MARINE LAUNCH AND RECOVERY ARRANGEMENT

Abstract: A launch and recovery arrangement (10) (Fig. 2) for a submersible body (11) from a floating vessel (12) comprises a boom (15) cantilevered outboard of the side of the vessel near its pitch axis and carrying a downwardly dependent jib (16), preferably pivotally hinged at (17) thereto but lockable in operation, which can be extended and retracted by telescopic hydraulic ram arrangements (24, 25). The jib (16) carries a device (22) for rigidly docking a submersible body and can be extended to below a turbulent interface zone (21) for docking or releasing the body. The body is moved through the lower parts of the interface zone by the rams and motion near the upper part and above surface is effected if necessary by luffing the boom with the jib locked thereto. The boom may be slewed and jib pivoted to transfer the body to the vessel. The rigid support of the body and forced motion in both directions through the interface makes the operation independent of external forces on the body and speed limitations of rope suspension systems. Rope suspension (31, 32, 36) may be employed for the submerged body and needs only the tensile capacity for the submerged body, not the extra required for recovering it through the interface.

Description: MARINE LAUNCH AND RECOVERY ARRANGEMENT This invention relates to marine launch and recovery arrangements for a submersible body and particularly, but not exclusively, to arrangements also capable of handling a submerged body suspended therefrom. The problems of lowering a freely suspended body from a floating vessel, subjected to indeterminate sea-induced motions, towards the moving sea surface or another vessel moving thereon are well known and documented, as are proposals, generically referred to as motion compensation devices, for negating or compensating for the motion of the body with respect to inertial space, for the comfort and/or protection of passengers or apparatus thereon, or with respect to the motion of the target point, that is, the sea surface or the other ship, so as to land thereon without damaging impact. This latter problem is encountered when lowering a body firstly into contact .with the sea surface and then continuing to lower it into a submerged position and exacerbated largely in view of difficulties encountered at the air-water interface, which may be defined, at least for the purposes of this specification, as an envelope of turbulent surface water extending from the maximum surface wave height to a depth of several metres below the nominal surface, at which changes in buoyancy of, and surface wave action and sub-surface turbulence currents on, the body occur and affect its behaviour as a freely suspended load. GB Patent Specification No.202 5359 proposes to minimise the time spent in the interface zone by a body being lifted by effecting a rapid luffing of a boom from which the body is supended. This is effective in lifting motion only and does not address fully the effects of lateral forces on the body for the albeit shorter time spent in the interface zone. Proposals have also been made to adapt motion compensation devices to accommodate suspension rope snatching and also maintain suspension rope tautness during such changes in buoyancy in both raising and lowering but problems still occur with lateral forces acting on the body at the interface zone which place undesirable strains on lowering apparatus that is designed to accommodate only the lowering and lifting forces, and permit swinging of the suspended body with respect to the vessel with the risk, of damaging impact. Susceptibility to such lateral forces is often aggravated by the proposals for dealing with the suspension forces at the interface. Proposals have been made for steadying suspended loads to be transferred between two well defined locations on relatively moving vessels but are complex and not suited to lowering bodies to and through a ser-air interface for submerged operation whilst still suspended from the lowering and lifting arrangement. It has been proposed in GB Patent Application No. 2003815A to lower a suspended submerged body to minimise difficulties encountered by sea pounding and changes in buoyancy and rope loading at the interface and motion of the surface handling support with respect to the submerged body. This arrangement comprises a guide frame fixed to the handling support and relative to which a traveller is constrained to travel in a nominally downward direction. The body is rigidly fixed at the frame for passage through the interface zone, thereby eliminating swinging associated with the lateral motion effects. Because the submersible body, with the additional weight of the frame, is lowered through the interface by gravity changes in buoyancy still are capable of introducing slackness in the suspension rope as are excessive snatching tensions during lifting unless the speed at which the body passes through the interface is reduced and such different raising and lowering speeds are accommodated by the use of a pulley system on the guide frame and traveller. Such arrangement will be seen to overcome the interface zone problems by means of a relatively massive and mechanically complex structure carried by and fixed to the support vessel in addition to the conventional winching provision for the suspension cable. Furthermore the submersible body is retrieved and raised only into the outboard frame and additional provisions are required to retrieve a submerged body onto the support vessel. It will be appreciated that the launch and recovery aspects of such handling arrangement are not self-contained and distinct from the support vessel enabling it to be used with any vessel of convenience but require structural modification of the support vessel. It is an object of the present invention to provide a self-contained launch and recovery arrangement of a submersible body which is of simpler construction than hitherto known and mitigates the effects of loading weight changes and lateral forces at the turbulant air water interface zone without adaptation of the support vessel. According to the present invention a launch and recovery arrangement for a submersible body and adapted to be carried by a support vessel subjected to pitching and rolling motions about pitch and roll axes thereof comprises a boom cantilevered outboard of a side of the vessel, a downwardly pointing jib rectilinearly extensible along an extension axis and connected to the outboard end of the boom along a junction extending orthogonally to the jib extension axis such that the jib and boom are rigid in respect of forces acting on the jib in the direction of the junction and operationally resistant to forces acting on the jib about the junction axis, a body docking device carried by the operationally lower end of the jib remote from, and displaceable relative to, the junction axis adapted to support a submersible body with respect to the jib, the jib at maximum extension supporting a body rigidly docked thereto below an air-water interface zone (as herein defined) and at minimum extension supporting a body rigidly docked thereto near the top of the interface zone, and docking device moving means including jib extension means, operable to apply extension or retraction forces between the docking device and the boom along the extension axis independently of external forces acting thereon, operable to move the docking device and a body docked thereto between a position and which the body is below the interface zone and a position at which the body is above the interface zone. Preferably the junction comprises a pivotal axis about which the jib is able to rotate with respect to the boom and the arrangement includes pivot control means operable to restrain the jib with respect to pivotal motion relative to the boom. An arrangement as defined in the preceding paragraph is particularly suited to launching and recovering a submersible body which is handled whilst submerged by being freely suspended from a rope or the like, by including a body suspension rope extending from a body coupling and passing through the docking device and by way of a sheave at the junction between jib and boom to a winching arrangement adjacent the end of boom carried on the vessel. In this specification the term rope is used for a body suspending medium out of convenience only in describing an elongate flexible member with the tensile ability to support the submerged body; it will be appreciated that the term rope is intended to include a more complex structure such as an electrohydraulic control umbilical which provides communication with, and control of, the body as well as its support. An embodiment of the invention- will now be described by way of example with reference to the accompanying drawings, in which:- Figure 1 is a sectional elevation through a launch and recovery arrangement according to the present invention deployed on a floating vessel and with a submersible body docked thereto in a submerged position, and Figure 2 is a perspective view of the arrangement of Figure 1 better illustrating boom and jib portions thereof and showing the body submerged undocked and suspended from a rope of an integral winching arrangement. Referring to Figures 1 and 2 a launch and recovery arrangement 10 for a submersible body 11 is carried by a floating support vessel 12. The arrangement 10 is conveniently self contained, being mounted on a base 13 so that it can be simply deposited on the deck of any vessel of opportunity without requiring special fittings and structures to be provided on the vessel superstructure or hull. It is preferred, but not essential, that the arrangement 10 is disposed as close to pitch ' axis 14 of the vessel as possible. The arrangement comprises, in addition to base 13, a boom 15 carried at one of its ends by support 13' on base 13 and cantilevered outboard of a side of the vessel, preferably in a direction which is parallel to, and as close as practicable to, the pitch axis 14 of the vessel. A rectilinearly extensible jib 16 joined to the outboard end of the boom along a junction 17 that extends (with the boom operatively disposed) substantially parallel to roll axis 18 of the vessel. Although not essential, as will be discussed hereinafter, the junction 17 is most usefully a pivotal joint and represents a pivotal axis for rotational motion of the jib relative to the boom thereabout. For simplicity the following description assumes that the jib is so pivotally mounted. The jib 16 is substantially planar in a plane containing the pivotal axis and extends downwardly from the boom along an extension axis 19 orthogonal to the pivotal axis 17. The boom comprises a pair of spaced substantially parallel members interconnected so as to resist twisting with respect to the vessel and between which the pivotal axis extends being of such length that rigidity of the jib in the plane of the pivotal axis ensures rigidity of the jib in that plane with respect to the vessel and the ability to resist external forces acting thereon in the direction of the axis. The jib is able to pivot relative to the boom in response to lateral forces acting on the jib other than in the plane of the jib axis and is controlled as to disposition with respect to the boom by pivot control means 20 including fluid pressure operated piston and cylinder arrangement 20'. The pivot control means enables the jib to be folded up to the boom for storage and be positioned with respect to the boom to assme a nominally vertical disposition for the operation of transporting a body 11 through an air-water interface zone 21. For the operation the boom may be locked by the pivot control arms in respect of further rotation of the jib relative to the boom. The jib 16 carries at the end remote from the pivotal axis a body docking device 22 adapted for remotely controlled, and possibly automatic, docking to a cooperating part 22' of the body 11 whereby the docked body becomes rigidly fixed with respect to the docking device. The jib is rectilinearly extensible along said extension axis, that is, the docking device is movable towards and away from the pivotal axis, by docking device moving means 23 including jib extension means 23' operable to apply extension or retraction forces between the pivot axis and docking device. Consequently the jib extension means comprises at least one telescopic fluid pressure operated piston and cylinder pair 24 comprising cylinder 24' and piston 24". To prevent other than the rectilinearly reciprocal motion of the docking member, and particularly rotation, further telescopic members are provided, conveniently in the form of a second telescopic fluid pressure operated piston and cylinder pair 25 comprising cylinder 25' and piston 25". The cylinders 24' and 25' are connected to the pivotal axis 17 and the pistons 24" and 25" extend therefrom for connection to the docking device. Although the piston and cylinder pairs may have the strength to provide the planar structural rigidity of the extensible jib it will generally be desirable to have the pistons 24" and 25" closer to each other than might be expected to provide a suitably rigid jib structure and still provide a docking device 23 of manageable dimensions. Preferably the jib is formed as an A-frame the limbs 26, 27 of which define the extremities of the pivotal axis 17 between the boom members and between the apex 28 of the A-frame and the pivotal axis 17 are supported the cylinders 24' and 25' in a rigid structure. The pistons 24" and 25" are fully rectractable within their respective cylinders such that the docking device abuts the A-frame apex 28 to define the minimum jib length and are extensible to define the maximum jib length. The piston and cylinder arrangement 20' conveniently comprises one piston and cylinder pair extending between each boom member and A-frame limb. The boom 15 may be luffed with respect to support 13' by boom luffing means 29 shown as comprising hydraulic piston and cylinder arrangement 29' and boom luffing control means 29", to define the height of the pivotal axis 17 and manoeuvre the raised jib and docked body between inboard and outboard dispositions in conjunction with slewing of the boom support 13' about a slew axis 30 whereby the boom can be slewed to place the jib 16 above the vessel deck so that the docking device can be lowerd thereto to attach to or detach from a submersible body. In launch and recovery of a body though interface interface zone the boom luffing means may comprise part of the docking device moving means with the jib extension means and provide upward or downward forces on the docking device superimposed upon those from the jib extension means. The dimensions and dispositions of various parts of the launch and recovery arrangement 10 will depend upon circumstances in which it is operated and the particular mode of operation employed. For the purposes of explanation it is convenient to describe an operating sequence from which said dimensions and definitions will be apparent. In one mode of operation the boom extends outboard as described in a nominally horiziontal altitude (ignoring rolling motion of the vessel) so as to distance the pivotal axis 17 and the jib maximally from the vessel. The jib is caused or permitted to depend, possibly under gravity, to a commonly vertical altitude, at which time it is 'locked* by the pivot control means 20 with respect to the boom 15. For a conventional vessel size, that is, boom height above the surface, and the depth of the interface zone it is considered practicable for the jib extension means to extend the jib, and displace the docking device 22, by about the depth of the interface zone 21. The jib is dimensioned such that the dependant unextended jib, substantially the A-frame, reaches from the boom to the top of the interface, that is, the sea surface, and the docking device of extended jib reaches to below the bottom of the interface zone. To recover a submerged body 11 the jib is extended to submerge the docking device and the body 11 is brought into docking engagement therewith. The docking device, with the body rigidly attached thereto, is raised with respect to the jib by retracting the hydraulic piston and cylinder pair through the interface zone and when nearly fully retracted the boom is luffed so as to raise the jib, rigidly disposed with 'respect thereto, and the body docked to the jib, until the whole body is clear of the water. Thereafter the pivot control means may be operated to lower the now-inclined jib back to the vertical by means of piston and cylinder arrang ent 20' or the luffed boom may be slewed about slew axis 30 to position. the body above the deck before pivoting the jib relation to the luffed boom to. restore its verticality extending and lowering the body onto the vessel for undocking, possibly in combination with further boom motion. It will be seen that the above procedure may readily be reversed so as to pick up a body from the vessel deck and position it at the bottom of the interface zone for undocking. It will be seen from the above that the body is taken through the turbulent interface zone 21 by a combination of rectilinear and rotational motions but in each case the body is rigidly docked to a rigid structure and the raising and lowering forces are applied by forcing means, namely the hydraulic fluid pressure systems, which are not dependent on gravity, that is, are not dependant on weight of the body or the changes thereto caused by external forces acting on it at the interface zone which give such trouble with suspended rope arrangements in times of rope slackening or snatching. Furthermore, because the transfer through the interface zone may be carried out at any speed at which the body can withstand any external impact or other force, the body may be moved through the interface zone in both directions more quickly than with other arrangements. It will be appreciated that the above described docking device moving means operation as a combination of reclitinear jib extension and arcuate luffing motions and the relative dispositions of boom and jib neglect any pitching and rolling motions of the vessel which will impart an arcuate component t the nominally recilitinear jib extension. As a result it is considered reasonable that the luffed boom should impart furthe arcuate movement to the body by lifting the jib with its pivot axis fixed in relation to the boom. It will be appreciated that if desired the pivot control means 20 may be arranged to maintain the jib in a substantially vertical plane during luffing of the boom, although this will decrease the speed at which the body leaves the dangerous interface zone. Furthermore the pivot control means may be employed to maintain the extended boom, and the submerged parts and docked body, in the vertical plane prior to luffing the boom to compensate for vessel roll motion by measuring the attitude of the jib extension axis about the pivotal axis with respect to the vertical and cause pivoting of the jib with respect to the boom to restore the extension axis T to the vertical. It will also be appreciated that if there is no requirement to transfer a docked raised body between the docking device and the vessel, so that there is no requirement to effect pivotal motion between the jib and boom, that the privoted axis may comprise a fixed rigid junction between the jib and boom. The above described docking device moving means function involves both extensions or retraction of the jib and luffing of the boom to transfer the body through such a distance that the top of the body is below the interface zone at one extreme and the bottom of the body is above the interface zone at the other extreme. It will be appreciated that for a body of suitable height dimensions and suitable jib length it may be possible to pass the body through the interface zone purely by rectilinear jib extension or retraction and without luffing the boom, whence the docking device moving means may comprise only the jib extension means. In such circumstances and if the boom does not require to be luffed to transfer the body to the vessel, the boom may be formed without luffing and slewing capabilities. The arrangement thus far described is suitable for launching and recovering any submersible body, such as a submarine vessel which may move freely from the vessel between unlocking and locking. A large number of submerged bodies require to be suspended from a tensile rope member for controlling descent, raising and station keeping and also be supplied with power and control signals by means of an umbilical, often integral with the suspension rope. In the arrangement 10, such a body suspension rope 31 is included between a body coupling 32 and passing through the docking device 23, along the jib 16, over a boom sheave 33 disposed near the pivot axis to a powered winching and storage arrangement 34 adjacent the end of the boom on the vessel base 13. The winching arrangement is arranged to pay out suspension rope when the submerged body is detached from the docking device, as shown in Figure 2, to permit and control sinking, or even powered movement, of the body away from the docking device and to haul the submerged body back into docking engagement with the docking device. The suspended rope winching arrangement may also be provided with a motion compensation device in respect of maintaining a submerged body position despite rolling motion of the surface vessel, the effects of which are magnified in proportion to the length of the cantilevered boom 15. By providing vertical acceleration responsive devices at the end of the boom near the pivotal axis or by using existing motion sensors of the vessel the vertical motion of the suspension point, the sheave 33 may be computed and an appropriate length of suspension rope winched in or out to compensate and maintain submerged body vertical station. The compensation may be employed with lowering of the body to a predetermined relationship with a relatively small subsea structure. The suspension rope motion compensation means may be used in conjunction with motion compensation for the boom-jib combination which involves compensatory luffing of the boom. It will be appreciated that as the body is only ever suspended by the rope when submerged, all support through the air being by jib member and docking device, the suspension rope only requires such strength as to support the reduced weight of the sea-buoyed body and does not have to accommodate the weight of - li ¬ the body in air or additional snatching tension which could be effected in the transfer. It is possible to deposit the submersible body on the vessel deck by only limited slewing of the boom about slew axis 30, say _ 50°, and as the rope is relieved of supporting tension with the body attached to the docking device and out of the water, the winching arrangement may lightly tension the rope to take up any slack. By having such limited boom slewing and no body-supporting tension in the rope the winching arrangement may conveniently be mounted directly on the base 13 in fixed attitude, rather than with the boom to be slewed therewith, with the boom sheave 33 mounted on an upstanding pivotal axis 34 so as to pivot with slewing of the boom to direct the rope from the jib onto the winching arrangement. Many of the features described and illustrated are inessential to the operation of the invention and a number of options .are permitted as the abve description shows. Many features may be clearly provided in different form from that described. For instance, although it is convenient to mount the arrangement or a base 13 for temporary placement on a support vessel, the boom end of appropriate the winching arrangement may be mounted directly and possibly permanently on a vessel. The jib extension means may comprise other than the fluid pressure operated piston and cylinder pair described and illustrated. For instance, the force actuated telescope member may be mechanically extended, comprising a screw jack (not shown) driven by a rotational device or a rack and pinion arrangement (not shown) , rack teeth being provided on a shaft equivalent to the piston 24" and driven by a pinion mounted in the jib A-frame. It will also be appreciated that although the jib 16 is conveniently constructed for rigidity in the appropriate directions as an A-frame, permitting dimensions at the apex smaller than those at the pivot axis 17, the jib may be of other configuration which has the same strength attributes. The telescopic fluid pressure or other force actuated extension means and additional devices for providing lateral and tensional rigidity of the docking device with respect to the jib need not be confined to a single plane as depicted by the two pistons 24", 25" illustrated but may comprise further such fluid pressure actuated pistons in the same or different plane or merely telescopically mounted rods to provide such rigidity without contributing to the extension force. The boom may be carried on the vessel at a position movable to and from the side of the vessel to define the body-to-vessel clearance.

Claims: Claims 1. A launch and recovery arrangement for a submersible body and adapted to be carried by a support vessel subjected to pitching and rolling motions about pitch and roll axes thereof, the arrangement comprising a boom cantilevered outboard of a side of the vessel, a downwardly pointing jib rectilinearly extensible along an extension axis of the jib and connected to the outboard end of the boom along a junction extending orthogonally to the jib extension axis such that the jib and boom are rigid in respect of forces acting on the jib in the direction of the junction and operationally resistant to forces acting on the jib about the junction axis, a body docking device carried by the operationally lower end of the jib remote from, and displaceable relative to, the junction axis adapted to support a submersible body with respect to the jib, the jib at maximum extension supporting a body rigidly docked thereto below an air-water interface zone (as herein defined) and at minimum extension supporting a body rigidly docked thereto near the top of the interface zone, and docking device moving means, including jib extension means operable to apply extension or retraction forces between the docking device and the boom along the extension axis independently of external forces acting thereon, operable to move the docking device and a body docked thereto between a position at which the body is below the interface zone and a position at which the body is above the interface zone. 2. An arrangement as claimed in claim 1 including boom luffing means operable to raise or lower the operatively disposed jib with respect to the vessel. 3. An arrangement as claimed in claim 2 in which the boom luffing means is arranged to luff the boom about an axis substantially parallel to the roll axis of the vessel. 4. An arrangement as claimed in claim 2 or claim 3 in which the docking device moving means includes said boom luffing means operable to raise and lower the jib with respect to the vessel in conjunction with raising and lowering of the docking device by the jib extension means. 5. An arrangement as claimed in any one of claims 1 to 3 in which at minimum jib extension the docked body is above the interface zone and the docking device moving means comprises only the jib extension means. 5. 6. An arrangement as claimed in any one of the preceding claims in which the boom is disposed to extend substantially parallel to the pitch axis of the vessel. 7- An arrangement as claimed in any one of the preceding claims in which the boom is mounted for slewing 10, relative to the vessel about a slew axis when the jib is at minimum extension whereby the docked body can be transferred between the docking device and the deck of the vessel. 8. An arrangement as claimed in any one of the preceding claims in which the jib extension comprises at least 15 one fluid pressure operated telescopic piston and cylinder pair. 9. An arrangement as claimed in claim 8 in which the fluid comprises a hydraulic fluid. 10. An arrangment as claimed in claim 8 or claim 9 in which the jib comprises one of the telescopic piston and 20 cylinder pair of the jib extension means fixed at the boom end of the jib and the other of the pair fixed to and carrying the docking device, and further telescopic members extending between the boom end of the jib and the docking device to prevent motion of the docking device other than along the extension axis. 25 11. An arrangement as claimed in claim 10 in which the further telescopic members comprise a second fluid pressure operated piston and cylinder pair disposed and operated in parallel to the first. 12. An arrangement as claimed in claim 11 in which 30 the two fluid pressure operated piston and cylinder pairs define a plane including the junction axis between jib and boom. 13. An arrangement as claimed in any one of claims 10 to 12 in which the jib comprises an A-frame the limbs of which define the extremities of the junction axis and between the apex 35 of which and the junction axis is supported the, or each, cylinder of the jib extension means. 14. An arrangement as claimed in claim 13 in which the or each, piston is retractable into its cylinder such that the docking device abuts the apex of the A-frame to define the minimum length of the jib. 15. An arrangement as claimed in claim 13 or claim 14 in which the boom comprise a pair of spaced substantially parallel cantilevered members each extending from a mounting point on the vessel to the ends of the junction axis and interconnected so as the resist twisting of the junction axis with respect to the vessel. 16. An arrangement as claimed in any one of the preceding claims in which the junction between the boom and the jib comprises a pivotal axis about which the jib is able to rotate with respect to the boom and including pivot control means operable to restrain the jib with respect to pivotal motion relative to the boom. 17. An arrangement as claimed in claim 16 when dependent upon any one of claims 13 to 15 in which the pivot control means comprises a telescopic fluid pressure operated piston and cylinder pair arrangement one of the pair being attached to the boom and the other of the pair being attached to the A-frame of the jib. 18. An arrangement as claimed in claim 16 or claim 17 in which the pivot control means includes measurement means operable to determine the attitude of the extension axis with respect to the vertical about about the pivotal axis and cause the relative orientation of the jib with respect to the boom to be adjusted to restore the extension axis to the vertical. 19. An arrangement as claimed in claim 18 in which the pivot control means is operable in conjunction with the boom luffing means. 20. An arrangement as claimed in any one of the preceding claims including a body suspension rope extending from a body coupling and passing through the docking device by way of a sheave at the junction axis between jib and boom to a winching arrangement adjacent the end of boom carried on the vessel. 21. An arrangement as claimed in claim 20 in which the winching arrangement is adapted to pay out suspension rope to permit movement of a submerged body from the docking device and haul in the suspension rope to draw a submerged body to dock with the docking device. 22. An arrangement as claimed in claim 20 or claim 21 when dependent on claim 7 in which the winching means is not mounted for slewing with the boom and the boom sheave is pivotable about an axis parallel to the boom slew axis to direct the cable passing thereover to the winching arrangement for limited slewing of the boom. 23. An arrangement as claimed in any one of claims 20 to 22 in which the rope winching arrangement includes motion compensation means for vertical motion of the surface vessel relative to the submerged body. 24. An arrangement as claimed in claim 23 in which the motion compensation means includes motion measuring means on the boom operable to determine motion of the suspension point at the sheave. 25. An arrangement as claimed in any one of the preceding claims in which the arrangement is mounted on a base structure unitarily separable from the vessel. 26. A launch and recovering arrangement for a submersible body and adapted to be carried by a support vessel subjected to pitching and rollng motions about pitch and roll axes thereof, the arrangement being sustantially as herein described with reference to, and as shown in, the accompanying drawings.

Inventors: LOGAN WILLIAM ALLAN DEMPSTER, TORGERSEN RICHARD CURTIS, LOGAN, WILLIAM, ALLAN, DEMPSTER, TORGERSEN, RICHARD, CURTIS
Applicants: FSSL LTD, MOBIL OIL CORP, FSSL LIMITED, MOBIL OIL CORPORATION
Application year: 1989
Main classification: B63B27
IPC codes: B63B27