Deep ocean mining ship

Abstract

A ship with special features for mining the ocean floor while operating in water depths in excess of 18,000 feet. These include first, a very large well in the center of the ship, passing through, but enclosed by the hull. The well is closable across the bottom by movable gates. Second, a pipe-handling system for moving large diameter mining pipe sections between the storage hold in the hull and the rig floor in the derrick where they are joined to or disconnected from the existing pipe "string" from which the mining machine is supported. Third, the lift system which operates to raise or lower the pipe string on continuous feed basis. Lastly, the derrick, derrick pipe-handling equipment and entire lift system are motion compensated in roll, pitch and heave such that the derrick and suspended pipe string remain vertical with respect to the earth, isolated from the actual sea-induced motions of the ship. The entire motion compensated system is supported over the center well by a large structural A-Frame.

Description

FIELD OF THE INVENTION

This invention relates to a ship useful in deep ocean mining, and more particularly, motion compensated apparatus for raising and lowering heavy equipment such as mining machinery from a floating surface vessel to the ocean floor.

BACKGROUND OF THE INVENTION

In the search for natural resources, men have been directing their search more and more to the vast ocean regions of the world. Explorations carried out in the deeper parts of the oceans have disclosed rich mineral deposits on the ocean floor. Because of the extreme depth at which the most productive of these deposits occur, for example, in the order of three or four miles below the ocean surface, economic mining and recovery of these mineral deposits has presented formidable problems. Some exploratory work at these depths has been carried out by submersible craft capable of operating at the extreme pressures encountered. However, submersible craft are not suitable for carrying on any large scale mining operations.

SUMMARY OF THE INVENTION

The present invention is directed to a surface ship which is capable of carrying a self-supporting system to a potentially productive mineral site and conducting mining operation once on station. Mining machinery can be lowered to, operated on, and retrieved from the ocean floor while the vessel holds position over the mineral site.

In brief, the present invention provides a means of carrying the mining machinery aboard the ship and lowering it to the ocean floor through a large opening in the hull of the ship, which can be closed from the sea by large movable gates. The mining machinery is suspended from the ship by segmented pipe string, the sections of pipe being joined or removed as the machinery is lowered and raised. Minerals can be brought to the surface through this same pipe.

The pipe sections are stowed in a large hold in the hull of the ship beneath the main deck. From here they are moved one section at a time to the rig floor of the derrick and lifted into the derrick by special handling equipment. Each pipe section is lowered into position to be joined to the preceding section to form a pipe string attached to the mining machinery beneath the ship. The support and vertical movement of the mining machinery and attached pipe string is accomplished through means of a lift system that is suspended on a gimballed platform. This platform also supports the derrick and derrick pipe-handling system. The entire gimballed system is supported on large vertically mounted cylinders. The pipe string and mining machinery are isolated from the ship's roll and pitch motion by the gimballing platforms and from the ship's heave motion by the large supporting cylinders. This arrangment allows the pipe string and mining machinery to remain vertical with respect to the earth without transmitting the tension, torsional and bending loads, which are normally seen by a pipe string in the drilling industry.

The entire motion-compensated system described above is supported over the center well by a large structural A-frame, which is firmly fixed to, and carries the loads into, the hull of the ship.

The ship also features two large extendable legs, one at each end of the center well. These legs can be extended beneath the ship to lower and retrieve the mining vehicle and safely return it to the confines of the ship. Once inside the well, the gates can be closed and the water pumped out of the well thereby forming a self-contained dry dock for maintenance on the mining machinery.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the invention, reference should be made to the accompanying drawings, wherein:

FIG. 1 is a perspective view of the deep ocean mining ship of the present invention;

FIG. 2 is a side elevational view of the ship;

FIGS. 3A and 3B provide a partial cross-sectional view taken laterally through the vessel approximately amidships and looking forward of the vessel;

FIG. 4 is a cross-sectional view of the gimballed platform and lift system taken lengthwise through the center portion of the ship looking to the port side; and

FIG. 5 is a cutaway perspective view of the heave compensation gimbal and lift system of the present invention.

DETAILED DESCRIPTION

FIGS. 1 and 2 show a perspective and side elevational view of a ship designed specifically for use in sub-sea mining operations. The ship has a number of unique features, in addition to those normal and necessary for any ship such as propulsion, tonnage, crew accommodations, etc. These special features include mineral processing labs and storage, pipe storage, and a mining operations control room. The ship's hull, indicated generally at 10, has a large center well 12 which can be closed to the sea by two large movable gates 23 and 25 on the bottom of the hull. The gates are movable lengthwise of the vessel in suitable guides 27. Details of the gates and their operation are described in copending application entitled "Closable Well in Hull of Deep Ocean Mining Vessel", U.S. Ser. No. 479,097, filed June 13, 1974, and assigned to the same assignee as the present invention. When the gates are closed the well can be pumped dry thereby providing a type of dry dock for storage and maintenance of the mining machinery, which can be raised or lowered into and out of the bottom of the well when the gates are open.

Above the main deck 22 there are several unique features, which include a conveyor 21 for transferring sections of pipe from a pipe storage hold 17 to a derrick 18 positioned over the well 12. The derrick 18 and associated derrick pipe handling system are mounted on a two-axis gimballed platform 20 consisting of an outer gimbal ring 58 and an inner gimbal frame 60. A lift system 14 is suspended from the platform 20 and, as hereinafter described, grips the pipe string and operates to lower (or raise) the pipe string without interruption as sections of pipe are added to the string. The heavy lift system is hydraulically operated as hereinafter described in more detail.

The gimballed platform is supported above the well 12 by an A-frame structure 16 that bridges the well. A heave compensation system 26, also described in more detail below, transfers the load of the gimballed platform 20 with the derrick 18 and heavy lift system 14 to the A-frame structure, while permitting relative vertical movement between the ship and the gimballed platform.

The derrick and pipe handling system are described in detail in copending application entitled "Automatic Roughneck", U.S. Ser. No. 478,930, filed June 13, 1974, and assigned to the same assignee as the present application. The derrick and pipe-handling system operate to transfer a pipe, one section at a time, from the conveyor means and attach it to a vertical string of pipe extending down through the well 12 and attached to the mining machinery.

The final special feature is two large vertical structures 11 at either end of the center well. These structures, called docking legs, are used to hold the mining machine while stowed in the well ant to lower or raise the mining machine at the start or conclusion of mining operations. The legs 11 can be raised or lowered by drive mechanism 13 and tilted fore and aft by tilt mechanism 15. Details of the docking legs are described in copending application entitled "Apparatus for Raising and Lowering Large Objects From a Surface Vessel", U.S. Ser. No. 479,095, filed June 13, 1974, and assigned to the same assignee as the present application.

At the start of the mining operations, the center well 12 is flooded, the gates 23 and 25 are unlocked and opened, and the docking legs 11 lower the mining machine below the ship. A section of pipe is moved from the storage hold 17 to the derrick 18 and, using the lift system 14, is lowered and joined to the mining machine. At this point with the pipe and mining machine held in the lift system, the docking legs 11 release the mining machine, the gimbal platform 20 is unlocked, and the heave compensator 26 is placed at mid-stroke. The derrick 18 and supported pipe string are now maintained vertical by gravity, essentially isolated from ship's roll, pitch and heave motions. The mining machine is lowered to the floor of the ocean with uninterrupted motion by adding successive lengths of pipe to the string.

Of that part of the ship's special features which are above the main deck, the structure that spans the center well 12 and all the complex systems that are supported thereon are more fully described below.

Referring specifically to FIGS. 3, 4, and 5, the entire lift system 14, heave compensation system 26 and derrick 18 are supported over the center well 12 by the A-frame structure 16. Loads of the combined supported structure, suspended pipe and mining machine are transmitted to the hull 10 through four A-frame pedestals 24. Two large vertically mounted cylinders or rams 50 and 52 are mounted on the A-frame lower chords 53 at the bottom and support the outer gimbal ring 58 through large yokes 46 and 48. The outer gimbal ring rotates about the roll axis by means of two axially aligned shafts 54 and 56 journaled in bearings 61 and 63. The yokes 46 and 48 ride in guides 38 and 40 as the heave compensating cylinders 50 and 52 respond to ship's heave motions. The guides 38 and 40 are mounted on and extend vertically above the A-frame lower chords 53, as seen in FIG. 4. An inner gimbal frame 60 is attached to the outer gimbal ring 58 by two axially aligned shafts 62 anad 64 journaled in bearings 66 and 68. The inner gimbal frame 60 can thus rotate about the pitch axis of the ship.

A derrick sub-base 72 supports the derrick 18 on the frame 60. A pair of upper lift cylinders 74 and 75 are also mounted on the gimbal frame 60. Suspended from the under side of the inner gimbal frame 60 is a cage structure 80 which houses a lower pair of lift cylinders 84 and 85. Through this overall arrangement the derrick and supported pipe string can be kept in essentially a vertical position isolated from ship's heave, roll and pitch motions. Hydraulic and electrical power are routed to the gimballed system, which is moving relative to the ship, by means of two tripods 96 and a series of hoses 95 and valves 94 and 98. Internal to the gimballed system, hard piping is used.

As a pipe section is lowered from the derrick 18, it is received and held by the lift system 14 by means of which the pipe string can be raised and lowered through the well 12 to and from the ocean floor. This lift system, as noted, includes the pair of upper hydraulic cylinders 74 and 75 mounted on the inner gimbal frame 60 on either side of the vertical centerline which corresponds to the centerline of the pipe string which is being raised or lowered. The cylinders 74 and 75 operate piston rods 76 and 77 which extend downwardly and are coupled at their lower ends by a bridginig upper yoke assembly 78. The upper yoke assembly 78 includes hydraulically operated means for releasable gripping the pipe string 90 at a pipe joint collar 92 so that hydraulic actuation of the upper cylinders 74 and 75 imparts vertical movement to the pipe string. Makeup of each new section of pipe to the existing string is always accomplished above the upper yoke 78.

The lower hydraulic cylinders 84 and 85 are positioned fore and aft of the vertical centerline, whereas the upper hydraulic cylinders 74 and 75 are located to starboard and port of the vertical centerline. The lower cylinders 84 and 85 actuate piston rods 86 and 87 which are coupled at their lower ends by a bridging lower yoke assembly 88. Like the upper yoke assembly 78, the lower yoke assembly 88 is also arranged to releasably grip the pipe string at a pipe joint. Thus, hydraulic actuation of the lower cylinders 84 and 85 likewise is capable of imparting a lowering or raising motion to the pipe string.

Referring to FIG. 5, the heave compensation and lift systems are shown in perspective. The pipe string is indicated generally at 90. The pipe string is made up of a plurality of detachable sections, each section having an internally threaded collar 92 at the upper end of the pipe section into which another pipe section can be stabbed and threaded into a locked position to join the sections together. The collar 92 at the top of each section provides a shoulder 93 by means of which the load imposed by the pipe string can be transferred alternately to either the upper yoke 78 or lower yoke 88.

As described in more detail in copending application SER. No. 479,094, filed June 13,1974, entitled "Hydraulically Operated Heavy Lift System for Vertically Moving a String of Pipe", by John R. Graham and Robert C. Crooke, inventors, and assigned to the same assignee as the present application, the upper cylinders 74 and 75 and lower cylinders 84 and 85 are alternately connected to the pipe string by means of the hydraulically-operated yokes 78 and 88 so that as one set of cylinders is in the process of either raising or lowering the pipe string, the other set of cylinders can be moved into position to receive the load and continue the raising and lowering operation.

The heave compensating system includes two hydraulic cylinders or rams 50 and 52 which are hydraulically connected, respectively, to the bottom ends of hydraulic-pneumatic accumulators 154 and 156. A rise of hydraulic fluid in the bottom half of an accumulator compresses the gas in the top half of the accumulator. The top ends of the accumulators in turn are pneumatically connected to a plurality of pressurized pneumatic tanks 166. The number of tanks connected in parallel to the respective accumulators can be controlled by the operator to change the gas volume of the pneumatic system. This arrangement provides a passive hydraulic-pneumatic spring between the gimbal system and the A-frame structure. As the vessel heaves the two hydraulic rams transfer the load to the bridging frame structure. The spring constant (the stiffness of the spring) can be varied by changing the volume of gas in the system. As described in the above-identified copending application, the operator can adjust the mid-stroke position of the rams by increasing or decreasing the air pressure in the system, thereby changing the spring stiffness to keep the stroke within specified limits.

Claims

What is claimed is:

1. A mining ship for lowering, operating and raising subsea mining apparatus, comprising a hull including a deck and having an opening extending vertically through the hull to provide access from the deck to the water below the hull, a frame mounted on the hull and bridging the opening, a two-axis gimbal system including an outer gimbal ring and an inner gimbal frame pivotally mounted on the outer gimbal ring, means pivotally mounting the outer gimbal ring on the bridging frame over the opening, and pipe lifting means mounted on the inner gimbal frame for raising and lowering mining apparatus through the opening, said means supporting the outer gimbal ring on the bridging frame including heave compensating means for controlling vertical movement of the gimbal system relative to the bridging frame in response to vertical movement of the ship.

2. Apparatus of claim 1 further including gate means for closing the well from the sea, and docking means for retrieving and stowing the mining apparatus within the well.

3. Apparatus of claim 1 further including a derrick mounted on top of the inner gimbal frame and tiltable therewith for moving pipe sections into and out of position to be lowered or raised as part of a connected string of pipe sections by the pipe lift means.

4. apparatus of claim 1 wherein the inner gimbal frame and pipe lifting means combined have a center of gravity below the axes of the gimbal system.

5. Apparatus of claim 4 further including a derrick mounted on top of the inner gimbal frame and tiltable therewith for moving pipe sections into and out of position to be lowered or raised as part of a connected string of pipe sections by the lifting means, the weight of the derrick not being sufficient to raise the center of gravity of the gimbal frame and lifting means above the gimbal axes.

6. In a vessel for lowering equipment to the ocean floor, the combination comprising gimbal support means mounted on the vessel, the gimbal support means including a platform tiltable relative to the vessel about two axes which permit the platform to remain substantially horizontal with rolling and pitching movement of the vessel, and lift means secured below the platform for imparting vertical movement to the equipment, the center of gravity of the platform and lift means being below said axes, said gimbal support means including means for continuously adjusting the vertical position of said platform relative to the vessel to compensate for heave motion of the vessel.

7. Apparatus of claim 6 wherein said epuipment includes a segmented string of pipe extending vertically through the center of the gimbal support means and through the lift means for raising and lowering said equipment.

8. Apparatus of claim 7 further including derrick means mounted on the platform above the lift means for moving pipe segments into and out of position to be added to or removed from said pipe string.

9. A deep ocean mining vessel for operation of mining machinery at great depths from the surface, the vessel comprising: a hull having a large open well in the center of the vessel extending laterally a major part of the beam of the hull and being longer in the fore-aft direction than laterally, a frame bridging the top of the well and anchored to the hull on either side thereof, a stable working platform, means supporting the platform, from said bridging frame above the well, the supporting means including a gimbal system providing tilt of the platform relative to the vessel about two perpendicular axes extending respectively longitudinally and laterally of the vessel, said means supporting the outer gimbal ring on the bridging frame including heave compensating means for controlling vertical movement of the gimbal system relative to the bridging frame in response to vertical movement of the ship, and means mounted on the platform and connected to the mining machinery through the well for raising and lowering the mining machinery in the water beneath the vessel.

10. Apparatus of claim 9 further including movable gate means along the bottom of the vessel for opening and closing the bottom of the well, and means for pumping water out of the well, thereby providing a dry storage and maintenance facility within the hull for the mining machinery.

11. Apparatus of claim 9 further including two rigid structural support members, one on either end of the opening in the ship, adapted to releasably grip the mining machinery, and means for moving the support members vertically to move the mining machinery into and out of the bottom of the well when the gates are open.