WO2013190316A1

WO2013190316A1 - A mounting system and method

Info

Publication number: WO2013190316A1
Application number: PCT/GB2013/051629
Authority: WO
Inventors: Richard Montague
Original assignee: Aquamarine Power Limited
Priority date: 2012-06-20
Filing date: 2013-06-20
Publication date: 2013-12-27
Also published as: US20150152621A1; GB201214962D0; EP2864551A1; GB201210882D0

Abstract

A mounting system comprises a base and a mounting structure for mounting to the base, wherein one of the base and the mounting structure comprises a bearing comprising a resiliently deformable member and having a bearing surface, the other of the base and the mounting structure comprises a further bearing surface for engagement with the bearing surface of the bearing, and the bearing is configured so that shear stress of the deformable member when the mounting structure is mounted to the base biases the bearing surface towards the further bearing surface.

Description

A Mounting System and Method

Field of the invention The present invention relates to a mounting system and method that can be used, for example in the installation of devices on the bed of a body of water such as the sea bed. The devices to be installed may, for example, be renewable energy devices that can be used to capture wave, tidal, current, wind or solar energy in offshore environments or may, for example, be devices used in oil or gas exploration or production, or in telecommunication systems.

Background to the invention

There has been vast activity in recent years in the development of renewable energy technology. Many renewable energy devices systems are intended for installation offshore, for example wave power devices, wind turbines, water current devices and tidal devices. Many other devices also need to be installed on the sea bed, for example oil or gas installations or communication devices.

There can be significant technical difficulties in installing devices offshore, for example mounting devices on the seabed, as such devices are subject to significant wave, tidal and other forces both during installation and after use. The devices must be able to cope with the extreme conditions that they may encounter during their lifetime. Many devices will be subject to significant lateral or heave forces.

It is known to drive piles into the bed of a body of water and then mount devices to the piles. The usual way of mounting the devices is to grout them into place using concrete or similar material. Such grouting procedures can be difficult and messy, require calm sea conditions and require divers to perform many of the grouting operations. It is critical that the devices are aligned correctly while the concrete or other grouting material sets. If a device is subsequently to be removed it may be necessary to destroy the grouting material in order to remove the device.

Summary of the invention

In a first, independent aspect of the invention there is provided a mounting system comprising a base and a mounting structure for mounting to the base, wherein one of the base and the mounting structure comprises a bearing comprising a resiliency deformable member and having a bearing surface, the other of the base and the mounting structure comprises a further bearing surface for engagement with the bearing surface of the bearing, and the bearing is configured so that shear stress of the deformable member when the mounting siructure is mounted to the base biases the bearing surface towards the further bearing surface. The shear stress may be in an engagement direction.

The mounting structure may be for attachment to, or may comprise, a further structure, for example a wave power device. The mounting structure may be for attachment to, or may comprise, a tidal energy device, a water current device, a wind turbine mast or other mast, an oil or gas production or exploration-related structure, or a structure relating to telecommunication installations. The mounting structure may be for installation on the bed of a body of water.

One of the base and the mounting structure may comprise a plurality of the bearings each comprising a resiliently deformable member and having a bearing surface, and the other of the base and the mounting structure comprises a plurality of the further bearing surfaces, each further bearing surface being arranged for engagement with the bearing surface of a respective one of the bearings.

Each of the plurality of bearings may comprise a discrete bearing and/or may be not in contact with each other bearing.

A first one of the bearings may be substantially opposed to a second one of the bearings, such that a reduction in compression of the first bearing causes an increase in compression of the second bearing.

The system may be configured so that reduction in compression of at least one of the bearings causes a release in shear stress, thereby to move the mounting structure and/or at least one of the bearings towards the base.

Lateral movement of the mounting structure in alternating directions may cause alternating bearing surfaces to move relative to corresponding further bearing surfaces thereby to move the mounting structure and/or the bearings towards the base.

in operation the lateral movement may be caused by action of waves, tides, currents or wind on the mounting structure or on a further structure attached to the mounting structure.

The mounting structure may have an engagement axis, the base may have an engagement axis and the mounting structure may be mounted to the base by moving the base and the mounting structure into contact with the engagement axis of the base and the engagement axis of the mounting structure substantially aligned.

The base and the mounting structure may be configured such that when the bearing surfaces and the further bearing surfaces are brought into contact without the at least one resiliently deformable member being under compressive and/or shear stress, there is a gap between an engagement surface of the mounting structure (for example a bottom surface of the mounting structure) and a corresponding surface of the base. The base and the mounting structure may be configured such that movement of the engagement surface into contact with the corresponding surface of the base (for example under the action of gravity on the mass of the mounting structure) causes compressive and/or shear stress in the at least one resiliently deformable member.

The shear stress of the deformable member that biases the bearing surface towards engagement with the further bearing surface may be shear stress in a direction substantially along the engagement axis, for example in a substantially downward direction along the engagement axis.

For the or each bearing, the bearing surface may be inclined with respect to the engagement axis of one of the base or mounting structure, and the further bearing surface may be inclined with respect to the engagement axis of the other of the base or mounting structure.

For the or each bearing and further bearing surface, the bearing surface may be inclined with respect to the engagement axis of one of the base or mounting structure by a bearing angle, and the further bearing surface may be inclined with respect to the engagement axis of the other of the base or mounting structure by a further bearing angle, and the bearing angle and the further bearing angle may be substantially identical.

For the or each bearing and further bearing surface, the angle between the bearing surface and the engagement axis of one of the mounting structure and the base may be less than the inverse tangent of the coefficient of friction between the bearing surface and the further bearing surface.

The base may be arranged so that when the mounting structure is mounted to the base the engagement axis of the mounting structure and the engagement axis of the base are aligned with the vertical.

The base and the mounting structure may be configured so that the bearing surface and the further bearing surface are arranged to be in sliding engagement with one another when the mounting structure is mounted to the base.

The at least one resiliently deformable member may have substantially different elasticity in different directions, optionally the different directions are a radial direction and an axial direction.

For the or each bearing, the ratio of the stiffness of the deformable member under compressive load to the stiffness of the deformable member under shearing load may be between 100:1 and 10,000:1 , optionally between 1 ,000: 1 and 10,000:1 , optionally between 500:1 and 2,000:1 , optionally greater than 1 ,000:1.

For the or each bearing, one side of the resiliently deformab!e member of the bearing may be attached to a body of one of the base and the mounting structure, and the bearing surface may comprise a substantially non-deformable material attached to the other side of the resiliently deformable material.

The substantially non-deformable material of the bearing surface may comprise a substantially rigid layer.

For the or each bearing and bearing surface, the bearing surface and/or the further bearing surface may comprise non-elastomer material, optionally at least one of steel, tungsten carbide, cobalt and/or chromium, further optionally tungsten carbide in a cobalt and chromium matrix.

The resiliently deformable member may comprise an elastomer. The resiliently deformable member may also comprise at least one non-elastomer.

The elastomer may comprise at least one of rubber, for example natural rubber, neoprene or polypropelene.

The resiliently deformable member may comprise a laminated structure, optionally comprising a plurality of elastomer layers interspersed with at least one non-elastomer layer.

The at least one non-elastomer layer may comprise a substantially rigid layer, optionally at least one plate.

The non-elastomer may comprise substantially rigid material, for example metal. The non-elastomer may comprise steel.

The non-elastomer may comprise substantially non-deformable material. The substantially non-deformable material may be bonded to the resiliently deformable member or members.

The resiliently deformable member may comprise a body of at least one first material and a surface layer of a second, different material on the body and comprising the bearing surface.

For the or each bearing and further bearing surface, the bearing surface and/or the further bearing surface may comprise non-elastomer material, optionally at least one of steel, tungsten carbide, cobalt and/or chromium, further optionally tungsten carbide in a cobalt and chromium matrix.

At least one of the bearing surface and the further bearing surface may be textured, for example at least one of grooved, ridged or roughened, thereby to provide a desired fiction coefficient. One of the base and the mounting structure may comprise a male portion and the other of the base and the mounting structure may comprise a female portion, and the base and the mounting structure may be configured so that the male portion mates with the female portion when the mounting structure is mounted to the base.

The male portion may comprise a spigot and/or the female portion may comprise a socket.

One of the male portion and the female portion may comprise the bearing or each of the bearings and the other of the male portion and the female portion may comprise the further bearing surface or at least one of the further bearing surfaces.

The bearing or bearings may be formed and arranged so that when the male portion is inserted into the female portion, the resiliency deformable member is, or resiliently deformable members are, deformed and held in shearing tension in an axial direction of the mounting structure.

The bearing surfaces, or the further bearing surfaces, may be disposed circumferentiaily around the male portion and may slope radially inwards in the direction of insertion of the male portion.

The bearing surfaces and the further bearing surfaces may be formed for gripping contact when the male portion is inserted into the female portion.

The bearings may be disposed circumferentiaily around the female portion and project radially inwards therefrom; or the bearings may be disposed circumferentiaily around the male portion and project radially outwards therefrom.

The system may further comprise means for applying shear force to the or each deformable member. The means for applying shear force may be operable to apply shear force when the base and the mounting structure are not engaged together. The means for applying shear force may comprise at least one of a ring beam and a tension member.

The system may further comprise means for releasing the mounting structure from the base.

The releasing means may comprise at least one of:- means for applying force to one of the base and the mounting structure; means for changing the friction between the at least one bearing surfaces and the at least one further bearing surface, for example by lubricating the at least one bearing surface and/or the at least one further bearing surface; means for altering the compressive load between the at least one bearing surface and the at least one further bearing surfaces; or means for altering the angle of inclination of at the at least one bearing surface and/or the at least one further bearing surfaces. The releasing means may comprise at least one of a plurality of jacks or a fluid supply means for providing fluid to the interface between the at least one bearing surface and the at least one further bearing surface.

In a further, independent aspect of the invention there is provided a bearing for attachment to a base or a mounting structure, the bearing comprising a resiliently deformable member and a bearing surface for engagement with a further bearing surface, wherein the bearing is configured so that shear stress of the resiliently deformable member biases the bearing surface in an engagement direction.

One side of the resiliently deformable member of the bearing may be for attachment to a body of one of the base and the mounting structure, and the bearing surface may comprise a substantially non-deformable material attached to the other side of the resiliently deformable material.

The bearing surface may comprise non-elastomer material, optionally at least one of steel, tungsten carbide, cobalt and/or chromium, further optionally tungsten carbide in a cobalt and chromium matrix.

The resiliently deformable member may comprise an elastomer. The elastomer may comprise at least one of rubber, for example natural rubber, neoprene or polypropeiene.

The resiliently deformable member may comprise a laminated structure, optionally comprising a plurality of elastomer layers interspersed with at least one non-elastomer layer. The at least one non-elastomer layer may comprise a substantially rigid layer, optionally at least one plate.

In a further independent aspects of the invention there is provided a base or mounting structure comprising at least one bearing as claimed or described herein.

The base or mounting structure may have an engagement axis that is substantially aligned with an engagement axis of a further mounting structure or base when the base or mounting structure is mounted to the further mounting structure or base.

For the or each bearing, the bearing surface may be inclined with respect to the engagement axis. For the or each bearing, the angle between the bearing surface and the engagement axis of one of the mounting structure and the base may be less than the inverse tangent of a coefficient of friction between the bearing surface and a further bearing surface with which the bearing surface engages in operation.

The base or mounting structure may comprise a male portion or a female portion that comprises the bearing or each of the bearings. In the case where the male portion or female portion is a male portion, the bearing surfaces may be disposed circumferentially around the male portion and slope radially inwards.

The bearings may be disposed circumferentially around the female portion and project radially inwards therefrom; or the bearings may be disposed circumferentially around the male portion and project radially outwards therefrom.

The base or mounting structure may further comprise means for applying shear force to the or each deformable member, wherein the means for applying shear force may be operable to apply shear force when the base and the mounting structure are not engaged together.

In a further, independent aspect of the invention there is provided a method of mounting a mounting structure to a base, wherein one of the base and the mounting structure comprises a bearing comprising a resiliently deformable member and having a bearing surface, the other of the base and the mounting structure comprises a further bearing surface for engagement with the bearing surface of the bearing, and the method comprises bringing the base into contact with the mounting structure such that shear stress of the deformable member biases the bearing surface towards the further bearing surface. The shear stress may be in an engagement direction.

The base may be installed on the bed of a body of water.

The method may comprise mounting an energy conversion device, for example a wave energy conversion device, to the mounting structure. The method may comprise allowing a reduction in compression of at least one of the bearings causing a release in shear stress, thereby to move the mounting structure and/or at least one of the bearings towards the base

The method may comprise providing for lateral movement of the mounting structure in alternating directions causes alternating bearing surfaces to move relative to corresponding further bearing surfaces thereby to move the mounting structure and/or the bearings towards the base.

The lateral movement may be caused by action of waves, tides, currents or wind on the mounting structure or on a further structure attached to the mounting structure.

The mounting structure may have an engagement axis, the base may have an engagement axis and the method may comprise moving the base and the mounting structure into contact with the engagement axis of the base and the engagement axis of the mounting structure substantially aligned.

The method may further comprise applying shear force to the or each deformable member prior to bringing the base into contact with the mounting structure.

The method may further comprise releasing the mounting structure from the base by at least one of:- applying force to one of the base and the mounting structure; changing the friction between the at least one bearing surfaces and the at least one further bearing surface, for example by lubricating the at least one bearing surface and/or the at least one further bearing surface; altering the compressive load between the bearing surfaces and the further bearing surfaces; or altering the angle of inclination of at the at least one bearing surface and/or the at least one further bearing surface(s).

The releasing may comprise operating a plurality of jacks to apply force to the base or mounting structure, or providing fluid to the interface between the at least one bearing surface and the at least one further bearing surface.

In further independent aspects of the invention there is provided one or more of a system, a bearing, a base or a mounting structure substantially as herein described with reference to the accompanying drawings.

In another independent aspect of the invention there is provided a method substantially as herein described with reference to the accompanying drawings.

In a further, independent aspect of the invention there is provided a mounting for securing a structure to an underwater foundation comprising a spigot connectable in use to the structure, a socket of the underwater foundation for receiving the spigot, and a bearing for mating the spigot to the socket. The bearing may comprise a resiliency deformable member or resiliently deformable members. The deformable member or resiliently deformable members may be disposed circumferentiaily about the spigot and may project radially outwardly therefrom. The bearing may be formed and arranged so that when the spigot is inserted into the socket the resiliently deformable member is, or members are, deformed and held in shear stress for example in the axial direction of the mounting.

The bearing may comprise at least two contact surfaces on the resiliently deformable member or members. The contact surfaces may be disposed circumferentiaily around the spigot and may slope radially inwards in the direction of insertion of the spigot. The contact surfaces may be formed for gripping contact with corresponding sloping contact surfaces provided on the socket when the spigot is inserted. The at least two contact surfaces on the resiliency deformable member or members may be made of portions of a substantially non deformable material bonded to, or otherwise engaged with, said resiliently deformable member or members.

The portions of a substantially non deformable material may be substantially wedge shaped to provide the sloping radially inwards contact surfaces.

The bearing may comprise a plurality of discrete resiliently deformable members, plurality of discrete resiliently deformable members may be disposed circumferentially about the spigot and may project radially outwardly therefrom.

The resiliently deformable members may comprise an elastomer.

At least one resiliently deformable member may have differing elasticity between the radial direction and the axial direction.

In a further, independent aspect of the invention there is provided a method of securing a structure to an underwater foundation comprising connecting a spigot as described and/or illustrated herein to the structure and mating the spigot to a socket of the underwater foundation using a bearing as described or illustrated herein.

There may also be provided an apparatus or method substantially as described herein with reference to the accompanying drawings.

Any feature in one aspect of the invention may be applied to other aspects of the invention, in any appropriate combination. For example, apparatus features may be applied to method features and vice versa.

Detailed description of embodiments Embodiments of the invention are now described, by way of non-limiting example, and are illustrated in the following figures, in which:-

Figure 1 is a schematic illustration of a mounting system according to an embodiment;

Figures 2 to 24 are schematic illustrations of successive stages of mounting or release operations; and

Figures 25 to 40 are schematic illustrations of mounting systems, or components of such mounting systems, in alternative embodiments.

A system 2 for mounting a structure to a base according to a first embodiment is illustrated in Figure 1 , which shows in cutaway a mounting structure 4 for mounting to a base 6. As can be seen in Figure 1 , the mounting structure comprises a male portion that is configured for insertion into a female portion of the base 6. In the embodiment of Figure 1 , the base 6 is in the form of a foundation unit installed on the seabed and the mounting structure 4 is a mounting for a wave energy converter device comprising a flap that is arranged to oscillate around a substantially vertical position in response to wave motion.

In this case, the wave energy converter is a variant of the flap-type wave energy converters described in WO 2006/100436, WO 2009/44161 , WO 2010/049708, WO 2010/084305, WO 2011/101102 and WO 201 1/073628, each of which is hereby incorporated by reference.

In the embodiment of Figure 1 the flap (not shown) is connected to and oscillates about the horizontal support structure 8 forming part of the mounting structure 4 shown in Figure 1. The mounting structure 4 in this case is constructed of several parts and includes a central pipe 18, a flexible mounting 20 to prevent bending loads fatiguing the central pipe 18, and a pipe clamp 22 that can resist heave motion. The base 6 includes a heave reaction feature 24 on a pile adaptor.

The structural connection between the wave energy converter and the base is made through pairs of tapered contact pads 10, 12 that are arranged into rows around the vertical cylindrical connection provided by the male portion and female portion of the mounting structure 4 and the base 6.

It can be seen in this case that the tapered contact pads 10 are arranged circumferentially around, and project radially outwards from, the male portion of the mounting structure and the surfaces of the contact pads 10 slope radially inwards in the direction of insertion of the male portion. The tapered contact pads 12 are disposed circumferentially around the female portion and project radially inwards therefrom.

Each of the contact pads 10 forms part of a respective bearing 14 on the mounting structure 4. The surface of a contact pad 10 provides a bearing surface of the bearing 14. Each bearing 14 comprises a resiliency deformable member in the form of a laminated elastomeric structure 16 that, in this case, comprises an elastomer in the form of natural rubber laminated together with a series of steel plates. Each of ihe contact pads 10 is wedge shaped and has a tapered bearing surface.

In the embodiment of Figure 1 , each contact pad 10 comprises a stainless steel body with a coating flame-applied to the base and providing the bearing surface. In this case, the coating comprises tungsten carbide in a cobalt and chromium matrix. The coating provides high corrosion resistance, appropriate frictional behaviour and is relatively hard, which should provide resistance to damage during either operation or maintenance. The contact pads 12 on the base 6 are of similar structure to the contact pads 10 and again comprise a stainless steel body with a flame-applied coating of tungsten carbide in a cobalt and chromium matrix that provides a bearing surface. The contact pads 12 are also wedge shaped and have a tapered bearing surface.

Each of the mounting structure 4 and the base 6 can be considered to have a respective engagement axis, such that to mount the mounting structure to the base the mounting structure is moved into contact with the base, with the engagement axis of the base and the engagement axis of the mounting structure substantially aligned, in the embodiment of Figure 1 the engagement axis of the base 6 is substantially aligned with the vertical, so the engagement axis of the mounting structure 4 is also substantially aligned with the vertical

It is a feature of the embodiment of Figure 1 that the angle the tapered bearing surfaces of the contact pads 10 of the mounting structure 4 make with the engagement axis of the mounting structure 4 is substantially the same as the angle the tapered bearing surfaces of the contact pads 12 of the base 6 make with the engagement axis of the mounting structure 4. Thus, when the mounting structure 4 is mounted to the base, with engagement axes aligned, each contact pad 10 is aligned and slidingly engaged with a corresponding contact pad 12.

The elastomeric bearings are able to shear in a direction parallel to the aligned engagement axes at a relatively low load, and each of the wedged contact pads 0, 12 is free to move independently of the others. The wedged contact pads 10, 12 allow ail of the bearing surfaces to be brought into contact, in spite of possible installation misalignments and manufacturing tolerances. The laminated construction of the elastomeric components then provides a stiff load path for the wave energy converter operational loads to be reacted into the base 6 in operation.

The faces of the contact pads 10, 12 are tapered to allow the base 6 and the mounting structure 4 to be brought together in an axial (in this case, vertical) direction. The tapers also allow lateral tolerances to be accommodated through shear in the bearings 14.

For lateral loads to be transferred successfully between the inclined bearing surfaces, the angles of the bearing surfaces are matched with the friction conditions of the surfaces, if the angle between the bearing surface and the vertical exceeds the inverse tangent of the friction coefficient, the bearing surfaces will slip. Therefore, the angles that the bearing surfaces make with the engagement axes is limited to less than the minimum friction angle at the interface, allowing a suitable margin, or offset angle, for safety. Axiai shear deformations are retained in the elastomeric bearings 14 after mating of the support structure 4 and base 6. The purpose of the residual shear deformation is to maintain a!! bearing surfaces in contact even once large operational loads are applied. Operationai loads can cause both the elastomeric bearings 14 and the structures to deform, changing the load distribution on the bearing surfaces. Should an individual bearing 14 become completely unloaded, the restoring force stored by the shear stress in the eiastomer causes the tapered bearing surfaces to slide in a direction which helps to maintain the bearing surfaces in contact.

The process whereby contact pads 10, 12 move to close gaps as the system is deformed under load also results in residual compressive pressures between the bearing surfaces once the load causing the deformation is removed. That can have three important consequences. Firstly, before the bearing surfaces can slide during subsequent load cycles it is necessary to overcome this preload. Additional movements are therefore suppressed unless larger forces are experienced than has previously been experienced. After an initial bedding-in period of the mounting structure 4 in contact with the base it is therefore not expected that any significant relative movement between the mounting structure 4 and the base 6 will be seen except under increasingly extreme sea conditions. This avoids continuous movements and so prevents wear on the bearing surfaces.

Secondly, once all of the pads 10, 12 are experiencing compressive load

(also referred to as the pads being pre-stressed or pre-loaded) after insertion of the mounting structure 4 into the base 6, they can react to additional loads by an increase or decrease in the compressive pressure. This means that the bearings 14 are able to react to both positive and negative forces, meaning that fatigue loads are distributed between all of the bearings 4.

Thirdly, the preload in the bearings 14 creates friction at the interface between contact pads 10, 12 that needs to be overcome before the wave energy converter can be removed for maintenance. The steeper the angle of the tapers, and the higher the maximum coefficient of friction of the bearing surfaces, the more difficult breaking the connection between the mounting structure and the base becomes.

The movement of the male portion of the mounting unit 4 into engagement with the female portion of the base 6, and the subsequent effects on the bearings 14 of forces experienced by the system are now discussed with reference to Figures 2 to 24, which are simplified illustrations of the system of Figure 1 , in which two bearings 14a, 14b positioned on opposite sides of the male portion are shown. For simplicity the movement of the male portion and the effects of forces, are described with reference to only those two bearings 14a, 14b. In the embodiment of Figure 1 there are two rows of bearings, each comprising eight bearings, but the effects of forces can be understood from the simple case of two opposed bearings shown in Figures 2 to 24.

Figure 2 shows the male portion of the mounting structure 4 being pulled down towards the base 6. In this case the mounting structure 4 is pulled down and guided by a winch arrangement (not shown). A wave energy converter apparatus comprising a flap (not shown) is attached to the top of the male portion as already described. The left-hand bearing 14a comprises contact pad 10a and elastomeric structure 16a, and the right hand bearing 14b comprises contact pad 10b and elastomeric structure 16b. in Figure 2, the bearing surface of the left-hand contact pad 10a has not yet contacted the bearing surface of the left-hand contact pad 12a of the base 6. Similarly, the bearing surface of the right-hand contact pad 10b has not yet contacted the bearing surface of the right-hand contact pad 12b of the base 6.

In Figure 3, the male portion of the mounting structure 4 has moved further down, and the bearing surface of the right-hand contact pad 10b has contacted the corresponding bearing surface of the right-hand contact pad 12b of the base 6. The bearing surface of the left-hand contact pad 10a has not yet contacted the corresponding bearing surface of the left-hand contact pad 12a of the base, due to a slight misalignment of the mounting structure 4 and base 6 that often occurs in practice. The misalignment is within the tolerances of the system, and in view of the wedge shaped bearing surface and the deformable nature of the bearings, the system can cope with such misalignments.

In Figure 4, the male portion of the mounting structure 4 has moved further down and the bearing surface of the left-hand contact pad 10a has now contacted the corresponding bearing surface of the left-hand contact pad 12a of the base. Due to the downward movement of the mounting structure 4 the right hand bearing 14b has begun to shear and the elastomeric structure 16b of the right hand bearing 14b is now under shear stress.

In Figure 5, male portion of the mounting structure 4 has moved further down and both bearings have sheared and the elastomeric structures 16a, 16b of both bearings are under shear stress. The shear stress acts in an engagement direction to bias the bearing surface of the left-hand bearing 14a towards the bearing surface of the left-had contact pad 12a of the base 6, and to bias the bearing surface of the right hand bearing 14b towards the bearing surface of the right-hand contact pad 12b of the base 6. In Figure 6, the male portion of the mounting structure 4 has moved even further down and the bottom of the male portion is in contact with the base 6. The wave energy converter is considered now to be in a captured state.

In some embodiments the buoyancy of the wave energy converter is then adjusted to its operational value, for example by flooding part of the flap with water, and the winch is disconnected, in some embodiments the wave energy converter has substantially neutral buoyancy in operation.

In Figure 7, the mounting structure 4 begins to experience a lateral load F, as indicated by the solid arrow. The central axis of the mounting structure is shown in Figure 7 by a dotted line. The load may come from any of a variety of sources, for example action of waves, tide or currents on the mounting structure 4 or attachments to the mounting structure, for example the flap.

In Figure 8, the mounting structure 4 has moved sideways to the right by distance x, where x=F/k thus compressing the elastomeric structure 16b of the right- hand bearing 14b. The mounting structure moves to the right until the force applied by the compressed elastomeric structure 16b equals the lateral external force F, as shown in Figure 8. A gap begins to open between the bearing surface of the contact pad 10a of the left-hand bearing 14a and the bearing surface of the left hand contact pad 12a of the base 6, as shown schematically in Figure 8. The contact pad 10a of the left hand bearing 14a then slips downward relative to the contact pad 12a of the base 6, due to partial release of the shear stress in the elastomeric structure 16a in an engagement direction that biases the bearing surface of the contact pad 10a towards the bearing surface of the contact pad 12a , and the bearing 14a thus move downwards. If the bottom surface of the mounting structure was not already resting on the base, the lateral movement could also cause the mounting structure as a whole to move further downwards relative to the base.

It can be understood from Figures 8 and 9 that it is a feature of the described embodiment that lateral movement of the mounting structure 4 due, for example, to external forces can act to cause the bearings of the mounting structure to engage more deeply with the base, due to the stored shear energy of the elastomeric bearings and the sloping nature of the bearing surfaces. Thus, for example, action of waves, tides or currents can actually act to embed the mounting more securely in the base rather than destabilising the mounting structure.

In Figure 10, the lateral load F is removed and the force F applied by the compressed elastomeric structure 6b of the right hand bearing moves the mounting structure towards a new equilibrium position, a displacement ½ x in a lateral direction from the original position, thereby compressing the left hand elastomeric structure 16a. The new equilibrium position is the position at which the compressive force, ½ F, applied by the right hand elastomeric structure 16b matches the compressive force now applied by the ieft hand e!astomeric structure 16a, as indicated in Figure 1 1.

It can be understood from Figures 10 and 1 1 that the application and subsequent removal of the lateral force F has caused the bearings both to embed more deeply in the base, and to increase the compression of the bearings.

Next, an external lateral force F is applied in the opposite direction towards the left-hand side, as shown in Figure 12. The mounting structure 4 moves until equilibrium is regained, when the lateral force F matches the force applied by the left- hand bearing 14a due to compression of the elastomeric structure 16a, as shown in Figure 13. The equilibrium position in this case is now the original equilibrium position (x=0). In equilibrium position there is now no compression in the right-hand elastomeric structure 16b.

It can be seen from Figure 12 that as the second lateral force F, applied in the left-hand direction, is no larger than the original lateral force, applied in the right-hand direction, it causes the mounting structure to move but does not cause a downward movement of either of the bearing surfaces.

Next, the force applied in left-hand direction increases to 2F, as indicated in Figure 14. In Figure 15, the mounting structure 4 has moved sideways to the left by distance x, where thus compressing the elastomeric structure 14a of the left-hand bearing 14a. The mounting structure 4 moves to the left until the force applied by the compressed elastomeric structure 16a equals the lateral external force 2F₍ as shown in Figure 15. A gap begins to open between the bearing surface of the contact pad 0b of the right-hand bearing 14b and the bearing surface of the right hand contact pad 12b of the base 6, as shown schematically in Figure 16. The contact pad 10b of the right hand bearing 14b then slips downward relative to the contact pad 12b of the base 6, due to partial release of the shear stress in the elastomeric structure 16b.

In Figure 17, the lateral load 2F is removed and the force 2F applied by the compressed elastomeric structure 16a of the left hand bearing moves the mounting structure 4 towards a new equilibrium position, which is the original position (x=0) in this case, thereby compressing the right hand elastomeric structure 16b. The new equilibrium position is the position at which the compressive force, F, applied by the left hand elastomeric structure 16a matches the compressive force now applied by the right hand elastomeric structure 16b, as indicated in Figure 18.

!t can be understood from Figures 17 and 18 that the application and subsequent removal of the further, increased lateral force 2F has caused the bearings both to embed more deeply in the base, and to increase further the compression of the bearings 14a, 14b.

Next, an external lateral force ½ F is applied towards the left-hand side, as shown in Figure 19. The mounting structure 4 moves until equilibrium is regained, when the lateral force ½ F plus the force ¾ F applied by the compressed right hand elastomeric structure 16b matches the force applied by the left-hand bearing 4a due to compression of the elastomeric structure 16a, as shown in Figure 20. The equilibrium position in this case is now at a displacement ¼x from the original equilibrium position (x=0) in a lateral direction. Thus, lateral loads are shared between the bearings 14a, 14b once the mounting structure 4 is embedded in the base 6. The sharing of the lateral !oads can be taken into account when calculating expected fatigue life of the bearings 14a, 14b or other components.

In some modes of operation the mounting structure is allowed to embed itself into the mounting and experience lateral forces for a period of time, to enable the bearings to embed themselves further and the compressive load on the bearings to increase and the mounting structure is then secured to the base with other securing devices, for example mounting bolts.

It may be desired subsequently to remove the mounting structure 4 from the base 2, for example for replacement or maintenance. It is a feature of the embodiment of Figure 1 that the compressive load present in the bearings at the time of removal is expected to be around half the maximum compressive load experienced by the bearings during operation. For example, in the sequence of operations described with reference to Figures 2 to 20 the maximum lateral load experienced was 2F, and the bearings at the end of the sequence of operations have a residual compressive load (also referred to as pre-load) of F in the absence of external lateral force, as indicated in Figure 21.

The expected residual loads will vary with the size of the apparatus and the range of sea conditions that are actually experienced.

The mounting structure 4 may be released to float back to the surface, for example after pumping water out of chambers in the flap or, if necessary, otherwise increasing the buoyancy of the flap or other components connected to the mounting structure 4. However, the mounting structure is prevented from being released from the base 6 by the friction between the bearing surfaces 10a, 12a and 10b, 12b as illustrated schematically in Figure 22.

In order to release the mounting structure it may be necessary to apply much more heave force (for example, 1000s of tonnes), change friction conditions (for example lubricate the bearing surfaces), reduce compressive load at the friction interface or change the taper wedge geometry to allow easy release.

A system according to one embodiment for releasing the mounting structure 4 is illustrated schematically in Figure 23, and comprises removable tooling 30 that comprises pairs 32 of short stroke jacks. In one embodiment having sixteen bearings 14, sixteen pairs of 100 tonne, short-stroke jacks are used. The jacks apply additional vertical force to separate the bearing surfaces by pulling up individually on each contact pad of the mounting structure 4.

A system according to one embodiment for releasing the mounting structure 4 is illustrated schematically in Figure 24, and comprises a high pressure water line 30 that communicates with grooves or pockets 42 in the contact pads. Water is applied to the bearing surfaces by the high pressure water line 30 to overcome the residual compressive force, reduce friction and allow the wedges to separate. The mounting structure can then "walk" free of the base 6. The water pressure applied in some embodiments is around 300 bar.

in the embodiment of Figure 1 , the bearings 14 are provided on the male portion of the mounting structure, and have outward facing bearing surfaces. Any other suitable configuration of the components can be used. For example, the bearings can be provided on the base rather than the mounting structure, or the bearings can be inward or sideways facing. Furthermore the male portion can be provided on the base, and the female portion can be provided on the mounting portion, or the base and mounting structure can be coupled, and the bearing surfaces engaged with one another, without using male and female portions.

An alternative embodiment is illustrated in Figure 25, in which a base unit 54 has a male portion and a mounting structure 52, also referred to as a support structure, has a corresponding female portion. Two rows 56, 58 of bearings 60 are provided on the male portion of the base unit 54, and corresponding contact pads 62 are provided on the female part of the mounting structure 52. The bearings 60 and contact pads 62 are of similar structure and composition to those described in relation to Figure 1.

The mounting structure is connected to a wave energy converter comprising a flap 50. The flap 50 is shown floating horizontally on the surface in Figure 25, before being hauled below the surface to a substantially vertical position as the mounting structure 52 is brought into engagement with the base 54.

A magnified view of the male portion of the base unit, and further magnified views of the top row of bearings 60 and bottom row of bearings 60, are provided in Figure 26. The top row of bearings 60 are mounted circumferentially around the male portion of the base 54 and face radially outwards from the male portion. The bearings 60 of the bottom row are mounted on arms 64 that protrude radially outward from the male portion and the bearings face sideways rather than radially outwards from the central axis

A further embodiment in which the bearings are mounted on arms of a mounting structure and project sideways is illustrated in Figure 27.

Further embodiments in which the bearings are mounted on the base, in this case a foundation, rather than the mounting structure are illustrated schematically in Figures 28 and 29.

A further alternative embodiment is shown in Figure 30, in which a base unit

104 installed on the sea bed 105 has a male portion and a mounting structure 102, also referred to as a support structure, has a corresponding female portion. Two rows 106, 108 of bearings 1 10 are provided on the male portion of the base unit 104, and corresponding contact pads 1 12 are provided on the female part of the mounting structure 102. The bearings 1 10 and contact pads 1 12 are of similar structure and composition to those described in relation to Figure 1.

Similarly to the embodiment of Figure 25, the mounting structure is connected to a wave energy converter comprising a flap 100. The flap 100 is shown floating horizontally on the surface in Figure 30, before being hauled below the surface to a substantially vertical position as the mounting structure 102 is brought into engagement with the base 104.

A magnified view of the male portion of the base unit, and further magnified views of the top row of bearings 110 and bottom row of bearings 1 10, are provided in Figure 31. The top row of bearings 110 are mounted circumferentially around the male portion of the base 104 and face radially outwards from the male portion. The bearings 1 10 of the bottom row are mounted on arms 1 14 that protrude radially outward from the male portion and the bearings face sideways rather than radially outwards from the central axis.

Figure 32 shows a magnified, cutaway view of part of the mounting structure 102 when engaged with the base unit 104. The structure 102 includes a clamp connector 120 that includes a single lead screw, a removal torque drive 122, a heave connection 124 arranged to resist heave forces when the mounting structure is connected to the base unit 104, a pin 126 that provides a backup release, and installation latches 128 that are operable to latch the mounting structure 102 to the base unit 104 when the mounting structure 102 and the base unit 104 are engaged. It is a feature of the embodiment of Figures 30 to 32 that the mounting unit also includes bearing pre-shear and release equipment 130, which is operable to place the bearings under shear before engagement with the base unit 104.

Figure 33 show the mounting structure 102 prior to engagement with the base unit 104. Cables 140 are attached between the flap 100 and moorings (not shown) and pulli-down winch lines 142 are connected between the mounting structure 102 and the base unit 104. The mounting structure 102 is positioned over the base unit 104.

A magnified view of the base unit 104 is shown in Figure 34. The base unit of the embodiment of Figures 30 to 34 includes ring beams 150 and tension members 152 that can be used to transfer force to the pads of the bearings 1 0. Operation of the ring beams 150 and tension members 152 is driven by removable cylinders (not shown) that are provided at the base of the base unit 104. Hydraulic power can be provided to the base unit, and to the removable cylinders, from a hydraulic power unit (HPU) on a support vessel, and can thus be provided independently of the wave energy converter/flap and can be fully tested in advance. In operation of the embodiment of Figures 30 to 34, force is applied to the elastomeric pads of the bearings 1 10 by operation of the cylinders, ring beams 150 and tension members 152, before engagement of the mounting structure 102 with the base unit 104.

Figures 35 to 35d show the relative positions of the base unit 104 and the wave energy converter (WEC) apparatus that includes the flap 100 and mounting structure 102. The flap 100 includes upper ballast compartments and ballast compartments near a hinge connection to the mounting structure 102.

At the first stage (Figure 35a), the WEC is in its tow condition, with the upper ballast compartments flooded and the hinge ballast compartments empty. The WEC is then towed above the base unit 104 and placed into its installation condition (Figure 35b) with both its upper ballast compartments and hinge ballast compartments flooded. The cables 140 and pull-down winch lines 142 are attached.

At the next stage (Figure 35c) the WEC is pulled down from the sea surface 103 using winches, and the top of the base unit 104 (also referred to in this case as the pile adaptor) enters the mounting structure 102 of the WEC. There is a large target region due to size differences between the top of the base unit 104 and the opening in the mounting structure 102. At this stage, the WEC is still free to surge due to the action of the waves. Any impacts are taken by guidance features of the base unit 104 and mounting structure 102.

At the next stage (Figure 35d), the WEC is pulled down further and a second point of engagement is reached. The WEC is now unable to surge (moment connection) and yaw restraint is provided by lower connector faces. Figure 36 provides a cut-away view of part of the mounting structure 102 engaged with the base unit 104. When the WEC is in the process of engaging with the base unit 104, the energy of impact can be absorbed by four Oleo (RTM) or other dampers 150 provided on the mounting structure 102. During engagement, a heave connection pipe hub 152 of the base unit 104 engages into a guide cone 154 provided on the mounting structure. The mounting structure 102 of the WEC is then latched to the base unit 104 using the installation latches 128, which in this case are ball grab mooring connectors.

Figure 37 is a close-up view of the heave connection 160 between the mounting structure 102 and the base unit 104. The heave connection 160 is a permanent heave connection that comprises a three-piece pipe clamp connector with a single lead screw, for example a Vector Optima (approx 26") connector. The connector may be remotely controlled from a support vessel with actuation being provided by any suitable standard remotely-operated vehicle (ROV) torque tool (for example complying with ISO 13628-8 Class 7). Figure 38 shows the clamp connector in isolation, in open and closed states.

During the installation procedure of the embodiment of Figure 30, once the heave connection is made, the cylinders shearing the pads of the bearings are released and all tolerances are closed up.

At the next stage, the flap 100 is ballasted into operational condition by pumping water out of the upper compartments to increase pitch stiffness and pumping water into the hinge compartments chambers to decrease buoyancy. Any ballast installation equipment is then recovered.

A control and instrumentation umbilical is then connected, and the main WEC hydraulics are also connected together, and local pressure tests of hydraulic connections are conducted. The mooring and pull down equipment, and installation tools are then recovered. For example, as indicated in Figure 39, the ROV torque tool can be recovered, the ball grabs can be recovered, and the pre-shear cylinders can be recovered.

With reference to Figure 40, subsequently if the mounting structure 02, and thus the WEC, is to be released from the base unit 104 the WEC hydraulics and umbilical are first disconnected. The flap is then ballasted into its tow condition by connecting ballast equipment to the flap 100, flooding the upper compartments of the flap 100 and emptying the hinge compartments.

The WEC is then connected to moorings and subsequently returned to its temporary stability condition. The pre-shear cylinders can be reconnected and used to apply force to release the elastomeric pads, the ball grabs can be used to provide temporary stability, and an ROV torque tool can be used to release the clamp of the heave connection. A backup release mechanism is provided by the pin 126, and rigging can be attached and used to release the pin if necessary, in case the clamp fails.

Next, the ball grabs are released using a remote hydraulic release provided at a support vessel. The WEC then resurfaces. Tow lines are then connected, the moorings are disconnected and the WEC can be towed to shore by the support vessel.

In alternative embodiments, different materials may be used for the bearings and the bearing surfaces. The particular materials used can be selected to provide a desired friction, compressive stiffness and shear stiffness characteristics. For example, in some embodiments the elastomer used in the deformable member may comprise, for example, neoprene, polypropylene or any other suitable elastomer material. The deformable member may also include substantially rigid material, for example the steel plates as already described. However any other suitable substantially rigid and/or substantially non-deformable material may be used and may be bonded to the elastomer.

The angles of the tapered bearing surfaces can vary in different embodiments. In the embodiment of Figure 1 the angle of taper is around 5 degrees, based on the use of a relatively low friction facing material (flame applied tungsten carbide). Other appropriate materials for the bearing surfaces include composite bearing materials (such as Orkot) or certain bronzes. The taper angle can be higher in some embodiments, if for example a higher friction interface is used such as rough steel on rough steel, which might be appropriate for applications where removal in service is not required. The maximum angle in such embodiments may be in the region of 20 degrees for this concept. The minimum angle may be as low as a Morse taper (2 to 3 degrees).

The ratio of elastomer stiffness under compressive and shear loading of the elastomeric pads can be high, for example in the region of 1000 to 1 in some embodiments. The ratio is different in different embodiments. The loads experienced by the elastomeric structure or other resiliently deformable member are application dependent.

In embodiments, axial shear deformations of individual, compliant bearings, when combined with tapered contact surfaces, allow for multiple bearing surfaces to be brought into contact in spite of installation misalignments and manufacturing tolerances. This can allow for increased load sharing between multiple bearings. If residual axial shear deformations are generated in compliant bearings during mating of the structure and foundation, all bearing surfaces can be maintained in contact even after loads are applied to the structure and cause it to deform. This occurs without any external intervention because if an individual bearing becomes unloaded, the restoring force from the pre-sheared compliant bearing causes sliding of the tapered contact surfaces to maintain contact. This sliding only happens during an initial "bedding-in" phase and after this there should be no relative motion between bearing surfaces. That can reduce wear.

The action described in the preceding paragraph pre-loads the connection so that reversing structural loads are resisted via fluctuating compressive pressures on all bearings, further distributing the loads.

Embodiments of the invention may be used to mount structures such as wave power devices (for example, wave energy convertors - WECs) but may also be used to install any structure requiring secure fixing to an offshore location. Suitable structures may include, for example, tidal energy devices, water current devices, wind turbine masts or other masts, oil or gas production or exploration-related structures, or structures relating to telecommunication installations. Embodiments of the invention may also be used on land.

Resiliently deformable (for example elastomer) parts of a bearing may assist in firmly and correctly locating a spigot in a socket and shearing stress (or other stored energy) acts to close gaps caused by larger lateral forces moving the spigot sideways. The spigot continuously "reseats" itself firmly in the socket in response to both small and large forces because of both the stored energy and the resilient compressibility of the resiliently deformable members.

Although the base of the embodiment of Figure 1 is installed on the bed of a body of water, it is not limited to being so installed. The base may be installed on land and/or may form part of a larger structure. The mounting structure may be any structure that can be mounted to the base.

In many circumstances the bearing is able to cope well with heave forces arising from action of waves, tides or currents, and is able to resist such heave forces effectively.

Use of the bearing in some embodiments may eliminate or reduce the use of concrete or other grouting material in the installation of a device at the bed of a body of water.

The mounting is expected to be secure and may require dedicated techniques to remove it. The term shear stress as used herein is intended to encompass the term shear tension.

it will be understood that the present invention has been described above purely by way of example, and modifications of detail can be made within the scope of the invention.

Each feature disclosed in the description, and (where appropriate) the claims and drawings may be provided independently or in any appropriate combination.

Claims

1 . A mounting system comprising a base and a mounting structure for mounting to the base, wherein:- one of the base and the mounting structure comprises a bearing comprising a resiliency deformable member and having a bearing surface;

the other of the base and the mounting structure comprises a further bearing surface for engagement with the bearing surface of the bearing; and

the bearing is configured so that shear stress of the deformable member when the mounting structure is mounted to the base biases the bearing surface towards the further bearing surface.

2. A system according to Claim 1 , wherein one of the base and the mounting structure comprises a plurality of the bearings each comprising a resiliency deformable member and having a bearing surface; and

the other of the base and the mounting structure comprises a plurality of the further bearing surfaces, each further bearing surface being arranged for engagement with the bearing surface of a respective one of the bearings.

3. A system according to Claim 1 or 2, configured so that reduction in compression of at least one of the bearings causes a release in shear stress, thereby to move the mounting structure and/or at least one of the bearings towards the base

4. A system according to any preceding claim, wherein lateral movement of the mounting structure in alternating directions causes alternating bearing surfaces to move relative to corresponding further bearing surfaces thereby to move the mounting structure and/or the bearings towards the base.

5. A system according to Claim 4, wherein in operation the lateral movement is caused by action of waves, tides, currents or wind on the mounting structure or on a further structure attached to the mounting structure.

6. A system according to any preceding claim, wherein the mounting structure has an engagement axis, the base has an engagement axis and the mounting structure is mounted to the base by moving the base and the mounting structure into contact with the engagement axis of the base and the engagement axis of the mounting structure substantially aligned.

7. A system according to Claim 6, wherein, for the or each bearing, the bearing surface is inclined with respect to the engagement axis of one of the base or mounting structure, and the further bearing surface is inclined with respect to the engagement axis of the other of the base or mounting structure.

8. A system according to Claim 6 or 7, wherein, for the or each bearing and further bearing surface, the angle between the bearing surface and the engagement axis of one of the mounting structure and the base is less than the inverse tangent of the coefficient of friction between the bearing surface and the further bearing surface.

9. A system according to any preceding claim, wherein the base and the mounting structure are configured so that the bearing surface and the further bearing surface are arranged to be in sliding engagement with one another when the mounting structure is mounted to the base.

10. A system according to any preceding claim, wherein, for the or each bearing, one side of the resiliently deformable member of the bearing is attached to a body of one of the base and the mounting structure, and the bearing surface comprises a substantially non-deformable material attached to the other side of the resiliently deformable material.

1 1. A system according to any preceding claim wherein, for the or each bearing and bearing surface, the bearing surface and/or the further bearing surface comprises non-elastomer material, optionally at least one of steel, tungsten carbide, cobalt and/or chromium, further optionally tungsten carbide in a cobalt and chromium matrix.

12. A system according to any preceding claim, wherein the resiliently deformable member comprises an elastomer.

13. A system according to Claim 12, wherein the elastomer comprises at least one of rubber, for example natural rubber, neoprene or polypropelene.

14. A system according to any preceding claim, wherein the resiliently deformable member comprises a laminated structure, optionally comprising a plurality of elastomer layers interspersed with at least one non-elastomer layer.

15. A system according to Claim 14, wherein the at least one non-elastomer layer comprises a substantially rigid layer, optionally at least one plate.

16. A system according to any preceding claim, wherein the at least one resiliently deformable member has substantially different elasticity in different directions, optionally the different directions are a radial direction and an axial direction.

17. A system according to any preceding claim, wherein one of the base and the mounting structure comprises a male portion and the other of the base and the mounting structure comprises a female portion, and the base and the mounting structure are configured so that the male portion mates with the female portion when the mounting structure is mounted to the base.

18. A system according to Claim 17, wherein one of the male portion and the female portion comprises the bearing or each of the bearings and the other of the male portion and the female portion comprises the further bearing surface or at least one of the further bearing surfaces.

19. A system according to Claim 17 or 18, wherein the bearing or bearings are formed and arranged so that when the male portion is inserted into the female portion, the resiliently deformable member is, or resiliently deformable members are, deformed and held in shearing tension in an axial direction of the mounting structure.

20. A system according to any of Claims 17 to 19, wherein the bearing surfaces, or the further bearing surfaces, are disposed circumferentially around the male portion and slope radially inwards in the direction of insertion of the male portion.

21. A system according to any of Claims 17 to 20, wherein the bearings are disposed circumferentially around the female portion and project radially inwards therefrom; or the bearings are disposed circumferentially around the male portion and project radially outwards therefrom.

22. A system according to any preceding claim, further comprising means for applying shear force to the or each deformable member, wherein the means for applying shear force is operable to apply shear force when the base and the mounting structure are not engaged together.

23. A system according to Claim 22, wherein the means for applying shear force comprises at least one of a ring beam and a tension member.

24. A system according to any preceding claim, further comprising means for releasing the mounting structure from the base.

25. A system according to Claim 24, wherein the releasing means comprises at least one of:- means for applying force to one of the base and the mounting structure;

means for changing the friction between the at least one bearing surfaces and the at least one further bearing surface, for example by lubricating the at least one bearing surface and/or the at least one further bearing surface;

means for altering the compressive load between the bearing surfaces and the further bearing surfaces; or

means for altering the angle of inclination of at the at least one bearing surface and/or the at least one further bearing surface(s).

26. A system according to Claim 25, wherein the releasing means comprises at least one of:- a plurality of jacks;

a fluid supply means for providing fluid to the interface between the at least one bearing surface and the at least one further bearing surface.

27. A bearing for attachment to a base or a mounting structure, the bearing comprising a resiliently deformable member and a bearing surface for engagement with a further bearing surface, wherein the bearing is configured so that shear stress of the resiliently deformable member biases the bearing surface in an engagement direction.

28. A bearing according to Claim 27, wherein one side of the resiliently deformable member of the bearing is for attachment to a body of one of the base and the mounting structure, and the bearing surface comprises a substantially non- deformable material attached to the other side of the resiliently deformable material.

29. A bearing according to Claim 27 or 28, wherein the bearing surface comprises non-elastomer material, optionally at least one of steel, tungsten carbide, cobalt and/or chromium, further optionally tungsten carbide in a cobalt and chromium matrix.

30. A bearing according to any of Claims 27 to 29, wherein the resiliently deformable member comprises an elastomer.

31 . A bearing according to Claim 30, wherein the elastomer comprises at least one of neoprene, polypropelene or rubber, for example natural rubber,.

32. A bearing according to any of Claims 27 to 31 , wherein the resiliently deformable member comprises a laminated structure, optionaily comprising a plurality of elastomer layers interspersed with at least one non-elastomer layer.

33. A bearing according to Claim 32, wherein the at least one non-elastomer layer comprises a substantially rigid layer, optionally at ieast one plate.

34. A bearing according to any of Claims 27 to 33, wherein the at Ieast one resiliently deformable has substantially different elasticity in different directions, optionally the different directions are a radial direction and an axial direction.

35. A base or mounting structure comprising at Ieast one bearing according to any of Claims 24 to 31.

36. A base or mounting structure according to Claim 35, having an engagement axis that is substantially aligned with an engagement axis of a further mounting structure or base when the base or mounting structure is mounted to the further mounting structure or base.

37. A base or mounting structure according to Claim 36, wherein, for the or each bearing, the bearing surface is inclined with respect to the engagement axis.

38. A base or mounting structure according to Claim 37, wherein, for the or each bearing, the angle between the bearing surface and the engagement axis of one of the mounting structure and the base is less than the inverse tangent of a coefficient of friction between the bearing surface and a further bearing surface with which the bearing surface engages in operation.

39. A base or mounting structure according to any of Claims 35 to 38, comprising a male portion or a female portion that comprises the bearing or each of the bearings.

40. A base or mounting structure according to Claim 39, wherein the male portion or female portion is a male portion, and the bearing surfaces are disposed circumferentially around the male portion and slope radially inwards.

41. A base or mounting structure according to Claim 39 or 40, wherein the bearings are disposed circumferentially around the female portion and project radially inwards therefrom; or the bearings are disposed circumferentially around the male portion and project radially outwards therefrom.

42. A base or mounting structure further comprising means for applying shear force to the or each deformable member, wherein the means for applying shear force is operable to apply shear force when the base and the mounting structure are not engaged together.

43. A method of mounting a mounting structure to a base, wherein:- one of the base and the mounting structure comprises a bearing comprising a resiliency deformable member and having a bearing surface;

the method comprises bringing the base into contact with the mounting structure such that shear stress of the deformable member biases the bearing surface towards the further bearing surface.

44. A method according to Claim 43, wherein the base is installed on the bed of a body of water.

45. A method according to Claim 43 or 44, comprising mounting an energy conversion device, for example a wave energy conversion device, to the mounting structure.

46. A method according to any of Claims 43 to 45, comprising allowing a reduction in compression of at least one of the bearings causing a release in shear stress, thereby to move the mounting structure and/or at least one of the bearings towards the base

47. A method according to any of Claims 43 to 46, comprising providing for lateral movement of the mounting structure in alternating directions causing alternating bearing surfaces to move relative to corresponding further bearing surfaces thereby to move the mounting structure and/or the bearings towards the base.

48. A method according to Claim 47, wherein the lateral movement is caused by action of waves, tides, currents or wind on the mounting structure or on a further structure attached to the mounting structure.

49. A method according to any of Claims 43 to 48, wherein the mounting structure has an engagement axis, the base has an engagement axis and the method comprises moving the base and the mounting structure into contact with the engagement axis of the base and the engagement axis of the mounting structure substantially aligned.

50. A method according to any of Claims 43 to 49, further comprising applying shear force to the or each deformable member prior to bringing the base into contact with the mounting structure.

51. A method according to any of Claims 43 to 50, further comprising releasing the mounting structure from the base by at least one of:- applying force to one of the base and the mounting structure;

changing the friction between the at least one bearing surfaces and the at least one further bearing surface, for example by lubricating the at least one bearing surface and/or the at least one further bearing surface;

altering the compressive load between the at least one bearing surface and the at least one further bearing surfaces; or

altering the angle of inclination of at the at least one bearing surface and/or the at least one further bearing surface.

52. A method according to Claim 51 wherein the releasing comprises operating a plurality of jacks to apply force to the base or mounting structure, or providing fluid to the interface between the at least one bearing surface and the at least one further bearing surface.

53. A method according to any of Claims 43 to 52, wherein the base and the mounting structure form part of a system according to any of Claims 1 to 23.

54. A method wherein the at least one bearing comprises at least one bearing according to any of Claims 27 to 34.