NL2015981B1

NL2015981B1 - Fairlead for a mooring leg

Info

Publication number: NL2015981B1
Application number: NL2015981A
Authority: NL
Inventors: Kruis Pim; Andries Rexwinkel Hendrik; Johannes Van Wezel Maurits
Original assignee: Ihc Holland Ie Bv
Priority date: 2015-12-17
Filing date: 2015-12-17
Publication date: 2017-07-05
Also published as: NL2015981A

Abstract

The invention relates to a fairlead (1) for a mooring leg (3) of an off-shore vessel (2) or installation comprising a frame (4) for guiding the chain (3) and attached or to be attached to an off-shore vessel (2) or installation, a chain stopper (9) mounted 5 in or on the frame (4), and one or more components (17) for operating the chain stopper (9). At least one of the components for operating the chain stopper (9) is detachable or detached from the rest of the fairlead (1).

Description

Fairlead for a mooring leg

The invention relates to a fairlead for a mooring leg of an off-shore vessel or installation, such as an Floating Production, Storage and Off-loading vessel (FPSO) or Single Point Anchor Reservoir (SPAR), comprising a frame for guiding the chain and attached or to be attached to an off-shore vessel or installation, a chain stopper mounted in or on the frame, and one or more components (17) for operating the chain stopper. A fairlead, e.g. an Integrated Stopper Arm Fairlead (ISAF), is part of the mooring system of e.g. Offshore Oil Production Platform's (OOPP's) and oil production ships, such as FPSO's. It is used to guide a mooring chain during tensioning or slackening / paying out of the chain and, after the chain has been installed, to transfer the mooring loads to the platform or hull. On a ship shape or mono-hull vessel, the ISAF can be located in or near the splash zone and on an OOPP, such as a SPAR, or semi-submersible, it is typically located subsea, down to 100 meters of sea water (msw). The chain stopper is used to lock the chain and transfer the mooring loads to the vessel hull. WO 98/40306 relates to an underwater self-aligning fairlead latch device for guiding and securing an anchor chain (denoted by "C" in the Figures of WO 98/40306) between an offshore structure (P) and an anchor (PA). The fairlead device includes a latch housing (14) pivotally mounted to a fairlead housing (12). The latch housing includes one or more latches (42) for securing the anchor chain in place.

The fairlead housing includes a bending shoe (28) which guides the anchor chain from its orientation within the bending shoe up the platform column (PC) to the deck. The fairlead housing is pivotally mounted to the offshore structure . US 2014/346420 relates to a self-aligning fairlead latch device which includes an upper retainer component that is coupled to an upper support structure and a lower support structure. The coupling of the upper retainer component to the support structures allow the fairlead latch device to be relocated by lifting of the device from the support structures . US 5,441,008 relates to a submerged fairlead for a mooring line for use on a structure at sea, which is rotatably mounted in a swivelling elongated rigid tube mounted on the structure and through which the mooring line passes, and the free end of which is equipped with a line stopper. The tube is several meters in length. It causes direct transfer of the mooring forces to the structure when the line stopper is activated. A fairlead chain stopper marketed under the name Pusnes is a combined swiveling fairlead and chain stopper designed in particular for passive mooring of floating production vessels. This design allows the chain to be locked at an underwater level constraining maximum loads to a limited area. The chain stopper is a ratchet type that closes automatically during pull-in. The ratchet can be opened hydraulically or mechanically during chain pay-out.

It is an object of the present invention to provide an improved fairlead, in particular to improve the reliability of critical components when the fairlead is installed in the splash zone or subsea environment.

To this end, the fairlead according to the invention is characterized in that at least one of the components for operating the chain stopper is detachable or detached from the rest of the fairlead. In an embodiment, at least one component for operating the chain stopper is mounted in or on a subframe and the component and the subframe are detachable or detached from the stopper and the frame. In another embodiment, at least one of the components is an actuator for opening and/or closing the stopper, a sensor or a junction box.

The subframe and the components it carries, in particular said actuator, thus form a module that can be demounted from the fairlead, e.g. to carry out maintenance or repairs, without the need to open the chain stopper and thus without slackening or removing of the mooring chain.

For instance, the module can be demounted, serviced on board and remounted or replaced by a spare unit, by means of an ROV, a diver or alternatively from deck level.

In an embodiment, the module is attached to one side of the fairlead, preferably the side of the fairlead facing away from the vessel or installation. Thus, only that side needs to be accessible during mounting and demounting.

In an embodiment, the stopper comprises at least one rotary stopper pawl, which is coupled to a rotary connector, and the actuator comprises a rotary connector counterpart.

In an example, the stopper comprises two rotary stopper pawls and/or the actuator in or on the subframe is a quarter turn actuator or a motor with gearbox, suitable for subsea use. In another example, the actuator comprises a pneumatic cylinder, a hydraulic cylinder, or an electric linear actuator that operates, when the module is mounted on the fairlead, one or more levers for rotation of a pawl shaft in the chain stopper. After opening, the pawl may be in an over-centered position for keeping the pawls in position without connection to an actuator, i.e. when the module has been removed from the fairlead.

In an embodiment, the rotary connector coupled to the pawl comprises a rotary bucket, preferable a rotary intervention bucket. Such rotary pawls and connectors, preferably buckets, facilitate establishing a connection, in particular a plug-in connection, between the actuator and the stopper. Also, buckets enable a torque tool, e.g. on an ROV or operated by a diver, to interface with fairlead when the subframe and actuator are not in place. In an embodiment, the bucket or buckets coupled to the at least one actuator are an ISO 13628-8 compliant design.

In another example, rotary connection of the subframe actuator to the ISAF pawl shaft is established by a square opening in the (driven) shaft and an actuator having a driving that fits the square opening on the fairlead. In an embodiment, such openings are provided with extra guidance to facilitate engagement of the pawl and actuator shafts. A flexible coupling between the pawl and actuator shafts or a flexible mounting of the actuator in the subframe may compensate misalignments.

To facilitate establishing contact between the module, i.e. the subframe and the components it carries, and the frame of the fairlead, the module and the frame comprise alignment and locking elements. E.g., one of the module and the frame comprises at least one protrusion, such as a stud, pin, key, or spline, preferably at least one protrusion on each side, and the other comprises at least one open-ended slot, preferably at least one open-ended slot on each side, to receive the at least one protrusion. In a refinement, the at least one slot comprises at least two edges and one of the edges of the slot extends beyond the other. E.g. if the frame comprises a pair of slots and the lower sides of the slots extend beyond the upper side, protrusions on either side of the module can be lowered onto the lower sides of the slots.

In another embodiment, the module comprises a sensor for detecting the open and closed chain stopper positions. The sensor can be mounted on the actuator or at a separate position and detect the position of the stopper, e.g., via detection of the rotary position of a pawl shaft or via detection of the position of the pawl itself.

The invention further relates to a method of mounting on a stopper frame of fairlead for a mooring leg of an off-shore vessel or installation as defined in the pre- amble, a module comprising one or more components for operating the chain stopper in the stopper frame, the method comprising the steps of manoeuvring the module to a position close to the stopper frame, engaging the module and the stopper frame, and operatively connecting the module and the stopper frame.

In a robust embodiment, at least a part of the component, e.g. an actuator, is plugged into the stopper, e.g. by sliding movement of the module.

In another embodiment, the module is releasably locked to the stopper frame.

Demounting the module from the fairlead is performed in reverse order.

The invention will now be explained in more detail with reference to the drawings, which schematically show embodiments of the device and method according to the present invention.

Figure 1 is a perspective view of a fairlead according to the present invention comprising a chain stopper and a module for operating the chain stopper.

Figures 2 and 3 show the chain stopper in the fairlead of Figure 1 in more detail.

Figure 4 shows the module on the fairlead of Figure 1 in more detail.

Figures 5A to 5F show six steps of the process of coupling a subframe and actuator to the chain stopper of a fairlead.

Figure 1 shows a so-called Integrated Stopper Arm Fairlead 1 welded to the hull 2 of an off-shore vessel, such as a floating production, storage and off-loading vessel (FPSO; not shown), or installation for guiding a mooring chain 3 during tensioning or slackening of the chain and to transfer the mooring loads to the hull after the chain has been installed. The fairlead comprises a stopper frame 4, which at its top section is attached, pivotable about a horizontal shaft, to a swivel of flag frame 5 that is mounted, pivotable about a vertical shaft, in brackets 6 that, as mentioned, have been welded to the hull of a vessel. The frame further carries, in its top section, a chain wheel 7 for guiding the chain to a winch on the deck of the vessel. The winch serves the tensioning or slackening of the mooring chain. A tube or stopper arm 8 is attached, e.g. bolted, to a bottom section of the frame 4 to reduce the Out of Plane Bending (OPB) effect, in a manner known in itself . A chain stopper 9, shown in more detail in Figures 2 and 3, is located inside the frame 4 below the chain wheel 7 and comprises a channel 10 for the chain and a pawl or pawls 11 to block the mooring chain 3, e.g. to hold the mooring chain in place after it has been installed. The stopper can also be actively opened and closed and to enable re-tensioning or slackening of the mooring chain.

In the present example, the stopper comprises two rotary pawls 11 on shafts 12 and an end of each of the shafts is provided with a rotary intervention bucket 13, preferably an ISO 13628-8 compliant bucket. The buckets are accessible from the outside of the stopper frame.

The pawls 11 are operated, e.g. opened or closed, by a module 15, shown in more detail in Figure 4, that is detachably mounted on the stopper frame 4. The module comprises a subframe 16 and two quarter turn actuators 17 mounted in the subframe. Each of the actuators is provided with an actuator connector shaft 18 (see also Figure 5A), enveloped by a bush to protect the shaft and facilitate alignment. The actuator connector shaft can be plugged in and coupled to the buckets in the stopper frame. To facilitate alignment, the shafts 18 are mounted on the drive shafts of the actuators 17 via resilient elements. Two sensors (not shown) are provided in the module for detecting the open and closed positions of the pawls. The module comprises alignment and locking elements, in this example three studs 20, 21, 22, on either side of the module 15, the first 20 and second 21 of which are positioned on a line that extends parallel to the rotary axes of the actuator connector shafts 18 and the first 20 and third 22 of which extend perpendicular to the rotary axes of the shafts 18, and eyebolts 23 and nuts, which, in this example are attached to the studs. To operate and power the actuators 17 and receive signals from the sensors, the module 15 further comprises a junction box 25, data cables 26, and a hydraulic hose 27.

In general, power supply can be hydraulic, pneumatic or electric. Power can be supplied e.g. from a power source on the OOPP by pneumatic or hydraulic hoses or piping and/or electric cables, either as an umbilical from the OOPP when using the stopper actuators or as fixed hoses, piping and/or cabling mounted to the OOPP and the ISAF. Alternatively, stored energy on the subframe can be used, e.g. electric batteries or pneumatic/hydraulic accumulators.

In an example, diver- or ROV operable wet mateable connectors are used for connection of a power supply to the subframe. In another example, connectors for cables and hoses that are part of an umbilical, are combined in one multi-connector e.g. an electro-hydraulic stabplate or a multicore connector. In yet another example, signal cables, preferably protected signal cables, can be used to transfer signals between the vessel or installation and the fairlead. In case a temporary umbilical from the vessel or installation is used to supply the stopper actuators, the signal cables can be part of this umbilical. Alternatively, an acoustic signal may be transferred between a transmitter/receiver on a subsea part of the vessel and a transmitter/receiver on the fairlead or the module.

The fairlead comprises alignment and locking elements complementary to those on the module. In this example, the frame comprises, on either side of the stopping mechanism, an open-ended slot 30 to receive the studs 20, 21 on the module 15 that extend parallel to the rotary axes of the actuator connector shafts 18. The lower edges of the slots 30 extend beyond the upper edges of the slots.

Figures 5A to 5F illustrate, by way of example, how the module is mounted on the fairlead. With the pawls closed, the module 15 is lowered or manoeuvred to a position close to the stopper frame 4 of the fairlead (Figure 5A). With the actuator connector shafts 18 facing the stopper frame 4, the first alignment studs 20, i.e. those closest to the shafts 18, are lowered onto the lower edges of the slots 30 on the fairlead (Figure 5B) , providing initial alignment. The module 15 is rotated, in this example until the third studs 22 engage the alignment elements on the fairlead (Figure 5C). Rotation to a lesser extent typically suffices. Next, the module 15 is slid and rotated towards the stopper frame 4 (Figure 5D), resulting in further alignment of the shafts 18 in de module and the buckets in the stopper frame 4 (Figure 5E). Finally, the module 15 is slid towards the stopper frame 4, thus inserting the actuator connector shafts 18 in the buckets (Figure 5F) and completing alignment, and the eyebolts 23 are closed and the hydraulic and electric couplings connected. Demounting the module from the fairlead is performed in reverse order.

When the module is dismounted, override is available, e.g. by operating the pawl shafts with a torque tool. In an example, the sensors include the option to detect sensor failure, for example by use of NAMUR type sensors .

The invention is not restricted to the above-described embodiments, which can be varied in a number of ways within the scope of the claims. For instance, module can be designed to normally stay in place on the stopper frame and demounted when it must be serviced or it can be designed to be used as a tool, to be attached to the stopper frame of the fairlead when the chain stopper must be opened or closed. In the latter design, one module can be employed in conjunction with a plurality of fairleads.

Claims

A chain guide (1) for a mooring line (3) of an offshore vessel (2) or an installation comprising a frame (4) for guiding the chain (3) and mounted or mounted to an offshore vessel (2) ) or installation, a chain stopper (9) mounted in or on the frame (4) and one or more components (17) for operating the cetting stopper (9), characterized in that at least one of the components for operating the chain stopper (9) is releasable or detached from the rest of the chain guide (1).

A chain guide (1) according to claim 1, wherein at least one component (17) for operating the cetting stopper (9) is mounted in or on a subframe (16) and the component and the subframe (16) are releasable from the stopper (9) and the frame (4).

Chain guide (1) according to claim 1 or 2, wherein at least one of the components is an operating part (17) for opening and / or closing the stopper (9), a sensor or a connection box.

Chain guide (1) according to one of the preceding claims, wherein the stopper (9) is provided with at least one rotating stopper catch (11) which is coupled to a rotating connector (13) and wherein the operating part (17) is / are provided of a rotating connector counterpart (18).

A chain guide (1) according to claim 4, wherein the rotary connector coupled to the pawl (11) is provided with a rotary bucket, preferably a rotary intervention bucket (13).

A chain guide (1) according to any one of the preceding claims, wherein the subframe (16) and at least one component (17) together form a module (15).

Chain guide (1) according to claim 6, wherein the module (15) and the frame (4) of the chain guide (1) contain alignment and locking elements (20, 21, 22, 23, 30).

Chain guide (1) according to claim 7, wherein of the module (15) and the frame (4) one is provided with at least one protrusion (20, 21, 22), preferably at least one protrusion on each side, and the other is provided with at least one open-ended slot (30), preferably at least one open-ended slot on each side, for receiving the at least one protrusion (20, 21, 22).

The chain guide (1) of claim 8, wherein the at least one slot (30) has at least two edges and one of the edges of the slot (30) extends beyond the other.

Chain guide (1) according to one of claims 6 to 9, provided with three posts (20, 21, 22) on either side of the module, the first (20) and second (21) of which are positioned on a line extends parallel to the axis of rotation of the rotating connector counterpart (18) and whose first (20) and third (22) are positioned on a line extending perpendicular to the axis of rotation of the rotating connector counterpart (18).

Chain guide (1) according to one of the preceding claims, comprising a sensor for detecting at least one of the open and closed positions of the chain stopper (9).

Chain guide (1) according to one of the preceding claims, comprising signal cables or an acoustic transmitter / receiver for transferring signals between the vessel (2) or installation and the chain guide (1).

A method for mounting a chain guide (1) for a mooring line (3) of an offshore vessel (2) or installation as defined in the preamble of claim 1, wherein a module (15) is provided on a stopper frame (4) of one or more components (17) for operating the chain stopper (9) in the stopper frame (4), which method comprises the steps of maneuvering the module (15) in a position close to the stopper frame (4), engaging the module (15) and the stopper frame (4), and operatively connecting the module (15) and the stopper frame (4).

The method of claim 13, including plugging at least a portion (18) of the module (5) into the stopper (19).

A method according to claim 13 or 14, comprising releasably locking the module (15) with the stopper frame (4).