Cassette assemblies, surface vessels, and methods for maintaining water-accessible structures

Abstract

The cassette assembly (200) is mountable to an end (102) of the surface vessel (100). The cassette assembly (200) includes a cassette portion (210) that abuts an external structure (300) in use. The cassette portion (210) is movable relative to the vessel (100) toward an opposite end of the vessel (100). A resilient shock absorber system (250) opposes movement of the cassette portion (210) when the vessel (100) is moved toward the external structure (300), the resilient shock absorber system (250) including a shock absorber (251) including a plurality of resiliently compressible elements (253) arranged in series. The surface vessel (100) includes a receiving portion (120) for receiving the cassette assembly (200) and can be used to service a water-accessible structure (300), such as a wind turbine.

Description

[Technical field]

[0001] The present disclosure relates to a cassette assembly for a surface vessel, a surface vessel for supporting the cassette assembly, and a method for servicing a water-accessible structure such as a wind turbine. [Background technology]

[0002] Various challenges arise when servicing a water-accessible structure, such as an offshore wind turbine with a surface vessel. One difficulty is allowing personnel to access the structure. In one example, a vessel may be purposefully navigated into a water-accessible structure, bringing the vessel into contact with the structure and allowing access to the structure. However, significant impact forces may be exerted on the structure and / or the vessel, potentially damaging the structure and / or the vessel.

[0003] GB 2390252 A1 discloses a surface vessel having a carriage assembly at one end of the vessel. The carriage assembly is moveable relative to the vessel and is shock absorbed so that impact forces are absorbed when the carriage assembly impacts a water-accessible structure. In order to safely use such a system without causing damage to either the vessel or the structure, constraints are imposed on its movement. This may include limiting the mass of the vessel incorporating the carriage assembly, the impact speed, and the impact angle of the vessel relative to the structure. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] GB 2390252 Summary of the Invention [Problem to be solved by the invention]

[0005] It is an object of the present invention to address these and any other problems which will become apparent to those skilled in the art from the disclosure herein. [Means for solving the problem]

[0006] According to the present invention there is provided an apparatus and method as set out in the accompanying claims. Further features of the invention will become apparent from the dependent claims and the following description.

[0007] According to a first aspect of the present disclosure, there is provided a cassette assembly mountable to one end of a surface vessel, comprising: a cassette part which in use abuts against the external structure, the cassette part being movable relative to the vessel in the direction of an opposite end of the vessel; a resilient shock absorber system for resisting movement of the cassette portion when the vessel is moved towards the external structure; Equipped with A resilient shock absorbing system is provided for the cassette assembly, which includes a shock absorber having a plurality of resilient compressible elements arranged in series.

[0008] The cassette part may be rotatable, preferably in a horizontal plane.

[0009] The cassette part may include a passageway formed in an upper surface thereof.

[0010] The resilient dampening system may comprise at least two dampers spaced across the width of the cassette part, and each damper of the resilient dampening system may comprise a plurality of resiliently compressible elements arranged in series.

[0011] The cassette part may comprise a fender part configured to contact the external structure. The fender part may be formed of a resilient material. The fender part may comprise a central projection and a pair of recesses located on respective lateral sides of the central projection. The recesses may comprise a stop surface to prevent outboard movement of the first support tube of the external structure beyond the stop surface. The recesses and the central projection may be configured such that contact between the first support tube and the stop surface causes rotation of the cassette part such that the fender part, suitably the central projection, contacts the second support tube of the external structure.

[0012] The external structure may be an offshore wind turbine. The external structure may be an offshore platform or other fixed or floating structure.

[0013] The elastically compressible elements may be tubular. The compressible elements may comprise selfenders. Each compressible element may have a longitudinal length of 250mm to 1000mm, suitably 450mm to 800mm, suitably about 500mm. The diameter of the tubular portion of the compressible elements may be 250mm to 1000mm, suitably 450mm to 800mm, suitably about 550mm. The compressible elements may have a maximum compression of more than 20%, suitably more than 30%, suitably more than 40%, suitably more than 50%, most suitably about 52.5%. Compression of the compressible elements may require an energy of 19 to 50kNm, suitably 20 to 40kNm, suitably 22 to 30kNm, suitably 23 to 28kNm, suitably about 26kNm. Compression of the compressible element may provide a reaction force of about 90-235kN, suitably 100-180kN, suitably 110-140kN, suitably about 120kN.

[0014] The resilient buffer system may comprise a vertical guide for limiting vertical movement of the buffer, suitably preventing vertical movement of the buffer. The vertical guide may comprise one or more guide protrusions formed in one of the buffer or the guide channel of the cassette part, the guide protrusions being configured to cooperate with slots formed in the other of the buffer or the guide channel. The protrusions may project radially from the buffer. The protrusions may be located between adjacent compressible elements.

[0015] The resilient shock absorber system may include a lateral guide for limiting a range of lateral movement of the shock absorber. The lateral guide may include a first contact element configured to contact a second contact element formed on a lateral edge of a guide channel formed on a lateral edge of the shock absorber. The guide channel may be sized to allow a predetermined range of lateral movement of the shock absorber.

[0016] Each shock absorber may comprise three compressible elements arranged in series. Each shock absorber may comprise four, five, six or more compressible elements arranged in series.

[0017] The resilient buffer system may include a stop element configured to limit movement of the cassette portion toward the opposite end of the vessel. The stop element may be formed of an elastically deformable material. The cassette portion may be configured to contact the stop element before the buffer reaches a maximum compression limit.

[0018] The cassette assembly may include an over-rotation prevention unit configured to prevent over-rotation of the cassette portion. The over-rotation prevention unit may comprise a plurality of restraining ties configured to prevent movement of the cassette portion that would extend the buffer beyond the uncompressed position.

[0019] According to a second aspect of the present disclosure there is provided a surface vessel comprising a receiver configured to receive a cassette assembly as defined herein.

[0020] The receiver may be configured to slidably support the cassette assembly. The receiver may rotatably support the cassette assembly.

[0021] The receiver may comprise a recess within the vessel, suitably at the front of the vessel. The receiver may comprise a rear wall. The rear wall may comprise at least two mounting posts for supporting the at least two shock absorbers. The receiver may comprise substantially vertical side walls.

[0022] The receiver may extend across at least 50% of the width of the forward portion of the vessel. Suitably, the receiver may extend across at least 60% of the width of the forward portion of the vessel. The receiver may extend across at least 70% of the width of the forward portion of the vessel.

[0023] The surface vessel may include a cassette assembly disposed in the receptacle.

[0024] Further suitable features of the vessel of the second aspect are defined above in relation to the cassette assembly of the first aspect and may be combined in any combination.

[0025] According to a third aspect of the present disclosure, there is provided a method of servicing a water-accessible structure using a surface vessel, the surface vessel comprising a cassette assembly disposed at one end, the method comprising: contacting a cassette portion of the cassette assembly with a water-accessible structure; using an elastic buffer system to counteract relative movement of the cassette part towards the opposite end of the vessel; Equipped with A method is provided in which a resilient shock absorber system includes a shock absorber having a plurality of resiliently compressible elements arranged in series.

[0026] The water-accessible structure may be a wind turbine.

[0027] Further relevant features of the method of the second aspect are defined above in relation to the cassette assembly of the first aspect and the vessel of the second aspect and may be combined in any combination.

[0028] According to a fourth aspect of the present disclosure, there is provided a use of a cassette assembly and / or a surface vessel as defined herein.

[0029] According to a fifth aspect of the present disclosure, there is provided a cassette assembly mountable to one end of a surface vessel, comprising: a cassette part which in use abuts the external structure and which is movable relative to the vessel towards an opposite end of the vessel; a resilient shock absorber system for resisting movement of the cassette portion when the vessel is moved towards the external structure; Equipped with The cassette portion is a fender portion configured to contact an external structure, A central protrusion; a pair of recesses located on each lateral side of the central projection; A cassette assembly is provided that includes a fender portion comprising:

[0030] The recess may include a stop surface to prevent overboard movement of the first support tube of the outer structure beyond the stop surface, and the recess and central projection may be configured such that contact between the first support tube and the stop surface causes rotation of the fender portion, suitably the cassette portion such that the central projection contacts the second support tube of the outer structure.

[0031] Further relevant features of the assembly of the fifth aspect are defined above in relation to the cassette assembly of the first aspect and the vessel of the second aspect and may be combined in any combination.

[0032] According to a sixth aspect of the present disclosure, there is provided a cassette assembly mountable to one end of a surface vessel, comprising: a cassette part which in use abuts the external structure and which is movable relative to the vessel towards an opposite end of the vessel; a resilient shock absorber system for resisting movement of the cassette portion when the vessel is moved towards the external structure; Equipped with A cassette assembly is provided in which the resilient buffer system includes an over-rotation prevention unit configured to prevent over-rotation of the cassette portion.

[0033] Further relevant features of the assembly of the sixth aspect are defined above in relation to the cassette assembly of the first aspect and the vessel of the second aspect and may be combined in any combination.

[0034] For a better understanding of the present disclosure, and to show how examples of the same may be put into effect, reference will now be made, by way of example only, to the accompanying schematic drawings. [Brief description of the drawings]

[0035] [Figure 1] FIG. 1 illustrates an overhead plan view of one end of an exemplary surface vessel including an exemplary cassette assembly. [Diagram 2] FIG. 2 is a side cross-sectional view of one end of the exemplary surface vessel of FIG. [Figure 3A] FIG. 13 is a front view of an exemplary guide channel of the cassette; [Figure 3B] FIG. 3B is a partially cut-away perspective view of the guide channel of FIG. 3A. [Figure 3C] FIG. 4 is a partially cutaway perspective view of the guide channel of FIGS. 3A-B with the shock absorber omitted. [Figure 4] FIG. 2 is a plan view of an exemplary fender portion. [Figure 5A] FIG. 3 is an overhead plan view of the exemplary surface vessel of FIGS. 1 and 2 in contact with a water-accessible structure. [Figure 5B] FIG. 3 is an overhead plan view of the exemplary surface vessel of FIGS. 1 and 2 in contact with a water-accessible structure. [Figure 5C] FIG. 3 is an overhead plan view of the exemplary surface vessel of FIGS. 1 and 2 in contact with a water-accessible structure. [Figure 6A] 1 is a side cross-sectional view of an exemplary surface vessel. [Figure 6B] 1 is a side cross-sectional view of an exemplary surface vessel. [Figure 7] 1 is a flow chart of an exemplary method for providing a water-accessible structure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] In the drawings, corresponding reference characters indicate corresponding components. Those skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of the various exemplary embodiments. Also, common but well-understood elements that are useful or necessary in commercially feasible embodiments are often not depicted to facilitate a less obtrusive view of these various exemplary embodiments.

[0037] In summary, an example of the disclosure provides a cassette assembly mountable to one end of a surface vessel, the cassette assembly comprising a movable cassette portion for abutting an external structure, and a resilient shock absorber system for resisting movement of the cassette portion, the resilient shock absorber system comprising at least two shock absorbers spaced across a width of the cassette portion, each shock absorber comprising a plurality of resilient compressible elements arranged in series. The series arrangement of the multiple resilient compressible elements may allow the shock absorber system to absorb more energy, but without causing a significant increase in collision reaction force.

[0038] 1 and 2 show a forward portion 102 of an exemplary surface vessel 100. A longitudinal centerline of the vessel 100 is indicated by reference numeral 101. The forward portion 102 extends horizontally or laterally such that it is approximately perpendicular to the centerline 101 when viewed in a plan view.

[0039] The vessel 100, and more particularly the forward portion 102, includes a cassette assembly, generally indicated by reference numeral 200. As best seen in Figure 2, the cassette assembly 200 is disposed within a receiver 120 formed within the structure of the vessel 100. For example, the receiver 120 takes the form of a recess extending laterally across the forward portion 102 that is configured to receive the cassette assembly 200.

[0040] The receiving portion 120 is coupled vertically by a generally horizontal deck plate of the vessel 100. For example, the receiving portion 120 is coupled by an overhanging hull structure 121 above the receiving portion 120 and a hull 122 below the vessel 100.

[0041] Similarly, the receiver 120 is horizontally bounded at its lateral ends by a generally vertical bulkhead. In one example, the vessel 100 is a catamaran. In such an example, a generally vertical bulkhead may be located on the centerline of each demi-hull of the vessel 100. The aft portion of the recess 120 may be formed by a generally vertical transverse bulkhead 123.

[0042] The cassette assembly 200 comprises a cassette part 210 or carriage. The cassette part 210 takes the form of a platform slidably mounted within the receiver 120 for movement in a longitudinal direction indicated by arrow A. The cassette part 210 can also rotate in a horizontal plane as indicated by arrow B. For example, the cassette part 210 may comprise arcuate portions on its lateral edges supported by corresponding arcuate channels.

[0043] The top surface 211 of the cassette portion 210 allows a user to access the water-accessible structure. For example, the walkway 220 may be formed in the top surface 211, although it will be appreciated that in some instances the entire top surface 211 may be walked on.

[0044] The forward portion 212 of the cassette portion 210 is configured to contact the water-accessible structure. The forward portion 212 (and thus the receiving portion 120) may extend approximately 65-70% of the width of the forward portion 102. As shown in FIG. 1, the forward portion 212 may include a fender portion 230. The fender portion 230 is formed of a flexible or elastic material that can be compressed upon contact with the water-accessible structure, such as rubber. The shape of the fender portion 230 is described in more detail below with reference to FIGS. 4 and 5. In some examples, the watercraft 100 may also include fender portions 105 disposed on either side of the cassette assembly.

[0045] The cassette assembly 200 also includes a resilient dampening system 250. The resilient dampening system 250 is configured to resist movement of the cassette portion 210 caused by contact between the cassette portion 210 and the water-accessible structure. The resilient dampening system 250 includes a pair of dampers 251. The dampers 251 are spaced across the width of the cassette portion 210.

[0046] The bumper 251 extends from the rear bulkhead 123 of the receiver 120 to a stop surface 213 of the cassette part 210. The stop surface 213 may be a generally vertical surface that forms one end of a horizontally extending guide channel 214 within the cassette part 210. The bumper 251 may be attached to the rear bulkhead 123 by a mounting post 252 extending horizontally from the rear bulkhead to which the bumper 251 can be secured.

[0047] Each shock absorber 251 comprises a plurality of resilient compressible elements 253. The compressible elements 253 are arranged in series in the direction A. The compressible elements 253 are generally tubular compressible members having opposed plates disposed at opposite ends of the tubular member. For example, the compressible elements 253 may take the form of rubber fender cells or cones. The compressible elements 253 may be compressed to absorb the energy of contact between the cassette portion 210 and the water-accessible structure. When the compressive force is removed, the compressible elements 253 are configured to receive a restoring force, thereby returning to their initial, substantially uncompressed state.

[0048] In the illustrated example, each bumper 251 includes three elastically compressible elements 253. In further examples, each bumper 251 may include two, four, five, six, or another number of elastically compressible elements 251.

[0049] In one example, the compressible elements comprise cell fenders. In one example, each compressible element has a longitudinal length of about 500 mm. The diameter of the tubular portion of the compressible elements may be about 550 mm. The diameter of the opposing plates may be about 650 mm. The compressible elements may have a maximum deflection or compression of about 52.5%. Compression of the compressible elements may require an energy of about 26 kNm and may provide a reaction force of about 120 kN. This may be rated performance data according to PIANC with an initial fast berthing speed of 0.15 m / s. For example, the performance may be at 23° C. + / - 5° C. and a compression angle of 0°. In one example, the compressible elements are SCK Cell Fenders provided by Trelleborg Marine Systems, suitably SCK 500 E1.3 cell fenders.

[0050] Guide projections 255, shown in detail in FIGS. 3A-3C, are attached between adjacent compressible elements 253. The guide projections 255 project radially from the compressible elements 253, for example in the vertical plane above and below the compressible elements 253. The guide projections 255 are configured to interact with the guide channels 214 to control the movement of the bumper 251. For example, the guide projections 255 cooperate with corresponding slots 255a defined in the channels 214. The slots 255a may be sized to prevent the bumper 251 from moving in the vertical direction. Thus, the depth of each slot 255a may be substantially the same as the height of the projection 255. In one example, each projection 255 includes a nylon shoe to reduce friction between the projection 255 and the slot 255a. The guide projections 255 and the corresponding slots 255a may form a first or vertical guide for the bumper 251, preventing vertical movement.

[0051] The second guide for the bumper 251 can limit the range of lateral movement of the bumper 251. For example, the lateral width of the channel 214 can limit the possible lateral movement of the bumper 251. In one example, the bumper 251 and / or the channel 214 comprises a low friction element that facilitates contact between the bumper 251 and the lateral edges of the channel. For example, the channel 214 may comprise a nylon block 257a, which is positioned to be contacted by a stainless steel block 257 formed on the lateral side of the bumper, e.g., mounted between adjacent compressible elements 253. The slot 255a may also have a width greater than the projection 255a to allow lateral movement of the bumper 251. Thus, the second guide limits the lateral movement of the bumper 251 in use to prevent shearing, while still allowing longitudinal movement and sufficient lateral movement to allow horizontal rotation of the cassette part 210.

[0052] The elastic buffer system 250 further comprises a stop element 258 configured to limit the movement of the cassette part 210 in the longitudinal direction A from the forward part 102 towards the opposite end of the vessel. The stop element 258 is arranged in the receiver 120 on the rear bulkhead 123. For example, there may be two stop elements 258 for each buffer 251 arranged respectively above and below the mounting post 252. The stop element 258 is thus configured to contact the cassette part 210 in the areas above and below the channel 215. The stop element 258 is formed of a flexible or elastic material that can be deformed on contact. For example, the stop element 258 may be a rubber fender block.

[0053] The stop element 258 ensures that if the cassette part 210 moves into contact with the aft bulkhead 252, the impact is buffered to prevent damage to the cassette part 210 and / or the vessel 100. In one example, the cassette assembly 200 is configured such that the cassette part 210 contacts the stop element 258 before the buffer 251 reaches its maximum compression limit. Thus, damage to the buffer 251 is prevented and the life of the compressible element 253 can be extended.

[0054] 4, the shape of fender section 230 will now be described in more detail. Fender section 230 includes a central projection 231 that projects longitudinally from substantially the lateral center of fender section 230. The fender section also includes two lateral projections 232a and 232b located respectively on the port and starboard sides of central projection 231. Port and starboard recesses 233a,b are located between central projection 231 and lateral projections 232a,b.

[0055] Each recess 233 has a first inclined portion 234, a second inclined portion 235, and a third inclined portion 236 arranged to extend continuously away from the central projection 231 to its respective lateral projection 232. The first inclined portion 234 inclines longitudinally inward (i.e., away from the front portion 102) as it extends laterally away from the central projection 231, and the second inclined portion 235 also inclines longitudinally inward as it extends away from the central projection 231. The inclination angle of the second inclined portion 235 is shallower than that of the first inclined portion 234. The recess 233 further comprises a third inclined portion 236 that inclines longitudinally outward (i.e., toward the front portion 102) as it extends toward the lateral projection. The angle α between the first and second inclined portions 234, 235 is about 130 degrees. The angle β between the second and third ramps 235, 236 is approximately 130 degrees.

[0056] Use of the vessel 100 and cassette assembly 200 will now be described with reference to Figures 5A-5C, which additionally show a water-accessible structure 300.

[0057] For example, the water-accessible structure may be an offshore wind turbine 300. The offshore wind turbine 300 includes an access structure 310 formed on one side thereof that allows access to the turbine 300. The access structure 310 includes a pair of spaced apart support tubes 311 and a ladder 312 disposed between the support tubes 311.

[0058] In use, the vessel approaches the turbine 300 and is navigated such that the fender portion 230 of the cassette assembly 200 impacts the support tube 311. When the fender portion 230 contacts the support tube 311, a reaction force is applied to the cassette portion 210. The reaction force biases the cassette portion 210 rearward. The resilient shock absorber system 250 absorbs the impact of the collision by compression of the shock absorber 251, thereby preventing damage to the vessel 100 and / or turbine 300.

[0059] When the vessel 100 is in contact with the turbine 300, the vessel 100 can be kept in position by applying forward thrust (e.g., via a propeller or other powered device of the vessel 100). Personnel wishing to access the turbine 300 can then board the gangway 220 and ladder 312. After the maintenance work is completed and the personnel return to the vessel 100, the vessel 100 applies reverse thrust, thereby moving away from the wind turbine 300. In doing so, the forces compressing the bumpers 251 are removed, allowing their elastic forces to re-expand the bumpers to the condition shown in FIG. 2.

[0060] In Fig. 5A, the vessel 100 is shown in collision aligned with the turbine 300 such that the longitudinal axis 101 of the vessel 100 is perpendicular to a notional line extending between the tubes 311. In this condition, the central protrusion 231 is received between the tubes 311, which contact the recesses 233a,b on either side of the central protrusion 231. This is an ideal situation in which the collision force is substantially aligned with the compression direction of the buffer 251. Furthermore, the position of the central protrusion 231 between the tubes 311 may help to hold the vessel 100 in place, for example, when wind or currents act on the vessel 100.

[0061] Figure 5B shows initial contact between the vessel 100 and the turbine 300, with the vessel 100 displaced approximately 10 degrees relative to the position shown in Figure 5A. In this displaced approach, a first one of the support tubes 311 is engaged by the port recess 233a and captured at the junction of the second and third ramps 235a, 236a. The second and third ramps 235, 236 thus act as stop surfaces, preventing further outboard movement of the first tube 311 relative to the fender section 230.

[0062] As can be seen in FIG. 5C, the impact causes the port side of the cassette section 210 to move inward and rotate the cassette section 210 in a horizontal plane. This causes the central projection 231 to contact the second tube of the support tube 311. The shape of the fender section 230 therefore ensures that both tubes are in contact even in the case of an out-of-position impact. This ensures that the impact is shared between both tubes 311, preventing damage to the tubes 311. This also helps ensure that both elastic shock absorbers 251 absorb the impact.

[0063] 6A and 6B show another exemplary cassette assembly 1200. Cassette assembly 1200 is similar to cassette assembly 200, being similar in structure and operation, and corresponding elements have corresponding reference numerals incremented by 1000.

[0064] The cassette assembly 1200 further includes an over-rotation prevention unit 1260. The over-rotation prevention unit 1260 comprises a plurality of captive ties 1261 extending from the stop surface 1213 to the mounting post 1252. For example, there may be at least two captive ties disposed proximate each lateral end of the stop surface 1213. The captive ties 1261 are configured to reach the tension shown in FIG. 6A and prevent the stop surface 1213 from moving farther from the mounting post 1252 than the length of the ties 1261. The length of the ties 1261 is selected such that the stop surface 1213 cannot move to a position where the elastic bumper 1251 is stretched beyond its uncompressed state. However, when the elastic bumper 1251 is compressed, the ties 1261 return to their relaxed state. Thus, the over-rotation prevention unit 1260 can prevent one end of the cassette part 1210 from contacting too hard and causing the cassette part 210 to over-rotate, thereby damaging the bumper 1251 at the other end of the cassette part.

[0065] Although the elastic buffer 1251 of the cassette assembly 1200 has only one elastically compressible element 1253, it will be appreciated that the over-rotation prevention unit 1260 may be incorporated into the cassette assembly 200.

[0066] It will be appreciated that in some instances, the cassette assembly 200 or 1200 may be retrofitted to the vessel 100 having a suitable receptacle. For example, the cassette assembly 200 or 1200 may be bolted or welded to the vessel's foredeck, for example, utilizing an open space typically located on the vessel's forward cargo deck. Similarly, the cassette assembly 200 or 1200 may be removable from the vessel 100, for example, for maintenance, repair, etc.

[0067] In some examples, the cassette assembly may include a buffer comprising multiple compressible elements arranged in series and a buffer comprising a single compressible element, and the present disclosure extends to any combination of any number of buffers comprising single or multiple compressible elements.

[0068] 7 illustrates a method of servicing a water-accessible structure using a surface vessel with a cassette assembly disposed at an end of the surface vessel. In block S701, a cassette portion of the cassette assembly is brought into contact with the water-accessible structure. In block S702, relative movement of the cassette portion toward the opposite end of the vessel is opposed using a resilient damping system.

[0069] Advantageously, the above-described examples provide an improved vessel for accessing underwater structures. The use of a shock absorber comprising multiple resilient elements arranged in series provides a system that can absorb more energy without a significant increase in impact reaction force. Thus, vessels having a larger mass can be used to service water-accessible structures and a larger tolerance in impact velocity can be tolerated. Additionally, the above-described examples provide a vessel that can approach structures from a wider range of angles without damage to either the vessel or the structure, thereby facilitating maneuvering of the vessel.

[0070] Attention is directed to all articles and documents related to this application that are filed contemporaneously or prior to this application and that are open to public inspection herewith, the contents of all such articles and documents being incorporated herein by reference.

[0071] All of the features disclosed in this specification (including the accompanying claims, abstract, and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations in which at least some of such features and / or steps are mutually exclusive.

[0072] Each feature disclosed in this specification (including the accompanying claims, abstract, and drawings), unless expressly stated otherwise, may be replaced by alternative features serving the same, equivalent, or similar purpose. Thus, unless expressly stated otherwise, each feature disclosed is only an example of a generic series of equivalent or similar features.

[0073] The invention is not limited to the details of the embodiment(s) described above.The invention extends to any novel, or any novel combination of features disclosed in this specification (including the accompanying claims, abstract and drawings), or to any novel, or any novel combination of steps of any method or process so disclosed.

Claims

1. 1. A cassette assembly mountable to one end of a surface vessel, comprising: a cassette part which in use abuts the external structure and which is movable relative to the vessel towards an opposite end of the vessel; a resilient shock absorber system for resisting movement of the cassette portion when the vessel is moved towards the external structure; Equipped with The resilient shock absorber system includes a shock absorber having a plurality of resiliently compressible elements arranged in series; the resilient buffer system comprises a vertical guide for preventing vertical movement of the buffer, the vertical guide comprising a radial guide protrusion formed in one of the buffer or the guide channel of the cassette part, the guide protrusion being adapted to cooperate with a slot formed in the other of the buffer or the guide channel; the over-rotation prevention unit comprises a plurality of restraining ties and is configured to prevent over-rotation of the cassette portion; Cassette assembly.

2. The cassette assembly of claim 1 , wherein the cassette section is rotatable in a horizontal plane.

3. 3. A cassette assembly as claimed in claim 1 or 2, wherein the cassette portion includes a passageway formed in an upper surface thereof.

4. A cassette assembly according to any preceding claim, comprising at least two buffers spaced across the width of the cassette part.

5. The cassette portion includes a fender portion configured to contact an external structure, A central protrusion; a pair of recesses located on each lateral side of the central projection; Equipped with the recess includes a stop surface to prevent overboard movement of the first support tube of the outer structure beyond the stop surface; 5. A cassette assembly according to claim 1, wherein the recess and the central protrusion are configured such that contact between the first support tube and the stop surface causes rotation of the cassette part such that the central protrusion contacts a second support tube of the external structure.

6. A cassette assembly according to any preceding claim, wherein the resilient dampening system comprises lateral guides for limiting the extent of lateral movement of the damper.

7. 7. The cassette assembly of claim 6, wherein the lateral guide comprises a first contact element formed on a lateral edge of the bumper, the first contact element being configured to contact a second contact element formed on a lateral edge of the guide channel of the cassette part.

8. A cassette assembly according to any preceding claim, wherein each buffer comprises three compressible elements arranged in series.

9. A cassette assembly according to any one of claims 1 to 8, wherein the resilient buffer system comprises stop elements arranged to limit movement of the cassette parts towards the opposite end of the vessel.

10. 10. The cassette assembly of claim 9, wherein the cassette parts are configured to contact the stop element before the buffer reaches a maximum compression limit.

11. A surface vessel comprising a cassette assembly as defined in any one of claims 1 to 10 and a receiver configured to receive said cassette assembly.

12. The surface vessel of claim 11 , wherein the receiver comprises a recess within the vessel.

13. A method of servicing a water-accessible structure using a surface vessel, the surface vessel comprising a cassette assembly according to any one of claims 1 to 10 disposed at one end of the surface vessel, the method comprising: contacting a cassette portion of the cassette assembly with a water-accessible structure; using an elastic buffer system to counteract relative movement of the cassette part towards the opposite end of the vessel; Equipped with The method, wherein the resilient shock absorber system comprises a shock absorber having a plurality of resilient compressible elements arranged in series.

14. The method of claim 13 , wherein the water-accessible structure is a wind turbine.

15. Use of a cassette assembly according to any one of claims 1 to 10 and / or a surface vessel according to any one of claims 11 to 12.

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