Arrangement and Method for Retrieving Broken Moorings

Abstract

The present invention relates to an arrangement for retrieving broken moorings comprising: at least three shackles; at least two slings; at least one mooring; at least one hook; at least one ROV needle rope; and a treble hook. The upper end of the mooring is connected to a working rope with a swivel link, and the lower end of the mooring is connected to the treble hook. In addition, the invention also describes a method for retrieving broken moorings, using said arrangement for retrieving moorings, comprising the following steps: positioning a treble hook close to a mooring to be retrieved; passing a sling around the mooring; connecting a sling to the hook; applying traction; and accommodating the mooring. In this way, the invention combines the flexibility and adaptability necessary to operate in different suspension conditions on the seabed, ensuring the efficient retrieval of the broken moorings, both in environments with high-suspension seabeds and in low-suspension seabeds.

Claims

1. An arrangement for retrieving broken moorings, comprising: at least three shackles; at least two slings; at least one mooring; at least one hook; at least one ROV needle rope; and a treble hook.

2. The arrangement according to claim 1, wherein the upper end of the mooring is connected to a working rope with a swivel link and the lower end of the mooring is connected to the treble hook.

3. The arrangement according to claim 1, wherein the third eye of the treble hook receives the sling, in which the two legs of the sling are joined by means of the shackle.

4. The arrangement according to claim 1, wherein the ROV needle rope is joined to the end of the sling by the eye splice technique, and the end of the sling is joined to the sling by the shackle.

5. The arrangement according to claim 1, wherein the hook must be connected to the mooring using at least one shackle in an intermediate link of the mooring.

6. The arrangement according to claim 5, wherein the hook must be connected to the intermediate link of the mooring in a position such that the distance between the hook and the treble hook is greater than the combined length of the slings.

7. A method for retrieving broken moorings using the arrangement for retrieving moorings as defined in claim 1, comprising: i. positioning a treble hook close to a mooring to be retrieved; ii. passing a sling around the mooring; iii. connecting a sling to the hook; iv. applying traction; and v. accommodating the mooring.

8. The method according to claim 7, wherein positioning a treble hook comprises: laying it on the seabed if the seabed has little suspension; and positioning it close to the bottom, but without touching the ground, if there is a lot of suspension.

9. The method according to claim 7, wherein passing a sling comprises: passing the needle rope, with the aid of an ROV, underneath the broken mooring and pulling the sling from the other side.

10. The method according to claim 7, wherein the connection of a sling to the hook comprises: displacing the sling, with the aid of the ROV, to the hook; and attaching the sling to the hook.

11. The method according to claim 7, wherein the application of traction comprises: monitoring the ROV; and pulling, by means of the AHTS, the working rope until the broken mooring accommodates itself in the treble hooks pocket.

12. The method according to claim 7, wherein, after the accommodation of the mooring, it comprises: slackening the sling; and releasing the connection with the hook.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be described below with reference to the typical embodiments thereof and with reference to the appended drawings, in which:

[0021] FIG. 1 is a representation of an example of a fishing arrangement from the State of the Art.

[0022] FIG. 2 is a representation of a broken mooring treble hooking operation, according to the State of the Art.

[0023] FIG. 3 illustrates the mooring retrieval arrangement, according to an embodiment of the present invention.

[0024] FIG. 4 illustrates a treble hook adapted with a hole in the end of two throats, according to an embodiment of the present invention.

[0025] FIG. 5 illustrates a treble hook adapted in the most recommended manner for application of the present Technique, with removal of three of the four throats and a hole in the end of the remaining throat.

DETAILED DESCRIPTION OF THE INVENTION

[0026] As mentioned, fishing for broken anchor lines is traditionally done by means of steel cable arrangements connected to the moorings by ROV in the case of congested subsea layouts. Since such arrangements need to be flexible enough to be manipulated by the ROV, it is quite common to observe the rupture of the arrangements followed by the fall of the broken line back to the seabed.

[0027] FIG. 1 shows an example of a fishing arrangement from the State of the Art, using steel cables. As can be seen, the typical fishing arrangements consist of a main steel cable (also called working rope) (2), shackles (4A, 4B, 4C), mooring tails (6A, 6B), detachable reduction links (8A, 8B), a swivel link (also called a swivel or untwist) (10), intermediate steel cables (12), a final steel cable (14), and a barbed hook (16).

[0028] The main steel cable (2) is connected to a shackle (4A), where mooring tails (6A, 6B) are attached, connected to a swivel link (10) by reduction links (8A, 8B). At the other end of the final portion of the mooring tails, another shackle (4B) is attached, which is connected to intermediate steel cables (12), which also contain a shackle (4C) at their other end.

[0029] A final cable (14) and a barbed hook (16) are attached to this shackle, in which typically the two ends of the final cable are connected to the shackle, and the two parallel halves of the final cable are joined by rope ties. In this arrangement, the main steel cable (2) is the high-capacity winch cable of the AHTS vessel, with diameters typically greater than 80 mm. Considering that the main steel cable (2) is too rigid for ROV operation, the arrangement has one or more intermediate steel cables (12), which are thinner, lighter and more flexible, with diameters between 25 mm and 51 mm, carrying at their lower end the final cable (14), with a diameter between 12 mm and 25 mm, and the hook (16), joined by the shackle (4C).

[0030] The function of the intermediate cables is to allow sufficient flexibility for the ROV to bring the hook (16) close to the point where it is desired to connect to the broken mooring. The ROV then passes the midpoint of the final cable (14) through a link of the broken mooring and connects the same to the hook (16).

[0031] Typically, it is more efficient to pass the midpoint rather than the end of the cable through the link, with the additional advantage that the traction in the final cable becomes approximately one-quarter of the load.

[0032] Within the variations of this type of arrangement, it is possible to replace the main steel cable with a high-capacity synthetic fiber cable, typically of torsion-neutral construction, where the swivel link (10), together with the elements (6A, 8A and 8B) become dispensable. It is also possible to use synthetic fiber cables with appropriate dimensions to replace one or more intermediate cables (12). However, in this case, the final cable (14) must be made of steel, since the synthetic fiber cable can be damaged by the ROVs hydraulic manipulators. Even with all possible optimizations, this type of arrangement still represents a weak point in the retrieval system, causing several ruptures with the broken mooring falling back to the seabed.

[0033] In this sense, FIG. 2 represents a broken mooring treble hooking operation, according to the State of the Art. As can be seen, an AHTS vessel (21) drags a treble hook (23) over a broken mooring hook (24). It is worth noting that the AHTS vessel (21) is connected to the treble hook (23) by a steel cable (22), with specifications similar to the main steel cable (2) in FIG. 1. Between the steel cable (22) and the treble hook (23), there is a similar set of elements that appear in FIG. 1 between the main cable and the secondary cable, these being: shackles (4A, 4B), mooring tails (6A, 6B), reduction links (8A, 8B), and swivel link (10). For the treble hooking operation to be successful, the catenary formed by the suspended steel cable (22) must never reach the treble hook (23); that is, there must be enough cable lying on the ground in front of the treble hook to compensate for the vertical movements of the vessel under the action of the sea. To achieve this, the total length of the cable must be at least 1.4 times the operating depth.

[0034] It is possible to slightly reduce the length of the cable required by adding a section of mooring of great dimension between the steel cable (22) and the treble hook (23) to provide ballast, and a small section of steel cable with a specification similar to the main cable.

[0035] The heavy mooring will tend to remain on the bottom, preventing the cable between the same and the treble hook (23) from being suspended. In both cases, the vessel will only be able to apply force to cause the treble hook to move after releasing the entire length of cable necessary for the operation into the water, so that, at the moment immediately prior to the application of force, several dozen meters of cable will be lying on the seabed.

[0036] Given the limitations of the fishing arrangements exemplified by FIG. 1 and the treble hooking method illustrated by FIG. 2, the present invention presents an arrangement for retrieving moorings, as shown in FIG. 3, comprising:

[0037] at least three shackles (30A, 30B, 30C);

[0038] at least two slings (32A, 32B);

[0039] at least one mooring (34);

[0040] at least one hook (36);

[0041] at least one ROV needle rope (38); and

[0042] a treble hook (40).

[0043] The upper end of the mooring (34) must be connected to the working rope with a swivel link, or polyester working rope from the AHTS. The treble hook (40) must be connected to the lower end of the mooring (34) using the shackle (30C). The sling (32A) must be passed through the third eye of the treble hook (40) (located at the end of the throat), as shown in FIG. 3. The two legs of the sling (32A) must be joined using a shackle (30C).

[0044] The ROV needle rope (38) must be joined to the sling (32B) using the common eye splice technique. The free end of the sling (32B) must be connected to the same shackle (30C) where the legs of the sling (32A) were joined.

[0045] In turn, the hook (36) must be connected to the mooring (34) using at least the shackle (30A) (more shackles of suitable dimensions may be used, if the dimensional difference between the hook and the mooring is too large) to connect the hook (36) to an intermediate link of the mooring (34). The hook (36) must be connected in a position such that the distance between the hook (36) and the treble hook (40) is greater than the combined length of the slings (32A, 32B). For this reason, the mooring (34) and the slings (32A, 32B) must be chosen such that the length of the mooring (34) is greater than the sum of the lengths of the slings (32A, 32B).

[0046] FIG. 4 presents a traditional treble hook adapted with a hole at the end of two throats. It is possible to observe the main eye (42), the throats (44A, 44B, 44C, 44D), the pockets (geometry for locking the links) (46A, 46B, 46C, 46D), the auxiliary eyes (48A, 48B), and the lower eye (50). The treble hook presented is a reinforced treble hook design, developed for loads of up to 400 ton.

[0047] FIG. 5 presents the treble hook adapted in the most recommended way for application of the present Technique, in which three of the four throats are removed. It is possible to observe the main eye (60), the body (62), the lower eye (64), the throat (66), the pocket (68), and the third eye (70).

[0048] Considering the arrangement proposed in this invention, the method of fishing for broken moorings comprises the following steps:

[0049] I. positioning of a treble hook;

[0050] II. passing of a sling;

[0051] III. connecting a sling to the hook;

[0052] IV. applying traction; and

[0053] V. accommodating the mooring.

[0054] In step I, the treble hook must be positioned close to the section of mooring that is to be retrieved. If the seabed has little suspension, the treble hook can be placed on the seabed. If there is a lot of suspension, the treble hook must be positioned close to the bottom, but without touching the ground.

[0055] Next, in step II, the ROV must pass the needle rope under the broken mooring and pull the sling from the other side. In this step, it is necessary to make sure not to pull the sling excessively to avoid jolting the ROV due to the movement of the vessel.

[0056] Step III comprises connecting the slings leg to the hook. The ROV, in possession of the sling, moves to the hook, where it attaches the sling.

[0057] In turn, in step IV, with ROV monitoring, the AHTS must slowly apply traction to the working rope. The sling will stretch first, guiding the broken mooring into the throat of the treble hook. The ROV has the function of providing visual feedback to the winch operator of the AHTS.

[0058] Finally, in step V, after the broken mooring is accommodated in the treble hooks pocket, the AHTS must relieve the traction on the working rope, moving the treble hook towards the seabed. Next, the ROV must slack the sling so that it is disconnected from the hook.

[0059] It is worth noting that other types of commercial hooks suitable for handling moorings can be applied to the present invention without prejudice to the same, as long as they have an eyelet at the end by design or adaptation, similar to the adaptations shown in treble hooks.

[0060] This approach allows the retrieval of broken moorings in congested subsea areas; that is, with subsea structures around the broken mooring, such as pipelines, production equipment and other anchor lines, by eliminating the need to drag the treble hook over the mooring, and mitigates the risk associated with the low load capacity of the retrieval arrangements consisting of exclusively of steel cables. In addition, the method combines the flexibility and adaptability necessary to operate in different suspension conditions on the seabed, ensuring the efficient retrieval of the broken moorings, both in environments with seabeds with high suspension and in seabeds with low suspension. By simplifying the procedures, the practicality and efficiency of the operation are increased, minimizing the risk of interferences and breakages during the mooring retrieval.