Method, devices and system for coupling a retrieval cable to an object in a body of water

Abstract

A method for coupling a retrieval cable to an object in a body of water, comprising the steps of: - providing an unmanned surface vessel (USV) comprising a pickup device, wherein the USV is coupled to a retrieval cable; - providing a pickup float coupled to said object, wherein said pickup float comprises an elongate pickup line and a floating member, wherein the pickup float is arranged to maintain the pickup line in a substantially horizontal and substantially elongate position without external support to the pickup float, on or near the water surface; - moving the USV towards the pickup float; - connecting the pickup device to the pickup float by piloting the USV over and across the pickup line.

Description

[0001] METHOD, DEVICES AND SYSTEM FOR COUPLING A RETRIEVAL CABLE TO AN OBJECT IN A BODY OF WATER

[0002] The present invention relates to a method, devices and system for coupling a retrieval cable to an object in a body of water.

[0003] In near shore and offshore operations, it is commonly required to retrieve an object in water, in some cases floating on water, towards a vessel or towards land, for example a quay, pier or dock. To retrieve such a floating object, it is required to couple a retrieval cable to said object, in order to drag the object towards the required location.

[0004] In methods to couple a retrieval cable from, for example, a vessel to an object in water as are currently known in the art, a vessel such as a tender or a utility vessel (for example a Multi Cat) is used to pick up one end of the retrieval cable from the vessel and to bring the one end of the retrieval cable towards the object, subsequently coupling said retrieval cable to the floating object.

[0005] A problem with the methods known in the art is that disproportionately many resources are required for performing a relatively light-duty task.

[0006] It is a goal of the present invention, next to other goals, to at least partially alleviate this problem and / or to provide an efficient method for coupling a retrieval cable to an object in a body of water.

[0007] This goal, amongst other goals, is met by a method according to appended claim 1. More specifically, this goal, amongst other goals, is met by a method according to claim 1 , more specifically by a method for coupling a retrieval cable to an object in a body of water, comprising the steps of: providing an unmanned surface vessel (USV) comprising a pickup device, wherein the USV is coupled to a retrieval cable; providing a pickup float coupled to said object; moving the USV towards the pickup float; connecting the pickup device to the pickup float.

[0008] This method preferably employs a very small, unmanned surface vessel (the USV) as pickup vessel to perform the relatively light duty task of bringing the retrieval cable towards the object in the body of water, and coupling the retrieval cable to said object. The use of for instance a Multi Cat as mentioned above is then no longer required. The pickup float may be separate from the object, and connectable and removable from said object. In other embodiments, the pickup float may be an integral part of the object.

[0009] The pickup vessel is arranged to couple to a pickup float coupled to the object in the body of water. The pickup float thereto preferably comprises an elongate pickup line arranged to couple to the pickup device of the vessel. Easy coupling of a passing vessel is achieved when the pickup float is arranged to maintain the pickup line in a substantially horizontal and substantially elongate position or near the water surface. A goal of the pickup float is to provide a user friendly device to couple the USV to, and this is achieved by a pickup float which is wide in at least one horizontal dimension, to provide a broad target for an operator or guidance system to pilot the USV towards. An elongate shape provides such a wide target. An additional benefit of the elongate shape is that it withstands and effectively transmits pulling forces applied along its length.

[0010] To provide the pickup line at a location at or near the surface of the water, the pickup float preferably is buoyant. Preferably the pickup float is arranged to maintain the position wherein the pickup line is provided in an elongated form at or near the surface of the water without external support to the pickup float. This beneficially allows the pickup float to be connected to any (floating) object without requiring additional devices or the like to be attached to the object.

[0011] A preferred embodiment of the method additionally comprises the step of connecting the pickup device to the pickup float by moving the USV over and / or across the pickup line. This beneficially allows for a user friendly method of connecting the USV to the pickup float, as only the piloting of the USV towards and across the pickup float is required to connect the USV to the pickup float.

[0012] Preferably, the pickup float comprises at least two floating members that are removably connected to the pickup float, such as buoys, to demarcate the pickup float. The USV can then simply pass between the floating members to cross over the pickup line, thereby engaging the pickup line with the pickup device.

[0013] In an embodiment of the method, the object comprises a floating object, such as a pipeline, preferably a floating pipeline. The floating pipeline is a type of pipeline which is commonly used in dredging and sand supplementation operations, for example. Especially in these operations the pipelines have to be frequently connected to and disconnected from various vessels, meaning that the benefit provided by the presently invented method is especially large. It will be appreciated that the pickup float as described above can be effectively used to retrieve a multitude of different types of objects provided in, on or near a body of water. For example, a pickup float may be connected to an object that is provided below the water surface, such as laying on the bottom of the body of water.

[0014] In an embodiment, the retrieval cable is coupled to a winch. Retrieval cables are very commonly coupled to winches as the winch allows the retrieval cable to be pulled in, retrieving the object to which the retrieval cable has been coupled. Other devices to retrieve cables are also suitable for use in combination with the present method comprising the use of a USV and a pickup float. The winch may also, for example, be part of a crane.

[0015] Preferably, the retrieval cable is removably coupled to the pickup device, and the pickup device is removably coupled to the USV. This allows the USV to be, for example, separated from the retrieval cable while the pickup device remains connected to the retrieval cable.

[0016] In another embodiment, the method additionally comprises the step of using the winch to pull the USV, the pickup float and the object coupled thereto towards the winch. This means that the USV is not used to actually retrieve the object. This allows for the use of a USV with relatively little thrust, as only sufficient thrust is required to bring the retrieval cable towards the pickup float and / or the object. As the USV is pulled back towards the vessel by the winch, the USV is retrieved in a relatively uncontrolled manner. The USV is preferably designed to be able to withstand this. For this purpose, resilient USVs currently for sale, such as a remote controlled life buoys, may be modified with a pickup device and a means such as a loop or other connector to couple to the retrieval cable.

[0017] In another embodiment, the method additionally comprises the step of winching the pickup float at least partially onto the winch. The option of winching the pickup float onto the winch is a benefit, as the pickup float then does not have to be removed from between the retrieval cable and the object, or from between the retrieval cable and another cable that couples the pickup float to the object. This beneficially allows for a more efficient deployment of the object back to the water from the vessel. In addition, if the USV is removable from the pickup device, the USV may be uncoupled from the pickup device and the retrieval cable, allowing the retrieval cable, pickup device and pickup float to be winched onto the winch. The pickup float that is still on the winch may simply stay connected to the object when the object is being used by the vessel. The object can then be lowered back into the water after use by the same winch with the same pickup float. If the object is disconnected from the retrieval cable and pickup float for use, the benefit still applies as the object may simply be reconnected to the same pickup float and lowered back into the water by the same winch. After retrieving the pickup float, the one or more floating members such as buoys may be disconnected and removed from the pickup line, prior to rolling or winching the pickup line onto the winch.

[0018] In a preferred embodiment, the method additionally comprises the steps of: providing a tension relief support; providing a tension relief member arranged on the pickup float; winching the USV and the pickup means towards the tension relief support; coupling the tension relief member to the tension relief support to relieve the tension in the USV, the pickup float and the retrieval cable.

[0019] As the tension in the retrieval cable, the USV and the pickup float is relieved, the retrieval cable may be disconnected from the USV and / or the pickup float without releasing the object that has just been retrieved from the vessel. After disconnecting the retrieval cable, the USV may be taken away and stored. The retrieval cable may then be connected to the pickup float, and subsequently the retrieval cable and the pickup float may be rolled onto the winch to pull the object further onto the vessel. Alternatively, the pickup float may additionally be removed, and the retrieval cable be directly coupled to the object or a cable that connected the pickup float to the object.

[0020] In the disclosed embodiments, the winch may be provided on a vessel. However, the winch may also be placed on land, and the method may then be used to retrieve an object in water towards land, such as towards a beach, quay, dock or pier.

[0021] Preferably, the tension relief support is provided on the vessel, if the winch is also provided on the vessel. If the winch is provided elsewhere, the tension relief support is preferably provided in the vicinity of the winch.

[0022] In a preferred embodiment of the method, the USV comprises an automatically closing pickup hook, wherein the pickup hook extends downwards from the USV to below the surface of the water when the USV floats on the water surface. Preferably, the step of connecting the pickup hook to the pickup float comprises moving the USV over the pickup line to drag the pickup hook over the pickup line, wherein the pickup hook automatically closes into a closed position and couples to the pickup line when the pickup hook engages the pickup line. This beneficially allows the USV to catch the pickup line of the pickup float simply by crossing over it. In order to securely retain the pickup float when winching the USV, pickup float and object towards the vessel, the pickup hook is preferably of a type that automatically closes when it engages an object. These automatically closing hooks are known in the art. A simpler hook design may also be used with spring loaded closing members that are biased towards the closed position. The pickup line engaging with the pickup hook then pushes a closing member aside, and subsequently the closing member closes again to retain the pickup line in the pickup hook. It will be appreciated that a hook design without a closing mechanism - i.e. an open hook - may also be used to engage the pickup line.

[0023] Preferably, the step of connecting the pickup hook to the pickup float comprises connecting the pickup hook to one loop, or one of a plurality of loops, suspended from the pickup line, wherein the loops are preferably at least partially formed by the pickup line. As the pickup line is open ended, the pickup hook risks simply sliding along the pickup line, and off the open end of the pickup line, when pulled upon. To prevent the pickup hook from sliding off the pickup line, a series of wires, cables or lines is suspended below the pickup line, forming loops in combination with the pickup line. Therefore, the pickup hook, when engaging the pickup line, also engages one of said loops. These loops then retain the pickup hook, preventing it from sliding along the length of the pickup line and sliding off the end of the pickup line.

[0024] Additionally or alternatively, the step of connecting the pickup device to the pickup float comprises retaining the pickup hook on the pickup line in at least a direction substantially parallel to the length direction of the elongate pickup line, wherein the step of retaining the pickup hook on the pickup line preferably comprises retaining the pickup hook by means of an end stop. The end stop thus prevents the pickup hook from sliding off an end of the pickup line. Preferably, the end stop is, in a plane perpendicular to the length direction of the elongate pickup line, in at least one dimension larger than the pickup line. Thus, while the pickup line is small enough to allow the pickup hook to engage it, the end stop cannot pass through the pickup hook.

[0025] In an embodiment of the method, more than one winch is used on the vessel retrieving the object. A first winch may initially be connected through a retrieval cable to the USV. The USV then connects the pickup hook to the pickup float, and the first winch is then used to pull the USV, pickup float and object connected to the pickup float towards the vessel. Preferably, the first winch is used to hoist the USV and pickup float onto the vessel. The pickup line may then optionally be connected to the tension relief support to relieve the tension in the retrieval cable, USV and pickup line. The retrieval cable of the first winch may then be disconnected from the USV. A second cable from a second winch may then be connected to the pickup line to, for example, hoist up the object onto the deck. For that purpose the second winch may have a higher winching capacity than the first winch, meaning that it can pull with more force. Alternatively, if the pickup float is also disconnected, the second cable may be directly connected to the object, optionally through a cable which before connected the pickup float to the object. A benefit is that the use of two winches may provide more flexibility. Another potential benefit is that the first winch can be used in combination with the USV to retrieve other pickup floats, while one or more other winches are then used to pull the retrieved pickup floats and objects towards and optionally onto the vessel. For example, a vessel may have three connectors for a pipeline each provided with a nearby winch, and three floating pipelines, each with a pickup float attached, are floating near the vessel. A fourth winch may then be used in combination with the USV to retrieve the three pickup floats. After the USV has been winched onto the vessel, the three winches associated with the pipeline connectors may then be used for the remainder of the retrieval operation, allowing the fourth winch to be used for other operations. After use, the objects, in this example the pipelines, may be released back into the water by said three winches, together with the pickup floats that remained rolled onto the winches, if they were first rolled onto the winches.

[0026] It will be appreciated that although the above mentioned method works particularly well when using an unmanned vessel, in particular the pickup float provided with for instance the pickup line could also be used in combination with a generic vessel, i.e., not necessarily unmanned.

[0027] However, according to a further aspect an Unmanned Surface Vessel (USV) is provided, preferably for use in the method as described above, comprising a pickup device, for instance in the form of an automatically closing hook, movably coupled to the USV and arranged to extend downwards into the water when the USV floats on the water surface, propulsion means, and preferably a remote control receiver arranged to control the propulsion means using signals received from a remote control transmitter. The USV is preferably light enough to be portable by a person. This makes the method especially user friendly and efficient, as no crane or the like is required to move the USV. A preferred USV is preferably less than 1 meter, more preferably around 80 centimetres in width, and preferably less than 1.5 meters, more preferably around 1 meter in length, and preferably less than 20 kilograms, more preferably less than 15 kilograms in weight. The USV is additionally preferably battery powered.

[0028] Preferably, the USV comprises a retrieval cable arranged to couple the USV to a vessel. This retrieval cable may be used in combination with a winch on the vessel to pull the USV, and if coupled to the USV the pickup float and / or the object towards the vessel. Preferably, the pickup device is removably coupled to the USV. More preferably, the retrieval cable is removably coupled to the pickup device. This allows the USV to be isolated from a load applied to the pickup device and which is transferred to the retrieval cable, and vice versa. In addition, the USV may be disconnected, while the pickup device remains coupled to the retrieval cable.

[0029] In a preferred embodiment, the USV comprises at least two thrusters, wherein the USV is propelled using at least two thrusters, and wherein the USV is arranged to be steered using differential thrust of the at least two thrusters. This design has relatively few components, for example no rudder, which makes the USV more robust. Preferably, the thrusters are arranged inside the hull of the USV, with inlets for water arranged on at least the underside of the USV. This design has no significant parts protruding from the bottom of the USV, allowing it to pass over the pickup line without having any components other than the pickup hook catching onto the pickup line. Preferably the USV is reversible, with inlets on both the top and the bottom of the USV, so that the USV may be deployed to water in any orientation. In another embodiment, the USV may comprise a rudder and for example a single thruster, such as a propeller or a waterjet.

[0030] According to a further aspect, a pickup float is provided, preferably for use in the method according to any of the embodiments described above, comprising an elongate pickup line and a floating member, wherein the pickup float is arranged to maintain the pickup line in a substantially horizontal and substantially elongate position at or near the water surface, preferably for pickup by the pickup device of a pickup vessel such as the USV. The pickup float is thus arranged to maintain itself in a stable, elongate shape when it is floating in water, thereby not requiring external support to keep it in a stable shape. This allows the pickup float to be free floating and to be connected to an object on only one end.

[0031] Preferably, the pickup line comprises one or more coupling mechanisms, for instance in the form of a loop, for coupling to the floating object and / or a winching cable, preferably at or near a free end of the pickup line. These coupling mechanisms, preferably loops, allow the pickup line to be connected to the object, and / or to a cable that connects to the object. The other loop can then, for example, be used to couple to the retrieval cable when the USV is pulled on board with the pickup float. The pickup line may then be rolled onto the winch, as described before.

[0032] In a preferred embodiment of the pickup float, the pickup line comprises a resiliently flexible member, such as a ribbon, arranged to maintain a resiliently constant form when the pickup float floats on the water surface. The resiliently flexible member is thus able to maintain a substantially straight elongate shape when floating in water, but also bend to be rolled onto a winch or be stored. This resiliently flexible member may also be a cable with a substantially circular diameter, or another shape of elongate member.

[0033] In an embodiment of the pickup float, the pickup line comprises one or more appliques arranged to increase or decrease the buoyancy of the pickup line. These appliques may be sections of foam or another material which are applied to the pickup line, for example by sowing, riveting or gluing. The composition of the appliques may be chosen to either increase or decrease the combined density of the pickup line.

[0034] Preferably, the pickup line is arranged to be at least neutrally buoyant in water, floating near the water surface or on the water surface. Depending on application, the buoyancy may be adjusted to fresh water or salt water.

[0035] In a preferred embodiment, the pickup float comprises one or more loops connected to the pickup line, the pickup line forming a part of one or more of the one or more loops, wherein the loops are arranged to extend downwards from the pickup line when the pickup float floats on water. As the pickup hook engages the pickup line, the pickup hook hereby also engages one of the loops suspended under the pickup line. The hook, when pulled on, then may pull on one of the loops, preventing it from sliding along the length of the pickup line, and potentially slipping off the end of the pickup line. Alternatively, a number of blocks may be arranged on the pickup line, which are preferably larger in diameter, or any other dimension of the said block, than the openings of the pickup hook. The pickup hook can then be retained on the pickup line by these blocks, also preventing it from sliding off the end of the pickup line.

[0036] In a preferred embodiment, the pickup float further comprises at least one end stop connected to the pickup line. An end stop, similar to the block as described above, is preferably arranged to retain the hook on the pickup line, also by preventing it from sliding off the end of the pickup line. Preferably, in a cross sectional plane perpendicular to the length direction of the elongate pickup line, the cross section of the end stop is in at least one dimension substantially larger than the cross section of the pickup line. Thus, for example a hook which is arranged to at least partially enclose the pickup line to engage it may not be large enough to (partially) enclose the end stop. Thus, the end stop may retain a hook which is large enough to at least partially enclose the pickup line, but too small to at least partially enclose the end stop. In a preferred embodiment, the pickup float comprises a stiffening member, such as a rod, connected to the pickup line arranged to maintain at least part of the pickup line in a substantially elongate position in an elongate form. The pickup line itself may then be a regular, easily bendable and non-resiliently flexible cable or wire. A drawback of this embodiment is that the stiffening member may prevent the pickup line from being rolled onto a winch. A benefit is the simpler construction, requiring only regular rope, cable or wire and a rod. This embodiment of the pickup line is preferably also equipped with at least two floating members, such as buoys, to provide the required buoyancy, as the pickup line itself may not be tuned to have a specific buoyancy. These buoys may then additionally be used to demarcate the ends of the pickup float, allowing an operator or autonomous guidance system to pilot the USV over the pickup line by piloting the USV to pass between said buoys. Said optional autonomous guidance system may also be used in combination with any other embodiment of the pickup float.

[0037] Preferably, the pickup float comprises two floating members arranged to float on the water surface. These floating members may be buoys or the like, and be removably connected to the pickup line. The primary purpose of the floating members is to demarcate the ends of the pickup line. An operator may then steer the USV (or the USV may steer itself if it is controlled autonomously) between the floating members to engage the pickup line with the pickup hook. The floating member may additionally provide additional buoyancy to the pickup float. If the pickup line is not by itself buoyant, the pickup line may be suspended from the floating members which do float on the water surface. In addition, the floating members may comprise end stops as described above.

[0038] Preferably, the pickup float is at least constructed of one or more of: high molecular polyethene (HMPE), aromatic polyamide (Aramide), polyethersulfone (PES), liquid crystal polymers (LCP). These materials may be used for the pickup line to provide a pickup line with the desired degree of flexibility. The materials may additionally specifically, but not exclusively, be used to manufacture the appliques. Using different amounts or formulations of said materials, buoyancy and flexibility characteristics may be adjusted to the desired value, for example to the density of fresh water or salt water.

[0039] It will be appreciated that the pickup float described above, while particularly suitable for use in combination with the described method, can also be used as part of other methods involving the coupling of a coupling member to the pickup float. Another aspect of the present invention relates to a system for executing the method according to any of the embodiments of the method, comprising a USV according to any of the described embodiments, and a pickup float according to any of the described embodiments.

[0040] Another aspect of the present invention relates to a vessel comprising a USV according to any of the described embodiments.

[0041] Another aspect of the present invention relates to an object comprising a pickup float according to any of the described embodiments. Said object may comprise a floating object, such as a floating pipeline.

[0042] The invention is further elucidated by means of the following figures: figures 1A, B: overview of the retrieval method using the USV; figures 2A, B: detailed view of the method of the USV coupling to the pickup means; figure 3: overview of the retrieval method of the floating object; figure 4: detailed overview of the retrieval method of the USV and the pickup float; figure 5: overview of an alternative retrieval method of the floating object; figure 6: overview of the USV; figures 7A-C: overview of embodiments of the pickup float; figure 8: overview of the pickup hook; figure 9: overview of the tension relief means; figure 10: overview of an embodiment of the pickup float; figure 11: detailed view of an embodiment of the pickup float; and figure 12: detailed view of an embodiment of the pickup float.

[0043] Figure 1A shows an overview of the first stage of the retrieval method of the floating object 4. In this embodiment of the method a floating pipeline 4 is retrieved towards a vessel 1. In figure 1A, the USV 2 has been lowered from the vessel 1 by means of the retrieval cable 22 and is floating on the water surface. An operator 13 uses a remote control 12 to direct the USV towards the pickup float 3 that is attached through cable 32 to the floating object 4. The pickup float 3 is floating on the water. A pickup line 31 is suspended near the water surface, below the water surface, and demarcated by floating members (buoys) 35. Below the pickup line 31 a plurality of loops 34 are suspended. The USV 2 is equipped with a self-closing hook 21 and sails across the pickup line 31, thereby dragging the hook 21 over the pickup line 31, thereby catching the pickup line 31. As the hook 21 catches the pickup line, the hook 21 is triggered to at least partially close around the pickup line 31. Figure IB shows an overview of a stage of the retrieval method subsequent to the stage shown in figure 1A. After the hook 21 has engaged the pickup line 31, the winch 11 is used to winch in the retrieval cable 22, thereby dragging the USV 2, the pickup float 3 and the floating object 4 towards the vessel 1. Preferably, the USV is not used to tow the pickup float 3 and the object 4 towards the vessel 1, as it lacks sufficient power. However, embodiments with a USV 2 that is powerful enough to tow a floating object 4 towards the vessel 1, and is used for that purpose instead of or in addition to the winch 11 , are also envisioned.

[0044] Figure 2A shows the USV 2 approaching the pickup float 3. The USV is equipped with an automatically closing hook 21, which is preferably in the open position when the USV 2 is deployed and approaching the pickup float 3. The hook 21 comprises two closing members 211 which are in the open position when the hook 21 is opened. To couple the USV 2 to the pickup float 3, the USV 2 is steered such that it passes between the floating members 35 and over the pickup line 31.

[0045] Figure 2B shows the USV 2 coupling to the pickup float 3. The USV sails over the pickup line 31, dragging the pickup hook 21 over the pickup line 31 so that the hook 21 engages the pickup line 31. As the hook 21 engages the pickup at least one closing member 211 is triggered to close, either by the physical engagement of the pickup line 31 or by an external control, to securely retain the pickup line 31 in the hook 21. The pickup line 31 forms part of the loops 34 that are suspended below the pickup line 31. Therefore, when the hook 21 engages the pickup line 31 the hook automatically also engages a loop 34. The loops 34 suspended below the pickup line 31 serve to support the hook 21 as the hook 21 is pulled on by the USV 2 and / or the retrieval cable 22.

[0046] Figure 3 shows the USV 2, the pickup float 3 and the floating object 4 being retrieved onto the vessel 1 in a possible step subsequent to the step shown in figure IB. After the hook 21 has engaged the pickup float 3 (shown in figure 2B), the winch 10 is used to pull the USV 2, the pickup float 3 and the floating object 4 connected to the pickup float 3 by cable 32 towards the vessel. At the moment shown in figure 3, the USV 2 and the pickup float 3 have been hoisted onto the vessel by means of the winch 10 and the retrieval cable 22. Once the USV 2 and the pickup float 3 have been hoisted onto the vessel 1, the USV may be disconnected from the hook 21. In addition, the floating members 35 may be disconnected from the pickup float 3. The retrieval cable, together with the hook 21 and the pickup line 31 may then be rolled onto the winch drum 11 to hoist the floating object 4 onto the vessel. A possible alternative subsequent step is shown in figure 4. Figure 4 shows a detailed overview of possible steps after the USV 2 and the pickup float 3 have been hoisted onto the vessel 1. An end block 36 arranged on the pickup float 3, on the pickup line 31 is coupled to a tension relief support 14 (shown in more detail in figure 9). Hereby the pickup float 3 and the cable 32 are supported by the tension relief means 14, relieving the tension in the winch 10 and the retrieval cable 22, as well as in the USV 2, specifically the hook 21, and the pickup line 31. The USV 2 may then be decoupled from both the retrieval cable 22 and the pickup float 3 and be stored on the vessel 1. The retrieval cable 22 may then be either connected to the free end connection 38 of the pickup line 31 - the other free end connection 38 of which is coupled to the cable 32 - or directly to the pickup cable 32 which is connected to the floating object 4. In the latter embodiment, the pickup float 3 is preferably disconnected and removed from the cable 32.

[0047] If the retrieval cable 22 is connected to the pickup line 31 , the floating members 35 are preferably disconnected from the pickup float 3 to be stored, and the pickup line 31 may then be rolled onto the winch drum 11 together with the cable 32, thereby hoisting the floating object onto the vessel 1. If the winch drum 11 is removed far enough from the tension relief means 14, it may be the case that only the retrieval cable 22 is rolled onto the winch drum 11 to hoist the floating member 4 up sufficiently.

[0048] If the retrieval cable 22 is coupled directly to the cable 32, the entire pickup float may be disconnected from the pickup cable 32 and then stored. The cable 32 is then rolled onto the winch drum 11 to hoist the floating object 4 onto the vessel 1. Again, if the winch drum 11 is removed far enough from the tension relief means 14, it may be the case that only the retrieval cable 22 is rolled onto the winch drum 11 to hoist the floating member 4 up sufficiently.

[0049] Figure 5 shows an alternative to the method shown in figure 4. In the shown embodiment, two winches 10, 15 are used instead of the one winch 10 used in the embodiment of the method shown in figure 4. One winch 15, possibly a smaller winch with less capacity, is used to retrieve the USV 2 and the pickup float 3. The second winch 10, possibly a larger winch with more capacity than the first winch 15, is then coupled to either the pickup line 31 or directly to the cable 32 to pull the floating object 4 towards and onto the vessel 1.

[0050] Figure 6 shows an overview of the USV 2. The USV 2 according to the invention comprises a remote controlled base USV 20 that is equipped with a pickup hook 21. The base USV 20 is equipped with two thrusters, a left thruster 23 and a right thruster 24. The thrusters are supplied by inlets 27 provided on the topside and bottom side of the base USV 20. The provision of inlets 27 on both sides of the USV allows it to function both “right side up” and “upside down”. A benefit of this arrangement is that no propellors, rudders or other significant components of the base USV 20 protrude beyond the underside of the base USV 20, such that no protruding members other than the hook 21 may accidentally catch the pickup float or other objects when the USV 2 passes over them. The base USV 20 further comprises a hook bar 25 to support the pickup hook 21. The winch cable 22 is connected to the pickup hook 21 by means of a hook 26, preferably a quick-release hook or carabiner 26. As the winch cable 22 is connected directly to the pickup hook 21, the winch pulls directly on the hook, which in turn pulls on the cable 32 (not shown) to which the floating object 4 (not shown) is attached. As the winch may pull with significant force, the present arrangement beneficially transfers this force directly to the hook 21, and not through the base USV 20. This beneficially allows the base USV 20 to be of a lighter construction. The base USV 20 further comprises a remote control receiver (not shown) to allow the USV 2 to be remote controlled. In an envisioned embodiment, the USV may additionally or alternatively be provided with an autonomous guidance system to pilot the USV.

[0051] Figure 7 A shows a first embodiment of the pickup float 3. This embodiment of the pickup float 3 comprises a pickup line 31 , which may be non-resiliently flexible and non-rigid, which is suspended from two floating members 35. The pickup line 31 is suspended to be slightly (less than 50 cm) below the water surface. Alternatively, the pickup line 31 may float on the water surface. A stiffening member 33, such as a rod 33, is suspended below the pickup line 31 by lines 39. The stiffening member 33 ensures that the pickup line 31 is kept substantially straight, even though the pickup line 31 itself may be non-resiliently flexible. The pickup line 31 , lines 39 and rod 33 form loops 34 to support the pickup hook 21 when it engages the pickup float 3 and is pulled on by the winch 10 (not shown). The pickup line 31 is further provided with end loops 38 which may be used to connect the pickup float 3 to the cable 32 (not shown) or the retrieval cable 22 (not shown). End blocks 36 may be provided to enable the pickup float to engage with a tension relief means (not shown).

[0052] Figure 7B shows a second embodiment of the pickup float 3. The end loops 38, loops 34 and end blocks 36 fulfil the same functions as described above under figure 7A. In the embodiment of the pickup float shown in figure 7B, the shown assembly, without the floating members 35, is preferably arranged to be at least neutrally buoyant in water. The applied sections 37 are used to fine tune the buoyancy of the assembly, and are for that purpose either less dense or more dense than water (either fresh water or salt water, depending on the application). In addition, the applied sections 37 may provide additional stiffness to the pickup line 31. As the pickup line 31 with all shown components attached, except the floating members 35, is buoyant, the floating members 35 are intended to indicate the ends of the pickup line 31 to aid an operator in steering a USV or other watercraft between the floating members 35, and thereby across the pickup line 31. The floating members 35 are removably connected to the pickup line 35, preferably by carabiner hooks or similar (not shown).

[0053] The pickup line 31 is further constructed of a resiliently flexible material, and as a result the pickup line 31 maintains a substantially straight form when in water. The flexibility of the pickup line 31 serves, among other purposes, to allow the pickup line 31 to be rolled onto a winch drum 10 (not shown). Optionally, but not essentially, the applied sections 37 are also resiliently flexible. As the pickup line 31 is able to maintain the desired straight shape by itself, the stiffening member 33 of the embodiment shown in figure 7A is not required and therefore omitted. The loops 34 may be formed with flexible wires, ropes or cables 39. Alternatively, the loops 34 are formed of resiliently flexible materials, for example the same material as the pickup line 31. This allows the pickup line 31 as well as the loops 34 to substantially retain their shape when floating in or on water.

[0054] Figure 7C shows a third embodiment of the pickup float 3. The end loops 38, floating members 35, applied sections 37 and pickup line 31 are constructed similarly and fulfil the same function as the second embodiment shown in figure 7B. The loops 34 are omitted, and the end blocks 36 are arranged to be larger in at least one dimension than the openings of the hook 21 (not shown) to stop the hook 21 from sliding off either end of the pickup line 31. The end blocks 36 serve as end stops to retain a pickup hook 21 (not shown), and prevent it from slipping off one of the two free ends of the pickup line 31. As the construction of the third embodiment of the pickup float 3 shown in figure 7C is different from the second embodiment of the pickup float 3 shown in figure 7B, the applied sections 37 may have a different buoyancy than in the second embodiment in order to fine tune the buoyancy of the assembly to the required application.

[0055] While figures 7A-C show three distinct embodiments of the pickup float 3, the components of the three embodiments are not inextricably linked, and may therefore be mixed and matched to a degree. For example, the second embodiment shown in figure 7B may be constructed without the applied sections 37. The pickup line 31 may then be naturally denser than water and consequentially be suspended below the water surface by the floating members 35. Alternatively, the pickup line 31 may be naturally buoyant, in which case the floating members 35 are not required for buoyancy, but simply serve as guidance for an operator to steer the USV or other watercraft between the floating members 35 and over the pickup line 31. In another alternative embodiment, the pickup line 31 of the first embodiment, shown in figure 7A, is provided with applied sections 37 to fine tune the buoyancy of the pickup float 3.

[0056] Figure 8 shows an overview of a possible embodiment of the pickup hook 21. The hook comprises two closing members 211, which can selectively be positioned in the open position, shown by the righthand closing member 211, or in the closed position, shown by the lefthand closing member 211’ . The pickup hook 21 is preferably deployed with the closing members 211 in the open position, so that the pickup hook 21 can catch an object such as a pickup line (not shown) unimpeded. When an object engages the hook 21, one or both of the closing members 211 are triggered to close, thereby enclosing the object. Alternatively, the closing members 211 are simply mounted to the hook 21 with a hinge connection and are spring loaded into the closed position. When the hook 21 catches an object, the object pushes the closing member 211 aside. The closing member 211 then snaps closed again to enclose the object. Both embodiments of the pickup hook 21 are commonly known in the art.

[0057] Figure 9 shows an example of a tension relief means 14 in interaction with an end block 36 of a pickup line 31. The tension relief means 14 may comprise a receptacle comprising a slit with a larger width on one side than the other. The large opening 141 accommodates an end block 36 provided on the pickup line 31, while the narrow opening 142 allows the pickup line 31 to pass through while blocking the end block 36. This allows the pickup line to be supported while a pulling force is applied to the pickup line 31 towards the narrow opening 142, in the direction indicated by the arrow.

[0058] Figure 10 shows a fourth embodiment of the pickup float 3, similar to the embodiment shown in figure 7C. The pickup line 31 comprises multiple components 310, 311 and 330 (shown in more detail in figures 11, 12) and the pickup line 31 is arranged to be resiliently flexible. The pickup float comprises end blocks 36, or end stops 36, which are, seen in a plane perpendicular to the elongate pickup line 31, in at least one direction larger than the pickup line 31. Thus, the end stops 36 serve to block for example a hook 21 (not shown) from sliding off the end of the pickup line 31. In addition, the end stops 36 are arranged to interact with a tension relief 14 (not shown) in a manner explained at least in relation to figures 4 and 9. At least one end loop 38 is provided to for example allow the pickup float 3 to be connected to (pickup) cable 32. In the shown embodiment, the end stops 36 comprise loops 36a to allow for example floating members 35 to be connected to the pickup line 31. Figures 11 and 12 show the composition of the pickup line 31 in more detail. The pickup line 31 comprises a stiffening member 330 which is preferably resiliently flexible, and thus arranged to maintain the pickup line 31 in a substantially elongated form when the pickup float 3 is suspended in water. The stiffening member 330 may for example comprise a glass fibre rod, which has suitable properties. Other materials known in the art with suitable properties may also be used. The pickup line 31 further comprises a centre ribbon 310, and a wrapper 311 which at least partially encloses the stiffening member 330 and centre ribbon 310 and is connected to at least the centre ribbon 310 to form the pickup line 31. The materials and / or composition of the parts 310, 311 and 330 may be adapted to achieve a desired overall buoyancy of the pickup line 31. Embodiments are also envisioned wherein the centre ribbon 310 is at least partially omitted, and the wrapper 311 at least partially connects to itself to enclose the stiffening member 330.

[0059] The present invention is not limited to the embodiment shown, but extends also to other embodiments falling within the scope of the appended claims.

Claims

Claims1. Method for coupling a retrieval cable to an object in a body of water, comprising the steps of: providing an unmanned surface vessel (USV) comprising a pickup device, wherein the USV is coupled to a retrieval cable; providing a pickup float coupled to said object, wherein said pickup float comprises an elongate pickup line and a floating member, wherein the pickup float is arranged to maintain the pickup line in a substantially horizontal and substantially elongate position on or near the water surface; moving the USV towards the pickup float; connecting the pickup device to the pickup float by moving the USV over and across the pickup line.

2. Method according to claim 1, wherein the object comprises a floating pipeline.

3. Method according to claim 1 or 2, wherein the retrieval cable is coupled to a winch.

4. Method according to any of the preceding claims, wherein the retrieval cable is removably coupled to the pickup device, and wherein the pickup device is removably coupled to the USV.

5. Method according to any of the preceding claims, wherein the winch is provided on a vessel.

6. Method according to claim 3 or 5, additionally comprising the step of using the winch to pull the USV, the pickup float and the object coupled thereto towards the winch.

7. Method according to any of the preceding claims 3-6, additionally comprising the step of winching the pickup float at least partially onto the winch.

8. Method according to any of the preceding claims 3-7, additionally comprising the steps of: providing a tension relief support; providing a tension relief member arranged on the pickup float; winching the USV and the pickup device towards the tension relief support; coupling the tension relief member to the tension relief support to relieve the tension in the pickup device the pickup float and the retrieval cable.

9. Method according to claim 8, wherein the tension relief support is provided on the vessel.

10. Method according to any of the preceding claims, wherein the pickup device of the USV comprises an automatically closing pickup hook, wherein the pickup hook extends downwards from the USV to below the surface of the water when the USV floats on the water surface.

11. Method according to any of the preceding claim 10, wherein the step of connecting the pickup device to the pickup float comprises moving the USV over the pickup line to drag the pickup hook over the pickup line, wherein the pickup hook automatically closes into a closed position and couples to the pickup line when the pickup hook engages the pickup line.

12. Method according to claim 11, wherein the step of connecting the pickup device to the pickup float comprises connecting the pickup hook to one of a plurality of loops suspended from the pickup line, wherein the loops are at least partially formed by the pickup line.

13. Method according to any of the preceding claims 11-12, wherein the step of connecting the pickup device to the pickup float comprises retaining the pickup hook on the pickup line in at least a direction substantially parallel to the length direction of the elongate pickup line, wherein the step of retaining the pickup hook on the pickup line comprises retaining the pickup hook by means of an end stop.

14. Unmanned surface vessel (USV) for use in the method according to any of the preceding method claims, comprising an automatically closing hook, movably coupled to the USV and arranged to extend downwards into the water when the USV floats on the water surface, propulsion means, and a remote control receiver arranged to control the propulsion means using signals received from a remote control transmitter.

15. Unmanned surface vessel (USV) according to claim 14, further comprising a retrieval cable arranged to couple the USV to a vessel.

16. Unmanned surface vessel (USV) according to claim 14-or 15, wherein the USV comprises at least two thrusters, wherein the USV is propelled using at least two thrusters, and wherein the USV is arranged to be steered using differential thrust of the at least two thrusters.

17. Vessel comprising a USV according to any of the claims 14-16.

18. Pickup float for use in the method according to any of the preceding method claims, comprising an elongate pickup line and a floating member, wherein the pickup float is arranged to maintain the pickup line in a substantially horizontal and substantially elongate position on or near the water surface for pickup by the pickup device of the USV.

19. Pickup float according to claim 18, wherein the pickup line comprises one or more coupling mechanisms, for instance in the form of a loop, for coupling to the floating object and / or a winching cable, at or near a free end of the pickup line.

20. Pickup float according to claim 18 or 19, wherein the pickup line comprises a resiliently flexible ribbon arranged to maintain a resiliently constant form when the pickup float floats on the water surface.

21. Pickup float according to any of the preceding claims 18-20, wherein the pickup line comprises one or more appliques arranged to increase or decrease the buoyancy of the pickup line.

22. Pickup float according to any of the preceding claims 18-21, wherein the pickup line is arranged to be at least neutrally buoyant in water.

23. Pickup float according to any of the preceding claims 18-22, further comprising one or more loops connected to the pickup line, the pickup line forming a part of one or more of the one or more loops, wherein the loops are arranged to extend downwards from the pickup line when the pickup float floats on water.

24. Pickup float according to any of the preceding claims 18-23, further comprising at least one end stop connected to the pickup line, wherein, in a cross sectional plane perpendicular to the length direction of the elongate pickup line, the cross section of the end stop is in at least one dimension substantially larger than the cross section of the pickup line.

25. Pickup float according to any of the preceding claims 18-24, further comprising a stiffening member connected to the pickup line arranged to maintain at least part of the pickup line in a substantially elongate position in an elongated form.

26. Pickup float according to any of the preceding claims 18-25, further comprising two floating members arranged to float on the water surface.

27. Pickup float according to any of the preceding claims 18-26, wherein the pickup float is at least constructed of one or more of: high molecular polyethene (HMPE), aromatic polyamide (Aramide), polyethersulfone (PES), liquid crystal polymers (LCP).

28. System for executing the method according to any of the method claims, comprising a USV according to any of the claims 14-16, and a pickup float according to any of the claims 18-27.

29. Object comprising a pickup float according to any of the claims 18-27.

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