Vessel and method of use of vessel

Abstract

A vessel 2 comprises first and second hulls 4 connected by connecting means 6. The connecting means are arranged to releasably receive one or more vessel modules 8 to extend between the first and seco

Description

This invention relates to a marine vessel and the use of the marine vessel in relation to offshore installation procedures, and relates, in particular, to a vessel having reliably attachable modules suited for the particular offshore procedure. Deployment, recovery, and operations and maintenance (O&M) are large factors in determining levelized cost of electricity (LCOE) for offshore energy generation and with an increase in offshore operations in the energy sector, lowering costs in relation to marine vessels that carry out installation and maintenance procedures is vital. There are energygenerating structures available that seek to alleviate some of these issues, for example the Applicant has developed a wing system that allows for removal of sets of tidal energy turbines at the same time without the need to remove or work on the foundations. Using commercial vessels with sufficient deck space for relatively large loads and cranage capabilities reduces the number of available vessels for deployment of devices to a handful. Add to this vessel availability and useful weather windows of operation can lead to marine operation projects failing to fulfil requirements. This results in vessel costs driving the costs of installation, decommissioning, and O&M. Current key challenges in this sector are as follows:- • Increase in turbine size leads to decrease in vessel choice. • Increase in turbine weight leads to decrease in vessel choice. • Decrease in vessel availability as tidal / offshore development increases. • Operations and maintenance opportunities governed by vessel availability. • Increase in costs to secure vessel availability. • Increase in losses from extended device downtime waiting for vessel availability. • With an increase in locations of offshore energy-generating devices, vessel opportunities will decrease without sufficient funding to support offshore developments. • Large vessel requirements lead to larger emissions and thus longer carbon payback periods. By limiting the design of energy-generating structures to be located offshore or parts thereof to fit vessel type / crane capabilities to ensure availability for existing installations or O&M, the possible energy yield of a location and the associated LCOE is increased. As designs change to improve LCOE, it is important that vessel requirements keep pace with that change. According to a first aspect of the present invention, there is provided a vessel comprising first and second hulls, the first and second hulls being connected by connecting means, said connecting means arranged to releasably receive one or more vessel modules to extend between the first and second hulls, a support structure for supporting a load, and a load locking device serving to lock the load to the support structure. According to a second aspect of the present invention, there is provided a method comprising providing first and second hulls of a vessel, releasably mounting one or more vessel modules to connecting means arranged to extend between the first and second hulls, and further providing a support structure and a load locking device serving to lock a load to the support structure. Owing to these aspects, the vessel provides the ability to lift large profile loads for transportation and provide modularity to marine operations. Preferably, the first and second hulls form a first pair of hulls and the vessel further comprises a second pair of first and second hulls. The connecting means is preferably at least one crossbeam member. Advantageously, the respective pairs of the first and second hulls are spaced apart and a gap therebetween is bridged by respective first and second supporting structures. The support structure is preferably of an arched form. Furthermore, the support structure preferably includes a horizontal section at a maximum height above an upper level of a platform formed by the vessel modules. Preferably, the first and second hulls include a lifting device serving to lift and lower the load secured to the or each supporting structure. In order that the present invention can be clearly and completely disclosed, reference will now be made, by way of example only, to the accompany drawings, in which:- Figure 1 is a perspective view of a vessel in accordance with the present invention, Figure 2 is a perspective view from below of supporting structures of the vessel of Figure 1, Figures 3a to 3c are plan views of different stages of attaching a large load to the vessel, and Figures 4a to 4c are elevational views of stages of an installation / O &M procedure carried out offshore. Referring to Figures 1 and 2, a vessel 2 comprises a plurality of hulls 4. The hulls are preferably arranged in pairs of first and second hulls 4 connected by connecting means 6 in the form of a least one crossbeam member. The cross-beam members are arranged to receive one or more vessel modules 8 which are at a level above a surface of water on which the vessel moves. Respective pairs of hulls are spaced apart by a gap 9 and bridgingly joined by respective supporting structures 10 arranged orthogonally to the crossbeam members 6 and which are advantageously of an arched form extending between respective ones of the first and second hulls 4 with a horizontal section 10a at a maximum height above an upper level of a deck 12 formed by the vessel modules 8. The horizontal section 10a spans across a majority of the distance of the gap 9. This multiple hull design ensures a reduction in the amount of metal used in vessel construction which ultimately reduces the cost of manufacturing the vessel 2. Owing to utilization of the vessel modules 8, it is possible to transport the constituent parts of the vessel 2 by road or otherwise shipped by sea to new locations and assembled / constructed close to a work site and subsequently disassembled / deconstructed for transport to another location. Different ones of the one or more vessel modules 8 can include a planar deck surface (which when arranged next to each other form a planar platform surface 8a of the vessel 2 or they may also support a variety of equipment 14, such as control and support equipment. Such modularity allows for the ability to change the configuration and / or character of the vessel 2, for example, from an installation configuration at one point in time for an offshore installation procedure into a minor maintenance vessel at a subsequent time, which can allow access to a recovered lifted load / item through a sliding platform (not shown) retractably extending from one or more of the platforms 8a of the vessel 2 formed by the vessel modules 8. To allow for adequate access to all required areas of the vessel 2, ladders and / or walkways 16 are provided, including a walkway attached to support structures 10 (preferably to the inner facing side, as shown) to allow access to both platforms 8a, especially when offshore. The first and second hulls 4 of one or both pairs may include a lifting device 18 in the form of respective winches for lifting and lowering of an item or load to be secured to the supporting structures 10 by way of suitable runners located along the support structures. By using the first and second pairs of the first and second hulls 4 (resulting in the four hulls shown in Figure 1) with the first and second hulls 4 of each pair connected by the crossbeam members 6 and respective first and second hulls 4 of each pair by the supporting structures 10, the limit to load size, and in particular to load width is significantly increased. Referring specifically to Figure 2, the supporting structures 10 further comprise a load locking device 20 of any suitable form capable of locking the particular load to the supporting structures 10. Where existing commercial vessels would typically require placing the load onto a deck surface with little to no overhang of the load beyond the outer boundaries of the vessel, the vessel 2 locks the load after lifting said load to the horizontal section 10a of the arched supporting structures 10 meaning the a dimension of the load, for example its width, can be independent of the width of the vessel 2 as the load is, for example, suspended in the gap 9 between the respective pairs of hulls rather than having to be placed on a deck surface. Each hull 4 further comprises mooring winches 22 to provide, in the example shown, a 4-point mooring system for effective positioning of the vessel 2 at a work site. To reduce weight of the vessel 2, railings 24 are used where appropriate and in other locations solid bulwarks 26 are used where waves may cause interference to work conducted in those areas. The equipment 14 of the vessel modules 8 may include generator units to provide power for the lifting devices 18 and the mooring winches 22 and are controlled from a control cabin fitted with viewing windows to allow an operator to visually observe a lifting operation. The hulls 4 are designed to be hydrodynamically efficient as to provide the following benefits:-• the vessel can be towed with smaller tug vessels, • there is less drag inferring less carbon emissions during towing, • there are better motion characteristics in heave, pitch, and roll., and • lower mooring forces compared to equivalent mono-hull and twin-hull designs. The load locking device 20 serves to prevent loads from shifting during transit. One or more launch and recovery systems (LARS) (not shown) may also be provided and secured to one or more of the support structures 10. The support structures 10 are of a large enough size with the horizontal section 10a spanning a suitable distance between the pairs of hulls to avoid collision of any parts of the load with the vessel 2. In addition, if the load includes turbine blades which often have quite large blase diameters, and for whatever reason the blades cannot be transported in a horizontal orientation and thus clear of the surface of the water, the vessel 2 can transport the load with the load partially or fully submerged if required (albeit at a likely lower vessel speed). Moreover, since the turbine blades are clear of the hulls 4 larger turbine diameters can be supported on the vessel 2. The constituent parts of the vessel are designed to be repeatedly assembled / constructed and disassembled / deconstructed and the vessel modules 8 aid in the breakdown of constituent part sizes, making transportation of the parts convenient. Referring to Figures 3a to 3c and 4a to 4c, an installation procedure includes the following steps:- • the load (in the case shown an elongate wing-like device 28 carrying a plurality of turbine devices 30 having blades 32) is initially transferred on a floating platform or barge 34 to the vessel 2 (Figure 3a) • the barge 34 is maneuvered into position, centrally of the vessel 2, beneath the supporting structures 10 and between the pairs of hulls using rigging under the support structures (Figure 3b) • Once connected to the lifting winches 18 of the vessel 2, the load is lifted from the barge 34 and is then locked into receptacles of the locking device 20 for transport to the work site • Prior to transport to the work site, the barge 34 is removed from between the hull pairs (Figure 3c) Transportation to the work site can be done by either towing and / or pushing the vessel 2 using tug vessels or the like or by installing individually controllable thrusters to the hulls 4 which provide self-propelled travel to the work site, which is advantageous particularly where the work site is a short distance from a port. Once at site, if self-propelled travel was used then the vessel 2 can also use a dynamic positioning system (or the 4-point mooring arrangement if self-propelled transport was not used) to hold station during lowering or lifting of the load in to or out of the water. Figures 4a to 4c show the load being lowered from the vessel 2, initially locked to the support structures 10 (Figure 4a) upon arrival at the work site, subsequently unlocked from the locking device 20 and lowered by operation of the lifting winches 18 to below the water surface WL (Figure 4b) to subsequently engage with a subsea frame 38 on a seabed SB (Figure 4c). After the load correctly engages with the subsea frame 38, cables of the lifting winches 18 can be disengaged from the load and recovered to the vessel 2. By using the smaller barge 34 as an initial loading pontoon, the vessel 2 allows for a reduction in shoreside cranage capabilities, further reducing the costs associated with operations. The design of the vessel 2 allows the load to be lifted centrally of the vessel avoiding the need for any ballast systems and therefore improves sea-keeping of the vessel 2. In addition, heave forces on the vessel 2 are reduced by lifting centrally of the vessel because the pitching of the vessel 2 is minimized around a midships region as compared to an equivalent mono-hull or twin-hulled vessel. After installation at a site, there will be a requirement to perform maintenance on the apparatus previously installed and the vessel 2 can be reconfigured and / or re-characterized by using different combinations of vessel modules 8 to suit subsequent procedures, such as recovering installed items for transport back to port for work to be carried out dockside. Alternatively, the vessel 2 can be reconfigured and / or re-characterized with suitable vessel modules 8 to conduct maintenance onsite and / or install replacement items while maintenance occurs on the removed item. This could involve movable or slidable platforms (as described hereinabove) to gain access to all parts of a recovered item for speeding up procedures on location in order to reduce downtime. The vessel 2 can be used to eliminate the need for any manual handling offshore and the lifted item is lowered straight down into the water column thereby avoiding pendular accelerations on the load. The vessel 2 therefore:- • May be conveniently constructed and deconstructed. • Provides modularity within operations through interchangeable vessel modules. • Provides the ability to lift wide profile loads for transport between docks and offshore locations. • Increases vessel availability by reducing required additional vessel capabilities to simple tug vessels or the like. • Provides potential for self-propulsion for limited movements depending on site locations. • Has low steel usage than an equivalent catamaran barge or mono-hull barge.

Claims

1. A vessel comprising first and second hulls, the first and second hulls being connected by connecting means, said connecting means arranged to releasably receive one or more vessel modules to extend between the first and second hulls, a support structure for having a load suspended therefrom, and a load locking device serving to lock the load to the support structure.

2. A vessel according to claim 1, wherein the first and second hulls are a first pair of hulls and further comprising a second pair of first and second hulls.

3. A vessel according to claim 1 or 2, wherein the connecting means is at least one crossbeam member.

4. A vessel according to claim 2 or 3, wherein the respective pairs of the first and second hulls are spaced apart and bridged by respective supporting structures.

5. A vessel according to any preceding claim, wherein the support structure is of an arched form.

6. A vessel according to any preceding claim, wherein the support structure includes a horizontal section at a maximum height above an upper level of a platform formed by the vessel modules.

7. A vessel according to any preceding claim, wherein the first and second hulls include a lifting device serving to lift and lower a load secured to the supporting structure.

8. A method comprising providing first and second hulls of a vessel, releasably mounting one or more vessel modules to connecting means arranged to extend between the first and second hulls, and further providing a support structure and a load locking device serving to lock a load to the support structure.

9. A method according to claim 8, wherein prior to locking the load to the load locking device, transferring the load on a floating platform or barge to centrally of the vessel, beneath the support structure and between pairs of the first and second hulls.

10. A method according to claim 9, wherein the load is lowered directly downwardly from the centrally mounted position into a water column.

11. A method according to any one claims 8 to 10, wherein the vessel is reconfigured and / or re-characterized subsequent to a marine operation by using different combinations of the vessel modules to suit a subsequent marine operation.

12. A method according to any one of claims 8 to 11, wherein constituent parts of the vessel are initially assembled / constructed and subsequently disassembled / deconstructed for transportation of the constituent parts.11

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