of the unit.

30. The combination as claimed in claim 29 in which the sling means reacts on the guide surface means and waist portions so that the horizontal and vertical components of force applied from tension in the sling means to the respective bosses intersects at a position which, in horizontal plane view, is in the central region of each boss.

31. The combination as claimed in claim 30 when appendantto claim 12 in which the said point of intersection is adjacent to the plane of the mounting plate.

32. A longitudinally extending boss member for use in a unit as claimed in any one of claims 1 to 28 and comprising a waist portion of substantially smoothly curved profile for receiving sling means and guide surface means for retaining the sling means longitudinally on the waist portion, said guide surface means having a substantially smoothly curved profile against which the sling means is intended to react when longitudinally retained thereby and wherein the profile of said guide surface means is arranged for directing the sling means laterally outwardly of the base member and at an acute angle relative to the longitudinal extent of that member.