WO2014083056A1

WO2014083056A1 - An underwater connecting system

Info

Publication number: WO2014083056A1
Application number: PCT/EP2013/074860
Authority: WO
Inventors: Kristoffer Kjellså JAKOBSEN
Original assignee: Aker Engineering & Technology As
Priority date: 2012-11-27
Filing date: 2013-11-27
Publication date: 2014-06-05
Also published as: NO335406B1; NO20121422A1

Abstract

An underwater connecting system comprising at least one first connector unit (3) and at least one second connector unit (4) to be located under water below said first unit in a secured position. The first unit is guided to the second unit, while hanging in a mooring line (2), by gravity and a tensioned guide line (5) to which both the first unit and the second unit are operatively connected. The second unit is so connected to the guide line that strain acting on the guide line due to movements between the first and second units is substantially reduced.

Description

An underwater connecting system

FIELD OF THE INVENTION The present invention relates in general to an underwater connecting system for connecting two parts of an under water link, especially a mooring connection, and to a method for achieving such connection.

Particularly, the present invention relates to a system and method for connecting two parts of an underwater link in a reliable manner that requires simple and light weight guiding and alignment means, and, simultaneously, the requirement for accurate positioning of the installation unit is substantially reduced and movements between the connecting parts while establishing the connection are substantially reduced.

More particularly, the present invention relates to an underwater connecting system according to the preamble of claim 1.

TECHNICAL BACKGROUND OF THE INVENTION

Off-shore operations, such as hydrocarbon exploration and production have become immensely important over the decades, with the increasing demand of the modern society. With Increase in various types of off-shore operations, anchoring of floating structures on the sea bed or with any other underwater substrate has become a daunting task for the engineers. This is particularly because floating structures need to be anchored at various distances away from the shore, and often far into the open sea. Consequently, floating structures have to withstand different degrees of adversities such as those of hostile weather and large waves. It is known to persons skilled in the art that such floating structures may be offshore oil platforms, vessels, wind turbines, wave power plants and any other type of floating structures that it is desirable to anchor. Underwater anchoring of floating structures is frequently achieved by connecting mooring lines by means of underwater links, the underwater links having an upper part and a lower part with respect to the anchoring substrate, such as a sea bed or any structure on a sea bed. For tethered devices, commonly one or more anchors and a part of the mooring line are pre-installed at the location some time before the unit to be tethered arrives. The primary purpose is to reduce the exposure of the facility to the weather during installation and to reduce the number of vessel days during the installation and thus the costs.

In recent years it has become common to connect the mooring lines by means of underwater links. This is especially true for the anchoring systems for large water depths and mooring systems with segments of fiber rope, because only a small part of the mooring line is required to be pre-installed with the anchor.

In shallower waters it is possible to obtain benefits through the use of underwater links, since only a small part of the mooring lines are installed with the anchor, resulting in a lower number of vessel days for installation vessels used during anchor installation. Smaller and less expensive vessels can in many cases be used to add the rest of the mooring line and connect it to the underwater link.

In conventional use of underwater connector, the pre-installed half of the coupling is arranged vertically on the seabed, either attached to the anchor or on a rest plate, also called mud mat, that rest on the seabed. The other half of the link is connected to the upper part of the mooring line on board the installation vessel and lowered to the seabed. Accurate positioning of the link is performed by displacement of the installation vessel. The disadvantages of the conventional coupling of the underwater connector are that the movements of the installation vessel are transmitted to the upper coupling half. Horizontal movements complicate the adjustment and make it more difficult to mate, while the vertical motion is prone to cause collisions between the parts with subsequent damage.

That apart it is often time consuming, especially in deep waters to get the installation vessel in the correct position above the underwater link, and a high degree of positioning accuracy to keep the installation vessel on the same spot is required.

The conventional coupling of underwater connectors requires that one of the, i.e. the lower, connector halves is attached to a solid base at the seabed and thereby restrained from movements.

This means that with the prior art hook-up systems it is not possible to establish the connection between two flexible mooring segments within the water column, i.e. perform hook-up with the connectors situated above the seabed but also under the sea surface, as the prior art solutions requires either that the lower connector is fixed relative to the seabed or that the lower connector is pulled up to a connector fixed on the platform or vessel.

If the lower connector is pulled all the way up to the platform or vessel it is not possible to adjust the mooring line tension by a winch on board the platform or vessel. Consequently, the wire line has to be connected under full pre-tension, which may be in the order of several hundred tons. Alternatively, clump weights must be attached after connection to increase tension to the desired level.

Many attempts have been made over the years to cope with the above defects during connection of the two parts of an underwater link.

For example, EP0034890 discloses a connector assembly having a first connector and a second connector. The first connector has a guide post and the second connector has means for receiving the guide post. These are all known features. According to the invention disclosed by this document, a line is releasably attachable to the guide post and extends from this. The line is passed through the receiving means of the second connector. The second connector slides down the line, onto the guide post of the first connector and into the receiving means of the first connector, thereby achieving connection.

The above reference does teach alignment or positioning of the first connector and second connector, reducing the requirement for displacement of the installation vessel for positioning of the two connectors for coupling. However, the possibilities of collision of different components of the connecting members, during connection procedure are still present. This is primarily because this reference does not teach minimal movement between the connecting members of the underwater link for achieving connection. Additionally and as a consequence to this, the construction disclosed requires good weather conditions. That apart, this reference discloses a very complicated construction, which renders the product costly and cumbersome.

US4459931 discloses a system for releasably connecting a marine vessel to an anchor base on the sea bed. The system has an anchor secured to the sea bed and a connector having an inner element and an outer element. The locking of the inner element and outer element is remotely controlled and simultaneously, the inner element is connected to a buoy. Due to this connection to a buoy, the inner element always has a vertical tension despite wave action, when the inner element is lowered into the outer element. During the final stages of installation, the vertical tension is released so that the inner element moves downward by gravity into the outer element and final connection is achieved.

From the above description, it ought to be clear to persons skilled in the art that the methodology as disclosed in the above paragraph involves creating and releasing vertical tension on and from the inner connector. Furthermore, the guide line for alignment of the connecting parts is constantly subject to strain from the buoy. Hence, the known methods demand a large winch and heavier wires/ropes to be able to sustain the stress of pulling the inner element down, and they are liable to malfunctioning, in addition to being costly. That apart the chances of collision between components of the connecting elements during installation very much exist, as the operation involves substantial movement of heavy parts. Also, in this method, upon installation of the mooring line, a large buoy will be hanging on the line. The handling of this buoy further complicates the procedure.

Additionally, in both US 4459931 and EP 0034890, the connector at the seabed is fixed to the seabed. If a rapid movement of the surface vessel takes place say due to wave action, a sudden jerk is likely to be imparted to the guideline, which might snap it. Hence, it is required according to these solutions that the guide line has to be made stronger, which also means thicker, resulting in a substantial increase in weight of the guide line which is typically more than 2000 metres long. This in turn requires the connections of the guideline also to be heavy and bigger resulting in increasing constructional complication and cost.

EP 1283158 describes an anchor line installation method and connector whereby a lower connector is attached via an anchor line to a subsea anchor. A guideline is fed through the lower connector and attached at one end to an upper connector. The guideline is used to pull the upper connector towards the lower connector and to mate the two.

A disadvantage of this method and apparatus is that the anchor line that extends from the anchor to the lower connector has a substantial weight. As the guideline is not only pulling the upper connector towards the lower connector, but also has to carry the weight of the lower connector and the anchor line. Especially this is true when an anchor chain is used instead of an anchor wire, as will be the case when large structures are to be moored.

Accordingly, there has been a need for a technology for connecting the parts of an underwater link in a safe and reliable manner by applying a reliable and simplified system, which needs lighter and simple guiding and alignment means and connections therefore. There is also a need to ensure that the requirements for accurate positioning of the installation unit are substantially eased, and movement between components of the elements of the link are substantially reduced while achieving connection. It is further desirable to be able to perform the connection while allowing both connector halves freedom of movement during the hook-up.

The present invention meets the above long felt need and other associated needs by providing a technology which applies a very simple and light weight guiding and alignment means for connecting the two parts of an underwater link for the purpose of anchoring a floating structure on the sea bed .

OBJECTS OF THE INVENTION It is principal object of the present invention to provide an underwater connection system and a methodology for connecting parts of an underwater link in a safe and reliable manner, which therefore needs lighter and simple guiding and alignment means and connections. It is another object of the present invention to provide an underwater connection system and a methodology for connecting parts of an underwater link, which substantially alleviates the requirements for accurate positioning of the installation unit, and also movement between components of the elements of the link are substantially reduced while achieving connection.

It is another object of the present invention to provide an underwater connecting system for connecting parts of an underwater link, which is simple in construction, requiring application of less complicated and light weight components, easy to operate and very cost effective.

It is another object of the present invention to provide a subsea connecting assembly and a methodology for connecting two parts of a subsea connector along a mooring line which can be applied with any type of anchoring structures on the seabed meant for anchoring offshore structures and is adapted to withstand adversities of weather conditions.

How the foregoing objects are achieved and other advantageous features will be clear from the following non-limiting description.

All through the specification, including the claims, the words, "underwater", "subsea ", "connector", "assembly", "off-shore structure", "installation vessel", "guide line/help line", "mooring line", "anchor line" are to be interpreted in the broadest sense of the respective terms and includes all similar items in the field known by other terms, as may be clear to persons skilled in the art. Restriction / limitation, if any, referred to in the specification, is solely by way of example and understanding the present invention. SUMMARY OF THE INVENTION

In a primary aspect the invention defines an underwater connecting system comprising at least one first connector unit and at least one second connector unit to be located under water below said first unit in a secured position, wherein said first unit is guided to said second unit, while hanging in a mooring line, by gravity and a tensioned guide line to which both said first unit and said second unit are operatively connected, said second connector unit is either loosely seated in a bracket attached to an anchor, or that said second connector unit is held on a staging device placed on the sea bed, said staging device acting to hold the second connector unit in a specific orientation, and said second unit being connected to a lateral side of the anchor by means of a flexible chain or wire.

Since the second (lower) connector has been given a predetermined position and orientation, the first (upper) connector can be lowered to a distance relatively close to the lower connector before there is a need to pull the guideline in order to mate the two connectors. There is a substantially reduced need to lift the lower connector from Its seat or the seabed. Hence, the guideline does not need to carry a substantial portion of the anchor chain or wire. If a sudden upward movement of the vessel that pulls the guideline should occur during the last part of advancing the upper connector towards the lower connector, which may cause a high strain on the guideline, the lower connector will be lifted from the seat or the seabed. Thereby the risk of the guideline breaking is reduced and the possibility of using a thinner guide wire than in the prior art is provided.

By letting the tensioned guideline extend from said first connector unit via said second connector unit to an installation vessel or an assist vessel at the surface, a convenient way of mating the two connectors is achieved.

In a preferred embodiment, the first unit is a male connector which is lowered down along a mooring line from an installation vessel and said second unit is a female connector connected to the side of an anchor on a seabed by a flexible means. This provides connectors with good mating ability.

In a further preferred embodiment, the tensioned guide line passes through a pulley mounted on said second connector unit. This further enhances the mating capabilities of the connectors.

In a preferred embodiment, the mooring line is a flexible chain and said flexible chain as well as said second connector unit are pre-installed on the sea bed.

In one embodiment, the guideline is pre-installed along with said anchor with its free end either placed on the seabed or hung off in a buoy at the surface. This provides for a simple procedure for hook-up. BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES Having described the main features of the invention above, a more detailed and non-limiting description of some preferred embodiments will be given in the following with reference to the drawing, in which: Figure 1 is a schematic view of a preferred embodiment of the underwater connecting system according to the present invention.

Figure 2(a) is a schematic view of a further preferred embodiment of the underwater connecting system according to the present invention.

Figure 2(b) is a schematic view of a subsequent stage as shown in figure 2(a) after connection and tightening of the anchor line.

Figure 3 is a schematic view of a further preferred embodiment of the underwater connecting system according to the present invention.

Figure 4 is a schematic view of another preferred embodiment of the underwater connecting system according to the present invention. Figure 5(a) is a schematic view of a preferred embodiment of the present invention, where the installation method according to the present invention is applied during hook up of a platform to the seabed.

Figure 5(b) is a view showing the details of the connecting elements shown In figure 5(a).

DETAILED DESCRIPTION OF THE INVENTION

The following provides a detailed, exemplary non-limiting description of preferred embodiments of the underwater connecting system and the methodology according to the present invention. The connection elements are shown as male and female connectors in the figures. This is for the sake of illustration and not by any means a limitation to the present invention, as the connectors may be any suitable mating elements. In the above context, it is hereby clarified that hereinafter, the present invention has been explained with reference to sea, seabed, mooring lines, installation vessels. It should be understood that these are all for the sake of explanation and not by way of any limitation. Further, the expressions "upper", "lower", "top", "Bottom" and similar expressions should be understood with respect to the sea bed or water level.

The present invention pertains to connecting all types of connectors of an underwater links as stated in the opening lines of this specification and includes all types of underwater installations, underwater links and substrates other than seabeds, as well as installation units other than vessels as will be known to persons skilled in the art. Reference to the expression "mooring line" is also likewise non-limiting, as this is also considered to include such elements as chains, ropes and wires. The present invention provides a system and procedure for connecting the mooring lines under water that is less affected by vertical and horizontal movements of the installation vessel and that put lower demands on positioning accuracy for the installation vessel and, consequently, positioning of the component parts in the strictest sense. Additional purposes of the invention, are that it saves time and reduces the possibility of damage to the underwater link.

Importantly, the construction is such that the guideline meant for guiding and alignment of connectors is subjected to less strain. Hence, the guide line and its connections can be made light weight and simple. The advantages will be understood from following description of the accompanying figures where like reference numerals represent like features.

The present invention is schematically illustrated in the accompanying figure 1. The underwater link essentially comprises an upper coupling element 3 and a lower coupling element 4. The lower coupling element 4 is connected by flexible means 14 such as a flexible chain or wire to an anchor 6 at the seabed 15. The lower coupling element 4 is connected at the side of the anchor 6 by the flexible means 14.

At the start of the pairing operation the lower coupling 4 of the underwater link and the anchor 6 are installed on the seabed 15. A guideline 5 extends from the surface 16, through the bottom section of the lower coupling 4 of the underwater link and up to the surface 16 again. Here the term surface refers to just above the water level.

On the installation vessel 1 the upper coupling element 3 of the underwater link is connected with the mooring line 2. The mooring line 2 is placed over the winch (not shown) or similar device adapted to lowering it down to the seabed 15. The winch or such similar device is known and not consequential to the present invention.

One end of the guide wire 5 is attached to the upper connector 3 and the other end is connected back to the installation vessel 1 through one or more pulleys 7 mounted on the lower connector 4. The other end may be attached to an auxiliary winch (not shown).

All types of under water links known in the art and the constituent components may be applied for the present invention and are not elaborated further, as those portions are not consequential to the present invention.

For better understanding of the invention, some additional embodiments will now be described, with reference to the remaining figures where identical reference numerals indicate similar features as in figure 1.

Figure 2(a) is a view of a further preferred embodiment. Here the upper connector 3 is being guided towards the lower connector 4 as in Figure 1. However, the lower connector 4 is connected to a lifting eye 8 down at the anchor 6 using a flexible chain 14 and rests on a rest plate 9 on top of the anchor 6. The lower connector 4 may be non -attached to the rest plate 9 or attached by a weak connection, so that it will detach if a pull over a certain limit is exerted on the guide wire 5. The rest plate 9 can be configured to orientate the lower connector 4 in an orientation which facilitates the mating with the upper connector 3.

The flexible anchor mooring chain 14 between the lower connector 4 and the anchor 6 is also shown here.

Figure 2(b) is a view of a stage subsequent to what is shown in figure 2(a), when the upper connector and lower connector 4 are in secured position.

Figure 3 is a view of a further preferred embodiment. It illustrates, how the present invention may be applied in conjunction with a "free drop anchor" 10 (also called torpedo anchor, "gravity installed anchor" or "deep penetrating anchor"). Here the lower connector 4 is attached to a rest plate 9, or mud mat that is adapted to rest on the seabed while holding the lower connector 4 In an upright position. The rest plate 9 may also facilitate the orientation of the lower connector 4. As for the embodiment in Figure 2(a), the connector may be non- attached to the rest plate or connected by a weak link, but can also be fixedly attached to the rest plate as the rest plate may lift from the seabed if the pull in the guide line exceeds the combined weight of the lower connector and the rest plate and hence avoid excessive loads in the guide line.

Figure 4 is a view of an embodiment similar to the embodiment illustrated in figure 3. The lower connector 4 is connected to the flexible anchor line 14, which lies on the seabed 15.

Figure 5(a) is a view of a preferred embodiment which shows a closely similar embodiment as in figures 2(a), 2(b) and figure 4. Figure 5(b) is an enlarged view of figure 5(a) which shows the components in more detail.

Now the functioning of the methodology and the advantages achieved by the constructional features are explained again with reference to the figures. The structural connections between the various components are not elaborated again as those have been already described.

Referring back to figure 1, the use of flexible means 14 for flexibly attaching the lower connector 4 to the anchor 6, ensures that the lower coupling element 4 is able to move and adjust itself in response to a sudden jerk caused by wave motions or by any other thing. This ability of the lower coupling element 4 to move in cases of jerks effectively reduces the strain on the guideline 5 and hence it can be made thinner as well as lighter.

Furthermore, connecting the lower coupling element 4 at the side of the anchor 6 ensures that the anchor 6 does not get uprooted from the seabed 15 easily because the force required to get the anchor loose from the seabed will be much greater in this arrangement, than in an arrangement where the lower coupling link is connected at the top of the anchor.

The gravity acting on the upper underwater connector 3 and the mooring line 2 is the driving force to bring the coupling elements 3 and 4 together as the tensioned guide line 5 controls positioning and movement of the upper part 3 of the underwater link.

Hence, the upper part 3 and lower part 4 of the underwater link are brought together, connected and locked. This combined effect of guided gravity movement by the guideline, effected by a simple arrangement of guide line, pulleys and winches all operatively connected, constitute the crux of the invention. In accordance with the present invention, the guideline 5 is kept relatively taught and the upper connector 3 sinks down by gravity. Thus, the guideline 5 can be made thinner. The arrangement reduces the requirement for accurate positioning of the installation vessel. It also substantially reduces the movements between the connecting components, as the simple arrangement of guidelines, pulleys and winches all ensure guiding the movement between the connectors. These components are all lightweight and easy to operate. The technology also ensures that the connecting parts are less not affected by the vertical and horizontal movement of the installation vessel and that the hook-up operation is not limited by vertical and horizontal movements of the installation vessel.

After the underwater connectors 3, 4 are locked; the guideline 5 may be disconnected from the underwater link by an ROV or another facility (not shown).

If the auxiliary winch keeps constant tension in the control line 5, it automatically pulls in roughly the same length of guideline 5 as the length of the mooring line 2 that is lowered. There is thus no need for continuous manual control by the winch. As the mooring line 2 has a different submerged weight than the guideline 5, it may in some cases be necessary to adjust the tension by using the winch to maintain the proper configuration of the mooring line as it is lowered. This may be relevant if the mooring line is lowered at an angle to the vertical.

The present invention thus describes a way to guide the connectors together, making installation easier and the installation vessel does not need to be completely still right above the lower connector (as is the case with "traditional pairing" of underwater connectors). The method can be used on ordinary anchor vessels without major modifications as only a small winch is required to handle the guideline 5.

The guideline 5 can be pre-installed with the anchor 6 and hung off in a buoy on the surface or may be placed on the seabed 15 and then picked up right before the installation. It can also be installed with an ROV directly prior to installation. Both ends of the control line 5 must be collected and taken on board the installation vessel 1.

Another option is to use a forerunner and buoy installed on the connector that is triggered by an acoustic signal. The buoy is picked up on the surface and the forerunner is attached to the guideline, which then is fed through the underwater link. Both ends of the forerunner must be picked up from the surface. To facilitate the pairing of the two parts of the underwater link, guide devices such as male and female cones (not shown) are used where the guideline 5 enters the lower part of the underwater link. Instead of passing the guideline through the connector, it may also connect to the outside of the connector. This is especially relevant for retrofitting of existing connector. It is also conceivable to use two essentially parallel guidelines for better control of the mating process.

An ROV near the ocean floor may be used to obtain a visual view of the horizontal and vertical distance between the coupling halves. When the coupling halves are centered over one another, they are brought together as the upper portion of the link is lowered and the link is locked by a self-locking device or by use of the ROV. Underwater connections are often constructed as male and female connectors with tapered transfer facilities to facilitate the engagement.

The pairing principle and the locking mechanism vary with different types of underwater links. In addition, the conventional "H-shackle^H with ROV equipment has been used as an underwater link, for anchor installation. Those are known to persons skilled in the art and are not elaborated herein as they are not consequential to the present invention.

In an alternative embodiment, a double acting guide line can be used to disconnect the guide line 5 from the underwater connector after installation without the use of ROVs. An embodiment of this is shown in figure 6. In this embodiment, the guideline 5 is not terminated in the upper underwater connector 3, but passes through this in a channel 21 and extends up to the installation vessel 1 as a recovery line 22. The guideline 5 has a load transfer member 23 fixedly attached. This load transfer member 23 is adapted to be received in a recess 24 in the upper connector 3.

The guideline 5 can be released from the underwater link, by disconnecting the tensioned end of the guideline 5 from the auxiliary winch 12 while the non- tensioned end 22 is hauled. The load transfer member 23 on the guideline 5 is drawn away from the recess 24. Hence, the guideline 5 is pulled out of the underwater link 3, 4 and up to the surface, and is thereby completely freed from the underwater link.

The channel 21 through the upper connector 3 is preferably straight, although a curved channel 21 is shown in figure 6. Preferably, the channel 21 is provided with a bushing or coating of plastic or Teflon. The channel 21 need not extend to the tip of the connector 3, but may extend only through a part of the connector 3. The load transfer member can be of any shape as long as it has a larger diameter than the channel. Instead of being accommodated in a recess 24, the load transfer member 23 can simply lie against the upper surface of the connector 3.

The locking mechanism to lock the upper and lower connectors together can be either seff-locking or locked by external actuation, such as operation of the ROV. Tension in the guideline 5 can be increased in connection with the lock operation to facilitate this.

The present invention embraces all the previously mentioned possibilities. Referring back to figures 2(a) and 2(b), the functioning is same as in the embodiment shown in figure 1. The rest plate 9 on top of anchor 6 does not rigidly receive the lower connector 4. The rest plate 9 may merely acts as a seat for the lower connector 4, which sits on it under gravity, or it may be attached by a weak connection, as stated above. It is displaced from the rest plate 9, once the guide wire 5 is under tension, so that the guide wire is not snapped. In any event, the connection between the connector 4 and the rest plate 9 is a weak one, so that it becomes loose in the event of a force beyond a certain value being extended on the guide line 5. The view in figure 2(b) shows the position when the upper connector 3 and the lower connector 4 are secured.

The anchor line is tightened at this stage, as can be seen from the position of the flexible mooring chain 14. It also shows the D shackle 4' of the lower connector 4 and the D-shackle 3' of the upper connector 3. In this figure, on connection with the upper connector 3, the lower connector 4 has moved from the rest plate 9 atop the anchor 6, but remains connected to the anchor 6 by means of the chain 14 and a lifting eye 8.

Coming back to figure 3 once again, the lower connector 4 is held on a staging device 9 placed on the seabed 15, before the freefall anchor 10 is dropped into the sea floor 15 and may be used to control the connector's orientation on the seabed 15.

Thereafter, connection between the upper connector 3 and the lower connector 4, takes place in the same way as described in connection with the preceding figures. This figure in particular illustrates and establishes that the method of the present invention can be combined with this anchor installation method by the guide wire 5 being used to guide the upper connector 3 into the lower connector 4. This embodiment can be of immense utility where the anchor cannot be positioned permanently and prior to the positioning of the lower connector 4.

Referring back to figure 4 the upper connector 3, again being lowered by the help of gravity, is guided towards the lower connector 4, while the tension from the guide wire 5 lifts the lower connector 4 from the seabed 15 and orients it. This ensures that the upper connector 3 can smoothly enter the lower connector A.

In this configuration, the tension in the guide wire is somewhat higher as the lower connector 4 and parts of the anchor line 14 have to be lifted up from the seabed during mating. However, this additional tension is also balanced, as it will be clear from the description provided hereinafter with reference to figures 5(a) and 5(b).

Now, coming back to Figure 5(a), it is a view of a preferred embodiment similar to figures 2(a) and figure 4, showing how the method described in this invention can be applied during hook-up of a platform 11. The anchor line 14 and the anchor 6 are pre-installed and picked up from the seabed 15 by the installation vessel 1. The weight of the lower part of the anchor line 14 and the lower connector 4 is held by the installation vessel 1 by means of the installation vessel's work chain 17 while the platform/vessel 11 is lowering the mooring line 2 with the upper connector 3. This substantially reduces the tension on the guideline 5, which is particularly helpful in the embodiment shown in figures 2(a) and 4, where the lower connector 4 has to be picked up from the sea bed during securing the upper connector 3 and the lower connector 4.

The winch 12 pulls the guide wire 5 as the mooring line 2 is lowered thus avoiding any extra load on the winch 12.

Figure 5(b) is an enlarged view of figure 5(a) showing the components illustrated in figure 5(a) in greater detail. It additionally shows the D-shackle 3' of the upper connector 3.

The purpose of the arrangement with the help line, pulleys and winches are not to pull connector parts together, but to guide them.

The possibility of drawing the guideline 5 back after the connection has been made, is not an essential part of the method, since the line can be detached from the connector in other ways, for example, by an ROV cutting it off. Thus, different types of subsea connectors are applied in the system and method according to the present invention. Furthermore, the configuration may be different depending on anchor type and structure of the mooring line (as shown in the figures). In some cases, it is possible that the two parts of the mooring line will be connected immediately after the anchor is installed, while in other cases, the connector would be lying around for some time, even years, on the seabed. If the connector is not to be in the sea for a long time before pairing, it will be most convenient to install the guideline before the lower part of the connector is submerged into the water. The guideline (help line) can be released with buoy and acoustic release or can be picked up by the ROV. If the connector is to be in the sea for a long time before pairing, it may be desirable to retrofit the help line. In all cases, it will be beneficial to have the opportunity to replace the sheave and the help line in case of wear. Design and methods will of course depend on the connector used.

For use with hook-up, as shown in the figures 5(a) and 5(b), the mooring line 2 with the anchor 6 and the anchor line 14 are pre-installed on sea bed 15. This method eliminates the need for installation chains, chain lockers for installation chains and the connection room for connection of the installation chain with the platform chain.

The method is as follows when the pre-installed line (14) is long enough to be pulled up onto the installation vessel 1 as shown in figure 5(a).

1. The installation vessel 1 picks up the end of the mooring line 14 from the seabed, pulls it up and secures it on deck.

2. The lower connector 4 is connected to the anchor line 14, if this is not pre- installed with the mooring line 14.

3. The guideline 5 is (pre)attached to connector 3 on platform chain 2 and is transferred to the installation vessel 1 from the device 1 1 to be installed. This is threaded through the lower connector 4 and attached at one end to the winch 12. (The winch can in principle be mounted on the installation vessel, the platform or on another vessel).

4. The lower connector 4 is attached to the work chain or wire and lowered down from the installation vessel 1 to the desired depth. The installation vessel 1 holds the weight of the lower connector 4 and the anchor line 14 by means of chain 17.

5. The upper connector 3 attached to the mooring line 2 is paid out from platform 11 using the platform mooring winch 20, while the winch 12 pulls the guide line 5 (for example, by the winch operated in the "constant tension mode") so that the upper connector 3 is guided towards the lower connector 4.

6. The operation is (optionally) monitored by ROV 7. Locking of the connector elements

8. The guideline is disconnected.

9. The weight of the lower mooring line/anchor line 14 is transferred from the work chain 17 to the upper mooring line 2.

10. The work chain 17 is released from the connector, e,g. by cutting the wire sling

11. The winch 20 on the platform is reeling in the platform chain to achieve the desired pre-tension level in the mooring line. The method is as follows when the pre-installed line is not long enough to be pulled up on the installation vessel (as shown in figure 4):

1. The guide line 5 is released from the lower connector 4, or connected by the assistance of the ROV

2. The guide line 5 is connected to the upper connector 3 and winch 12

3. The winch 12 and guideline 5 is used to lift the bottom connector 4 and the anchor line 14 closer to the surface. Tension in the guideline 5 will constantly be increased by this connection method,

4. When the lower connector 4 is pulled high enough up, the upper mooring line 2 and the upper connector 3 are lowered, while the winch 12 pulls an equal length of the guideline 5. In this phase, the tension in the guide line 5 is nearly constant

5. The operation is monitored by ROV

6. Locking the connector elements

7. The guide line 5 is disconnected

8. The winch 20 on the device / platform is reeling in the platform chain to achieve the desired pre-tension level in the mooring line.

The latter method requires a stronger guideline, pulley and wire when it is used to lift the lower connector.

Alternatively, the work chain 17 may be connected to the connector 4 while the connector 4 is on the seabed, e.g., by a hook at the end of the work chain 17 that hooks up with a wire sling on the connector 4, optionally by the aid of an ROV. Then the work chain 17 can be used to lift the connector 4 to a desired depth. Guide lines can be coupled to the connector 3 either before or after the work chain 17 is hooked up with the connector 4 and has lifted the connector 4 to a desired depth.

From the foregoing description and from the appended claims it would be clear tq persons skilled in the art, that all the objectives of the present invention are achieved. The technology in accordance with the present invention can be applied in both deep sea and shallow sea and can function irrespective of the underwater condition.

The present invention has been described with reference to preferred embodiments and illustrative drawings for the sake of understanding only and it should be clear to persons skilled in the art that the present invention includes all legitimate modifications within the scope of what has been described hereinbefore and claimed in the appended claims.

Claims

Patent claims

1.

An underwater connecting system comprising at least one first connector unit (3) and at least one second connector unit (4) to be located under water below said first unit

(3) in a secured position, said first unit (3) is adapted to be guided to said second unit

(4) , while the first unit (3) is hanging in a mooring line (2), the guiding being performed by gravity and a tensioned guideline (5) to which both said first unit (3) and said second unit (4) are operatively connected, ch a ra cteri sed i n that said second connector unit (4) is either loosely seated in a bracket (9) attached to an anchor, or that said second connector unit (4) is held on a staging device (9) placed on the sea bed (15), said staging device acting to hold the second connector unit (4) in a specific orientation, and said second unit (4) being connected to a lateral side of the anchor (6) by means of a flexible chain (14) or wire.

2.

The underwater connecting system according to claim 1, ch a racte ri sed i n that the second unit (4) is attached relative to the seabed so that it can move relative to the seabed if a pulling force from the guideline (5) exceeding a certain limit is exerted.

3.

The underwater connecting system according to any of the claims 1 - 2, ch a racte ri sed i n that said tensioned guideline (5) extends from said first connector unit (3) via said second connector unit (4) to an installation vessel (1) or an assist vessel at the surface.

4. The underwater connecting system according to any of the claims 1 - 3, ch a racte ri sed i n that said first unit (3) is a male connector which is lowered down along a mooring line (2) from an installation vessel (1) and said second unit (4) is a female connector connected to the side of an anchor (6) on a sea bed (15) by a flexible means (14).

The underwater connecting system according to any of the preceding claims, ch a racte ri sed i n that said tensioned guideline

(5) passes through a pulley (7) mounted on said second connector unit (4).

6.

The underwater connecting system according to any of the preceding claims, ch a racte ri sed i n that said mooring line is a flexible chain (14) and said flexible chain (14) as well as said second connector unit (4) are pre-installed on the sea bed (15).

7.

The underwater connection system according to any of the preceding claims, ch a racte ri sed i n that said guideline (5) is pre-installed along with said anchor (6) with its free end either placed on the seabed (15) or hung off in a buoy at the surface (16).

8.

The underwater connection system according to any of the preceding claims, ch a racte ri sed i n that the guideline (5) extends through at least a part of the first unit (3) and is equipped with a load transfer member (23) that is adapted to transfer tension in the guideline (5) to the first unit (3), that a part (22) of the guideline (5) that extends away from the second unit (4), extend to the water surface and being adapted to be used for recovering the guideline (5)