WO2009048323A1

WO2009048323A1 - Mooring system for mooring a first vessel to a mooring cable connected to an offshore construction or to a second vessel

Info

Publication number: WO2009048323A1
Application number: PCT/NL2008/000222
Authority: WO
Inventors: Reinout Klaar Norfolc Jaap Prins
Original assignee: P & R Systems
Priority date: 2007-10-09
Filing date: 2008-10-09
Publication date: 2009-04-16
Also published as: EP2195231A1; NL1034492C2

Abstract

A mooring system for mooring a first vessel 20 to an offshore construction 1 or to a second vessel, where the offshore construction 1 or the second vessel is provided with a mooring element; and the first vessel 20 is provided with a telescopically extendable swivel arm 21, which swivel arm 21 carries a coupling device 30 at its free end which is adapted to clasp the mooring element and which swivel arm 21 at its other end is mounted on the vessel 20 and can be moved around a horizontal and vertical shaft, in which drive means are provided for swivelling the swivel arm 21 around the horizontal and vertical shaft or for retracting or extending the swivel arm 21 during mooring. The mooring element comprises a mooring cable 7 attached to an upper or lower part of the offshore construction 1 or of the second vessel.

Description

Short description: mooring system for mooring a first vessel to a mooring cable connected to an offshore construction or to a second vessel.

The invention relates to a mooring system for mooring a vessel to an offshore construction or to another vessel, e.g. a supertanker or similarly large ship.

From WO 02/20343 a system is known that is used for achieving a flexible walkway connection between a vessel and an offshore construction. For this purpose, the vessel is provided with a telescopically extendable walkway which at one end is movably mounted on the vessel around two shafts. At the free end of the walkway a coupling device is provided, which is made in such a way that it can be coupled to a substantially vertically pointing grip bar connected to the offshore construction. While mooring, the vessel is manoeuvred to a suitable starting position in relation to the grip bar. Next, the walkway is aimed towards the middle part of the grip bar by means of a suitable swivel movement and the walkway is extended until the coupling device encompasses the grip bar. Then, the coupling device's two hydraulically controlled coupling jaws - which can move towards each other from an open position - are closed. They are closed in such a way, that the coupling device still has the freedom to move upwards along the grip bar during the coupling phase. After reaching the required coupling position just below the landing, the coupling claws are moved closer towards each other in order to tightly clamp onto the grip bar and fix the position at that location. Finally, a number of degrees of freedom of the walkway are released, i.e. the movability around the two shafts and the telescopic extendibility. By using rotatable screws and satellite navigation, the vessel can be kept at its location without strong forces being submitted to the walkway and/or the grip bar.

A disadvantage here, is that the coupling procedure can sometimes be somewhat cumbersome, especially during stormy weather. The forces that are generated at the moment that the arm hits the grip rod, are very hard to control under these circumstances. This is due to the fact that at the moment of contact, both large weights have to be slowed down and the drives concerned must be switched off immediately at the same time. Additionally, during the coupling phase, closing the coupling jaws has to be accurately attuned to the release of the walkway's remaining degrees of freedom, in order to avoid damages to the vessel. Another disadvantage is that the vertical grip rod has to extend over a large range, making it relatively expensive and difficult to assemble. Furthermore, the known system proved to be unsuitable for smaller vessels that are not 'dynamic positioned', i.e. they are not equipped in such a way that they can be kept in position by means of rotatable screws and satellite navigation.

The present invention aims to at least partially solve the abovementioned disadvantages, or to provide a usable alternative. In particular, the invention aims to provide a user friendly, reliable anchoring between a first vessel and an offshore construction or a second vessel, which will give safe access to the offshore construction or second vessel, even during stormy weather.

The invention achieves this aim by means of a mooring system between a first vessel and an offshore construction or second vessel, according to claim 1. The first vessel is provided with a telescopically extendable swivel arm that is moveably mounted on the first vessel around two essentially perpendicular shafts, carrying a coupling device at its free end. Furthermore, drive means are provided for swivelling the swivel arm around the mentioned shafts as well as for extending and retracting the telescopically interlocking parts of the swivel arm. In correspondence with the invention, the offshore construction or second vessel is equipped with a mooring cable tightened between an upper and lower part of it. The coupling device is adapted to clasp the mooring cable. The mooring cable has the great advantage that it is easy to install on the offshore construction or second vessel. The mooring cable can easily cover a large range, in particular a range of more than 3 metres, without needing any additional support for that purpose. Installing such a flexible and supple mooring cable will always be simple and inexpensive. This will allow users to equip more offshore constructions or vessels with such a mooring cable, within a short time-frame and against minor costs. The size of the mooring cable and its specific positioning can easily be adapted to specific circumstances, such as the weather conditions, current and surge to be expected at a location where a particular offshore construction or vessel is positioned. The mooring cable is preferably hanging vertically. Although a slight inclination is no problem. The flexibility of the mooring cable has the additional advantage that damages are less likely to occur. This is due to the fact that, to a certain extent, the mooring cable is able to absorb and dampen the forces that occur, both during the mooring process and after the coupling has been made. In this way, the mooring system allows fast and reliable coupling, without having the risk that parts of the first or second vessel or of the offshore construction are damaged during the coupling phase, e.g. because one or more degrees of freedom of the swivel arm are not released in time.

The mooring system is particularly suitable for anchoring (smaller) vessels that are not 'dynamic positioned' to the offshore construction or the other vessel. In that case, the swivel arm and the mooring cable can function as a force transferring anchoring element. Although the mooring system can also be used in combination with (larger) 'dynamic positioned' vessels. In a special embodiment, the mooring cable is connected to a spring device. This device can be provided, for instance, in or near the lower and/or upper securing point of the mooring cable to the offshore construction or second vessel. The spring device has the advantage that it can offer additional buffering of forces submitted to the mooring cable by the vessel. Also, the spring device will - advantageously - keep the mooring cable at tension, so that it will remain perfectly tight. This, in turn, will make it easier to make the coupling between the swivel arm and the mooring cable.

In an advantageous variation, the coupling device comprises a coupling hook and a locking element that can switch between an opened and closed position. During the coupling phase, this hook arm should clasp the mooring cable and hook behind it, through suitably manoeuvring the first vessel and the swivel arm. The locking element is made in such a way that, in the closed position, the mooring cable is locked between the locking element and the hook arm. Preferably, the cable part is enclosed in such a way, that the coupling device has the freedom to move up and down along the mooring cable. The coupling between the coupling device and the mooring cable is advantageously independent from hydraulic systems or other power systems. This will increase safety.

In a further embodiment, the connection of the lower part (to which the mooring cable is attached) to the upper part of the offshore construction or second vessel (to which the mooring cable is also attached) can be adjusted in height. This will allow the user to adapt the height, if necessary, to current circumstances like water level, wave height, etc. and/or the dimensions of the vessel to be moored.

In yet another further embodiment, the lower part to which the mooring cable is attached, is suspended from the upper part of the offshore construction or second vessel to which the mooring cable is also attached. This suspension can, for instance, take place from a lowerable and/or folding stair construction, or from several cables or other types of suspension elements.

The lower part of the offshore construction or second vessel can be advantageously suspended from the mooring cable. This will automatically make sure that the mooring cable is tensioned and offers the advantage that the mooring cable can have a double functionality, i.e. as a mooring element and suspension element.

Other preferred embodiments based on the invention are stated in the subclaims. The invention also relates to a method according to one of the claims 16-19.

The invention will be further explained with reference to the included drawing, in which:

- fig. 1 is a schematic side view of an offshore construction with mooring cable according to the invention; - fig. 2 is an enlarged view of the lower securing point of the mooring cable from fig. 1 ;

- fig. 3a up to e show a schematic view of the subsequent steps when mooring the vessel according to the invention at the offshore construction from fig. 1 ;

- fig. 4a up to e show schematic top views in correspondence with the views from fig. 3; - fig. 5a and b show a top or side view of the swivel arm from fig. 3b;

- fig. 6a and b show a top or side view of the swivel arm from fig. 3d;

- fig. 7a and b show a top or side view of the swivel arm from fig. 3e;

- fig. 8 shows a top view of the coupling device in opened position;

- fig. 9 is a view corresponding to fig. 8 in the coupled position; - fig. 10 is a view in perspective of a variation with a bottom landing suspended from a mooring cable, in correspondence with the invention; and

- fig. 11 shows schematic views of fig. 10 in various positions for the bottom landing that is adjustable in height.

In fig. 1 an offshore construction in its entirety is referred to by means of the reference number 1. The offshore construction 1 comprises several bearing columns 2 supporting a platform 3. A landing 4 is provided between the bearing columns 2, offering access to the offshore construction 1 from a vessel. From the landing 4, personnel can reach the higher platform 3 by means of a staircase 5. Furthermore, the offshore construction 1 is provided with a steel mooring cable 7 extending between the platform 3 and the landing 4.

At its lower end, the mooring cable 7 is connected to a spring device 10 (see fig. 2). The spring device 10 is housed in a recess in the landing 4, and in its turn, the lower end of the spring device is connected to a limiting element 11. The limiting element 11 makes sure that the mooring cable 7 and the spring device 10 can be under strain of tension without getting loose from the landing 4. At the place where the mooring cable7 is secured to the landing 4, a support point 14 with a spherical part 15 is provided. Its function will be explained below. The support point 14 is provided with a through going opening 16 for the mooring cable 7 towards the spring device 10. The dimensions of the opening 16 and the mooring cable 7 are such, that the mooring cable 7 has the freedom to move up and down in the opening 16.

In order to be able to realize a safe crossing for personnel from a vessel 20 (see fig. 3 and 4) to the landing 4 and vice versa, at any time between low and high tide, as well as during stormy weather, a telescopically extendable swivel arm 21 is used, over which a walkway 22 can be mounted that is also telescopically extendable.

Around a horizontal shaft x, the swivel arm 21 is hingedly connected to a step platform 25 at the upper end of a column 26, and by means of a revolving ring, this column 26 is rotatably mounted to the deck of the vessel 20, around a vertical shaft y. Between the rotating column 26 and a point at the underside of the swivel arm 21 , a hydraulic piston/cylinder device (not shown in detail) extends, which can adjust the slope angle of the swivel bridge 21 around the shaft x. The telescopic parts of the swivel arm 21 are retractable and extendable by means of a hydraulic piston/cylinder device which is also not shown in detail. Instead of the abovementioned hydraulic piston/cylinder device and/or as a supplement to it, other types of drive means can also be used, such as a winch device.

At its free end, the swivel arm 21 is provided with a coupling device 30. The coupling device 30 is used to make a connection with the mooring cable 7 and thus moor the vessel 20 to the offshore construction 1.

An embodiment of the coupling device is shown in fig. 8 and 9 and comprises a hook arm 31 which here is composed of two rotatably connected parts around a vertical hinge shaft 32. In the closed position, indicated in fig. 8 by means of interrupted lines and also shown in fig. 9, the hook arm parts 31a,b together form a U shape, between which the mooring cable 7 fits. Between both legs formed by the hook arm parts 31 a, b a locking element 34 under spring tension is provided. Under the influence of a force F, the locking element 34 can be rotated to an open position against the spring tension of a spring 35. The hook arm part 31a can be locked in its closed position by means of a locking catch 36. Here, the hook arm part 31a and the locking catch 36 are under spring tension from a spring 37. By hooking hook arm 31 in closed position behind the mooring cable 7, the generated force F between the mooring cable 7 and the locking element 34 will make sure that the locking element 34 is pushed to its open position. As a result, the mooring cable 7 will move deeper into the U shape of the hook arm 31 , and the locking element 34 will be pressed back to its closed position by the spring 35 as soon as the mooring cable 7 has passed (fig. 9). Then, the mooring cable is trapped in the coupling device 30, and can only move out of it after the locking element 34 is released, or the hook arm part 31a is brought to its open position. The latter will take place when the mooring cable 7 applies force to the hook arm part 31 a as a result of which the locking catch 36 is pressed open against the spring tension of the spring 37, if the force between the mooring cable 7 and the coupling device 30 exceeds a certain limit value, e.g. if the vessel 20 has to sail away in case of an emergency. The hook arm part 31a can also be actively released in order to move to its open position, by pulling away the locking catch 36 by means of a line 38 (fig. 8).

Based on fig. 3 and 4 we will now describe a possible coupling method: The vessel 20 positions itself with its back to the mooring location near the landing 4 (fig. 3a, 4a). Next, the swivel arm 21 is swivelled to the outside (fig. 3b, 4b) and at the same time it may or may not be telescopically extended. Then, the swivel arm 21 is swivelled and/or extended further, until it pushes sideways against the mooring cable 7 (fig. 3c, 4c). A so- called constant tension drive on the swivelling movement of the swivel arm 21 makes sure that the swivel arm 21 will continue to push against the mooring cable 7. The flexibility of the cable part 7 in combination with the spring device 10 makes sure that the shock caused at the moment that the swivel arm 21 hits the mooring cable 7 is limited. In a next action, the coupling will take place. For this, the swivel arm 21 , while lying against the mooring cable 7, can be retracted telescopically until the mooring cable 7 in the hook arm 31 is pulled passed the locking element 34 (fig. 3d, 4d). Additionally, the vessel 20 can sail away from the mooring cable 7, in order to speed up the coupling procedure. After that the swivel arm 21 is lowered just enough, until its coupling device 31 lies on the support point 14, in such a way that the hook arm 31 fully rests against the spherical part 15 of the support point. Together they will advantageously form a type of ball-and-socket joint. Finally, the walkway 22 is rolled out over the swivel arm 21 and locked in this extended position to the free end of the swivel arm 21 (fig. 3e, 4e).

After the coupling has been made in this way, the movements of the swivel arm 21 around the horizontal and vertical shafts are released by switching off their respective drives. The telescopically interlocking parts of both the swivel arm 21 and walkway 22 can also be released by switching off their respective drives. However, between both telescopically interlocking parts of the swivel arm 21 and/or the walkway 22 a spring is advantageously provided in order to retract and extend the swivel arm 21 and the walkway 22 connected to it with a certain pre-tension. These spring means can advantageously be part of or be formed by the drive means such as the hydraulic piston/cylinder device or the winch device for extending the swivel arm 21 and/or walkway 22. The spring means will, together with the flexibility of the mooring cable 7 and the spring device, make sure that after anchoring a certain amount of flexibility is guaranteed, as a result of which the vessel 20 can follow wave motions. Here, the amount of flexibility can be influenced by adapting the characteristics of the spring device 10 and/or the spring means and/or the chosen mooring cable 7. The hinge joint between the coupling device 30 and the support point 14 will make sure that the rotations between the swivel arm 21 and the offshore construction 1 are allowed.

Figure 10 shows a supertanker 100 on which a stair construction 101 is attached to the upper deck. The stair construction 101 comprises a top landing 102, a number of stair segments 103, and a bottom landing 104 which are hingedly connected and which can switch between a folded and lowered position. The bottom landing 104 is hanging in the lowered position by means of three cables 105, 106, 107 from the top landing 102. The cable 106 at the front functions as a mooring cable, according to the invention. The cables 105, 106, 107 run over controllable winches. By winching up the cables 105, 106 and 107 to a further or lesser extent, the bottom landing 104 can be adjusted in height along the ship's side of the tanker 100. In order to ease the movement of the bottom landing 104 along the ship's wall, it is further provided with friction reducing means, which here are formed by guide wheels 110. In the fully lifted and therefore fully folded position of the stair construction 101 , it can also optionally be swung back around a horizontal hinge shaft, so that the stair construction 101 is lying completely on top of the upper deck and no longer extrudes the ship's outline (see fig. 11). Mooring the vessel 20 with its swivel arm 21 and telescopically extendable walkway 22 to the mooring cable 106 can take place in the same way as described for the previous figures.

The construction shown in fig. 10 and 11 can also be used for installation on an offshore construction, in the same way as the construction shown in figures 1-9 can also be used for installation on a further vessel. Furthermore, it is also possible to suspend the bottom landing partly from the mooring cable and partly from other types of suspension elements or to connect it hingedly to the vessel or offshore construction.

In addition to the shown embodiment, many variations are possible. For instance, instead of vertical, the mooring cable can also be suspended with a slight inclination. A deviation of appr. 15° in relation to a vertical suspension will cause no problems here.

Instead of separately, the swivel arm and walkway can also be telescopically retracted and extended together. In yet another variation, the walkway and the swivel arm can be made as an integral set. The mooring cable can also be made from another material, such as a fibre reinforced plastic, as long as it combines sufficient strength with a required flexibility or suppleness. Instead of one mooring cable, it is also possible to provide several mooring cables on the offshore construction, so that it can be easily approached by the vessel under any wind direction.

Thus, a mooring system is provided according to the invention, which can easily be applied to already existing offshore constructions, with which a vessel can be reliably anchored to the offshore construction in a flexible way, and which system is particularly suitable for anchoring relatively small vessels to the offshore construction. Furthermore a mooring system is provided according to the invention, which can easily be applied to already existing vessels, with which a vessel can be reliably coupled to another vessel in a flexible way, and which system is particularly suitable for coupling relatively small vessels to relatively large vessels such as super tankers, container ships and the like.

Claims

C L A I M S

1. Mooring system for mooring a first vessel to an offshore construction or a second vessel, wherein:

- the offshore construction or second vessel is equipped with a mooring element; and

- the first vessel is provided with a telescopically extendable swivel arm, which swivel arm carries a coupling device at its free end which is adapted to clasp the mooring element and which swivel arm is at the other end moveably attached to the first vessel around a horizontal and vertical shaft, in which drive means are provided for swivelling the swivel arm around the horizontal and vertical shafts resp. for retracting and extending the swivel arm while mooring, characterized in that, the mooring element comprises a mooring cable attached to an upper and lower part of the offshore construction or second vessel, wherein the coupling device is adapted to clasp the mooring cable.

2. Mooring system according to claim 1 , wherein the mooring element also comprises a spring device connected to the mooring cable.

3. Mooring system according to claim 2, wherein the spring device is provided at a point where the mooring cable is secured to the lower or upper part of the offshore construction or the second vessel.

4. Mooring system according to one of the previous claims, wherein near a securing point of the mooring cable to the lower part of the offshore construction or second vessel a support point is provided for supporting the swivel arm after the coupling with the mooring cable has been made.

5. Mooring system according to claim 4, wherein the support point comprises a spherical part which together with the coupling device forms a ball-and-socket joint after the coupling device of the swivel arm is resting on the spherical part.

6. Mooring system according to one of the previous claims, wherein the lower part of the offshore construction or the second vessel with which the mooring cable is connected, forms a landing from which the mooring cable extends upwards, and which landing gives access to the offshore construction or the second vessel for personnel from the first vessel.

7. Mooring system according to one of the previous claims, wherein a walkway is provided that is positionable on the swivel arm.

8. Mooring system according to one of the previous claims, wherein the drive means are arranged to provide a constant sideway pressure for when the swivel arm makes contact with the mooring cable.

9. Mooring system according to one of the previous claims, wherein the coupling device comprises a coupling hook in order to hook behind the mooring cable when clasping it, as well as a locking element that is movable between an open and closed position, making it possible to trap the mooring cable between the closed locking element and the coupling hook.

10. Mooring system according to one of the previous claims, wherein the drive means are arranged to, after the coupling has been made, release the movability of the swivel arm around its horizontal and vertical shafts.

11. Mooring system according to one of the previous claims, wherein the telescopically extendable parts of the swivel arm are provided with activatable spring means, in particular hydraulic spring means that are part of said drive means.

12. Mooring system according to one of the previous claims, wherein the mooring cable extending between the upper and lower part of the offshore construction or the second vessel deviates between +/- 15 degrees in relation to vertical.

13. Mooring system according to one of the previous claims, wherein the lower part of the offshore construction or the second vessel has a height adjustable connection to the upper part of the offshore construction or the second vessel.

14. Mooring system according to one of the previous claims, wherein the lower part of the offshore construction or of the second vessel is suspended from the upper part of the offshore construction or of the second vessel.

15. Mooring system according to claim 14, wherein the bottom part of the offshore construction or of the second vessel is at least partly suspended from the mooring cable.

16. Method for coupling a first vessel to an offshore construction or to a second vessel according to one of the previous claims, comprising the following steps:

- positioning the first vessel near the offshore construction or near the second vessel;

- swivelling or extending the swivel arm in the direction of the mooring cable, until it makes 5 contact with the mooring cable; and

- retracting/extending the swivel arm until the coupling device clasps the mooring cable;

- releasing the movability of the swivel arm around its horizontal and vertical shafts.

17. Method according to claim 16, furthermore including the step of: 10 - mounting a walkway on the swivel arm.

18. Method according to claim 16 or 17, furthermore including the step of:

- activating spring means between the telescopically extending parts of the swivel arm.

15 19. Method according to one of the claims 16-18, furthermore including the step of:

- moving downward the coupling device along the mooring cable until the coupling device rests on a support point that is provided near a point where the mooring cable is secured to the lower part of the offshore construction or of the second vessel.