A transportation and installation system and method
Field of the invention
The invention concerns seagoing vessels for transporting and/or installing structures such as structures and equipment related to offshore or inshore wind power plants. A transportation vessel is transporting structures and equipment from shore to offshore location and the structures and equipment could thereafter be transferred to an installation vessel at offshore location and being installed by the installation vessel to substructures at offshore location. The invention will ensure a safe offshore load transfer from a transportation vessel to an installation vessel, where both vessels are exposed for waves generating wave motions of the vessels. The invention will further ensure a safe load transfer from installation vessel to a fixed offshore substructure, eliminating wave motions of the installation vessel.
Background of the invention
There are several types of floating crane vessels. One type is the semisubmersible crane vessel (SSCV) that has a semisubmersible hull shape and revolving cranes able to rotate the jib (slewing) as well as luffing (moving the jib up and down). These types of cranes are very expensive and require strong foundation in the vessels able to handle loads and moments from the slewing crane/cargo within all angles the crane is operating. These vessels require also a sophisticated ballast system for counter ballast in order to operate cranes in different slewing angles. Examples of such SSCV's are the vessels "Thialf ' and "Saipem 7000".
Other types of crane vessels comprise monohull vessels and catamaran-shaped crane vessels, also outfitted with revolving cranes. These are more weather sensitive compared to semisubmersible crane vessels due to larger waterplane area, and need also strong support and sophisticated ballast system for the same reason as mentioned above.
Shear leg cranes are another type of floating crane vessels having a barge-shaped hull or catamaran- shaped hull with large waterplane area compared to semisubmersible crane vessels, and the lifting devices have one or two lifting frames with a hoisting
arrangement at the top of the frame(s). A lifting frame is a jib attached to a hull with hinges able to rotate round the hinges (luffing) but not able to slew. The lifting frames are located side-by-side for vessels outfitted with two lifting frames. The lifting frames are far less expensive than revolving cranes and the ballast system less sophisticated since it is mainly needed for compensating vessel trim moment when lifting and not heal moment. The main disadvantages with shear leg cranes is shallow draught and large waterplane area which makes them very weather sensitive. The hull needs to rotate in order to lift/place cargo in the correct orientation relative the substructure were cargo to be placed. This could also require lifting in beam sea where shear leg will be exposed for roll motions. Shear leg cranes are therefore more suitable for inshore lift where they are not exposed to large waves.
Offshore wind turbine generators were in the past erected by conventional ships, outfitted with cranes and stabilizing legs fitted to the side shell of the vessels and deployed to seabed to minimize roll, pitch and heave motions. The hull was not lifted out of water and these vessels were therefore suited for more shallow water due to large exposed area to waves.
Jack-up construction vessels are now the most common lifting tool for installation of offshore wind turbines. The jack-up vessels deploy legs onto the seabed and the hull is elevated above seabed to be less weather dependant during lifting operations. These vessels are outfitted with revolving cranes, which are more expensive than lifting frames and need strong support for the same reason as described above. The leg and elevating mechanism for lifting the hull out of water is also heavy and expensive. The weight of an elevated hull with cargo could be some 50 - 100 times bigger than the weight of the cargo to be lifted by the cranes. This gives large ground pressure from the footings of the legs, with risk for punch-through (rapid penetration of legs through layer(s) of soil if ground pressure from legs footings exceed breaking load of the soil layer).
The jack-up vessels have also a large waterplane area compared to semisubmersible vessels and are weather sensitive for deploying legs and bring the hull out of water (or reverse operation). It is therefore common that these types of vessels need to wait on weather (sometimes for several weeks) in order to be able deploy legs and elevate the hull out of water before lifting operations can commence. The jack-up vessels normally transport the structure and equipment all the way from shore to offshore location and thereafter install the structure and equipment to substructures at offshore location since it is difficult perform load transfer offshore from transportation vessel to jack-up vessel at offshore location due to relative wave motions of the vessels. A jack-up vessel is expensive compared to a transportation vessel and have; less transit speed, more fuel consumption, more stringent sailing limitation due to larger beam and large required air gap for the retracted legs compared to a
transportation vessel. The installation period for a offshore windfarm will also be longer since the jack- up vessel spend lot of time performing transports and not performing installation tasks only, due to lack of safe method perform offshore load transfer operation offshore from transportation vessel to jack-up vessel.
EP 2 251 254 Al describes a semi-submersible vessel for transportation and installation of foundations to wind turbines and transportation and installation of wind turbines. The semisubmersible is equipped with a revolving crane and not lifting frame(s). Cargo is brought onboard by skidding cargo on skid tracks mounted on the pontoon; and not lifted onboard. The system cannot be used for offshore load transfer of structures and equipment from a cargo vessel.
Further, skidding (or use of multi-wheel trailers) for loading from shore requires correct level of vessel skid tracks relative skid tracks on quay (sometimes not even possible due to height of freeboard, quay height, tidal variation or required water depth) and complex ballast operation for load transfer and for tidal variation.
US No. 5 037 241 A describes a cantilevered support extending past the edge of a vessel carrying cargo on top of this support.
WO 03/057556 Al describes a U-shaped vessel mainly designed for topside installation by float over technology. It shows also an application where a lifting frame is mounted on deck, over the U-shaped slot, and outfitted with a hoisting system..
WO 2011/102738 A2 describes a mono hull vessel (not semi submersible vessel) developed for transportation and installation of fully assembled wind turbines including foundations. The concept is based on skidding fully assembled wind turbines from shore (not lifting), further skid the fully assembled in a parking position onboard and then repeat this operation until the vessel is fully loaded with fully assembled wind turbines. The system cannot be used for offshore load transfer of structures and equipment from a cargo vessel.
GB 2 434 823 A describes a purpose-built frame and a spreader beam for lifting an assembled wind turbine from shore, transportation to offshore location by a crane vessel and landing the assembled wind turbine on a purpose built landing platform on top of a pre-installed foundation at offshore location. The system cannot be used for offshore load transfer of structures and equipment from a cargo vessel.
GB 060 2503.5 describes a catamaran shaped vessel (SWATH = small waterplane area twin hull) outfitted with a fixed lifting tower for transport and installation of assembled wind turbine generators as well as transportation and installation of foundations for wind turbine generators. The cargo is supported to a wind turbine engagement device running on a trolley along vertical tracks on the lifting tower. An active compensator connected to the wind turbine engagement device is intended used as a compensator for horizontal movement of the vessel, whilst the wind turbine tower is kept in a vertical position. The hoisting system could have an active heave compensation device to cope with heave motions while installing cargo. The system cannot be used for offshore load transfer of structures and equipment from a cargo vessel.
The applicant has devised and embodied this invention to overcome certain
shortcomings of the prior art and to obtain further advantages. Brief description of the drawings
Figure 1 shows an embodiment of the invented installation vessel, with the legs extended;
Figure 2 shows the installation vessel of figure 1, in the water;
Figure 3 shows the installation vessel of figure 1, afloat in the water;
Figure 4 shows the installation vessel of figure 1, with the legs extended to the seabed;
Figure 5 shows an embodiment of the invented transportation vessel, loaded with a number of wind turbine (tower, generator (in nacelle) and rotor);
Figure 6 shows the installation vessel in position next to the transportation vessel, in the process of lifting a wind turbine ;
Figure 7 shows the wind turbine supported on the installation vessel;
Figure 8 shows the installation vessel, carrying a wind turbine, sailing towards a pre- installed foundation;
Figure 9 shows the installation vessel legs extended to the seabed, in preparation for lifting the wind turbine onto the foundation;
Figures 10 and 11 show the wind turbine having been lifted onto the foundation;
Figures 12-14 (deleted);
Figures 15 - 18 provide further exemplary particulars re the installation vessel;
Figure 19 (deleted);
Figure 20 (deleted);
Figures 21 and 22 are an outline of the transportation and installation of wind turbines; Figure 23 illustrates the same situation as figure 6;
Figure 24 illustrates the wind turbine (WTG) being lifted off the transportation vessel, and the roll and pitch compensation system; and
Figure 25 illustrates an embodiment of the movable crane block on a tiltable gantry beam at the top of the lifting frame. Detailed description of a preferential embodiment
A Transportation/Installation vessel for wind turbine generators
Vessel for transportation/installation of wind turbine generators (WTG) (including nacelle, rotor, blades and towers fully assembled or in parts or other structures for other applications) consisting of a semisubmersible shaped hull with pontoon(s), upper deck and columns between pontoon(s) and upper deck, outfitted with lifting frame(s) able to lift WTGs from transportation vessel (or quay side) and bring WTG onboard the vessel by luffing (tilting) the lifting frame(s) towards the vessel. During luffing/tilting, the frame tilt in a plane herein referred to as its "tilting plane" around the hinge points to the frame. Transportation of the WTGs onboard the vessel to installation location by own propulsion or in tow. Stabilize the hull from motions caused by environmental loading by deploying legs to the seabed hindering roll, pitch, heave, sway, yaw and surge motions. Positioning the WTG above the pre-installed foundation by luffing the frame(s) in X direction (typically vessel longitudinal direction), adjusting block and tackle (or other hoisting device) in Y direction (perpendicular to X direction) and rotate WTG in a swivel hook by tugger winches before lowering the WTG to foundation (in Z direction) by paying out on a block/tackle system (or other hoisting device) from the lifting frame(s).
The invention is the combination of using a semisubmersible hull together with the use of lifting frame(s) and stabilizing legs for transportation and installation of wind turbine generators.
A semisubmersible hull is less weather sensitive compared to a mono hull or catamaran shaped hull in respect of wave motions (i.e. less motion) and wave drift forces due to relative small projected areas at water level, both in the horizontal plan (waterplane area) as in the vertical plan and pontoon(s), when submersed, acting as damper.
Lifting frame(s) has less weight and is less expensive compared to an offshore revolving crane with similar capacity and is more stiff compared to a more slender shape of jib on revolving cranes since hinge points of jib more apart for this type of structure. The hinges on the lifting frame (A frame) are far apart from each other's (close to the side shells of the vessel) given a stable structure perpendicular to the tilting plane with large stiffness.
As shown in Fig. 25, the upper hoisting block could be supported by a trolley running on a tiltable gantry beam (tilted round Y axle) at the top of the lifting frame to allow certain adjustment of WTG in transverse direction relative the installation vessel. This might be required after the vessel has fixed its position offshore by the legs to the sea bed.
Counter ballast is mainly needed for trim moment since lifting frame is not revolving and ballast system will therefore be less complex compared to a vessel with a revolving crane that requires counter ballast also for heeling moment, when turning (slewing) crane with cargo.
The hull of the semisubmersible crane vessel (with A-frame) needs to rotate in order to lift/place cargo in the correct orientation similar to conventional shear leg crane vessel, but a semisubmersible vessel is not sensitive for wave directions compared to mono hull or catamaran shaped crane vessels and is more suited to operate in omnidirectional wave conditions.
Installation by lifting of WTGs (or components of WTGs) at offshore location is more delicate and challenging than installation of foundations to WTGs. Foundations consists mainly of steel and will be lowered into water where the water is damping horizontal motions. The lifting height could be smaller compared to cranes required for WTGs to be lifted some 100 - 120 meter above sea level (depending on size of WTG). The WTG is also more sensible with mechanical and electrical components. Only one degree roll or pitch motion gives a couple of meter in horizontal motions at the top of the WTG (single amplitude). The semisubmersible crane vessel could therefore be outfitted with legs, going through the columns and to be deployed at installation site towards the seabed to eliminate roll, pitch, heave, yaw, surge and sway motion.
A jack-up construction vessel requires calm condition for deploying legs and to elevate the hull out of water (same in a reverse operation) with typical limitation in significant wave height (Hs) of 1 to 1,5 meter whilst the semi submersible crane vessel can deploy legs in more rough conditions with Hs of 3+ meter. Further, a semisubmersible vessel is not sensitive for wave directions compared to a floating jack-up construction vessel (mono hull) and is more suited to operate in omnidirectional wave conditions.
The semisubmersible vessel could be positioned by own thrusters and a dynamic positioning system before deploying the legs towards the seabed. When reaching target position (within given tolerances) the legs will be lowered to seabed. The footings of the legs for jack-up vessels have normally fixed tip that penetrate first. The speed of the mechanism driving the legs is limited with risk the vessel come outside given tolerances before the tip of the leg penetrate and "secure" the horizontal position of the jack-up. The proposed semisubmersible vessel could have a movable tip activated by a hydraulic cylinder (or other mechanism) in order to secure the horizontal position in a quicker way than the mechanism for driving the legs could manage. The extended and penetrated tip together with the footing of the leg gives also better holding capacity towards horizontal forces compared to a short and fixed tip on a conventional footing.
The legs and elevating mechanisms for lifting the hull out of water of a jack- up construction vessel are heavy and expensive. The weight of elevated hull with cargo could be some 50 - 100 times bigger than the weight of the cargo to be lifted by the cranes. This gives large ground pressure from the footings of the legs with risk for punch through (rapid penetration of legs through layer(s) of soil if ground pressure from legs footings exceed breaking load of the soil layer).
The hull of the proposed semisubmersible vessel is not lifted out of water but legs are preloaded towards the seabed by ballasting the hull and or legs in order to always have contact towards seabed within the design condition. Weight and moment from cargo is mainly taken by buoyancy of the hull in combination with ballast in the hull (for moment). Mechanism for running/holding the legs will therefore be considerable lighter (and less expensive) compared to jack-up construction vessels and less energy is required since the hull is not elevated out of water. It is also less risk for punch through since ground pressure is considerable lower compared to the ground pressure from an elevated loaded jack-up construction vessel.
The semi submersible vessel has an operation limitation when having the hull buoyant that is stricter compared to an elevated jack- up construction vessel and the vessel need to retract the leg and go to a standby position with retracted legs if waves exceed a certain sea state (because of bending moment in the legs). For long term operation (several days' operation in bad weather season) this is a disadvantage., however installation of WTGs are a quick operation. The WTG could be installed in matters of hours after the semisubmersible vessel has been positioned and legs deployed why this operation limitation is not considered to be a bottle neck in an installation campaign for WTG.
B Roll and pitch compensator
Load transfer of cargo from a transportation vessel to a crane vessel in open sea is challenging due to relative motions between the two vessels caused by environmental loading (mainly waves and wind). It is even more challenging if the cargo is tall and transported in upright position where even small roll and pitch angles on the
transportation vessel results in large moment at the top of the cargo. Transportation vessels are normally monohull and therefore sensitive for roll and pitch motions. The crane vessel could be of a semisubmersible; less sensitive in respect of motions. New technology has therefore been invented to solve the problem related to lifting cargo from vessel exposed for waves in open sea.
The invention further comprises a roll and pitch compensator connected to the cargo, minimizing cargo to "roll and pitch" (rotation round x axis and y axis) and be kept in a vertical position whilst the transportation vessel follows the sea with roll and pitch motions.
The invented compensator comprises a passive system placed on bottom of a cargo hold or deck of the transportation vessel and an active system located above the passive system at deck level or above deck level on supporting structure
The weight of the cargo is resting on the passive system and is kept in a vertical position by the active system whilst the vessel is rolling and pitching following the sea. (Could also be the vice versa application if it is natural, taking the load in the upper support and have an active system in the lower support).
The passive system allows the cargo to rotate in the vertical planes and comprises in one embodiment of a structure on which the cargo is resting, supported by hydraulic jacks connected hydraulically in a single suspension mode where hydraulic oil is free-floating between the hydraulic jacks, allowing the cargo to tilt in any direction in the vertical planes. It could also comprise of a mechanical system with the same feature such as a single ball-bearing.
Moment required to keep the cargo in upright position is taken by passive stoppers connected to the lower part of the cargo, either directly or via the structure in the passive system resting on hydraulic jacks, and by the active system above the passive system.
The stoppers and the active system are taken the vertical forces acting on the cargo.
The active system comprises in one embodiment of an inner frame (or other structure) running in longitudinal (or transverse) direction of the transportation vessel in an outer frame (or other structure) running in the perpendicular direction to the inner frame on supports attached to the transportation vessel.
Hydraulic jacks or other type of linear actuators are moving the inner and outer frame controlled by a computer system with input from a gauge system measuring
accelerations and angles of the vessel (or other required input) to ensure the cargo maintain in its vertical position whilst the vessel roll and pitch. (Active compensation by hydraulic jacks or other types of linear actuators are considered as known technology in other application). The inner and outer frames may also be replaced by three or more hydraulic jacks, or other linear actuators, attached to cargo directly or indirectly to move the upper part of the cargo in the horizontal plan (or by other means) whilst cargo is resting on a pivot point to compensate for the roll and pitch motions and keep the cargo in a vertical position.
The active support could either be locked or activated during transport of cargo to the installation area but will be activated whilst deploying lifting attachment from a crane vessel and performing the lift off of cargo from the transportation vessel.
The crane vessel could be outfitted with a heave compensation system in order to avoid snatch loading in the lifting gear and cargo when transportation vessel and crane are exposed for relative motions in the vertical direction. The heave compensation could be of a passive type (saving weight and costs) with increased stiffness when load is transferred gradually from the transportation vessel to the crane vessel.
The passive system at the bottom of the cargo, previously supporting the weight of the cargo, and the stoppers at the bottom of the cargo could be retracted at moment of lift off in order to achieve sufficient air gap between support and cargo to avoid a "second contact" if hoisting speed of crane vessel is slower than the relative vertical motions between the transportation vessel and the crane vessel. Hydraulic pressure in the hydraulic jacks supporting the structure carrying the weight of the cargo on the transportation vessel could be measured to follow percentage load transfer from the transportation vessel to the crane vessel and give a signal when load, or majority of load, is transferred to the crane to retract the support and stoppers.
The inner frame (or other structure) of the active system, minimizing cargo pitch (or roll) motions, could be outfitted with a series of rollers forming a diameter in the horizontal plan for embracing cylindrical cargo such as towers to wind turbines (or other shapes). The diameter could be adjusted by moving the rollers in a radial directions by means of linear actuators (such as hydraulic jacks) or by other means. The diameter could also be adjusted whilst lifting cargo out from the cargo holds if the diameter of the cargo varies, such as for towers to wind turbines.
After liftoff of the cargo from the structure the weight of the cargo was resting on (passive system), the cargo is lifted out of cargo hold guided by the rollers in the inner frame in the active system. The roll and pitch compensator could still be active during lifting cargo free from transportation vessel but could also be locked and cargo rotating round the rollers whilst being lifted free from the transportation vessel.
A series of roll/pitch compensators could be installed onboard the transportation vessel to allow a number of fully assembled wind turbines generators being transported to offshore location and lifted off the transportation vessel for installation.