Patent Publication Number: US-11639214-B2

Title: Chain tensioner with chain switch device

Description:
BACKGROUND 
     The invention relates to a chain tensioner for employment on a bottom of a water body. Such tensioner is configured for adjustment of the length of a tensioning chain that extends between the chain tensioner and a floating offshore facility, such as a Floating Production, Storage and Offloading (FPSO) facility, or a floating wind turbine for generating electricity offshore. Multiple chain tensioners and tensioning chains may be used, that are connected with mooring lines that are distributed around the floating offshore facility in a catenary configuration to secure the position with respect to the bottom of the water body. 
     A known chain tensioner for offshore application comprises a chain stopper for locking the tensioning chain with respect to the chain tensioner, and a gipsy wheel to guide the free end of the tensioning chain that is pulled away from the chain stopper by an anchor handling vessel to shorten the length of the tensioning chain between the chain tensioner and the floating offshore facility. 
     SUMMARY OF THE INVENTION 
     A disadvantage of the known chain tensioner is that the chain stopper is hard to handle from an anchor handling vessel. The chain stopper may be activated by making complex maneuvers, or it works like a one way ratchet mechanism that has to be released by employment of a remotely operated underwater vehicle (ROV). This is in particular disadvantageous for a newly installed floating offshore facility, as the mooring lines need to be re-tensioned after the initial time span of the service life. 
     It is an object of the present invention to provide a chain tensioner for employment on a bottom of a water body, which can be operated with control. 
     According to a first aspect, the invention provides a chain tensioner for employment on a bottom of a water body, wherein the chain tensioner is configured for adjustment of the length of a tensioning chain that extends between the chain tensioner and a floating offshore facility, wherein the tensioning chain comprises a series of connected links each having a main plane, wherein the links alternatingly have their main plane in a first orientation and in a second orientation that is under an angle with respect to the first orientation, wherein the chain tensioner comprises a frame that bounds a chain passage for the tensioning chain and that has a bottom wall or skid to stand on the bottom of the water body, a chain lock that is fixedly connected with the frame for engaging and confining a link of the tensioning chain in the chain passage from aside the tensioning chain, and a chain switch device comprising a chain guide for engaging the tensioning chain in the chain passage from aside the tensioning chain, wherein the tensioning chain is sidewardly moveable by means of the chain guide of the chain switch device by moving the chain guide with respect to the frame over a switching stroke between a first position in which the chain lock engages a link of the tensioning chain, and a second position in which the tensioning chain passes the chain lock. 
     The chain tensioner according to the invention is configured to be employed on a bottom of a water body, where it stands on by means of its bottom wall or skid. The chain tensioner remains permanently positioned on the bottom due to its own weight. The chain tensioner has a chain lock and a chain switch device with a chain guide that both engage the tensioning chain from aside. The chain tensioner can be locked and unlocked by toggling the chain switch device between the first position and second position, which moves the tensioning chain sideward with respect to the engaging chain lock. The chain switch device may be easy operated from a vessel, for example by connecting a pulling line to the chain switch device. 
     In an embodiment thereof the frame has with respect to the bottom wall or skid a front entrance of the chain passage at a front side of the frame, and a top entrance of the chain passage at a top side of the frame. The front entrance may be directed towards the floating offshore facility, while the top entrance is directed towards the water surface where a handing vessel pulls on the free end of the tensioning chain. 
     In an embodiment the chain switch device comprises a control cam between the frame and the chain guide, wherein the control cam is rotatable with respect to the frame between a first position and a second position, wherein in the first position of the chain switch device the cam and the chain guide are in their first position, and in the second position of the chain switch device the cam and the chain guide are in their second position. The control cam provides a control mechanism that can be operated even when marine fouling has been set on it, or when it has been penetrated by soil. 
     In an embodiment thereof the control cam is located above the chain passage, whereby it can be easily operated from a vessel on the water surface. 
     In an embodiment the chain switch device comprises a shackle on the control cam for connecting it with a pulling line, for example a pulling line of a vessel on the water surface. 
     In an embodiment the chain switch device comprises a first chain switch that is located with respect to the bottom wall or skid above the tensioning chain in the chain passage, wherein the first chain switch comprises a first chain guide that faces the chain passage, wherein the first chain switch is moveable with its first chain guide between a first position in which the first chain guide is aligned with the chain lock, and a second position in which the first chain guide is out of alignment with the chain lock. The first chain switch extends above the tensioning chain, whereby a sideward downward displacement of the tensioning chain is partly facilitated by the own weight of the tensioning chain. 
     In an embodiment thereof the first chain guide is convex curved towards the chain passage, whereby it can smoothly guide the tensioning chain when it is curved towards a vessel. 
     In an embodiment thereof the first chain guide curves in a direction from the front entrance to the top entrance. 
     In an embodiment the first chain switch is hingeable connected with the frame to hinge between its first position and second position. The hinge connection can be operated even when marine fouling has been set on it, or when it has been penetrated by soil. 
     In an embodiment the first chain switch comprises two first guide edges that extend parallel and spaced apart from each other to define a first link passage in between, wherein the first link passage has a width that allows passage of the links in their first orientation only, wherein the links in their second orientation slide along the first guide edges. The links that are in their first orientation are confined in sliding between the two guide edges to keep the links in their second orientation in contact with the first guide edges. In this manner the sliding movement of the tensioning chain along the first chain switch may be limited to the trajectory as defined by the first guide edges. 
     In a practical embodiment thereof the first chain switch comprises a plate shaped left switch body and a plate shaped right switch body having the first guide edges, wherein the left switch body and the right switch body are connected parallel and spaced apart from each other to define the first link passage in between. 
     In an embodiment the chain switch device comprises a second chain switch that is located with respect to the bottom wall or skid below the tensioning chain in the chain passage, wherein the second chain switch comprises a second chain guide that faces the chain passage, wherein the second chain switch is moveable with its second chain guide between a first position in which the second chain guide is aligned with the chain lock, and a second position in which the second chain guide is out of alignment with the chain lock. The second chain switch extends below the tensioning chain, whereby the tensioning chain may partly lie onto the second chain switch under its own weight to facilitate a sideward displacement of the tensioning chain. 
     In an embodiment thereof the second chain guide is convex curved towards the chain passage. 
     In an embodiment the second chain switch is hingeable connected with the frame to hinge between its first position and second position. The hinge connection can be operated even when marine fouling has been set on it, or when it has been penetrated by soil. 
     In an embodiment the second chain switch comprises two second guide edges that extend parallel and spaced apart from each other to define a second link passage in between, wherein the second link passage has a width that allows passage of the links in their first orientation only, wherein the links in their second orientation slide along the second guide edges. In this manner the sliding movement of the tensioning chain along the second chain switch may be limited to the trajectory as defined by the second guide edges. 
     In a practical embodiment thereof the second chain switch comprises a plate shaped left switch body and a plate shaped right switch body having the second guide edges, wherein the left switch body and the right switch body are connected parallel and spaced apart from each other to define the second link passage in between. 
     In an embodiment the chain lock comprises two hook sections that are fixed to the frame and that project from the frame into the chain passage, wherein the hook sections extend spaced apart from each other to define a link passage in between, wherein the link passage has a width that allows passage of the links in their first orientation only, wherein the hook sections engage the links in their second orientation. The tensioning chain is positioned with respect to the chain lock by the links in their first orientation, whereby the two hook sections can reliably engage the first entering link in its second orientation on both sides of it. 
     In an embodiment the hook sections each comprise a catch aperture for confinement of the engaged link. 
     In a combined embodiment the chain switch device comprises a connecting yoke between the first chain switch and the second chain switch for synchronous movement of the first chain switch and the second chain switch. 
     In an embodiment thereof the control cam is operatively connected with the first chain switch and the second chain switch. 
     According to a second aspect, the invention provides a method for operating a chain tensioner for employment on a bottom of a water body, wherein the chain tensioner is configured for adjustment of the length of a tensioning chain that extends between the chain tensioner and a floating offshore facility, wherein the tensioning chain comprises a series of connected links each having a main plane, wherein the links alternatingly have their main plane in a first orientation and in a second orientation that is under an angle with respect to the first orientation, wherein the chain tensioner comprises a frame that bounds a chain passage for the tensioning chain and that has a bottom wall or skid to stand on the bottom of the water body, a chain lock that is fixedly connected with the frame for engaging and confining a link of the tensioning chain in the chain passage from aside the tensioning chain, and a chain switch device comprising a chain guide for engaging the tensioning chain in the chain passage from aside the tensioning chain, wherein the tensioning chain is sidewardly moveable by means of the chain guide of the chain switch device by moving the chain guide with respect to the frame over a switching stroke between a first position in which the chain lock engages a link of the tensioning chain, and a second position in which the tensioning chain passes the chain lock, wherein the tensioning chain has an operational tensioning chain section that extends between the chain tensioner and the floating offshore facility, and an adjustment chain section that extends freely from the chain tensioner, wherein the method comprises the step of picking up the adjustment chain section, switching the chain guide of the chain switch device into its second position, pulling on the adjustment chain section, whereby the chain lock releases the tensioning chain and the tension chain slides through the chain passage, and switching the chain guide of the chain switch device into its first position, whereby the chain lock engages a link of the tensioning chain. 
     In an embodiment thereof the adjustment chain section is pulled upwards while the chain tensioner remains in contact with the bottom of the water body. 
     The various aspects and features described and shown in the specification can be applied, individually, wherever possible. These individual aspects, in particular the aspects and features described in the attached dependent claims, can be made subject of divisional patent applications. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be elucidated on the basis of an exemplary embodiment shown in the attached drawings, in which: 
         FIGS.  1 A and  1 B  show an offshore setup having a floating offshore facility that is anchored to a sea bottom by means of an anchor, with a chain tensioner according to an embodiment of the invention interposed that is shown in its unlocked and in its locked position, respectively; 
         FIGS.  2 A and  2 B  are respectively an isometric view of the chain tensioner in its unlocked position as shown in  FIG.  1 A , and a side view thereof wherein some parts have been removed for illustrative purposes; and 
         FIG.  3    is a side view of the chain tensioner in its locked position as shown in  FIG.  1 B , wherein some parts have been removed for illustrative purposes. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS.  1 A and  1 B  show an offshore setup in a water body, in this example a sea  1 , above a water body bottom, in this example a seabed  3 . The offshore setup is configured with a floating offshore facility at the level of the water surface  2 , such as a Floating Production, Storage and Offloading (FPSO) facility, or a floating wind turbine  6  for generating electricity offshore as shown in  FIGS.  1 A and  1 B . The floating wind turbine  6  is connected to multiple mooring lines that are distributed around it to form a plurality of catenaries to secure the position of the wind turbine  6  with respect to the seabed  3 . For illustrative purposes the  FIGS.  1 A and  1 B  show only one mooring line  7  thereof. The water is relatively shallow, but for illustrative purposes a notional steep catenary configuration of the mooring line  7  is shown. 
     The mooring line  7  is a rope based on a synthetic fiber, for example polyethylene (PE) or Dyneema®, but alternatively a traditional steel cable may be used. The mooring line  7  is connected with a steel tensioning chain  25  that due to its high own weight normally rests on the sea floor  3  over practically its entire length, even when sideward wind forces act on the wind turbine  6 . The tensioning chain  25  is fed through a chain tensioner  30  according to an embodiment of the invention that rests on the upper surface  4  of the seabed  3 . The chain tensioner  30  is anchored to the sea bed  3  by means of a heavy marine anchor  21  that is connected therewith via a steel anchor chain  20 . The heavy duty marine anchor  21  is for example a 10-30 tons marine anchor, such as the Vryhof Stevpris MK6 30-tons anchor. The chain tensioner  30  is destined for to remain positioned on the sea floor  3 , that is, during the operational lifespan of the floating wind turbine  6  or the marine anchor  21 , except on extreme cases where it can be temporary lifted by the mooring line  7  itself. 
     As shown in  FIGS.  2 A,  2 B and  3   , the tensioning chain  25  comprises a series of connected ring shaped or donut shaped steel links  26  each having a main plane M that is equal to the plane of symmetry. The links  26  have with respect to the notional center line of the anchor chain  25  alternatingly a first orientation and a second orientation in which the main planes M thereof are oriented under right angles with respect to each other, in particular when the tensioning chain  25  is under tension. In this example the links  26  have in the first orientation their main plain practically upright, and in the second orientation practically horizontal. The chain tensioner  30  divides the tensioning chain  25  in two notional chain sections. The operational tensioning chain section  27  thereof extends between the chain tensioner  30  and the mooring line  7 , and the not operational adjustment chain section  28  thereof extends freely from the chain tensioner  30 . 
     As best shown in  FIG.  2 A , the chain tensioner  30  comprises a steel frame  31  that is made of steel plate elements, comprising a skid or bottom wall  32  with a rectangular outline, and a left sidewall  33  and a right sidewall  34  that extend upright and parallel to each other from the bottom wall  32 . The left sidewall  33  and the right sidewall  34  have the same outline and are connected to each other with a top wall  35  that extends parallel to the bottom wall  32 . The left sidewall  33  and the right sidewall  34  are sideways stiffened by means of a left front wall  36  and a right front wall  37 , respectively, that extend perpendicular thereto. The bottom wall  32 , the left sidewall  33 , the right sidewall  34  and the top wall  35  together bound an internal chain passage  40  having a front entrance  41  and a top entrance  42  for the tensioning chain  25 . 
     As shown in  FIGS.  2 A,  2 B and  3   , the chain tensioner  30  comprises a steel anchoring lug  45  that is welded between the back ends of the left sidewall  33  and the right sidewall  34  via steel intermediate ribs  47 . The anchoring lug  45  comprises an end eye  46  that extends beyond the left sidewall  33  and right sidewall  34 . The anchor chain  20  is connected with the chain tensioner  30  by means of a steel shackle  50  having its mounting pin or mounting bolt  51  through the eye  46 . 
     As shown in  FIGS.  2 A,  2 B and  3   , the chain tensioner  30  comprises a steel chain lock  50  inside the chain passage  40 . The chain lock  50  comprises a plate shaped left hook body  51  and a plate shaped right hook body  52  that are welded parallel to each other against the left sidewall  33  and the right sidewall  34 , respectively. The left hook body  51  and the right hook body  52  have the same outline, having a catch aperture  53  that upwardly merges into a first guide edge  54  and that downwardly merges into a shorter hook edge  55  on a projecting hook section  56 . The catch aperture  53  debouches inside the chain passage  40  in the direction away from the front entrance  41 , wherein the first guide edge  54  and the hook edge  55  subsequently diverge from the catch aperture  53  into the chain passage and towards the top entrance  42 . The hook section  56  comprises a frontal second guide edge  57  that extends from the top plate  35  obliquely into the chain passage  40 . The left hook body  51  and the right hook body  52  are positioned spaced apart from each other to define a link passage  58  in between, having a width that allows loose passage of the links  26  in their first orientation only. Only in the second orientation the links  26  enter and fit loosely in the catch apertures  53 . 
     As shown in  FIGS.  2 A,  2 B and  3   , the chain tensioner  30  comprises a steel chain switch device  60  for positioning the tensioning chain  25  with respect to the chain lock  50 . The chain switch device  60  comprises a first chain switch  70  that is located on top and partly inside the frame  31 , a second chain switch  90  that is located fully inside the frame  31 , two external connecting yokes  110  between the chain switches  70 ,  90  and a control cam  130  to position the chain switches  70 ,  90  with respect to the frame  31 . The first chain switch  70  and the second chain switch  90  form chain guides of the chain tensioner  30 . 
     The first chain switch  70  comprises a plate shaped left switch body  71  and a plate shaped right switch body  72  that are welded parallel and spaced apart from each other to a top plate  73  and to two spacer pins  74 . The left switch body  71  and the right switch body  72  have the same outline, having a fluently curved first guide edge  76  that extends through the top entrance  42  of the frame  31  and that is convex towards the chain passage  40 , an end lug  78  that extends below the top wall  35  of the frame  31 , and a control lug  79  that extend above the top wall  35  of the frame  31 . The first chain switch  70  is hingeably connected to projecting top lugs  38  of the left sidewall  33  and the right sidewall  34  by means of a hinge pin  80 . 
     The left switch body  71  and the right switch body  72  of the first chain switch  70  define a first link passage  75  in between, having a width that allows loose passage of the links  26  in their first orientation only. Only in their second orientation the links  26  slide along and over the curved first guide edges  76 . The first chain switch  70  can toggle in direction C between a first position as shown in  FIG.  3    in which the first guide edge  76  on the end lug  78  is vertically aligned with the catch apertures  53 , and a second position as shown in  FIGS.  2 A and  2 B  in which the first guide edge  76  on the end lug  78  extends fully below the projecting hook sections  56 . 
     The second chain switch  90  comprises a plate shaped left switch body  91  and a plate shaped right switch body  92  that are welded parallel and spaced apart from each other to two spacer pins  94 . The left switch body  91  and the right switch body  92  have the same outline, having a fluently curved second guide edge  96  that ends at a front side  98  of the body that is located at the front entrance  41  of the frame  31 . The second guide edge  96  is convex towards the chain passage  40 . The second chain switch  90  is hingeably connected to the left sidewall  33  and the right sidewall  34  by means of a hinge pin  100 . 
     The left switch body  91  and the right switch body of the second chain switch  90  define a second link passage  95  in between, having a width that allows loose passage of the links  26  in their first orientation only. Only in their second orientation the links  26  slide along and over the curved second guide edges  96 . The second chain switch  90  can toggle in direction D between a first position as shown in  FIG.  3    in which the second guide edge  96  on the front side  98  is vertically aligned with the catch apertures  53 , and a second position as shown in  FIGS.  2 A and  2 B  in which the front side  77  of the guide edge extends fully below the projecting hook sections  56 . 
     As shown in  FIGS.  2 A,  2 B and  3   , the control lugs  79  of the first chain switch  70  are via a first hinge pin  111  hingeably connected with the upper ends of the connecting yokes  110 . The second chain switch  90  is via a second hinge pin  112  hingeably connected to the lower ends of the connecting yokes  110 . The first hinge pin  111  also hingeably connects the control cam  130  with the first chain switch  70 . 
     As best shown in  FIG.  3   , the control cam  130  comprises a first practically straight first abutment edge  131  at a first distance H 1  with respect to the center of the first hinge pin  111 . The first abutment edge  131  merges via a convex guide edge  132  into a practically straight second abutment edge  133  at a second distance H 2  with respect to the center of the first hinge pin  111 , wherein the second distance H 2  is smaller than the first distance H 1 . The control cam  130  comprises oppositely to the first abutment edge  131  an end eye  134  with a shackle  136 . By manipulating at the shackle  136 , the control cam  130  can toggle between a first position as shown in  FIG.  3    in which the first abutment edge  131  abuts the top wall  35  of the frame  31 , and a second position as shown in  FIGS.  2 A and  2 B  in which the second abutment edge  133  abuts the top wall  35  of the frame  31 . For illustrative purposes the abutting first abutment edge  131  and second abutment edge  133  are shown spaced apart from the top wall  35 . 
     The control cam  130  is used to change the chain tensioner  30  between a locked position and a unlocked position for the tensioning chain  25 . In the locked position of the chain tensioner  30  as shown in  FIG.  3   , the control cam  130  is in its first position, whereby it keeps the first chain switch  70  and via the connecting yokes  110  the second chain switch  90  in their first positions. In the unlocked position of the chain tensioner  30  as shown in  FIGS.  2 A and  2 B , the control cam  130  is in its second position, whereby the first chain switch  70  and via the connecting yokes  110  the second chain switch  90  are allowed to fall down to their second positions. It is possible to apply a small lost motion between the first chain switch  70  and the second chain switch  90 , for example by using elongate slots instead of round holes for the first hinge pin  111 . This facilitates that one of the first chain switch  70  and second chain switch  90  is operated first. This can be advantageous when the switches  70 ,  90  are stuck due to marine fouling or ingress of soil. 
       FIGS.  1 A and  1 B  show the offshore operations when the mooring line  7  is tensioned or re-tensioned. Re-tensioning is for example necessary to compensate slack that has been caused by initial relief that originates from the manufacturing process of the mooring line  7 . The operations are performed by using an anchor handling vessel  140  comprising a first hull  141  with a first winch  142  around which a first pulling line  143  is wound, and an auxiliary anchor handling vessel  150  comprising a second hull  151  with a second winch  152  around which a second pulling line  153  is wound. The chain tensioner  30  stands in its locked position on the seabed, having the control cam  130  in its upright, first position. 
     In this example the operations are performed by the two distinct vessels  140 ,  150 . However, the operations may also be performed by the anchor handling vessel  140  only, having both the first winch  142  and the second winch  152 . 
     As a first step as shown in  FIG.  1 A , the adjustment chain section  28  of the tensioning chain  25 , which lies freely on the surface  4  of the seabed  3  is picked up and attached to the first pulling line  143 , for example by means of a not shown remotely operated underwater vehicle (ROV). In the same manner the second pulling line  153  is attached to the shackle  136  of the control cam  130 . 
     As a second step, the second anchor handling vessel  150  with its second pulling line  153  is maneuvered such that the control cam  130  is toggled in direction E from its first position into its second position. Hereby the chain tensioner  30  changes into its unlocked position, wherein the first guide edge  76  guides the tensioning chain  25  inside the inner passage  40  downwards away from the chain lock  50  while the second guide edge  96  retracts over the same stroke from the chain lock  50 . By the pulling on the first pulling line  143  in pulling direction B, the link that is engaged in the catch apertures  53  is then released and the entire tensioning chain  25  moves in direction A through the chain tensioner  30  until the desired tension in the mooring line  7  or the desired length is reached for the mooring line  7 . During this operation, the tensioning chain  25  is smoothly guided upwards by the first guide edges  76  of the first chain switch  70 . 
     As a third step, as shown in  FIG.  1 B , the auxiliary vessel  150  with its second pulling line  153  is maneuvered such that the control cam  130  is toggled back in direction E from its second position into its first position. Hereby the first chain switch  70  and the second chain switch  90  move into their first position, whereby the second guide edges  96  urge the tensioning chain  25  into the chain lock  50 . By paying out the first pulling line  143  over a small stroke, the first link  26  in the second orientation that abuts the first guide edges  54  of the chain lock  50  becomes engaged in the catch apertures  53 . The pulling lines  143 ,  153  can then be disconnected and hauled in. 
     When above-described operations are performed only by the anchor handling vessel  140  having both the first winch  142  and the second winch  152 , the attached first pulling line  143  is initially kept slack while the anchor handling vessel  140  maneuvers to pull and toggle the control cam  130  into its second position. Thereafter the anchor handling vessel  140  maneuvers into its position as shown in  FIG.  1 B  in which it can pull with the first pulling line  143  on the tensioning chain  25 . When the desired length is reached for the mooring line  7 , the second pulling line  153  is pulled simultaneously to toggle the control cam  130  back in direction E into its first position. 
     The chain tensioner  30  according to the invention is configured to remain on the seabed  3  during use and during the entire above described tensioning or re-tensioning operation. 
     It is to be understood that the above description is included to illustrate the operation of the preferred embodiments and is not meant to limit the scope of the invention. From the above discussion, many variations will be apparent to one skilled in the art that would yet be encompassed by the scope of the present invention.