Abstract:
Tanker loading assembly includes a first on-board hose arrangement with first coupling portion and a second submerged buoyant hose arrangement provided with second coupling portion for cooperation with the first coupling portion for obtaining a fluid-tight connection between the first and second hose arrangements. The first coupling portion is positioned in an internal vertical passage of the tanker, wherein a lifting device is provided for engaging the second coupling portion and lifting it towards the position for engaging the first coupling portion.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a Section 371 National Stage Application of International Application PCT/EP2006/068954 filed Nov. 27, 2006 and published as WO 2007/063050 in English. 
     BACKGROUND 
     The invention relates to a tanker loading assembly, comprising a first on-board hose arrangement with first coupling portion and a second submerged buoyant hose arrangement provided with second coupling portion for cooperation with the first coupling portion for obtaining a fluid-tight connection between the first and second hose arrangements. 
     Tanker-loading offshore, whereby a dynamically positioned tanker is employed, is a well establish practice. In general, such tankers are fitted out such that that they are able to arrive at a designated location at sea, position themselves in a stable mode, pick up the second coupling portion which is attached at one end of a tethered submerged buoyant hose arrangement, and connect this second coupling portion to the mating on-board first coupling portion. 
     Picking up the second coupling portion is often a process involving manual labour due to need to pick up messenger wires and to connect these to winches on the ship. Since the working on open decks of vessels, particularly in freezing or high wave conditions is dangerous, it is obvious that a fairly low operability is achieved in the more onerous seas such as the North Sea, for example. 
     The other end of the hose arrangement which is permanently attached to an oil or gas production facility, allows the oil or gas to flow into the tanker. During this operation the tanker maintains its position by appropriate means (e.g. its DP capability). 
     One such hose arrangement, to work in conjunction with a DP tanker, is described in U.S. Pat. No. 5,275,510 “Offshore Tanker Loading System”. 
     A complication occurs if such operation is to be performed in ice infested waters. Particularly if significant ice sheets and smaller and larger iceberg bits are present, the damage potential of the hose arrangement is very high if such hose arrangement is connected to the tanker at some over the side position. One logical solution would be to pull in the hose into a moonpool created inside the tanker hull boundaries where ice sheet cannot get. It has been observed in testing however that ice sheets, when they break up under the action of the vessel moving relative to the ice, also often slip under the bottom plate of the hull. Therefore any hose parts exiting downwardly from a moonpool through the tanker bottom, also risks being damaged by ice sheets. 
     SUMMARY 
     In a first aspect of the invention it is an objective to provide a solution for the protection of the hoses exiting the bottom of the tanker, to provide an easy pick up of the second coupling portion and to simplify its connection to the on-board mating first coupling portion. 
     In a second aspect of the invention it is also an objective of the invention to provide a second hose arrangement layout/geometry which provides a maximum of tanker excursion opportunity. This in turn allows the tanker to continue to break the ice sheets by moving continuously in the operating area by “trashing” around and avoid being caught in ice sheets of larger extent which, due to changing sea currents, may drift in directions not aligned with the longitudinal axis of the tanker. 
     Tankers of such ice breaking design and capability already exist, and in another aspect of the invention, a further objective of this invention is therefore to be able to maximise the efficiency of these tankers when being deployed at oil loading terminals in ice infested waters. 
     In yet another aspect of the invention, it is also an objective of the invention to create a flexible hose arrangement having a very high throughput, such that the tanker need not be exposed to severe offshore ice conditions for a long period of loading. 
     In accordance with an aspect of the present invention the first coupling portion is positioned in an internal vertical passage of the tanker, wherein a lifting device is provided for engaging the second coupling portion and lifting it towards the position for engaging the first coupling portion. This enables a safe and easy pick-up of the second coupling portion and connection to the first coupling portion. 
     In an embodiment the lifting device comprise a casing which is movable vertically within the passage and which supports the first coupling portion. As a result the first coupling portion can be lowered to receive the lifted second coupling portion. 
     In a further embodiment, the submerged hose arrangement comprises a pick-up buoy positioned above the second coupling portion and connected therewith by a cable, and wherein the lifting device further comprise a gripping device for gripping the cable. This combination of components provides a stable positioning of the second hose arrangement during the pick-up. 
     In this embodiment, the lifting device engages and lifts the pick-up buoy. This offers the possibility of lifting the second coupling portion through the pick-up buoy. 
     When, in accordance with yet another embodiment of the invention, the casing comprises a guiding and latching arrangement for the second coupling portion, the second coupling portion can be stabilised for connecting it to the first coupling portion. 
     In an embodiment, the first coupling portion is horizontally displaceable relative to the casing. Thus it can be moved out of the way of the lifting device lifting the pick-up buoy. 
     Further, in an advantageous embodiment the second hose arrangement comprises at least one fluid line describing at least partially an inverted catenary shape and creating a connection to the seabed. This allows the tanker to move around sufficiently for breaking ice, if needed. 
     Then it is possible that each fluid line having the inverted catenary shape is connected to a ballast block positioned below the second coupling portion and connected thereto by means of a respective intermediate fluid line. In a disconnected situation the ballast block rests on the seabed. In the connected situation the ballast block is lifted from the seabed. 
     The ballast block and second coupling portion further are connected by a cable which is shorter then the intermediate fluid line. This diminishes or eliminates loads on each intermediate fluid line. 
     Hereinafter the invention will be explained further by reference to the drawings schematically showing an embodiment of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1-5  show an embodiment of the assembly according to the invention during five successive operational stages, each in a schematical side elevational view (a) and a schematical vertical view (b); 
         FIG. 6  shows an overall view of a tanker with assembly in a disconnected situation, and 
         FIG. 7  shows an overall view of a tanker with assembly in a connected situation. 
     
    
    
     DETAILED DESCRIPTION 
     The tanker hull  1  is provided with a passage  2  (a so-called moonpool) in which a casing  3  is vertically movable. The moonpool  2  and casing  3  are generally conforming in cross-section which may be round, or square as shown in the figures. 
     The casing  3  is able to be positioned by appropriate auxiliary devices  4  (e.g. hoisting cables) in any predefined elevated position. In its lowest position (as will be described later in detail) a first coupling portion  5  of a first hose arrangement  6  can be coupled with a second coupling portion  7  of a second, submerged buoyant hose arrangement  8  to allow the flow of oil or gas. This lowest position may be 5 to 20 meters below the keel of the vessel. 
     The first hose arrangement comprises a first part  6   a  connected to the first coupling portion  5  with a fixed vertical position relative to the casing  3 , a second part  6   b  connected to the deck  9  of the tanker and a flexible part  6   c  (here an articulated part) connecting the first and second parts, such as to allow unimpeded movement of the casing  3  in the tanker moonpool  2 . 
     In its highest position, the casing  3  can be locked to the hull  1  (by a locking device not shown) for normal sea voyage. This highest position may be between 0 and 10 metres above the vessel keel. As will be described later, an intermediate elevation for the lower end of the casing  3  is selected during a pick-up of the second coupling portion  7 . 
     This second coupling portion  7  is provided with a very short section of cable or messenger wire  10 , to the free end of which a pick-up buoy  11  is connected. 
     The lower side of the casing  3  further is provided with a mobile lifting fork  12 , in one embodiment, of a foldable nature to allow storage in or adjacent to the casing  3 . This fork  12  comprises two gripping arms  13  pivotable around respective vertical axes  14 , and two separately pivotable guiding sections  15 . This fork  12  is attached to a vertically extendable casing part  16  and thus can be deployed further downward than the casing  3  to engage the messenger wire  10 . The fork  12  has in its deployed position an open side (between the guiding sections  15 ) of some 6 meters or more. Near its closed end (at the tips of the gripping arms  13  in the gripping position) it is located under the vertical centreline  17  of the casing  3 . The fork  12  at its open end may also be fitted with a catch (not illustrated) which prevents the wire  10  disengaging from the fork, once caught in it. 
     A lifting jack  18  is mounted in the casing  3  and has an extendable piston rod  19  for engaging the pick-up buoy  11 . 
     The casing  3  further is provided with a tapering guiding and latching arrangement with a tapering channel  20  and latches  21  at its top for engaging counter parts (not shown) on the second coupling portion  7 . 
     The first coupling portion  5  is displaceable horizontally relative to the casing  3 , for example by a pivotal movement. 
       FIG. 1  shows the starting position in which the tanker approaches the second hose arrangement  8 . The casing  3  is retracted into the moonpool  2  and the casing part  16  is retracted into the casing  3 . The lifting fork  12  is in a storage position within the boundaries of the casing  3  (see  FIG. 1   b ). 
     Next,  FIG. 2 , the casing part  16  is lowered and the fork  12  is brought in a position in which the guiding sections  15  define a narrowing guiding channel for the messenger wire  10  and wherein the tips of the gripping arms  13  are in a touching relation. The vessel drift direction is indicated by arrow  28 . 
     Once the messenger wire  10  is caught in the fork  12  and centred under the casing  3  ( FIG. 3 ), the casing is lowered (by its auxiliary devices  4 ) such that the pick-up buoy  11  enters the casing  3  through the tapering or funnel shaped channel  20 . The fork  12  may be retracted to its storage position shortly before the buoy  11  passes the channel  20 . 
     Simultaneously or next, the hydraulically operated jack  18  lowers its piston rod  19  ( FIG. 3 ) and latter engages the top of the pick-up buoy  11  by a latching device (not illustrated). This jack  18  then lifts the pick-up buoy  11  ( FIG. 4 ) and with it the entire second hose arrangement  8  with second coupling portion  7 . The first coupling portion  5  will be displaced to a position aligned with the second coupling portion  7  ( FIG. 5   b ) when the pick-up buoy  11  has passed the channel  20  and first coupling portion  5 . 
     When the second coupling portion  7  has been lifted sufficiently it mates with the channel  20  and is latched by the latches  21  and then can be coupled with its mating first coupling portion  5 . 
     The hose connector defined by the first and second coupling portion may be executed as a structural element, including a bearing arrangement to allow the tanker to weathervane while connected to the second hose arrangement. 
     Advantageously, while the tanker is being loaded, the casing  3  is progressively raised inside the moonpool  2  to adjust the global geometry to the draft increase of the vessel. As such a disconnect, once fully loaded or in an emergency, can be readily executed in a well defined configuration. 
     Referring to  FIGS. 6 and 7 , the second coupling portion  7  is connected to a ballast block  22  resting on the seabed when not in use. The second coupling portion  7  also has connected at its lower end, one, but typically more than one, intermediate fluid lines  23 . Each intermediate fluid line  23  is at its lower end connected the ballast block  22 . As such, when the system is not in use, the ballast block rests on the seabed  24 , the second coupling portion  7  has sufficient buoyancy to maintain itself in a tethered mode whereby a cable (not shown) connecting the ballast block  22  and second coupling portion  7  takes the tether loads and the intermediate fluid lines  23  are generally unstretched. In certain cases the cable may be omitted. 
     From the ballast block  22 , flexible fluid lines  25  run in an inverted catenary to a pipeline end  26  on the seabed. There may be one or more such pipeline ends and inverted catenaries. The catenaries are created by fitting distributed buoyancy modules  27  along the length of the fluid lines  25 . By varying the amount and location of such buoyancy modules  27 , the configuration can be adapted to suit any depth limit or any ice keel level. 
     The global geometry of the inverted catenaries and the long vertical riser string (intermediate fluid lines  23 ) allow the tanker large excursions. The pipeline ends  26  may be located such that the overall system has a strong equilibrium position of a symmetrical nature. 
     When the system is in use, the ballast block  22  is only free from the seabed  24  by a nominal amount, allowing for a tanker motion in response to waves and any low tides without touching the seabed. This allows an emergency disconnect to be performed in a virtual “free fall” mode. 
     It is noted that any of the above described features of the system and method of the invention can be used separately or in any suitable combination. Therefore the invention is not restricted to the specific embodiments described which can be varied in a number of ways within the scope of the invention as defined by the appending claims.