Patent Publication Number: US-6334401-B1

Title: Floating structure for the transfer of cargo

Description:
FIELD OF THE INVENTION 
     This invention relates to a floating vessel or transhipper for the transfer of cargo from a ship, such as a cape-size bulk carrier to a barge or a shoreside conveyor at a dock, as well as for other cargo transfer operations. The invention also relates to a method of cargo transfer. 
     BACKGROUND OF THE INVENTION 
     It is a problem with harbours without deep water docking facilities that large cargo ships cannot be accommodated. One solution to the problem is to anchor the vessel in open water and to unload the cargo onto a lighter vessel which can be accommodated in the harbour. 
     Since the deep water locations are sometimes exposed to the open sea and subject to wave action, the stability of the transshiper is a concern. In addition, the efficient unloading of the ship is important for carrying out the cargo transfer operation economically. 
     SUMMARY OF THE INVENTION 
     According to the invention there is provided a sea faring transhipper for transferring cargo from a bulk carrier to a secondary vessel, comprising a pair of units provided with mutually engaging connectors for connecting the units together along a direction of travel of the transhipper, wherein each unit comprises a pair of spaced buoyant vessels; a platform supported by the buoyant vessels in a raised position above the buoyant vessels through wall members extending upwardly from the buoyant vessels; a hull contacting member extending between the buoyant vessels for contacting the underside of a bulk carrier being unloaded, the platform, wall members and hull contacting member defining an opening for surrounding the bulk carrier being unloaded; and a ballasting system for maintaining the hull contacting member in contact with the hull of the bulk carrier being unloaded. 
     Also according to the invention there is provided a method of unloading cargo from a bulk carrier using a transhipper comprising a pair of units provided with mutually engaging connectors for connecting the units together along a direction of travel of the transhipper, wherein each unit comprises a pair of spaced buoyant vessels; a platform supported by the buoyant vessels in a raised position above the buoyant vessels through wall members extending upwardly from the buoyant vessels; and a hull contacting member extending between the buoyant vessels for contacting the underside of a bulk carrier being unloaded, the platform, wall members and hull contacting member defining an opening for surrounding the bulk carrier being unloaded, comprising the steps of positioning the transhipper with the units connected together with said opening surrounding the bulk carrier; disconnecting the units from one another; moving the units away from each other along the length of the bulk carrier to selected unloading positions; and ballasting the units to engage the underside of the bulk carrier, whereby the units are stabilized through said engagement with the bulk carrier. 
     Further objects and advantages of the invention will become apparent from the description of preferred embodiments of the invention below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
     FIG. 1 is a side view of a cargo unloader vessel according to the invention; 
     FIG. 2 is a transverse section of the cargo unloader vessel of FIG. 1; 
     FIG. 3 is top view of pontoons and girder mesh of the vessel of FIG. 1; 
     FIG. 4 showns a side view of a crane trolley and winch system, with a grab and conveyor system of the vessel of FIG. 1; 
     FIG. 5 is another transverse section of the vessel of FIG. 1 illustrating an unloading operation; 
     FIG. 6 is a plan view illustrating an unloading operation; 
     FIG. 7 is a fragmentary side view showing the locking of a wheel of the trolley of FIG. 4 between a pair of tracks; 
     FIG. 8 is a schematical side view of a cargo unloader vessel showing details of a coupler system connecting two parts of the unloader vessel together; and 
     FIG. 9 is a plan view of the unloader vessel of FIG.  8 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
     With reference to FIGS. 1 to  3 , reference numeral  10  generally indicates a cargo unloader vessel, which comprises two units  12  and  14  that in use span over two hold spaces  17  of a cape-size bulk carrier  16 . The units  12 ,  14  can be interlocked to act as one vessel and can be separated during an unloading operation. Each unit  12 ,  14  comprises two buoyant vessels or pontoons  38 ,  39  connected by solid girders  40  which form a steel grillage extending between the pontoons, as shown in FIG.  3 . 
     In FIG. 2, a pair of wall-sided caissons  18 ,  19  extend upwardly from each of the pontoons  38 ,  39 , respectively, and support a platform deck  20 , spanning the space between the caissons  18 ,  19 . The caissons  18 ,  19  are hollow shells and act as the main buoyancy units. As shown in FIG. 3, ballast tanks  21  are provided in the caissons  18 ,  19  to maintain the required immersion level before, during and after a cargo handling operation, with suitable valves for the inflow and outflow of water. They also serve to balance the moving loads within the cargo bay area or hold space  17  of the carrier  16 . Water tight bulkheads  23  are provided between the ballast tanks  21 , both vertically and horizontally between the caissons  18 ,  19 . The caissons  18 ,  19  may also serve as storage space for fuel oil tanks and utility tanks, the depletion or replenishment of which tanks is compensated by appropriate ballast control. The caissons  18 ,  19  also accommodate machinery and pump rooms. Access ducts for personnel are present to allow passage to various areas. Conduits for service lines are also provided. The caissons  18 ,  19  have bottom and bilge strakes which are longitudinally stiffened, with intercostal transverse members. The caissons  18 ,  19  have top plates which are also stiffened longitudinally. 
     The cargo unloader vessel  10  further comprises material handling apparatus  15  as shown in FIGS. 4 and 5, for transferring material or cargo from the bulk carrier  16  to the platform deck  20 , which material is further transferred by a reversible shuttle load-out conveyor  22  to a transfer vessel or barge  27  alongside the bulk carrier  16  (FIG.  6 ). Each unit  12 ,  14  has a grab crane  46  including a grab  24  for the handling of cargo. The grab  24  is supported on a fixed steel girder  26  located above the platform deck  20 . A trolley  28  equipped with a hoisting/closing winch  29  enables the grab  24  to travel horizontally along the girder  26 . 
     A pair of spaced tracks  51  is provided on opposite sides of the trolley  28 . The trolley  28  has wheels  53  which run along the tracks  51  and are locked between the tracks  51 , as shown in FIG.  7 . 
     An accommodation module  30  is located on the platform deck  20  for housing crew (FIG.  1 ). A cargo control room  32  and a navigational control room  34  extend vertically from the platform deck  20 . 
     The platform deck  20  is supported on elevated portals  36  above the caissons  18 ,  19 . The platform deck  20  is provided with a large deck opening for the material handling apparatus  15  and cargo movements. It is strengthened transversely and longitudinally by web structures and girders at appropriate intervals. The platform deck  20  forms a side-to-side continuous deck on each unit  12 ,  14 . In use, the platform deck  20  spans the hold of the carrier  16  and provides the space for the grab crane  46 , a hopper  48 , and a conveyor system  50  (FIG.  4 ). 
     The hopper  48  is movable transversely of the carrier  16 , in the same direction as the trolley  28 , and is winch-operated for effecting this movement. 
     As shown in FIG. 1, the units  12  and  14  are integrated into a single vessel by a suitable coupler system  52 . Details of a suitable coupler system are shown in FIGS. 8 and 9. The unit  12  is provided with tapered pins  90  which are received in corresponding recesses provided on the unit  14 , thereby locating the units  12 ,  14  in position together. The units  12 ,  14  are then locked together by means of a locking pin  92  extending through corresponding pin holes in the units  12 ,  14 . The connection is rigid along the horizontal, vertical and longitudinal axes. The units  12 ,  14  remain interlocked during engagement and disengagement phases with the bulk carrier  16 . Once the engagement phase is completed, the two units  12 ,  14  separate and move to their respective cargo hold positions along the length of the carrier  16  using self-tensioning winches. 
     Each unit  12 ,  14  is equipped with a pair of rudder propellers  56 , such as those available under the name Schottel®, for sailing as well as for precision maneuvering around ships, before, during, and after cargo handling operations. Each rudder propeller  56 , is a propulsion and steering unit comprising a propeller encased in a housing whereby the housing is able rotate horizontally to modify the direction of the unit  12 ,  14  or the entire vessel  10 . In FIG. 3, these propellers  56  are fitted at the starboard-rear of the starboard caisson  18  and the starboard-forward of the port caisson  19  of unit  12  and the port-forward of the port caisson and the port-aft of the starboard caisson of unit  14 . The cargo unloader vessel  10  can propel independently of the bulk carrier  16  and each unit  12 ,  14  can propel and function independently of the other when spanning over the bulk carrier hold  17  using laser guided positioning systems. 
     Trim tanks are used to bring the positions of the interlocking mechanisms of the coupler system  52  on each of the units  12 ,  14  in line with one another. Sensors are used along with the rudder propellers  56 , ballast and trim control to achieve the interlocking sequence. 
     Prime movers for the rudder propellers  56  are arranged within the caissons  18 ,  19  at a sufficient height above the pontoons  38 ,  39 . 
     Fender systems are provided either on a permanent basis, or as a temporary attachment to provide for differences in bulk carrier  16  dimensions. Bottom wheel fenders  64  are located on the solid girders  40  forming the grillage between the pontoons  38 ,  39  and move along the lower surface of the bulk carrier  16  hull when the cargo unloader vessel  10  is engaging the bulk carrier  16 . The grillage therefore acts as a hull contacting member which presses against the hull of the carrier  16 . In this way each unit  12 ,  14  is anchored to the carrier importing stability to the units  12 ,  14  and counteracting relative movement between the carrier  16  and the units  12 ,  14 . 
     Inboard side fenders are located on the inside walls of the caissons  18 ,  19  and are capable of absorbing the normal pressures exerted by the ship hull under normal operating conditions. Undue motions are absorbed by this fender system. An external floating fender system is located on the outside walls of the caissons  18 ,  19 . These outboard side fenders are provided to facilitate secondary host ships or barges  27  coming into sufficient proximity of the platform deck  20  during unloading operations. Contact loads between the secondary vessel  27  and the ship are absorbed by the external fender system. 
     Self-tensioning winches  70  having cables  71  are used to keep the platform deck  20  in the required horizontal position with respect to the bulk carrier  16 . These winches are on an elevated partial deck above the caisson  18 ,  19  top level. The positioning of the platform deck  20  is achieved by constant tension of the winches on the platform deck  20 . The winches are driven in pairs and controlled by command inputs from the cargo control room  32  located on the platform deck  20 . The drives are load dependent. In this condition, the velocity of the drive is proportional to the load applied. The constant tension operating condition allows the drives reverse direction when the maximum load setting is reached. This allows the unit  12 , 14  to rise and fall due to wave action but with a dampened response. The line tension and velocity are adjustable within the performance range to the drive and respond directly to input commands from the control room  32 . 
     As shown in FIGS. 4 and 5, the crane trolley  28  and winch system  29  are supported above the platform deck  20  by two diagonal supports  31  extending from the platform deck  20 . The grab  24  descends vertically from the crane trolley  28  and is power-operated with the winch  29 . The grab  24  descends through control flow gates  74  on the platform deck  20 , down to the cargo hold  17  of the bulk carrier  16 . Material or cargo is lifted by the grab  24 . Material from the grab  24  is discharged into the winch operated travelling hopper  48  located at the top of the floating caisson  18 ,  19  structive, and gravity feeds to the reversible shuttle load-out conveyor  22  which delivers material into the secondary transfer vessel or barge  27 . The conveyor  22  is reversible. It is also retractable when not in use. A trim chute  78  is located at the end of the conveyor  22  for the release of cargo or material into the transfer vessel  27 . The grab  24 , travelling hopper  48  and reversible shuttle load-out conveyor  22  are all powered by the electrical generators located on the platform deck  20 . 
     Deck equipment for anchoring, mooring and maneuvering are arranged on partial elevated decks aft of the aft unit  12  and the forward end of the forward unit  14  at the caisson  18 ,  19  coaming level. Deck equipment includes facilities for anchor handling and storing, rope handling systems for mooring and maneuvering winches, and other utility arrangements. Additional deck equipment is arranged on another elevated deck level near the interface of the two units  12 ,  14 . 
     In use, the cargo unloader vessel  10  approaches a bulk carrier  16  under its own power, propelled by the rudder propellers  56 . It is maneuvered by means of the rudder propellers  56  so that the U-shaped hull configuration of the cargo unloader vessel  10  slips under the bow of the bulk carrier  16  and envelopes the bulk carrier hull. 
     The cargo unloader vessel  10  makes contact with the bulk carrier hull with wheel fenders  64 . The wheel fenders  64  roll along the hull of the bulk carrier  16  as the cargo unloader vessel is engaging it. The inboard side fenders absorb normal pressures exerted by the bulk carrier hull. 
     Once the cargo unloader vessel  10  has enveloped the bulk carrier hull, the units  12  and  14  are separated by disengaging the locking system  52  and using their rudder propellers  56  to move independently and precision maneuvering along the bulk carrier  16 . 
     Each unit  12 ,  14  uses the ballasting tanks  21  located in the caissons  18 , 19  to ballast or deballast, using a suitable valve for the flow of water in and out of the ballast tanks  21  in order to adjust the draft and trim of the units  12 , 14 . 
     The unloading operation is performed by the winch controlled grab  24  descending from the crane trolley  28 . As the winch  29  is activated, the grab  24  is lowered through the control flow gates  74  on the platform deck  20  into the bulk carrier hold  17 , where the grab  24  can transport front end unloaders  19  to and from the bulk carrier hold  17 . The grab  24  can also lift material or cargo from the bulk carrier hold  17  up to the hopper  48 . The cargo or material is gravity fed to the reversible shuttle load-out conveyor  22  which brings the material or cargo to the trim chute  78  for release into the secondary transfer vessel  27 . This cycle is repeated as the grab  24  descends back down into the bulk carrier hold  17  to lift up more material or cargo. 
     Once the bulk carrier hold  17  has been emptied of its contents by the above described unloading operation, the reversible shuttle load-out conveyor  22  is retracted into the unit  12 ,  14  and the self-tensioning winches  71  are released. With the rudder propellers  56 , the two units  12 ,  14  will adjust adjacent trim with the ballasting tanks  21  and join and lock together with the locking system  52 . The cargo unloading vessel  10  will adjust the ballast to its transit mode and debark from the bulk carrier  16  under its own propulsion power. The secondary transport vessel  27  with the reclaimed material or cargo is now able to transport the shipment to its destination port. 
     Although certain preferred embodiments of the present invention have been shown and described in detail, it should be understood that various changes and modifications may be made therein without departing from the scope of the appended claims.