Classifications

• • E—FIXED CONSTRUCTIONS
  • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
  • E02B—HYDRAULIC ENGINEERING
  • E02B3/00—Engineering works in connection with control or use of streams, rivers, coasts, or other marine sites; Sealings or joints for engineering works in general
  • E02B3/04—Structures or apparatus for, or methods of, protecting banks, coasts, or harbours
  • E02B3/06—Moles; Piers; Quays; Quay walls; Groynes; Breakwaters ; Wave dissipating walls; Quay equipment
  • E02B3/068—Landing stages for vessels
• • E—FIXED CONSTRUCTIONS
  • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
  • E02B—HYDRAULIC ENGINEERING
  • E02B3/00—Engineering works in connection with control or use of streams, rivers, coasts, or other marine sites; Sealings or joints for engineering works in general
  • E02B3/04—Structures or apparatus for, or methods of, protecting banks, coasts, or harbours
  • E02B3/06—Moles; Piers; Quays; Quay walls; Groynes; Breakwaters ; Wave dissipating walls; Quay equipment
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B63—SHIPS OR OTHER WATERBORNE VESSELS; RELATED EQUIPMENT
  • B63B—SHIPS OR OTHER WATERBORNE VESSELS; EQUIPMENT FOR SHIPPING 
  • B63B22/00—Buoys
  • B63B22/02—Buoys specially adapted for mooring a vessel
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
  • B65D—CONTAINERS FOR STORAGE OR TRANSPORT OF ARTICLES OR MATERIALS, e.g. BAGS, BARRELS, BOTTLES, BOXES, CANS, CARTONS, CRATES, DRUMS, JARS, TANKS, HOPPERS, FORWARDING CONTAINERS; ACCESSORIES, CLOSURES, OR FITTINGS THEREFOR; PACKAGING ELEMENTS; PACKAGES
  • B65D88/00—Large containers
  • B65D88/78—Large containers for use in or under water
• • E—FIXED CONSTRUCTIONS
  • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
  • E02B—HYDRAULIC ENGINEERING
  • E02B3/00—Engineering works in connection with control or use of streams, rivers, coasts, or other marine sites; Sealings or joints for engineering works in general
  • E02B3/04—Structures or apparatus for, or methods of, protecting banks, coasts, or harbours
  • E02B3/06—Moles; Piers; Quays; Quay walls; Groynes; Breakwaters ; Wave dissipating walls; Quay equipment
  • E02B3/062—Constructions floating in operational condition, e.g. breakwaters or wave dissipating walls

Definitions

• the present invention relates to transport of oil and gas at sea, more specifically a device as specified in the preamble of the independent claims.
• the invention relates to installation and operation of a harbour plant for storage and loading or unloading of hydrocarbons, such as liquefied natural gas at a distance from the shore in shallow waters, where the alternative is to build storage installations for liquefied natural gas on shore or as a moored, floating installation.
• hydrocarbons such as liquefied natural gas
• the invention relates to a harbour plant for storage, loading and unloading of hydrocarbon products at sea, comprising a number of units being mutually placed on the seabed so that a harbour plant is formed.
• the units are intended to be placed independently, in a spaced relation at a given distance D apart in sideways direction and having a front surface along and against which a vessel is intended to be moored.
• the units form passage(s) for parts of the waves, and are configured to dampen a part of the incoming waves while allowing other parts of the waves and current to pass through the harbour plant, the sideways distances between two neighbouring units being governed by the frequency of the waves to be dampened and the frequencies of the waves allowed to pass in between the units.
• the invention relates also to a method for establishing a mooring
• LNG Liquefied Natural Gas
• LNG Liquefied Natural Gas
• the invention is also applicable to other types of petroleum products, such as chilled gases such as ethane, methane, propane and butane.
• the invention can be used for storage, loading and unloading of oil and oil products.
• articulated arms or hoses that are well insulated and flexible are often used.
• the hoses are often in fact very rigid and very inflexible.
• the articulated arms move normally in one plane only and do not tolerate sideways movements. This requires that a LNG vessel must properly moored in protected harbours both during loading or unloading operations, lying leeward.
• NO 126927 describes a harbour site comprising a number of units that are afloat or sunk and otherwise constructed for placement on the seabed. Each unit comprises a base, load-carrying structure and moveable wave-breaking elements that can be moved according to need.
• US 3,958,426 describes a harbour site comprising a number of units placed apart on the seabed, so that at least one straight mooring location is formed.
• the units are provided with fenders and wave dampening devices.
• WO2006/041312 discloses a harbour plant for storage, loading and unloading hydrocarbons such as LNG at sea, the whole content of which hereby being included by the reference.
• the harbour comprises three units built from steel or concrete, placed on the seabed. The units are placed in sidewise relation in-line.
• the harbour is configured to dampen the waves, the vessel being intended to ly on the leeward side of the mooring.
• US 2004/001 1424 discloses a unit for transferring a fluid between a carrier and a harbour plant consisting of a number of separated piled structures as strong points in the mooring system.
• this publication relates to the fluid transfer system, such fluid transfer system consisting og rigid pipe lined and pivotable joints. It should be appreciated, however, that the publication also indicate a mooring system.
• the harbour plant disclosed the vessel id moored on the windward side of the harbour plant.
• An object of the present invention is to provide an improved harbour plant with incorporated and integrated storage units and an improved method for establishing such harbour plant providing a safe haven for vessels during offshore loading and unloading, for example of hydrocarbons such as LNG.
• a further object of the present invention is to provide an improved harbour plant where the mooring conditions for large vessels, for example for transport of LNG, are optimized, eliminating, or at least reducing the effects of wind, waves and current on the moored vessel, thus also providing wind shielding for the moored vessel.
• a still further object of the present invention is to provide an improved harbour plant where the criteria and international standards for mooring large vessels are met, thereby satisfying the relevant requirements and standards.
• relevant standards the content of which being included by the reference:
• Another object of the present invention is to provide an improved harbour plant with protecting means associated therewith, protecting the moored vessel form impacts and collision caused by drifting vessels, more or less without
• Yet another object of the present invention is to provide an improved harbour plant allowing a part of the waves to pass more or less unhindered, while the remaining part of the waves are dampened.
• Another object of the invention is to provide an improved bottom-located harbour site at sea which can store, load or unload LNG directly between vessel and harbour site where the effect of the movements of the ship is minimised in a simple and cost-effective way.
• Another object of the invention is to provide an improved harbour site where the wave dampening is best for medium wave frequencies, for example, for waves up to 8-10 seconds frequency, where it might be required for the ship to be able to operate.
• Yet another object of the invention is to enable building of each of the units of the harbour site at reasonable price and efficiently and as complete as possible at a traditional construction site, preferably at a dockyard with the use of a dry dock.
• each of the units is brought or towed to the installation location, finally to be lowered down with the use of known techniques.
• a further object of the present invention is to provide an improved harbour site which can be placed on the ocean bottom at a pre-calculated, relative distance which maximises the wave-dampening effect, and that the units can be given a shape giving the best wave-dampening effect possible, so that the LNG vessel has advantageous movements during loading/unloading operation at the harbour site.
• an object of the invention is to provide a harbour plant enabling mooring hawsers between the vessel and the mooring to lead downwards from the vessel towards the mooring point on the harbour plant with an angle of at least 2 degrees, preferably with a larger angle according to international standards.
• the mooring points should be arranged in the vicinity, but above the sea level,, to also allow smaller vessel to be moored to the plant and still maintain said downward lead on the mooring lines or hawsers.
• the front surface of one of the units is offset with a distance Z relative to the front surfaces of two neighbouring units in a transverse direction away from said predominating direction of incoming waves, an that R is a distance in the range of a distance 0 to Z, where Z is the length of offset central unit
• the distance Z may preferably be equal to the length of the largest vessel to be moored along a longitudinal side of the central, offset unit .
• the units are configured in such way that the width of the passage between two neighbouring units increases or decreases in direction of the wave motion.
• the offset distance of said unit may preferably be in the range 2 to 60 metres, and the foot print of the displaced unit may preferably trapezoidal, where the parallel side surfaces are perpendicular to the predominant direction of the waves.
• the units may be configured in such way that a width of the passage between two neighbouring units decreased in direction of the incoming wave. Also the footprint of the two neighbouring units may preferably, but not necessarily be is trapezoidal.
• the minimum width (Q) of the passage corresponds to approximately 1 ⁇ 4-1 ⁇ 2 times the wavelength of the wavelength that is desired to damp.
• an angle( a) between one of the two parallel sides of the unit and at least one of the slanted sides of a unit may be in the range 0 to 30 degrees.
• the angle (a) may be different for one of the side walls of a unit.
• the distance between two neighbouring units and/or the laterally offset distance between two units may preferably be such that there is no visual opening in the passage, perpendicular to the front face of the unit.
• the mean sideways distance may preferably be between around 20 metres when the units are placed at a water depth of 18 metres.
• the units may be arranged so that two or more mooring points are formed, and where said mooring points form an angle in relation to each other, such as 90 degrees.
• the units may be provided with means for protecting the units from damages caused by collision, said means comprising elements projecting out from surfaces facing vessels, said means also preferably serving as anchoring points for a vessel intended to be moored along the harbour plant and also preferably contribute to a wave breaking effect.
• the means for collision protection may be configured to extend down through waterline when in installed position.
• the height of the mooring platform should be arranged above the sea level, at a low, but safe height, providing flexibility for mooring a wide range of different sized vessels.
• a method for constructing and placing of a harbour site comprises the following steps:
• Said distance between the units may preferably be determined by the following steps:
• An advantage with placing the units in the harbour site according to the invention a distance apart from each other will be that the required parts of the wave spectrum can be dampened while waves which can lead to extreme strain on the harbour site will travel through.
• the units which the harbour site is composed of can be built cheaper and easier, at the same time as one achieves dampening of the parts of the wave spectrum where it is relevant for the ships to operate near or at the harbour site.
• the waves are dampened efficiently by breaking and cancellation effects which are due, among others things, to reflection from many walls and one thus avoids that the wave energy is deflected and appears at focal points other places in the vicinity of the harbour site.
• a further advantage according to the present invention is that the units constituting the harbour site for LNG according to the invention can be lowered down to the ocean bottom, be removed, be moved and be replaced to form new individual configurations as required using known techniques.
• the units according to the invention forming the harbour site are placed apart at a required distance.
• the distance between the units is decided by the wave frequencies intended to be dampen and the frequencies allowed to pass between the units. This distance can be calculated with known methods or be found by means of basin experiments.
• the units By placing the units a distance apart both sideways and in the prevailing direction of waves, the effect of a build up of wave energy between harbour wall and side of the ship is avoided.
• stationary waves which may be created between a continuous structure and the side of a ship due to reflections between the vertical sides are avoided or at least substantially reduced. Detrimental and extreme parts of the wave energy will thus slip between the units. Since the wave energy is in this way partially is broken up and partially pass between the units, an advantageous cancellation effects and thereby a reduction of the wave energy in the area around the harbour site and the ship is provided.
• Waves with this wavelength are normally formed in connection with storms and hurricanes and then the ship will normally not be able to operate because of the wind. Hence the vessel will thereby not be moored in the harbour site.
• the friction and thereby the wave dampening can be increased in that the units are fitted partially with sharp edges.
• a non-linear dampening is provided, thus removing energy that affects the ship.
• a favourable form of the units will be to expand the volume of the units below the surface of the water, where a stowing of the waves can be provided so that the waves break, also contributing sometimes to wave dampening and reducing the waves on the leeward side of the harbour site.
• the shape and form of the structure below water can be varied dependent on the surroundings and which wave periods to be dampened.
• Favourable shapes could be an inclined surface corresponding to a beach, a built up structure with sharp edges, a structure which is partially hollow or full of holes etc.
• the distance on the seabed between the units will be decided by the wave spectra that occur at the installation location and by the chosen wave spectra to be dampen, causing favourably affects on the movements of the LNG ship.
• Calculations of a possible shape of a harbour site have shown that a quadratic or trapezoidal shape of the units and with a distance of 40 meters apart between the units, placed at a water depth of 18 metres and with no expansion of the volume below the sea level, will dampen waves with wavelengths less than 80 metres.
• calculations have shown that large waves with a wavelength above 200 metres will pass with minimum loss of energy.
• movements of the vessel in a favorable way can thereby be achieved by, for example, by increasing the volume of the units below sea level, for example, from 5- 10 meters depth and down to the ocean bottom.
• This increase of volume can be limited to the volume between the units and be omitted along the mooring face where the LNG ship is moored.
• the increase of volume can be combined with securing a good and sound foundation of the units on the sea bed.
• the units must, however, be configured so that waves are not reflected towards the LNG vessel, causing detrimental and undesired movements.
• Parts of the wave spectrum can also be dampened, for example, by
• the LNG vessel By providing a harbour site comprising several units installed near each other on the sea bed, the LNG vessel can easily be moored and operate along the harbour site. If the LNG ship lies at the windward side of a harbour site according to the invention, reflection of waves towards the ship and the unfavourable, stationary waves produced between the ship and the harbour wall, are avoided.
• the LNG ship can be moored on the leeward side of the harbour site according to the invention.
• a pre-estimated part of the wave energy will be able to pass between the units and it will be possible to dampen some of the wave energy.
• forming of a dangerous focal point for the waves on the leeward side is avoided at the same time as the wave energy on the leeward side results in reduced and favourable ship movements.
• a particularly advantageous configuration of the harbour site according to the invention will be to arrange the units so that several mooring areas are formed and that these mooring areas form an angle with respect to each other, for example, of 90 degrees. It is possible to adjust the angle and positioning to known wave directions at the installation location of the harbour site.
• the movements of the ship will, in general, be in the form of heaving and stamping, giving considerably lower movements and dynamic forces mid-ship where the loading and unloading operations of LNG will take place.
• the harbour site for LNG vessels according to the invention can, if required, also be configured as a U or a V, if one wishes to protect the harbour operations themselves as much as possible and moor the ship in a more protected area where the waves are dampened to a desired extent. This is particularly effective if the underwater part of the units is formed as wave-dampeners, preferably in the direction towards the neighbouring units.
• the units making up the harbour site will preferably be provided with a number of skirts of steel or concrete to be forced down into the sea bed, contributing to a stable construction against the sea bed.
• the skirts have a cylindrical shape with a circular cross sectional area in the horizontal plane, intended to be penetrated into the sea bed. The skirts will contribute to the stability of the units against tiling and vertical and horizontal displacement.
• each of the units can possibly be positioned on the sea bed using known techniques, alternatively be placed on top of a pre-installed base, positioned on the sea bed.
• each unit of the plant is given a substantial height, also proving wind protection for a moored vessel.
• the distance between the offset central unit and at least one of the neighbouring units should be Q meter where Q should be in the range from 0 meter to Z meter, Z being preferably minimum 25% of the length of the largest vessel to be moored along the leeward side of the offset central unit.
• the moored vessel is prevented from pivoting about the offset central unit when subjected to wind, current or waves from any direction. This is advantageously, in particular for loading or de-loading LNG, since such loading system is based on rigid steel pipes and pivotable joints.
• Figures 1 shows schematically a view seen from above of an embodiment of the harbour site according to the invention; where three units are placed a distance apart on the seabed, the middle one being positioned in a retracted position with regard to the wave direction;
• Figure 2 shows schematically a view seen from above of a second
• Figure 3 shows schematically a view seen from above of a third embodiment of the harbour site corresponding to the embodiment shown in Figure 1 , wherein the units forming the harbour plant are provided with additional mooring and/or wave breaking or damping means;
• Figure 4 shows schematically a vertical section in longitudinal direction of the units shown in Figure 3, seen along the line 4-4 in Figure 3;
• Figure 5 shows a side view of an ocean installation where the units are configured to provide two mooring positions, the two mooring positions being arranged at an angle with respect to each other;
• Figure 6 shows schematically a side view of a unit provided with ice breaking buffering structures on two opposite sides of a unit
• Figure 7 shows schematically a side view of a plant unit according to the present invention, also indicated schematically a vessel moored to the unit, the Figure indicating the direction of the mooring hawser;
• Figure 8 shows schematically another configuration of the units forming the plant
• FIGs 1 shows schematically a view seen from above of an embodiment of the harbour site 10 according to the invention.
• the harbour site shown comprises three identical units 1 1 , 1 1 ', configured to rest stably on a sea bed 12 due to gravity.
• the three units 1 1 ,1 1 ' are placed a distance Q apart on the seabed 12, the middle unit 1 1 ' also being positioned in a retracted position in respect to the two other units 1 1 with a retracted distance R, the middle unit 1 1 ' being retracted in a same direction as the general, predominant direction 13 of the waves the waves.
• a vessel 14 is moored along the middle unit 1 on the leeward side of the units 1 1 , 1 1 '.
• the mooring system used for mooring the vessel 14 to the units 1 1 1 , 1 1 ' comprises one or more forward mooring line 15 extending from the bow 16 of the vessel 14 to a fore mooring point 20 at the far leeward corner of one of the units 1 1 .
• the one or more hawsers 15 have a forward lead, i.e. forming an oblique angle with the longitudinal axis of the vessel 14 in fore direction.
• one or more aft mooring line 15' extend between the stern 17 of the vessel 14 and an aft mooring point 20' at the far leeward corner of the adjacent unit 1 1 , forming a lead in aft direction of the vessel 14, such lead also forming an oblique angle with the
• the mooring system comprises forward brest mooring lines 18 extending from the bow region 16 of the vessel to the adjacent unit 1 1 , the direction of the one or more hawsers being more or less perpendicular with respect to the front of the adjacent unit 1 1 , the forward brest mooring line 18 being connected to a mooring point 9 in the middle region of the adjacent unit 1 1 .
• a corresponding one or more aft brest mooring lines 18 extend between the stern region 17 and a aft mooring point 19' on the adjacent unit 1 1 , the hawser direction being more or less perpendicular to the front side of the adjacent unit 1 1 .
• the mooring system comprises also one or more fore spring mooring lines 21 extending from the bow region 16 towards a mooring point 22 on the adjacent leeward corner of the retracted middle unit 1 1 ', providing a lead in aft direction of the vessel, the fore spring mooring lines 21 forming an acute angle in rear direction of the vessel.
• one or more aft spring mooring lines 21 ' extend from the stern region 17 of the vessel to a mooring point 22' on the adjacent leeward corner of the middle, retracted unit 1 1 ', the lead being in forward direction.
• the units 1 1 may be provided with collision dampers 23 rigidly fixed to the surface of the units 1 1 , intended to face the vessel 14 when in moored position. It should be noted that the Figure shows two variants of such dampers 23. These will be described in more detail below in connection with Figure 4.
• the dampers 23 may serve as reinforced support points for the mooring points 19,20,22.
• the middle unit 1 1 1 ' on the face intended to face the vessel 14 in moored position, is provided with strong dampers 24, securing a distance D between the hull of the vessel 14 and the structural wall of the middle unit 1 1 '.
• the Figure discloses a middle unit 1 1 ' retracted in a same direction as the incoming predominant waves direction, the middle unit 1 1 ' may be displaced in opposite direction, i.e. in a direction towards the predominant wave direction.
• the mooring system may have another configuration and/or another number of hawsers, etc. Further, also the various mooring points may differ without deviating from the inventive idea.
• Figure 2 shows schematically a view seen from above of a second
• the mooring configuration and the mooring points 19, 19', 20,20', 22,22', including the collision dampers 24 correspond to the ones shown in Figure 1 .
• the embodiment shown provide a passage between two adjacent units which has a small opening (Q) upstream the waves and an increasing opening in downstream prevailing direction of the waves.
• Q small opening
• the units 1 1 , 1 1 ' may be placed in a closer spaced relation, leaving a reduced, or actual no visual sightline in the wave direction.
• the units may be placed in a configuration where the shorter sides of the trapezoids of the units 1 1 ,1 1 ' face the waves.
• the opening between two adjacent units 1 1 , 11 ' is largest in upstream direction of the waves, the opening being narrower in direction away from the wave direction.
• the trapezoidal shape may be regular, i.e. the acute angle a formed between the front side and one of the side surfaces, are equal.
• one of the side surface may form an angle ⁇ with the front side, where ⁇ differs from a.
• the angle a and ⁇ be adjusted depending on required maximum wave breaking effects.
• the variation in the reflection and diffraction caused by the alteration of the angle a and ⁇ changes the interference pattern of the approaching waves. This results in an effective reduction of the wave height or causes increased wave breaking, resulting in a reduction of th propagated wave energy.
• the direction of the waves propagating between the units will be altered, resulting in a change of region effectively "shadowed" by the structure.
• both the distance Q and R may also be adjusted for the same purposes.
• the adjustment of the angle a and Q and R will increase or widen the wave direction (wave protection angle) and give the harbour design a wider range of reflection angles to create damping effects.
• the distances and angles can be tuned towards the predominant wave pattern and direction for maximum protection of the harbour operation.
• Figure 3 shows schematically a view seen from above of a third embodiment of the harbour site 10 corresponding to the embodiment shown in Figure 1 , wherein the units 1 , 1 1 ' forming the harbour plant 10 are provided with additional mooring and/or wave breaking or damping means
• Figure 4 shows schematically a vertical section in longitudinal direction of the units 1 1 , 1 ', shown in Figure 3, seen along the line 4-4 in Figure 3.
• the mooring configuration being identical with the ones shown in Figures 1 and 2, the difference being the types of collision dampers used.
• the various dampers are disclosed in more details in Figure 4. Two types of dampers may be used.
• One damper, type A is of a type extending down through the water line 25, projecting outwards from the side and/or the front walls of the units 1 1 , 1 1 '.
• the dampers A,B may also dampen the effects of the waves and/or also function ad supports for the mooring points 19, 19', 20, 20', 22, 22'.
• the dampers may be of a type projecting outwards from the units 1 1 , 1 10n the front and/or side walls of the units 1 1 ,1 1 ', the dampers (type B) being terminated above the sea level 25.
• Said type B dampers may also be used for supporting the mooring points 19, 19', 20, 20', 22, 22'.
• Type B dampers are terminated above the sea level 25.
• the units 1 1 1 , 1 1 ' may be provided with tanks for storage of hydrocarbons, such as for example LNG. From a safety point of view, only the wing units 1 1 , may be provided with such tanks. It should be appreciated that the mooring system 10 according to the present invention also may be provided with means, such as loading systems, cranes, etc.
• Figure 5 shows a side view of an ocean installation where the units 1 1 , 1 1 ' are configured to provide two mooring positions, the two mooring positions being arranged at an angle with respect to each other.
• the harbour site for LNG vessels according to the invention can, if required, also be configured as a U or a V, if one wishes to protect the harbour operations themselves as much as possible and moor the ship in a more protected area where the waves are dampened to a desired extent. This is particularly effective if the underwater part of the units is formed as wave-dampeners, preferably in the direction towards the neighbouring units.
• the dampers A,B or the units 1 1 1 , 1 1 ' may also be provided with mooring fenders so that it is possible to safely moor the LNG ships 14 to the harbour site 10 by means of the mooring arrangement.
• the mooring fenders can be made from known, flexible materials according to known techniques. However, they do not have to comprise the mooring arrangement, as an alternative embodiment can be that the mooring installation is placed a distance from the harbour site itself.
• FIG. 6 shows schematically a side view of a mooring and storage unit 1 1 , resting on the sea bed due to its own weight, possibly with additional ballast and the weight of the plant, equipment and stored fluid.
• the plant unit 11 is provided with ice breaking buffering structures 26 arranged in the region of the water line 25 on two opposite sides of a unit 1 1.
• the ice breaking buffering structure 26 may have an inclined upper and/or lower surface, configured for breaking up the ice and possibly securing an oblique impact between the broken ice and the vertical walls of the unit 1 1 .
• the free end of the ice breaking buffering structure 26 may be positioned slightly below the sea level.
• the unit 1 1 may also be provided with storage tanks for hydrocarbons, for example insulated storage tanks for LNG.
• the unit shown is also provided with a mooring point 20 arranged above the highest expected tidal height and below the top surface 27 of the unit, thus enabling a negative lead of an angle a' for the mooring hawsers (not shown) extending between vessel 14 and the plant unit 1 1.
• a mooring point 20 arranged above the highest expected tidal height and below the top surface 27 of the unit, thus enabling a negative lead of an angle a' for the mooring hawsers (not shown) extending between vessel 14 and the plant unit 1 1.
• said indicated mooring point may be any one of the mooring point required for safely mooring the vessel 14 to the plant.
• Figure 7 shows schematically a side view of a plant unit 1 1 according to the present invention, also indicated schematically a vessel 14 moored to the unit 1 1 , the Figure indicating the vertical orientation and direction of any one of the mooring hawser 15, 15', 18, 18' 21 , 21 '.
• the vessel 14 moored to the plant is indicated by a cross sectional view through the vessel 14.
• the height of the plant unit 1 1 may be so high that the hull of the vessel 14 more or less is shielded by unit 1 1 .
• Figure 8 shows schematically another configuration of the units 1 1 forming the plant. According to this configuration, the configuration of the units shown in Figure 2 is used. In addition, another unit 1 1 ' is added, the orientation being such that a shelter is established, preventing waves coming from a direction more or less parallel with the longitudinal direction of the three units 1 1 . It should be appreciated that the mooring lines, mooring points etc. is not shown. Such gear and equipment may be a duplicate of the ones shown in the other Figures. The Figure also indicates as an option an end of a pier 28 for access from ashore to the plant. The bridges between the pier and the plant unit 1 and between the various plant units 1 1 are not shown.
• the units 1 1 , 1 1 ' may be constructed at the harbour site 10, build at a remote construction site, towed and placed on the ocean bottom 12.
• the units 1 1 ,1 1 ' and the harbour site 10 are formed according to the local environmental conditions such as depth of water, type of ocean bottom, wave formations and where possible, negative effects from environmental forces such as waves, wind and current are minimised.
• the units 1 1 ,1 1 ' are placed on the ocean bottom in a desired configuration such that the desired loading conditions for the LNG ship are the best possible according to operative and safety considerations.
• the shape of the units 1 , 1 1 ' into an installed harbour site 10 is adapted to the local wave spectrum at the installation location so that waves that lead to movements of the ships during operations at the harbour site 10 are dampened as much as possible, while other waves are permitted to pass the harbour site 0.
• Adjustments to the waves can be achieved by setting the units 1 1 , 1 1 ' at a distance from each other on the ocean bottom. Small waves will be dampened by short distances and big waves will be dampened by large distances, respectively. Calculations have shown that it is particularly favourable to use a distance between the units 9 that approximately correspond to 1 ⁇ 4-1 ⁇ 2 times the wavelength of the waves that one wishes to dampen.
• a statistical distribution such as significant values of said wave spectrum, one can determine which type of wave frequencies and wave heights is wanted, in the main, to dampen. With significant values, it is meant the mean value of the third of the waves that is highest over a 20 minute period (for measuring the wave height).
• Other forms of statistical distribution can also be used and as this is known for a person skilled in the art they are not described further herein.
• the size of the base of the unit can be adapted to achieve the best possible wave dampening. It is advantageous that the upper part of the base is placed below the ocean surface itself, so that a form of a bank is created between the upper part of the base and the ocean surface. Calculations have shown that it is particularly advantageous to place the unit(s) 1 1 ,11 ' around half a wave height below the ocean surface in relation to wave height and associated wavelength one wishes to dampen. An example of this will be that if the wave height one wishes to dampen is 8 metres, then it is advantageous to place the top of the base approximately 4 metres below the sea level 25. To achieve such a distance between the sea level 25 and base, the size of the base is adjusted accordingly.
• the appearance of the base also has an influence on the dampening of the waves around the harbour site 10. It is an advantage that the base has a quadratic form in the horizontal plane, where it will, in such an example, only be necessary to carry out changes in the height to adapt the base in relation to the ocean surface. However, it shall be mentioned that other appearances of the base can be applied and they are described in more detail later in the description.
• the base of the unitsl 1.1 1 ' can also be formed in a number of ways dependent on aims, needs and wishes.
• the units 1 1 ,1 1 ' may have a relatively large and voluminous base (not shown) where these bases are placed relatively near each other.
• a harbour site 10 functioning as a wave dampener or wave breaker for the desired parts of the wave spectrum, for example, waves with periods of less than 10 seconds.
• the longer period swells will be able to slip through the harbour site 10 if this is desired.
• the units 1 1 ,1 1' may be formed with more inclined sidewalls and be placed closer to each other.
• the units 11 ,1 1 ' and the bases can be formed with rougher or perforated surfaces, sharp edges, protrusions, etc., if one wishes increased interaction with, and further dampening of, the waves (not shown).
• the units 1 1 ,11 ' do not need to lie in a straight line in relation to each other, but can be placed at a desired angle in relation to each other as shown in figure 5. This is advantageous if one wishes to avoid negative effects of, for example, swells that come from varying directions.
• swells that come from varying directions.
• the strong waves or swells come in the direction alongside of the ship.
• the response of the LNG ship 14 to waves in the direction alongside the ship thereby comes in the form of considerably lower rolling and stamping movements and reduced midship dynamics.

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