Patent Description:
Various challenges arise in servicing water-accessible structures such as offshore wind turbines with waterborne vessels. One difficulty is that of allowing personnel access to the structure. In one example, the vessel may be deliberately navigated into the water-accessible structure, bringing the vessel into contact with the structure and allowing access thereto. However, a significant impact force can be imparted to the structure and/or the vessel, potentially damaging the structure and/or vessel.

UK Patent Publication No. <CIT> discloses a waterborne vessel with a carriage assembly at one end of the vessel. The carriage assembly is movable relative to the vessel and buffered such that, when the carriage assembly impacts the water-accessible structure, the impact force is absorbed. In order to safely use such a system without damaging either the vessel or the structure, constraints are placed on the operation thereof. This may include limiting the mass of the vessel incorporating the carriage assembly, the impact velocity and the angle of impact of the vessel to the structure. <CIT> relates to a maritime hydraulic impact-absorbing device. <CIT> relates to an apparatus for stabilising a floating craft. <CIT> relates to a bow fender on a crew transfer vessel.

It is an aim of the invention to address these difficulties, and any other difficulties that would be apparent to the skilled reader from the disclosure herein.

According to a first aspect of the disclosure there is provided a cassette assembly attachable to an end portion of a waterborne vessel, the cassette assembly comprising:.

The cassette section is rotatable in a horizontal plane relative to the vessel.

The cassette section may comprise a walkway formed on an upper surface thereof.

The resilient buffer system may comprise at least two buffers spaced apart across a width of the cassette section.

The cassette section may comprise a fender section configured to contact the external structure. The fender section may be formed of a resilient material. The fender section may comprise a central protrusion, and a pair of recesses positioned at respective transverse sides of the central protrusion. The recesses may comprise a stop surface, to prevent outboard motion of a first support tube of the external structure beyond the stop surface. The recesses and central protrusion may be configured so that contact between the first support tube and the stop surface causes rotation of the cassette section such that the fender section, suitably the central protrusion, contacts a second support tube of the external structure.

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

The buffer may be rotatably attached to the cassette section, suitably to permit rotation in a horizontal plane. The buffer may be rotatably attachable to the vessel, suitably to permit rotation in a horizontal plane.

The fluid-operated buffer may be a hydraulic buffer. The fluid-operated buffer may be a pneumatic buffer.

The cassette assembly may comprise a fluid-operated system configured to operate the fluid-operated buffer. The fluid operated system may comprise an accumulator configured to supply fluid to the buffer, suitably to counter compression of the buffer. The accumulator may be a pneumatically-charged accumulator. The fluid-operated system may comprise a flow control unit disposed on a fluid flow path between the buffer and the accumulator. The flow control unit may be configured to provide fluid to the buffer from the accumulator at a predetermined pressure. The flow control unit may comprise a flow restrictor. The flow control unit may comprise a check valve, arranged in parallel with the flow restrictor. The fluid-operated system may comprise a pressure bypass valve disposed on the fluid flow path between the buffer and the accumulator. The pressure bypass valve may be configured to bypass the flow control unit in response to the pressure exceeding a predetermined bypass pressure.

The cassette assembly may comprise a controller configured to adjust an energy absorption and reaction force provided by the buffer. The controller may be configured to adjust a flow rate of the flow control unit and/or a flow rate of the accumulator.

The resilient buffer system may comprise stop elements configured to limit the motion of the cassette section towards the opposite end of the vessel. The stop elements may be formed of a resiliently deformable material. The cassette section may be configured to contact the stop elements before the buffers reach a maximum compression limit.

According to a second aspect of the disclosure there is provided a waterborne vessel according to claim <NUM>.

The receiving portion may be configured to slidably support the cassette assembly. The receiving portion may rotatably support the cassette assembly.

The receiving portion may comprise a recess in the vessel, suitably in a front portion of the vessel. The receiving portion may comprise a rear wall. The rear wall may comprise at least two mounting posts to support the at least two buffers. The receiving portion may comprise substantially vertical side walls.

The receiving portion may extend across at least <NUM>% of the width of a forward portion of the vessel. Suitably, the receiving portion may extend across at least <NUM>% of the width of a forward portion of the vessel. The receiving portion may extend across at least <NUM>% of the width of a forward portion of the vessel.

Further suitable features of the vessel of the second aspect are defined hereinabove in relation to the cassette assembly of the first aspect, and may be combined in any combination.

According to a third aspect of the disclosure there is provided a method of servicing a water-accessible structure using a waterborne vessel, the waterborne vessel comprising a cassette assembly arranged at an end portion of the waterborne vessel, the method comprising:.

The water-accessible structure may be a wind turbine.

Further suitable features of the method of the second aspect are defined hereinabove in relation to the cassette assembly of the first aspect and vessel of the second aspect, and may be combined in any combination.

According to a fourth aspect of the disclosure there is provided use of a cassette assembly and/or waterborne vessel as defined herein.

According to a non-claimed fifth aspect of the disclosure there is provided a cassette assembly attachable to an end portion of a waterborne vessel, the cassette assembly comprising:.

The recesses may comprise a stop surface, to prevent outboard motion of a first support tube of the external structure beyond the stop surface. The recesses and central protrusion may be configured so that contact between the first support tube and the stop surface causes rotation of the cassette section such that the fender section, suitably the central protrusion, contacts a second support tube of the external structure.

Further suitable features of the assembly of the fifth aspect are defined hereinabove in relation to the cassette assembly of the first aspect and vessel of the second aspect and may be combined in any combination.

For a better understanding of the disclosure, and to show how examples of the same may be carried into effect, reference will now be made, by way of example only, to the accompanying diagrammatic drawings in which:.

In the drawings, corresponding reference characters indicate corresponding components. The skilled person 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 to improve understanding of various example embodiments. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various example embodiments.

In overview, examples of the disclosure provide a cassette assembly attachable to an end portion of a waterborne vessel, comprising a movable cassette section to bear against an external structure and a resilient buffer system to counter movement of the cassette section, wherein the resilient buffer system comprises a fluid-operated buffer, such as a hydraulic or pneumatic buffer. In some examples, the resilient buffer system comprises two buffers spaced apart across a width of the cassette section. The use of a fluid-operated buffer allows the energy absorbed and reaction force exerted by the buffer system to be tuned, for example to suit the vessel or the intended use thereof.

<FIG> and <FIG> show the forward portion <NUM> of an example waterborne vessel <NUM>. The longitudinal centreline of the vessel <NUM> is indicated by reference numeral <NUM>. The forward portion <NUM> extends in a horizontal or transverse direction, such that it is generally perpendicular to the centreline <NUM> when viewed in plan.

The vessel <NUM>, particularly the forward portion <NUM>, comprises a cassette assembly, generally indicated by reference number <NUM>. As can be best seen in <FIG>, the cassette assembly <NUM> is disposed in a receiving portion <NUM> formed in the structure of the vessel <NUM>. For example, the receiving portion <NUM> takes the form of a recess extending in the transverse direction across the front portion <NUM>, configured to receive the cassette assembly <NUM>.

The receiving portion <NUM> is bound vertically by substantially horizontal deck plate of the vessel <NUM>. For example, the receiving portion <NUM> is bound by overhanging bulwark structure <NUM> above the receiving portion <NUM> and the hull <NUM> of the vessel <NUM> below.

Similarly, the receiving portion <NUM> is bound horizontally by at its transverse ends by substantially vertical bulkheads. In one example, the vessel <NUM> is a twin-hull vessel. In such an example, the substantially vertical bulkheads may be arranged on the centreline of each demi-hull of the vessel <NUM>. The rear of the recess <NUM> may be formed by a substantially vertical transverse bulkhead <NUM>.

The cassette assembly <NUM> comprises a cassette section <NUM> or carriage. The cassette section <NUM> takes the form of a platform, slidably mounted in the receiving portion <NUM>, so that it may move in the longitudinal direction indicated by arrow A. The cassette section <NUM> also rotates in a horizontal plane, as indicated by arrow B. For example, the cassette section <NUM> may comprise arcuate sections at its transverse edges, supported by corresponding arcuate channels.

The upper surface <NUM> of the cassette section <NUM> allows users to access the water-accessible structure. For example, a walkway <NUM> may be formed on the upper surface <NUM>, though it will be understood that in some examples the whole of the upper surface <NUM> may be walked upon.

A front portion <NUM> of the cassette section <NUM> is configured to contact the water-accessible structure. The front portion <NUM> (and therefore the receiving portion <NUM>) may extend approximately <NUM>-<NUM>% of the width of the forward portion <NUM>. As shown in <FIG>, the front portion <NUM> may comprise a fender section <NUM>. The fender section <NUM> is formed of a flexible or resilient material which may compress on contact with the water-accessible structure, such as rubber. The shape of the fender section <NUM> will be discussed in more detail with reference to <FIG> and <FIG> hereinbelow. In some examples, the vessel <NUM> may also comprise fender sections <NUM> disposed at either side of the cassette assembly.

The cassette assembly <NUM> also comprises a resilient buffer system <NUM>. The resilient buffer system <NUM> is configured to counter movement of the cassette section <NUM> caused by contact between the cassette section <NUM> and the water-accessible structure. The resilient buffer system <NUM> comprises a pair of buffers <NUM>. The buffers <NUM> are spaced apart across the width of the cassette section <NUM>.

The buffers <NUM> extend from the rear bulkhead <NUM> of the receiving portion <NUM> to a stop surface <NUM> of the cassette section <NUM>. The stop surface <NUM> may be a substantially vertical surface, forming the end of a guide channel <NUM> extending horizontally into the cassette section <NUM>. The buffers <NUM> may be mounted to the rear bulkhead <NUM> by virtue of a mounting post <NUM> extending horizontally from the rear bulkhead, to which the buffers <NUM> may be secured.

Each buffer <NUM> comprises a fluid-operated ram. For example, the ram <NUM> may be a hydraulic ram. The ram <NUM> is rotatably attached to the stop surface <NUM>, so that the ram <NUM> may rotate in a horizontal plane with respect to the stop surface <NUM>. Similarly, the ram <NUM> is rotatably attached to the mounting post <NUM>, so that the ram <NUM> may rotate in a horizontal plane with respect to the mounting post <NUM>. For example, the ram <NUM> may be coupled to the mounting post <NUM> and/or stop surface <NUM> using vertical pins, a ball and socket joint or any other suitable means of providing the desired rotation.

The resilient buffer system <NUM> furthermore comprises stop elements <NUM>, configured to limit the motion of the cassette section <NUM> in the longitudinal direction A, towards the opposite end of the vessel from the forward portion <NUM>. The stop elements <NUM> are disposed in the receiving portion <NUM>, on rear bulkhead <NUM>. For example, two stop elements <NUM> may be present for each buffer <NUM>, respectively disposed above and below the mounting post <NUM>. Accordingly, the stop elements <NUM> are configured to contact the cassette section <NUM> at regions above and below the channel <NUM>. The stop elements <NUM> are formed of a flexible or resilient material, which may deform upon contact. For example, the stop elements <NUM> may be rubber fender blocks.

The stop elements <NUM> ensure that, if the cassette section <NUM> is moved such that it would contact the rear bulkhead <NUM>, the impact is cushioned so as to prevent damage to the cassette section <NUM> and/or vessel <NUM>. In one example, the cassette assembly <NUM> is configured so that the cassette section <NUM> contacts the stop elements <NUM> before the buffer <NUM> reaches its maximum compression limit. Accordingly, damage to the buffer <NUM> is prevented.

An example fluid-operated system <NUM> for operating the ram <NUM> is illustrated in <FIG>. In the example of <FIG>, the fluid-operated system <NUM> is a hydraulic system. The system <NUM> includes the ram <NUM>, and a hydraulic accumulator <NUM> configured to supply fluid to the ram <NUM> so as to counter the compression of the ram <NUM>. The accumulator <NUM> may be pneumatically charged, for example with a multi-stage pump. In other examples, the accumulator <NUM> may be a spring accumulator.

The ram <NUM> may be a double-acting ram, wherein the rod port of the ram <NUM> is connected to a fluid reservoir <NUM> at very low pressure, so as to prevent rusting in use.

In one example, the system <NUM> also comprises a flow control unit <NUM>. The flow control unit <NUM> may comprise a flow restrictor <NUM>, such as an orifice plate, and a check valve <NUM>. In one example, the check valve <NUM> and flow restrictor <NUM> are arranged in parallel. The flow control unit <NUM> ensures a predetermined pressure is supplied to the ram <NUM> and may assist in dissipating heat generated by the system <NUM>.

The system <NUM> may also comprise a pressure bypass valve <NUM>, fluidly connected between the ram <NUM> and the accumulator <NUM>. The pressure bypass valve <NUM> may bypass the flow control unit <NUM> in the event of excess pressure, for example caused by a strong impact to the ram <NUM>, thereby avoiding overload of the system <NUM>.

The system <NUM> is configured to provide a resilient bias to the ram <NUM>. Particularly, compression of the ram <NUM> causes hydraulic fluid in the system <NUM> to flow to the accumulator <NUM>, where it is stored under pressure. The accumulator <NUM> will then discharge the pressured fluid via the flow control unit <NUM> to counter the compression of the ram <NUM>.

In addition, by adjusting the parameters of the accumulator <NUM> and/or flow control unit <NUM>, the system <NUM> can be tuned to absorb a desired amount of energy, and to exert a desired reaction force. For example, the flow rate or pressure provided by the accumulator <NUM> and/or the flow control unit <NUM> may be adjusted.

In one example, the parameters may be adjusted passively. In other words, the parameters may be tuned upon installation of the system <NUM> to the vessel <NUM>. This may allow the system <NUM> to be adjusted according to the characteristics of the vessel <NUM> (e.g. the mass), as well as the intended usage, without substantial re-engineering of the system <NUM>.

In another example, the parameters may be adjusted actively. For example, the system <NUM> may comprise a controller (not shown), which may comprise a processor and a memory, configured to adjust the parameters in response to user input. Accordingly, a user may vary the operational characteristics of the fluid-operated system <NUM> after installation, for example in accordance with the usage or load of the vessel.

In one example, a fluid-operated system <NUM> is provided for each buffer <NUM>. Accordingly, the example shown in <FIG> may comprise two fluid-operated systems <NUM>. In another example, one fluid-operated system <NUM> may be associated with a plurality of buffers <NUM>.

Whilst the example of <FIG> is a hydraulic system in which the fluid is a liquid, such as an oil, in other examples the system may be a pneumatic system in which the fluid may be a gas, such as air.

Turning now to <FIG>, the shape of the fender section <NUM> will be discussed in more detail. The fender section <NUM> comprises a central protrusion <NUM>, protruding longitudinally from substantially the transverse centre of the fender section <NUM>. The fender section also comprises two transverse protrusions 232a and 232b, respectively arranged port and starboard of the central protrusion <NUM>. Disposed between the central protrusion <NUM> and the transverse protrusions 232a,b are port and starboard recesses 233a,b.

Each recess <NUM> has a first sloping portion <NUM>, second sloping portion <NUM> and third sloping portion <NUM>, arranged consecutively extending away from the central protrusion <NUM> to its respective transverse protrusion <NUM>. The first sloping portion <NUM> slopes longitudinally inward (i.e. away from the front portion <NUM>) as it extends transversely away from the central protrusion <NUM>, and the second sloping portion <NUM> also slopes longitudinally inward as it extends away from the central protrusion <NUM>. The angle of slope of the second sloping portion <NUM> is shallower than the first sloping portion <NUM>. The recess <NUM> further comprises a third sloping portion <NUM>, which slopes longitudinally outward (i.e. towards the front portion <NUM>) as it extends towards the transverse protrusion. The angle α between the first and second sloping portions <NUM>, <NUM> is approximately <NUM> degrees. The angle β between the second and third sloping portions <NUM>,<NUM> is approximately <NUM> degrees.

Use of the vessel <NUM> and cassette assembly <NUM> will now be described with reference to <FIG>, which additionally show a water-accessible structure <NUM>.

For example, the water-accessible structure may be an offshore wind turbine <NUM>. The offshore wind turbine <NUM> comprises an access structure <NUM> formed on one side thereof, which allows access to the turbine <NUM>. The access structure <NUM> comprises a pair of spaced apart support tubes <NUM>, and a ladder <NUM> disposed between the support tubes <NUM>.

In use, the vessel approaches the turbine <NUM>, and is navigated so that the fender section <NUM> of the cassette assembly <NUM> impacts the support tubes <NUM>. Upon the fender section <NUM> contacting the support tubes <NUM>, a reaction force is imparted to the cassette section <NUM>. The reaction force causes the cassette section <NUM> to be urged in a rearward direction. The resilient buffer system <NUM> absorbs the shock of the impact by virtue of the compression of the buffers <NUM>, thereby preventing damage to the vessel <NUM> and/or the turbine <NUM>.

When the vessel <NUM> is in contact with the turbine <NUM>, the vessel <NUM> may be maintained in position by applying a forward thrust (e.g. via a propeller or other motive arrangement of the vessel <NUM>). Personnel wishing to access the turbine <NUM> may then step onto the walkway <NUM>, and onto the ladder <NUM>. Once any maintenance work has been completed and the personnel have returned to the vessel <NUM>, the vessel <NUM> applies a reverse thrust, thereby moving away from the wind turbine <NUM>. In doing so, the force which had compressed the buffers <NUM> is removed, and their resilient nature allows them to re-expand to the condition shown in <FIG>.

In <FIG>, the vessel <NUM> is shown in aligned impact with the turbine <NUM>, such that the longitudinal axis <NUM> of the vessel <NUM> is perpendicular to a notional line extending between the tubes <NUM>. In this state, the central protrusion <NUM> is received in between the tubes <NUM>, with the tubes <NUM> contacting the recesses 233a,b at either side of the central protrusion <NUM>. This is the ideal situation, with the impact force substantially aligned to the direction of compression of the buffers <NUM>. Furthermore, the location of the central protrusion <NUM> between the tubes <NUM> may assist in retaining the vessel <NUM> in location, for example in the event of wind or current acting on the vessel <NUM>.

<FIG> shows initial contact between the vessel <NUM> and the turbine <NUM>, with the vessel <NUM> approximately <NUM> degrees out of alignment with respect to the position shown in <FIG>. In this misaligned approach, a first tube of the support tubes <NUM> is engaged by the port recess 233a, and captured at the junction of the second sloping portion 235a and third sloping portion 236a. Accordingly, the second and third sloping portion <NUM>,<NUM> act as a stop surface, preventing further outboard motion of the first tube <NUM> with respect to the fender section <NUM>.

As can be seen in <FIG>, the impact causes the port side of the cassette section <NUM> to move inwardly, causing rotation of the cassette section <NUM> in the horizontal plane. This brings the central protrusion <NUM> into contact with the second tube of the support tubes <NUM>. Accordingly, the shape of the fender section <NUM> ensures that both tubes are contacted, even in the event of a misaligned impact. This ensures the impact is shared between both tubes <NUM>, to prevent damage thereto. It also assists in ensuring that both resilient buffers <NUM> absorb the impact.

It will be appreciated that, in some examples, the cassette assembly <NUM> may be retrofitted to a vessel <NUM> having a suitable receiving portion. For example, the cassette assembly <NUM> could be bolted or welded to the foredeck of the vessel, for example utilising the open space typically situated on the forward cargo deck of a vessel. Equally, the cassette assembly <NUM> may be attachable to and detachable from the vessel <NUM>, for example for servicing, repair and the like.

In one example, the cassette assembly may include a fluid-operated buffer <NUM> and a buffer comprising a compressible element. The compressible element may comprise a fender cell or cone, for example formed from a resiliently compressible material such as rubber. The compressible elements may be capable of being compressed to absorb the energy of the contact between the cassette section <NUM> and the water-accessible structure. Once the compression force is removed, the compressible elements are configured to experience a restoring force, thereby returning to their initial, substantially uncompressed state. The buffer comprising a compressible element may be a buffer comprising a plurality of compressible elements, which may be arranged in series to form the buffer. The disclosure extends to any combination of any number of fluid-operated buffers and buffers formed from compressible elements, including buffers comprising single or multiple compressible elements.

<FIG> illustrates a method of servicing a water-accessible structure using a waterborne vessel comprising a cassette assembly arranged at an end portion of the waterborne vessel. In block S601, a cassette section of the cassette assembly is brought into contact with the water accessible structure. In block S602, relative movement of the cassette section in a direction towards an opposite end of the vessel is countered using a resilient buffer system.

Advantageously, the above-described examples provide an improved vessel for accessing structures in water. The use of fluid-operated buffers results in a system that can be readily tuned to provide a desired energy absorbance and reaction force. Accordingly, substantially the same hardware may be fitted to a wide range of vessels with different masses and different operating restrictions. This may avoid the necessity of procuring different resiliently compressible elements comprised in the buffers for different vessels. In addition, in some examples, the system may be actively tuned, allowing the provision of a desired energy absorbance and reaction force to account for the characteristics of the vessel and/or the external structure being accessed. Furthermore, the use of fluid-operated buffers provides a system able to absorb more energy whilst not exerting a significant increase in impact reaction force. Accordingly, vessels having a greater mass may be used to service water-accessible structures, and a larger tolerance of impact velocities may be permitted. Furthermore, the above-described examples provide a vessel which is able to approach the structure from a wider range of angles without causing damage to either the vessel or the structure, thereby easing operation of the vessel.

Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification.

Claim 1:
A cassette assembly (<NUM>) attachable to an end portion of a waterborne vessel (<NUM>), the cassette assembly (<NUM>) comprising:
a cassette section (<NUM>) to bear against an external structure in use, the cassette section (<NUM>) movable relative to the vessel in a direction towards an opposite end of the vessel; and
a resilient buffer system (<NUM>) to counter movement of the cassette section (<NUM>) when the vessel is moved towards the external structure,
wherein the resilient buffer system (<NUM>) comprises a fluid-operated buffer,
characterised in that the cassette section (<NUM>) is rotatable in a horizontal plane relative to the vessel (<NUM>).