AU2011226775A1

AU2011226775A1 - High tonnage lifting hooks

Info

Publication number: AU2011226775A1
Application number: AU2011226775A
Authority: AU
Inventors: John Dinse
Original assignee: Individual
Current assignee: Individual
Priority date: 2011-09-20
Filing date: 2011-09-20
Publication date: 2013-04-04
Anticipated expiration: 2031-09-20
Also published as: WO2013040637A1; AU2011226775B2

Abstract

In one preferred form there is provided an accessory (28) for a shank type lifting hook (30). The accessory (28) comprises a mounting portion (32) for receiving the shank (34) of the lifting hook (30). An actuator mechanism (36) is provided for being operated to 5 limit movement of a safety gate (38) to provide a number of operating conditions (58). The operating conditions (58) include a locked condition (40) in which the safety gate (38) is secured in a closed condition (42) so as to extend across the opening of the hook portion (46) of the lifting hook (30)so that the hook portion (46) is able to securely hold a lifting load. Fig.4 Fig.5 28 coo co coo coo "t CD co

Description

Australian Patents Act 1990 COMPLETE SPECIFICATION Standard Patent Invention Title: HIGH TONNAGE LIFTING HOOKS The invention is described in the following statement: P00009 (0709) 1 HIGH TONNAGE LIFTING HOOKS FIELD OF THE INVENTION In preferred forms, the present invention relates to high tonnage lifting hooks and subsea lifting operations. 5 BACKGROUND To THE INVENTION In the subsea industry safety is one of the primary concerns involved in the deployment, recovery, maintenance and repair of subsea assets. Conventional subsea lifting hooks include eye type lifting hooks and shank type lifting hooks. Generally subsea lifting hooks have lifting capacity of 5 to 40 tonnes or more. 10 The use of subsea lifting hooks has associated problems which the industry would like to mitigate. It is considered that one such problem comprises the industry wide problem of 'sling roll out'. In subsea lifting operations water movement at both the interface and subsea level can cause upward movement of the load. This in turn can cause a sling or strop to move 15 over the tip of a lifting hook and comprise the safety of the lifting operation. It is against this background and the problems and difficulties associated therewith that the present invention has been developed. SUMMARY OF THE INVENTION According to a first aspect of preferred embodiments herein described there is provided a 20 accessory for a shank type lifting hook, the accessory comprising: a mounting portion for receiving the shank of the lifting hook; and an actuator mechanism for being operated to limit movement of a safety gate to provide a number of operating conditions; the operating conditions including a locked condition in which the safety gate is secured in a closed condition so as to extend across the opening of the hook portion of the lifting hook 25 so that the hook portion is able to securely hold a lifting load. Preferably the actuator mechanism is adapted to provide an unlocked condition in which the safety gate is secured in an open condition extending away from the opening of the hook portion to allow the hook portion to release or receive a lifting load.

2 Preferably the actuator mechanism is adapted to provide a safety release condition in which the safety gate is moveable between its closed condition extending across the opening of the hook portion and its open condition in which the safety gate extends away from the opening of the hook portion. 5 Preferably the accessory includes an internal safety facility for biasing the safety gate towards the closed condition. Preferably the mounting portion includes a body adapted to receive the shank of the lifting hook, the body providing a casing for protecting the actuator mechanism. Preferably the body of the mounting portion comprises two impact resistant portions, the 10 impact resistant portions comprising two halves each having a channel portion for receiving the shank of the lifting hook. Preferably the impact resistant portions are able to be fixed together with the channel portions providing a a passage through which the shank of the lifting hook extends when the accessory and lifting hook are assembled. 15 Preferably the accessory includes a handle portion extending from the mounting portion. Preferably the actuator mechanism includes at least one selector operable to select a desired operating condition, the at least one selector being connected to a selector shaft extending through the body of the mounting portion for engaging an actuator member. Preferably the accessory includes two selectors positioned on opposite sides of the 20 mounting portion to allow ready subsurface access. Preferably the actuator member comprises an elongate rack member, the selector and actuator member forming rack and pinion type vertical adjustment in which at least one gear element connected to the selector shaft rotates to extend or retract the elongate rack member, the elongate rack member extending in the direction of the length the lifting 25 hook. Preferably the mounting portion is adapted to provide a longitudinal channel for housing the elongate rack member between the selector shaft and the shank of the lifting hook. Preferably the accessory includes an internal facility for biasing the actuator member towards the hook portion of the lifting hook, the internal facility including a spring 3 arrangement for pushing the actuator member towards the hook portion in the direction of the length of the lifting hook. Preferably the actuator mechanism includes a securing arrangement having a quick release facility, the quick release facility being operable by pushing or pulling the selector 5 to move the selector shaft to release the safety gate from the closed condition. Preferably the securing arrangement includes a first component connected to the selector shaft and a second component spaced therefrom, the first and second components being able to be engaged by moving the selector shaft such that the first component is aligned with the second component. 10 Preferably the second component is provided as a locking hole in a plate element through which the selector shaft extends, the first component being provided as a locking pin received within the selector shaft, the locking hole being shaped to receive the locking pin in a manner preventing rotation of the selector shaft. Preferably the actuator mechanism includes a coupling for engaging the safety gate at the 15 end of the lifting hook adjacent the hook portion, the coupling comprising a restraint for controlling the rotation of the safety gate, the safety gate being pivotally mounted to the neck of the hook portion. Preferably the coupling comprises a pin and slot mechanism, with the rotational position of pin being related to the position of the pin in the slot. 20 Preferably the safety gate is provided with a pin spaced away from the position at which the safety gate is pivotally mounted, the actuator mechanism including slot for receiving the pin and controlling the longitudinal position of the pin relative to the length of the lifting hook. Preferably the accessory includes an encased internal facility for biasing the safety gate 25 towards the locked position, the accessory being configured to be fitted to an existing certified lifting hook for high tonnage subsea operations. According to a second aspect of preferred embodiments herein described there is provided a method of providing an improved lifting hook comprising: fitting an accessory to a shank type lifting hook, the accessory including a mounting portion and an actuator 4 mechanism, the actuator mechanism being moveable along the length of the lifting hook and the mounting portion encasing the actuator mechanism around the shank of the lifting hook. Preferably the method includes operating the actuator mechanism to secure a safety gate 5 in a closed condition using a securing arrangement of the actuator mechanism. Preferably the lifting hook is a standard shank type lifting hook with an annular-type shaft for high tonnage operations. According to a thrid aspect of preferred embodiments herein described there is provided a high tonnage lifting hook comprising an actuator mechanism for being operated to limit 10 movement of a safety gate to provide a number of operating conditions, the operating conditions including a locked condition in which the safety gate is secured in a closed condition so as to extend across the opening of the hook portion of the lifting hook so that the hook portion is able to securely hold a lifting load. As will be discussed in further detail below, embodiments of the present invention are 15 considered to provide a number of preferred arrangements including: (i) Shank type lifting hooks and accessories that assist with facilitating improved 'fail safe' lifting operations; (ii) Shank type lifting hooks and accessories that allow an appropriately configured remotely operated vehicle or diver interface to perform operations as desired; 20 (iii) Shank type lifting hooks and accessories that provide two interface drives positioned on opposite sides of the lifting hook. (iv) Shank type lifting hooks and accessories that provide robust safety operation and which mitigate snagging and impact risks; (v) Shank type lifting hooks and accessories that do not alter existing hook lifting 25 specifications; (vi) Shank type lifting hooks and accessories that provide relatively improved 'fail safe' spring loaded return gate operation; (vii) Shank type lifting hooks and accessories that provide quick release actuation in the event that a quick disconnect is required.

5 (viii) Accessories for shank type lifting hooks that can be readily scaled for application on more than one size of conventional shank type lifting hook. Further advantages and preferred features of embodiments of the present invention will be apparent from the drawings and a reading of the specification as a whole. The present 5 invention is to be construed beneficially to the applicant. BRIEF DESCRIPTION OF DRAWINGS In order to facilitate a better understanding of the present invention, several preferred embodiments will now be described with reference to the accompanying drawings, in which: 10 Figures la and lb provide side views of conventional lifting hooks used in the subsea industry; Figure 2 provides an illustration of the problem of sling roll out; Figure 3 provides a side view one manner of limiting the likelihood of sling roll out; 15 Figure 4 provides a perspective view of an accessory for a lifting hook, the accessory according to a preferred embodiment of the present invention; Figure 5 provides a side view of the accessory shown in Figure 4; Figure 6 provides an exploded view of the accessory shown in Figure 4; Figures 7 to 9 provide side views illustrating three modes of operation of the 20 accessory shown in Figure 4; and Figures 10 and 11 illustrate a lifting hook according to a further preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS It is to be appreciated that each of the embodiments is specifically described and that the 25 present invention is not to be construed as being limited to any specific feature or element of any one of the embodiments. Neither is the present invention to be construed as being limited to any feature of a number of the embodiments or variations described in relation to the embodiments.

6 Referring to Figures 1 a and lb there is shown a conventional shank type lifting hook 10 and a conventional eye type lifting hook 12. In the subsea industry lifting hooks of this type are generally designed for high tonnage operations and are manufactured to a variety of engineering certification standards. 5 The problem of sling rollout is illustrated in Figure 2. In the case of sling rollout, as shown, a sling 14 is generally received by a lifting hook 16. Water movement at the interface and sub sea then causes movement of the load in an upward direction. As shown in the Figure 2 this can cause the sling 14 to move over the tip 18 of the lifting hook 16. Subsequent downward movement of the sling 14 causes the sling 14 to bear 10 downwardly on the safety gate 20 which generally results in the sling 14 sliding free. In order to limit this problem some subsea lifting hooks are designed with a projecting tip 22. Such tips are generally considered however to be of limited use in mitigating the problem of sling rollout. For this reasons, some hooks such as hook 24 (shown in Figure 3) include a hole 26 for 15 receiving a split pin for locking the safety gate 25 of the hook 24 in a closed position. Among other things, the use of a split pin on site is problematic as the split pin used could be compromised through repeated use or otherwise. Turning to Figures 4 and 5 there is shown an accessory 28 according to a first preferred embodiment of the present invention. The accessory 28 is able to be advantageously 20 mounted to a conventional shank type high tonnage lifting hook 30 as shown in Figure 6. It is considered that the accessory 28 is advantageously able to be used by an ROV or diver interface for relatively improved fail safe operation. Referring to Figure 6, the accessory 28 includes a mounting portion 32 for receiving the shank 34 of the lifting hook 30 and an actuator mechanism 36 for being operated to limit 25 movement of a safety gate 38 to provide a number of operating conditions. In this embodiment, the original safety gate of the lifting hook 30 (if present) is first removed and replaced with the safety gate 38 provided by the accessory 28. As shown in Figure 7, the actuator mechanism 36 is operable to limit movement of the safety gate 38 to provide a locked operating condition 40 in which the safety gate 38 is 30 secured in a closed condition 42. In the closed condition 42 the safety gate 38 extends 7 across the opening 44 of the hook portion 46 of the lifting hook 30 so that the hook portion 46 is able to securely hold a lifting load. In this embodiment there is very little movement of the safety gate 38 when in the locked operating condition 40. The safety gate 38 in secured in position because it is not able to move an appreciable amount 5 forwards in a direction 48 nor an appreciable amount backwards in a direction 50. As shown in Figure 8, the actuator mechanism 36 is further provides an unlocked operating condition 52 in which the safety gate 38 is secured in an open condition 54 so as to extend away from the opening 44 of the hook portion 46 to allow the hook portion 46 to release or receive a lifting load. 10 As shown in Figure 9, the actuator mechanism 36 is further adapted to provide a safety release condition 56 in which the safety gate 38 is readily moveable between the closed condition 42 and the open condition 54. The safety release condition 56 allows free movement between the closed conditions 42 and the open condition 54. As will be described in further detail below the unlocked operating condition 52 is biased towards 15 the safety gate 38 being in the closed condition 42. Consequently the actuator mechanism 36 of the accessory 28 is able to limit movement of the safety gate 38 to provide a three operating conditions 58, namely: the locked operating condition 40, the unlocked operating condition 52 and the safety release condition 56. 20 An exploded view of the accessory 28 is illustrated in Figure 6. As shown the mounting portion 32 includes a body 60 adapted to receive the shank 34 of the lifting hook 30. The body 60 comprises two impact resistant portions 62. The impact resistant portions 62 comprise two halves 64 that are are dome shaped as illustrated in Figure 6. The impact resistant portions 62 include a plurality of mounting holes 66 for receiving 25 fasteners 68. The fasteners 68 are secured to fix the impact resistant portions 62 together. Each of the impact resistant portions 62 includes an open channel portion 70. When the impact resistant portions 62 are fixed together, the channel portions 70 receive the shank 34 of the lifting hook 30. Whe channel portions 70, when assembled, provide a passage 72 through which the shank 34 of the lifting hook 30 extends. The passage 72 is 30 hexagonal and closely fits the shape of the shank 34 of the lifting hook 30. In this regard 8 the lifting hook 30 is generally annular having a cross section of a similar width and height. The body 60 of the mounting portion 32 advantageously provides a casing 74 for protecting the actuator mechanism 36. The casing 74 fully surrounds the actuator 5 mechanism 36 and is advantageously impact resistant. The body 60 further includes two gripping portions 76 configured to assist with allowing the accessory 28 and lifting hook 30 to be readily grasped by a diver. The gripping portions 76 are formed in the outer surface 78 of the body 60 as open channels 80. The impact resistant portions 62 each include a recess 82 and a recess 84. As shown in 10 Figure 6 a first selector 86 of the actuator mechanism 36 is provided in the recess 82. A second selector 88 is provided in the recess 84. The first selector 86 and the second selector 88 are advantageously operable to select a desired one of the operating conditions 58. Each selector 86 is provided in the form of a triangular handle 90 that provides an ROV/diver interface. Each handle 90 is connected to an opposite end of a selector shaft 15 92. The provision of two selectors on opposite sides of the mounting portion 32 is considered to advantageously allow ready subsurface access by an ROV. The selector shaft 92 extends through the body 60 of the mounting portion 32 behind and substantially perpendicular to the shank 34 of the lifting hook 30. The selector shaft 92 is provided for engaging a rack type actuator member 94. 20 The actuator member 94 is provided as an elongate member having an engagement surface with number of gear teeth 96. The gear teeth 96 extend across the actuator member 94. The actuator member 94 is of an appreciable width so as to able to be driven by two gear elements 98. The gear elements 98 comprise drive pinions and are rotationally secured to the selector shaft 92 using a number of spring pins. 25 Two guide housing elements 100 and plate element 102 separate the gear elements 98. The guide housing elements 100 comprise a guide housing plate 104 and a guide housing bush 106. The first one of the gear elements 98 is rotationally secured to the selector shaft 92 by a spring pin 108 that extends through a passage 110 provided in the selector shaft 92. The 9 other one of the gear elements 98 is rotationally secured to the selector shaft 92 by a split pin 112 that extends through a further passage 114 provided in the selector shaft 92. As shown in Figure 6, the actuator mechanism 36 further includes a locking pin 116. The locking pin 116 is fixed in position in a passage 118 provided in the selector shaft 92. 5 The passage 118 is disposed between the passage 110 and the passage 114. The locking pin 116 is accordingly located between the gear elements 98. As shown in Figure 6 the accessory is symmetrical about a mirror plane extending through the plate element 102. The actuator mechanism 36 includes a number of bushes 120. The bushes 120 are provided either side of the gear elements 98 on the opposite sides to the guide housing 10 elements 100. The handles 90 are secured to the selector shaft 92 using a spring pins 122. Conventional spring plungers 124 are used to assist with allowing ready location of the handles 90. As would be apparent the gear teeth 96 extending across the actuator member 94 are provided to engage the corresponding teeth of the gear elements 98. On rotation of the 15 gear elements 98, the teeth of the gear elements 98 and the teeth of the actuator member 94 operate to extend and retract the actuator member 94 in the longitudinal direction of the shank 34(i.e. along the shank). A rack and pinion type vertical adjustment is accordingly provided in which the actuator member 94 extends in the direction of the length the lifting hook 30. 20 The mounting portion 32 provides a longitudinal channel 126. The channel 126 is provided to house and guide the actuator member 94. More particularly, the channel 126 serves to position the actuator member 94 between the selector shaft 92 and the shank 34 of the lifting hook 30. Advantageously the accessory 28 further includes an internal facility 128 for biasing the 25 actuator member 94 towards the hook portion 46 of the lifting hook 30. The internal facility 128 is advantageously housed and protected by the casing 74 of the mounting portion 32. The internal facility 128 includes a spring arrangement 130 in the form of two compressions springs 132. The compressions springs 132 are guided by two spring plungers 134 and serve to bias the actuator member 94 towards the hook portion 46 (in 30 the longitudinal direction).

10 The actuator member 94 includes openings 136 in its topmost surface 138 spaced away from the hook portion 46. The openings 136 are positioned for receiving the spring plungers 134. The spring plungers 134 are provided as cylindrical members with enlarged heads for bearing against an upper portion 140 in the form of a top keeper plate. 5 The top keeper plate is positioned in a recess 142 provided by the mounting portion 32. A securing arrangement 144 is provided in order to dispose the actuator mechanism 36 in the locked operating condition 40 and the unlocked operating condition 52. The securing arrangement 144 includes a locking opening 146 provided in the plate element 102. The locking opening 146 is able to selectively engage and secure the locking pin 116 in a 10 predetermined rotational disposition. The locking opening 146 is generally circular and receives the selector shaft 92 therethrough. The locking opening 146 also includes recesses 148 adapted to engage to locking pin 116. When secured in the recesses 148 the locking pin 116 serves to securely hold the actuator mechanism 36 in the secured conditions, namely, the locked operating 15 condition 40 and the unlocked operating condition 52. The securing arrangement 144 also advantageously provides a quick release facility 150. The quick release facility 150 is operable to move the locking pin 116 out of engagement with the recesses 148. Advantageously this is achieved by pushing or pulling the handle 90 to move the selector shaft 92 and release the safety gate 38 from the secured 20 conditions. The ability to push or pull the handle 90 is considered to be advantageous in an emergency condition when a person is not familiar with the operation of the accessory 28. Furthermore the push pull feature allows for symmetrical operation of the selector 86 and the selector 88. 25 The securing arrangement 144 can be considered as including a first component connected to the selector shaft 92 and a second component connected to the mounting portion 32. The first and second components are able to be engaged by moving the selector shaft 92 such that the first component is aligned with the second component. In this embodiment, the first component is provided in the form of the locking pin 116 held 30 by the selector shaft 92. The second component is provided in the form of the locking 11 opening 146 in the plate element 102, through which the selector shaft 92 extends. The locking opening 146 is shaped to receive the locking pin 116 in a manner preventing rotation of the selector shaft 92. The securing arrangement 144 further includes a locator 152 in the form of a spring 5 plunger for assisting in providing feedback as to the alignment of the locking pin 116 and the plate element 102. The plate element 102, in addition to providing the locking opening 146, provides a handle portion 154 that extends outwardly away from the mounting portion 32. The handle portion 154 provides an ROV interface stabilising handle. In addition the handle 10 portion 154 allows external coupling devices such as shackles to be connected to the accessory_28 In terms of controlling the position of the safety gate 38, the actuator mechanism 36 includes a coupling 156 for engaging the safety gate 38 at the end 158 of the lifting hook 30. As shown the safety gate 38 is pivotally mounted to an extension 160 of a neck 162 15 of the hook portion 46. The coupling 156 comprises a restraint 164 for controlling the rotation of the safety gate 38. The safety gate 38 is provided with a pin 166 spaced away from the extension 160. The restraint 164 includes slot 168 for receiving the pin 166. The slot 168 extends laterally across the length of the lifting hook 30 to allow the restraint 164 to readily control the 20 longitudinal position of the pin 166. In the safety release condition 56 the safety gate 38 is able to move from the closed condition 42 to the open condition 54. As this occurs the pin 166 moves inwardly towards the longitudinal axis of the shank 34 along the slot 168. By virtue of the slot 168, the pin 166 moves upwardly towards the body 60 of the mounting portion 32.. The upward movement is controlled by the restraint 164 (which 25 also moves upwardly). A slot mechanism 170 is accordingly provided. Advantageously the system makes use of a lifting hook 30 already meeting industry and application specific certification standards for lifting operations. This means that various industry standard hooks can be used. Advantageously the main load lift is provided by the body of the lifting hook 30 itself which is advantageously not modified. As discussed 30 only the safety gate of the lifting hook 30 is replaced with the safety gate 38 of the 12 accessory 28. The biasing of the safety gate 38 is provided by a reliable internal safety facility involving a compression spring arrangment. Figures 10 and 11 illustrate a high tonnage lifting hook 172 according to a further preferred embodiment of the present invention. Advantageously the lifting hook 172 can 5 be used to secure a safety gate in a closed condition. The lifting hook 172 comprises an actuator mechanism 174 for being operated to limit movement of a safety gate 176 to provide a number of operating conditions 178. The operating conditions 178 include a locked condition in which the safety gate 176 is secured in a closed condition so as to extend across the opening of the hook. 10 The actuator mechanism address the problem of sling/strop exit from a shackle hook profile due to subsea heave motion during operations or top side forces and thus serves to mitigate the risk of uncontrolled lift. In the embodiment an accessory is provided in the form of a Subsea Sling Retainer 'SSR' fitted to an existing Crosby (TM) shank on the surface in a position ready to be deployed. 15 In order to cause the safety gate 176 to move to the required or nominated lock and un lock positions the ROV manipulator or Diver either leaves the actuator handle 180 in the neutral position (default - closed -unlocked position). Alternatively the actuator handle 175 is turned clockwise to lock the safety gate 176 in the closed position. The safety gate 176 being in the closed position allows the strop/sling to ride over the profile and 20 maintain its original tension lift position. The design is enclosed by an impact absorbing material casing and is profiled to deflect load impacts. The outside casing provides a relatively secure and fixed location for the ROV / Diver interfacing handle. The casing also provides a guide for the actuation rack and top and bottom keeper plates. 25 The actuator mechanism includes an actuating shaft retaining a guide pin. Indexing the shaft via the actuator handle 180 enables 2 gate positions to be secured and locked. Pushing / pulling the actuating handle in a linear direction and then indexing the actuating handle either clockwise or anti-clockwise enables the gate to be locked either in an open position or a closed position via locking pins inserted into the actuating shaft. The 13 position is maintained via grooves in the actuator shaft by a spring loaded plunger as the actuator shaft moves the rack via actuator drive pinions in 2 positions. The assembly mechanism is kept in its default position via compression springs when unlocked. Its default position being free movement i.e. gate spring loaded return to an 5 unlocked closed position. Accordingly, the gate mechanism is spring loaded in the neutral position (which is unlocked) to facilitate capturing the intended strop/sling. After the strop/sling has been loaded the safety gate mechanism is spring locked in the locked position capturing the applicable positioned strop/sling. Advantageously visual indication is achieved by the actuating shaft being proud of the 10 outside surface revealing a red indication marker (on both sides). Indexing of the ROV interface drive feature allows release of the sling. The SSR secures the strop/sling via the spring loaded (return) gate 176. This is actuated by the ROV interface drive feature located on both sides of the 'SSR'. Thus the lifting hook 172 captures the strop / sling via the return (compression) spring 15 loaded gate. This is automatic in the neutral position but can be locked open or locked close via the ROV / Dive actuator handle 180. Furthermore, the high tonnage lifting hook 172 advantageously does not alter existing hook certification while providing a spring loaded (return gate). The certified lifting hook housed by the accessory is of conventional design (apart from the replacement or 20 inclusion of a specifically adapted safety gate 176). The system is considered to have universal HSE application, be operable over full ocean depth and have a relatively safe mechanical gate operation. The design is considered to represent a unique application with several advantages in terms of safety and ease of Diver and ROV application. The lifting hook is of advantageously light design (20kg in 25 air). The safety actuation mechanism is non-load bearing and can be ROV active subsea and manually topside. More particularly the lifting hook 172 is considered to: (i) Allow an ROV / Diver to facilitate the mechanism using a suitable ROV/Diver interface and provide relatively fail safe operation; 14 (ii) Provide an outside profiled design to limit snagging and catch points on impact; (iii) Allow for the use of existing lifting hook certifications with relatively fail safe spring loaded return of gate operation; (iv) Provide a design that is not main load bearing; 5 (v) Provide a design where one design when suitably scaled is able to fit a range of sizes; (vi) Provide visual registration on actuation showing application positions where the mechanism is protected within an impact housing; and (vii)Provide an ROV interface stabilising handle and a Manipulator (Common) 10 interface. Further advantages and preferred features will be apparent from a reading of the specification as a whole. Other advantageous features are shown in the drawings. It is to be recognised that various alterations and equivalent forms may be provided without departing from the spirit and scope of the present invention. This includes 15 modifications within the scope of the appended claims along with all modifications, alternative constructions and equivalents. There is no intention to limit the present invention to the specific embodiments shown in the drawings. The present invention is to be construed beneficially to the applicant and the invention given its full scope. It is to be recognised that any discussion in the present specification is intended to explain 20 the context of the present invention. It is not to be taken as an admission that the material discussed formed part of the prior art base or relevant general knowledge in any particular country or region. In the present specification, the presence of particular features does not preclude the existence of further features. The words 'comprising', 'including' and 'having' are to be 25 construed in an inclusive rather than an exclusive sense. The present invention may find application beyond subsea lifting. High tonnage shank type lifting hooks are considered to have a load capacity of 5 to 40 tonne or more. Generally such hooks have a shank length of at least 20 cm.

Claims

1. An accessory for a shank type lifting hook, the accessory comprising: a mounting portion for receiving the shank of the lifting hook; and an actuator mechanism for being operated to limit movement of a safety gate to provide a number of 5 operating conditions; the operating conditions including a locked condition in which the safety gate is secured in a closed condition so as to extend across the opening of the hook portion of the lifting hook so that the hook portion is able to securely hold a lifting load.

2. An accessory as claimed in claim 1 wherein the actuator mechanism is adapted to 10 provide an unlocked condition in which the safety gate is secured in an open condition extending away from the opening of the hook portion to allow the hook portion to release or receive a lifting load.

3. An accessory as claimed in claim 1 or 2 wherein the actuator mechanism is adapted to provide a safety release condition in which the safety gate is moveable 15 between its closed condition extending across the opening of the hook portion and its open condition in which the safety gate extends away from the opening of the hook portion.

4. An accessory as claimed in claim 1, 2 or 3 wherein the accessory includes an internal safety facility for biasing the safety gate towards the closed condition. 20

5. An accessory as claimed in any one of claims 1 to 4 wherein the mounting portion includes a body adapted to receive the shank of the lifting hook, the body providing a casing for protecting the actuator mechanism.

6. An accessory as claimed in claim 5 wherein the body of the mounting portion comprises two impact resistant portions, the impact resistant portions comprising 25 two halves each having a channel portion for receiving the shank of the lifting hook. 16

7. An accessory as claimed in claim 6 wherein impact resistant portions are able to be fixed together with the channel portions providing a a passage through which the shank of the lifting hook extends when the accessory and lifting hook are assembled. 5

8. An accessory as claimed in claim 5, 6 or 7 including a handle portion extending from the mounting portion.

9. An accessory as claimed in any one of claims 1 to 8 wherein the actuator mechanism includes at least one selector operable to select a desired operating condition, the at least one selector being connected to a selector shaft extending 10 through the body of the mounting portion for engaging an actuator member.

10. An accessory as claimed in claim 9 including two selectors positioned on opposite sides of the mounting portion to allow ready subsurface access.

11. An accessory as claimed in claim 9 or 10 wherein the actuator member comprises an elongate rack member, the selector and actuator member forming rack and 15 pinion type vertical adjustment in which at least one gear element connected to the selector shaft rotates to extend or retract the elongate rack member, the elongate rack member extending in the direction of the length the lifting hook.

12. An accessory as claimed in claim 11 wherein body of the mounting portion is adapted to provide a longitudinal channel for housing the elongate rack member 20 between the selector shaft and the shank of the lifting hook.

13. An accessory as claimed in any one of claims 9 to 12 including an internal facility for biasing the actuator member towards the hook portion of the lifting hook, the internal facility including a spring arrangement for pushing the actuator member towards the hook portion in the direction of the length of the lifting hook. 25

14. An accessory as claimed in any one of claims 9 to 13 wherein the actuator mechanism includes a securing arrangement having a quick release facility, the 17 quick release facility being operable by pushing or pulling the selector to move the selector shaft to release the safety gate from the closed condition.

15. An accessory as claimed in claim 14 wherein the securing arrangement includes a first component connected to the selector shaft and a second component spaced 5 therefrom, the first and second components being able to be engaged by moving the selector shaft such that the first component is aligned with the second component.

16. An accessory as claimed in claim 15 wherein the second component is provided as a locking hole in a plate element through which the selector shaft extends, the first 10 component being provided as a locking pin received within the selector shaft, the locking hole being shaped to receive the locking pin in a manner preventing rotation of the selector shaft.

17. An accessory as claimed in any one of claims 1 to 16 wherein the actuator mechanism includes a coupling for engaging the safety gate at the end of the 15 lifting hook adjacent the hook portion, the coupling comprising a restraint for controlling the rotation of the safety gate, the safety gate being pivotally mounted to the neck of the hook portion.

18. An accessory as claimed in claim 17 wherein the coupling comprises a pin and slot mechanism, with the rotational position of pin being related to the position of 20 the pin in the slot.

19. An accessory as claimed in claim 17 or 18 wherein the safety gate is provided with a pin spaced away from the position at which the safety gate is pivotally mounted, the actuator mechanism including slot for receiving the pin and controlling the longitudinal position of the pin relative to the length of the lifting 25 hook.

20. An accessory as claimed in any one of claims 1 to 19 including an encased internal facility for biasing the safety gate towards the locked position, the 18 accessory being configured to be fitted to an existing certified lifting hook for high tonnage subsea operations.

21. A method of providing an improved lifting hook comprising: fitting an accessory to a shank type lifting hook, the accessory including a mounting portion and an 5 actuator mechanism, the actuator mechanism being moveable along the length of the lifting hook and the mounting portion encasing the actuator mechanism around the shank of the lifting hook.

22. A method as claimed in claim 21 including operating the actuator mechanism to secure a safety gate in a closed condition using a securing arrangement of the 10 actuator mechanism.

23. A method as claimed in claim 21 or 22 wherein the lifting hook is a standard shank type lifting hook with an annular-type shaft for high tonnage operations.

24. A high tonnage lifting hook comprising an actuator mechanism for being operated to limit movement of a safety gate to provide a number of operating conditions, 15 the operating conditions including a locked condition in which the safety gate is secured in a closed condition so as to extend across the opening of the hook portion of the lifting hook so that the hook portion is able to securely hold a lifting load.

25. A device substantially as herein described with reference to the accompanying 20 figures.

26. A method substantially as herein described with reference to the accompanying figures.