Offshore vessel for production and storage of petroleum products

Abstract

The present invention relates to a longitudinal vessel for production and/or storage of hydrocarbons. The vessel comprises a hull which extends along a longitudinal axis between a bow and a stern of the vessel. The hull is provided with a longitudinal well for a multiple riser arrangement. The longitudinal well is located on or adjacent to a centerline along the longitudinal axis of the hull and extends vertically through the hull.

Description

TECHNICAL FIELD

The present invention generally relates to offshore vessels used for the production and/or storage of petroleum products. More specifically, the present invention relates to offshore vessels for connection of a plurality of submarine risers, such as a Floating Production, Storage and Offloading vessel (FPSO).

BACKGROUND AND PRIOR ART

A Floating Production, Storage and Offloading (FPSO) system is a floating facility above or close to an offshore oil and/or gas field to receive, process, store and export hydrocarbons.

The system consists of a floater, which may either be a purpose built vessel or a converted tanker that is moored at a selected site. The cargo capacity of the vessel is used as buffer storage for the oil produced. The process facilities (topsides) and accommodations are installed on the floater. The mooring configuration may be of a spread mooring type or a single point mooring system, generally a turret.

The high pressure mixture of produced fluids from the well is delivered to the process facilities on the deck of the vessel, where the oil, gas and water are separated. The water is reinjected in the reservoir or discharged overboard after treatment eliminating hydrocarbons. The stabilized crude oil is stored in the cargo tanks of the vessel and subsequently transferred into shuttle vessels, either direct, via a buoy, or by laying side by side/in tandem to the FPSO vessel.

The gas may be used for enhancing the liquid production through gas lift and/or for energy production onboard the vessel. The remainder of the gas may be compressed and transported by pipeline or reinjected into the reservoir.

There are three main types of mooring systems for FPSO vessels:

• • spread mooring systems, wherein the FPSO vessel is moored in a fixed position,
  • single point mooring (SPM) systems, wherein the FPSO vessel weathervanes around a fixed point, and
  • Dynamic Positioning (DP) systems which do not require anchor wires or chains or piled/seabed anchors. These systems are the most accurate for station keeping, but the most expensive to operate.

WO 2015/038003 A1 discloses a platform arranged to float in water. The platform comprises a hull with a main portion which is substantially symmetrical about a center axis. The upper end of the platform is supporting a deck and the lower end of the platform, situated below a nominal water line, is provided with a stabilizing element which protrudes from the main portion.

WO 2012/104308 A1 discloses a platform for production and storage of hydrocarbons. The substantially circular hull of the vessel is configured to allow suspension of risers on at least one frame arranged in a moonpool in the center of the hull. The frame is placed so that connection of risers may be performed above the water when the platform has its minimum draft. The moonpool may comprise a conical form at its lower end allowing static and dynamic angular deflections of the risers. The moonpool extends above the main deck wherein the extended vertical moonpool is narrowed down for increasing the space availability on the deck. The hull may further be equipped with a protrusion to reduce stamping and rolling movements.

WO 98/30439 A1 discloses a drilling and production vessel comprising one or more wells extending through the hull for inward and outward flow of water from below. The vessel comprises a number of lips as water flow delaying elements.

The above mentioned prior art does not provide an optimized longitudinal vessel comprising a protective moonpool/well. Further, prior art does not provide an optimized area configuration for the risers, access to the risers, suspension for the risers, or connection or disconnection of the risers.

Consequently, the object of the present invention is to provide a longitudinal vessel for production and/or storing of hydrocarbons arranged to float in a body of water, where the vessel provides an optimal protective well, as well as an optimized solution for a multiple riser arrangement.

A second object of the present invention is to provide a vessel with optimized solutions for a vessel's motion characteristics, for example a longitudinal vessel having reduced motions in heave, roll and pitch. Such motion reduction will reduce mooring system requirements and/or renders possible use of free-hanging rigid risers at deep depths instead of traditional flexible risers. Deep depths may be depths exceeding 1000 meters, for example deeper than 2000 meters

A third object of the present invention is to provide a longitudinal vessel providing optimized usage of a vessel's deck area, for example for installation of equipment/tools used during production of oil and gas.

A fourth object of the present invention is to provide a longitudinal vessel with a large storage capacity for produced oil and/or gas compared to the vessels total size, in view of the prior art.

A fifth object of the present invention is to provide a longitudinal vessel that provides an increased safety in view of the prior art in case of incidences such as gas leakage.

A sixth object of the present invention is to provide a longitudinal vessel able to withstand severe forces from waves without leading to significant hull deflection/deformation.

A seventh object of the present invention is to provide a longitudinal vessel having the possibility of combining drilling and production of oil and gas.

These objects are obtained according to the present invention represented by the features disclosed in the following independent claim, with additional features of the invention set forth in the dependent claims and the description below.

SUMMARY OF THE INVENTION

The above mentioned objects are obtained by the invention as set forth and characterized in the main claims, while the dependent claims describe further embodiments of the invention.

In particular, the present invention relates to a longitudinal vessel for production and/or storing of hydrocarbons arranged to float in a body of water. The vessel may also be combined with drilling and/or utilized for cooling and storage of gas.

The longitudinal vessel comprises a hull that extends between a bow and a stern of the vessel along a longitudinal axis of the vessel, where the hull is provided with at least one longitudinal well for a riser arrangement comprising an upper section and a lower section, the at least one longitudinal well being arranged on or adjacent to a centerline along the longitudinal axis of the vessel and extending vertically through the hull. Thus the bottom of the well is open to the sea.

The hull of the present invention is hereinafter defined as the area of the longitudinal vessel situated below the deck area of the vessel.

When fully assembled and in use, the longitudinal well(s) of the inventive vessel may accommodates a riser arrangement comprising a plurality of risers arranged successively along the longitudinal axis of the well(s).

The longitudinal well(s) may be arranged on or close to the centerline, following the centerline along the longitudinal axis of the vessel. In case of a plurality of longitudinal wells, the wells may be arranged successively on the center line. Alternatively, or in addition, the longitudinal well(s) may be arranged adjacent to the centerline, following the center line along the longitudinal axis of the vessel. For example, two longitudinal wells may be arranged adjacent to each other with the center line as a mirror line.

The longitudinal well(s) may advantageously extend over at least 20% of a length of the hull and advantageously up to 10% of a maximum width of the hull. In case of a plurality of wells, the wells may advantageously have the same length and/or width. However, it should be understood that the longitudinal wells may also be provided with different lengths and/or widths.

The longitudinal vessel may advantageously have a length/width ratio of less than 2, more preferably a length/width ratio of less than 1.75, more preferably equal or less than 1.5. Compared to longer vessels, a length/width ratio of less than 2 reduces the effect that the waves have on the movements on the vessel.

In order to prevent undesired motions of the vessel, the vessel may in one embodiment comprise at least one suppressing element protruding outwards from an area of the hull located below the vessel's maximum draught, typically several meters outwards from the vessel. Furthermore, the at least one suppressing element may be provided fully around a circumference of the hull, or may alternatively extend partially around the circumference of the hull. As a person skilled in the art will recognize, the at least one suppressing element may be provided with or without local recesses. The suppressing element reduces the movement of the vessel due to waves, reducing especially the heaving, stamping, and rolling of the vessel.

Due to less movement of the vessel the mooring arrangement, which typically comprises a plurality of mooring lines/wires, can be operated satisfactory with a reduced number of mooring lines compared to the prior art, thus reducing the cost of the mooring arrangement.

In one embodiment of the present invention, the hull comprises double sides and possibly a double bottom. Such hull configurations may be used as ballast tanks for protection of the loading tanks and/or storage tanks situated inside the hull.

A first track arrangement for at least one winch may advantageously be arranged in the upper section of the longitudinal well(s). The first track arrangement may be arranged over at least a part of the length of the longitudinal well, preferably over at least 20% of the length of the longitudinal well(s), more preferably over at least 50% of the length of the longitudinal well(s), most preferably over the entire length of the longitudinal well(s). During assembly and use, the multiple risers are placed underneath the first track arrangement.

In one advantageous embodiment of the invention, the longitudinal well(s) may comprise a plurality of hang-off structures or support structures for connection and/or disconnection of risers. Through this arrangement the at least one winch can be moved along the longitudinal well(s) in order to handle the risers when the risers are to be connected and/or disconnected from the hang-off structures. The support structure(s) may be located at the upper section of the well, underneath the winch(es) and first track arrangement, providing a configuration most suitable for flexible risers.

In another advantageous embodiment of the invention the upper section may be isolated from the adjacent storage and/or loading tanks by cofferdams.

In yet another advantageous embodiment of the invention the support structure is located at the upper section of the well(s), and the lower section of the well(s) comprises a plurality of guide pipes. These guide pipes are configured to guide risers vertically through the well(s) and may comprise riser bending restrictors, or connections for riser bending restrictors, at their lower ends.

In yet another advantageous embodiment of the invention, the support structure(s) is/are located at the lower section of the well, thereby providing a configuration most suitable for rigid risers such as steel catenary risers (SCR). However, the configuration may accommodate flexible risers as well.

In yet another advantageous embodiment of the invention, at least one ventilation duct is connected to an area of the longitudinal well(s), preferably in the upper section of the longitudinal well(s) for ventilating the well(s). The at least one ventilation duct may further comprise at least one valve for controlling the ventilation of the well(s).

In yet another advantageous embodiment of the invention, the lower part of the lower section of the well(s) is provided with at least one support structure securely suspending the risers during use. The support structure may comprise a locking device enabling locking of the risers.

In yet another advantageous embodiment of the invention, the longitudinal well(s) may be provided with an enlarged area underneath the support structure(s). The enlarged area can be gradually extending in its width towards the bottom of the well(s). Such a configuration is especially advantageous during use of rigid risers, such as the above mentioned SCR-risers or any other risers having stiffness in a similar range. The reason is that the risk of riser fracture/damage caused by movement of the vessel is decreased since the enlarged area provides space for the risers to swing/deflect away from the vertical axis. It should be understood by a person skilled in the art that any configurations suitable for rigid risers will also be applicable for flexible risers. However, the opposite case may not necessarily be the case.

In yet another advantageous embodiment of the invention, the lower part of the lower section of the well(s) is provided with a support structure. A platform may be used to guide the riser into the locking device of the support structure. The guiding process involves guiding the riser past the support structure and into the locking device in the support structure. The platform may in this embodiment comprise a guiding arrangement to move the riser sideways within the longitudinal well(s). Furthermore, the platform may be arranged on a second track arrangement extending over at least a part of the length of the respective longitudinal well, preferably over at least 20% of the length of the respective longitudinal well, more preferably over the entire length of the respective longitudinal well. The platform, the guiding arrangement and the second track arrangement is positioned above the support structure.

The well(s) and the risers should be positioned in areas where the movements of the vessel are smallest. The well zone(s)/area(s) in which the risers are connected or disconnected is/are preferably protected from external weather conditions. Hence, the equipment required for pulling, connecting and disconnecting the risers is situated in the protected zone(s), thus requiring less maintenance and providing higher security. The riser arrangement of the present invention further allows connection and disconnection of the risers to be performed in a water-free and dry environment.

Due to ventilation ducts, the present invention enables ventilation of possible gas leakages or the like to be evacuated from the main deck and/or the processing area(s). By installing valves on the ventilation ducts control of potential gas leakages is ensured, thereby reducing significantly the risk of fire and explosions.

Furthermore, a robust construction of the part of the hull surrounding the well contributes to a hull damage control in the unlikely event of gas explosion and/or fire.

The combination of reduced movement, large deck area, large load capacity and a large storage volume are all important characteristics for FPSOs, storage vessels and units for floating production, cooling and storage of natural gas (FLNG). The combination of a longitudinal vessel with length/width ratio of less than two and the riser arrangement within longitudinal well(s) situated on or adjacent to a center line along the longitudinal axes of the hull contributes to these characteristics.

The particular design of the hull of the vessel enables the use of SCR risers. This is a great advantage over use of traditional flexible risers since the latter solution is in general more expensive, gives a more complex installation and requires more maintenance compared to a solution with rigid risers. Furthermore, flexible risers are more sensitive to irregularities during operation and have a shorter lifetime than rigid risers. Since repair of a flexible riser has proved difficult, they are often exchanged with new ones, thereby increasing cost further.

By connecting the risers inside wells, protected from external weather conditions, an efficient arrangement for connection and operation is established, enabling connection/disconnection of the risers in a dry environment.

In the following description, numerous specific details are introduced to provide a thorough understanding of embodiments of the claimed longitudinal vessel. One skilled in the relevant art, however, will recognize that these embodiments can be practiced without one or more of the specific details, or with other components, systems, etc. In other instances, well-known structures or operations are not shown, or are not described in detail, to avoid obscuring aspects of the disclosed embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the attached drawings, wherein:

FIG. 1 is a side view of a vessel according to a first embodiment of the present invention,

FIG. 2 is a top view of the vessel according to FIG. 1,

FIG. 3 is a longitudinal cross-section through the vessel according to FIG. 1,

FIG. 4 is a traverse cross-section through the vessel according to FIGS. 1 and 3,

FIG. 5 is a longitudinal cross-section through a vessel according to a second embodiment of the present invention,

FIG. 6 is a traverse cross-section through the vessel according to FIG. 5,

FIG. 7 shows in greater detail a riser arrangement according to the second embodiment as shown in FIGS. 5 and 6.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a first embodiment of a longitudinal vessel 1 according to the present invention. The vessel 1 comprises a hull 2, a deck structure 5, the latter comprising a main deck D, a processing deck P, and living quarters A. Below the vessel's 1 maximum draught (w(l)), the hull 2 is provided with a suppressing element 6 protruding outwards from the hull 2.

The suppressing element 6 inter alia reduces the stamping, rolling and heaving of the vessel 1 caused by external forces such as waves. The suppressing element 6 is thus designed to influence the amplitude and frequency of the vessel's movements such that it does not coincide with the amplitude and frequency of the external forces. The coupling effect between the inertia forces, dampening forces and buoyancy force influence the movements of the vessel as well. The combination of change in amplitude and frequency of the movements and the effects from the inertia, dampening and buoyancy forces results in a significant reduction in vessel movements.

A total of twelve risers 9 are shown supported from within the vessel 1. In FIG. 1 only part of the risers 9 that are suspended from the bottom of the well 7 of the vessel 1 are seen. The number of risers shown is for example only. The present invention may allow use of more than 60 risers if deemed necessary.

FIG. 2 illustrates a top view of the vessel 1 according to FIG. 1. The vessel comprises a plurality of storage and/or loading tanks 100, and a plurality of fuel tanks 102 and a pump room 103 located at the fore of the vessel 1. Alternatively the pump room and fuel tanks may be arranged in the aft part of the vessel. The vessel 1 is further provided with protective ballast tanks 101 arranged along the sides of the vessel 1, adjacent to the storage and/or loading tanks 100, fuel tanks 102 and pump room 103. Protection of the storage and/or loading tanks 100, fuel tanks 102 and pump room 103 may further be ensured by a double bottom, which may also be used as a ballast tank 101. Such a tank arrangement, combined with the low width/length ratio of the vessel 1 (less than two) results in high vessel stability. Such a high stability allows arrangement of large process apparatus/systems, either for using the vessel 1 as a FPSO, or as a FLNG. If using the vessel 1 for natural gas, the storage and/or loading tanks should be separated from tanks for fluid cooled natural gas.

FIG. 2 also shows a mooring arrangement M comprising a plurality of mooring lines arranged at the fore and on aft corners of the vessel 1. Such a spread mooring system ensures a fixed, non-rotatable vessel position during hydrocarbon production.

The vessel 1 is further provided with a longitudinal well 7 for a multiple riser arrangement. The longitudinal well 7 is in FIG. 2 shown located on and along a centerline of the vessel 1.

FIG. 3 shows a longitudinal cross-section of the vessel. The longitudinal well 7 is seen extending vertically through the vessel's hull 2. The well 7 may be divided into an upper section 7A and a lower section 7B, where the upper section 7A includes a hang-off support structure 8 for a plurality of risers 9. This arrangement is particularly applicable to flexible risers since rigid risers such as SCR risers have a tendency to break when guided through the lower section 7B of the well, or they may break during use since the width of the well 7 only allows small movements of the risers.

The upper section 7A is connected to two ventilation ducts 13. Possible gas leakage or the like in the upper section 7A may thus be effectively removed, avoiding any exposures to the main deck D and/or the processing deck P. These ventilation ducts 13 may be arranged horizontally and/or vertically, preferably at each end of the upper section 7A. The ventilation ducts 13 may further comprise valves (not shown), enabling controlled opening/closing and thereby full gas control of the whole well 7.

The well 7 and the ventilation ducts 13 may comprise gas detectors (not shown) which enables fast detection of any gas leakage, and therefore also fast closing and sealing of the upper section 7A. By a rapid closing of the valves within the ducts 13, any potential explosion caused by gas leakage may be completely isolated inside a well 7 having surrounding walls configured/manufactured to sustain such explosions without severe damage. One or more winches 11 are moving horizontally along the upper section 7A on an upper track arrangement 12. The winches 11 are used for handling of the risers 9, i.e. to lift or lower a single riser 9 during connection or disconnection to/from the support structure 8.

A plurality of guide pipes 10A, one for each riser 9, is arranged at a distance from each other along the longitudinal well 7. One end of each guide pipe 10A is provided with a connection 10B for riser bending restrictors 10C. The water level w(l) is shown for a loaded vessel 1 at it's maximum draft. Hence, the support structure 8 in FIG. 3 is arranged above the water level w(l) enabling connection and disconnection in a dry environment.

FIG. 4 shows a transverse cross-section of the vessel 1 in FIG. 3. The upper section 7A, comprising the hang-off support structure 8 for a plurality of risers 9, is seen isolated from the adjacent storage and/or loading tanks 100 through cofferdams 7C, increasing operation safety further.

As in FIG. 3, FIG. 4 illustrates a riser arrangement most suitable for flexible risers 9. Through the use of the winch 11, the riser 9 may be lifted up through the guide pipe 10A and connected to the support structure 8. The riser bending restrictor 10C is further connected to the bending restrictor connecter 10B arranged at the lower end of the guide pipe 10A. In this first embodiment the upper section 7A has a width B that is larger than a width b of the lower section 7B in order to provide space for required equipment in the upper section 7A when the lower section 7B comprises guiding pipes.

The area adjacent to the guide pipes 10A is in the embodiment shown in FIG. 4 used as ballast tanks 101 and addition to the ballast tank 101 formed by the double bottom of the hull 2.

FIG. 5 shows a longitudinal cross section of a second embodiment of the vessel 1. As in the first embodiment the vessel 1 is provided with a longitudinal well 7 for a multiple riser arrangement, where the longitudinal well 7 extends vertically through the vessel's hull 2. The upper section 7A of the longitudinal well 7 is further connected to two ventilation ducts 13 so that a possible gas leakage or the like in the upper area of the longitudinal well 7 can be vented, and thereby effectively removed from the main deck D and/or the processing deck P. The ventilation duct 13 may comprise valves (not shown), and the ventilation duct 13 and/or the well 7 may further comprise gas detectors (not shown). In both FIGS. 3 and 5 the ventilation duct 13 in the bow end of the well 7 is arranged horizontally, while the ventilation duct 13 at the aft end of the well 7 is arranged vertically. One or more winches 11 (where only one is shown in FIG. 5) is arranged in the upper section 7A of the longitudinal well 7, and configured to move horizontally along the longitudinal well 7 on an upper track arrangement 12. The winch(es) 11 is/are used for handling of the risers 9, i.e. to lift or lower a single riser 9 when the single riser 9 is to be connected/disconnected to/from a support structure 8 constructed for suspending a plurality of risers 9.

However, in contrast to the first embodiment illustrated in FIGS. 2-4, the support structure 8 is arranged at the lower area 7B′ of the lower section 7B of the well 7.

A winch wire 11′ suspended from the winch 11 is guided through a guiding arrangement 16 situated on a platform 14, the latter being arranged on a lower track arrangement 18, thus enabling horizontal movement along the lower section 7B of the longitudinal well 7.

In FIG. 5, the water level w(u) for a vessel 1 at its minimum draft is indicated. At this water level the support structure 8 is located above the water level w(u) and the connection of the riser may thus occur in a water-free and dry environment.

FIG. 6 shows a transverse cross-section of the vessel 1 according to FIG. 5. The longitudinal well 7 extends from the deck 5 to a bottom 20 of the hull 2. A lower part of the longitudinal well 7 has an enlarged area 17 where the width of the enlarged area gradually increases towards the bottom of the well 7. The purpose of the enlarged area 17 is to reduce, or remove, the risk of fracturing/damaging & breaking rigid risers during connection, disconnection and production.

FIG. 7 shows in greater details the lower area 7B′ of the lower section 7B of the longitudinal well 7. A wire 11′ from the winch 11 is seen connected to the flexible coupling element 19 of a riser 9. The winch 11 may thus lift the riser 9 into a desired vertical position within the well in order to hang off the riser 9 in the support structure 8. The support structure 8 is in FIG. 7 seen to include a locking device 15 in form of a recess suitable for receiving the flexible coupling element 19. The support structure 8 displays an opening (not shown) for pulling the riser 9 with the flexible coupling element 19 through and above the support structure 8. After lifting the riser 9 and the flexible coupling element 19 passed and above the support structure 8, the guiding arrangement 16 positions the riser 9 directly above the locking device/recess 15 and the winch 11 lowers the coupling element 19 into the locking device.

The configuration of the locking device 15 of the support structure 8 and the enlarged area 17 of the well 7 renders the risers 9 to have a pendulum movement without breaking.

Since the well 7 is open to the sea at the bottom 20 the lower section 7B can be partly or fully filled with water depending on the vessel's loading condition.

In the preceding description, various aspects of the vessel according to the invention have been described with reference to the illustrative embodiment. For purposes of explanation, specific numbers, systems and configurations were set forth in order to provide a thorough understanding of the vessel and its workings. However, this description is not intended to be construed in a limiting sense. Various modifications and variations of the illustrative embodiment, as well as other embodiments of the vessel, which are apparent to persons skilled in the art to which the disclosed subject matter pertains, are deemed to lie within the scope of the present invention.

LIST OF REFERENCE NUMERALS/LETTERS

• 1 vessel
• 2 hull
• 3 bow
• 4 stern
• 5 deck/deck structure
• 6 suppressing element
• 7 well
• 7A upper section of the well
• 7B lower section of the well
• 7B′ lower area of the lower section 7B.
• 7C cofferdam
• 8 support structure
• 9 riser
• 10A guide pipes
• 10B connection
• 10C riser bending restrictor
• 11 winch
• 11′ wire
• 12 first/upper track arrangement
• 13 ventilation duct
• 14 platform
• 15 locking device
• 16 guiding arrangement
• 17 lower part of the well
• 18 second/lower track arrangement
• 19 flexible coupling element
• 20 bottom of the hull
• 100 storage tanks/loading tanks
• 101 ballast tanks
• 102 fuel tanks
• 103 pump room
• A living quarters
• D main deck
• M mooring arrangement
• P processing deck
• w(l) water level of the vessel at its maximum draft
• w(u) water level of the vessel at its minimum draft

Claims

1-20. (canceled)

21. A longitudinal vessel for production and/or storing of hydrocarbons arranged to float in a body of water,

the vessel comprising a hull extending between a bow and a stern along the longitudinal axis, wherein the hull is provided with at least one longitudinal well for a multiple riser arrangement comprising an upper section and a lower section, the longitudinal well being located on or adjacent to a centerline along the longitudinal axis of the hull and extending vertically through the hull.

22. The vessel according to claim 21, wherein the at least one longitudinal well extends over at least 20% of a length of the hull.

23. The vessel according to any one of claims 21-22, wherein each of the at least one longitudinal well extends maximum 10% of a maximum width of the hull.

24. The vessel according to claim 21, wherein the upper section comprises at least one winch, the at least one winch being movable along at least a part of a length of the longitudinal well through a first track arrangement.

25. The vessel according to claim 21, wherein the upper section comprises at least one support structure for the connection of risers.

26. The vessel according to claim 21, wherein the lower section comprises a plurality of guide-pipes, each guide-pipe being configured to guide a riser vertically through the well.

27. The vessel according to claim 21, wherein the lower section comprises at least one support structure for the connection of risers.

28. The vessel according to claim 21, wherein the lower section of the well further comprises at least one platform for handling risers situated above the at least one support structure, wherein the at least one platform is movable horizontally along at least a part of a length of the longitudinal well, through a second track arrangement.

29. A spread moored vessel for production and/or storage of hydrocarbons, the vessel comprising

a laterally extending main deck,

a mooring arrangement for mooring the vessel to a seabed when the vessel is floating in a body of water,

a longitudinal hull comprising a bow, a midbody, a stern and a protrusion protruding out from the longitudinal hull, below the vessel's maximum draft, for reducing movement of the vessel due to waves,

wherein

the ratio between a maximum length and a maximum breadth of the longitudinal hull, at the vessel's maximum draft, is less than 2.

30. The vessel according to claim 29, wherein the ratio between the maximum length and the maximum breadth of the longitudinal hull, at the vessel's maximum draft, is less than 1.5.

31. The vessel according to claim 29 or 30, wherein the protrusion protrudes out from the bow, the midbody and the stern, below the vessel's maximum draft.

32. The vessel according to claim 29, wherein the protrusion protrudes laterally from a lowermost part of the hull.

33. The vessel according to claim 29, wherein the midbody comprises a port side portion and a starboard side portion, where the longitudinal length of the midbody are flat and oriented parallel to a center plane of the hull, the center plane being the plane intersecting the hull midway between the port and starboard side portions and aligned perpendicular to the laterally extending main deck.

34. The vessel according to claim 29, wherein the lateral cross section of the midbody and the stern at the vessel's maximum draft has a rectangular shape.

35. The vessel according to claim 29, wherein the transition region between the bow and the midbody forms abrupt change of angle at the vessel's maximum draft, relative to a center plane, the center plane being the plane intersecting the hull midway between the port and starboard side portions and aligned perpendicular to the laterally extending main deck.

36. The vessel according to claim 29, wherein the mooring arrangement comprising a plurality of mooring lines, wherein

at least one mooring line is moorable from a location at or near the center of the bow relative to the hull's breadth,

at least one mooring line is moorable from a location adjacent the stern at the port hull side and

at least one mooring line is moorable from a location adjacent the stern at the starboard hull side.

37. The vessel according to claim 36, wherein the protrusion displays recesses at the lateral locations of the plurality of mooring lines when the vessel is moored to the seabed.

38. The vessel according to claim 29, wherein

the longitudinal length of the vessel is separated into storage tanks, ballast tanks and fuel tanks.

39. The vessel according to claim 38, wherein the ballast tanks are situated adjacent to the storage tanks.

40. The vessel according to claim 37, wherein the fuel tanks are located within the bow.

41. The vessel according to claim 29, wherein the longitudinal hull comprises at least two walls having a space therebetween, into which at least one ballast tank is located.

42. The vessel according to claim 29, wherein the projected lateral surface area of the hull at the vertical position of the main deck is larger than the projected lateral surface area of the hull at the vertical position of the vessel's maximum draft.

43. The vessel according to claim 41 or 42, wherein the onset of increase of the projected lateral surface area of the hull from the vertical position of the vessel's maximum draft to the vertical position of the main deck commences at or above the vessel's maximum draft.

44. The vessel according to claim 42, wherein the increase of the projected lateral surface area of the hull from the vertical position of the vessel's maximum draft to the vertical position of the main deck is constant.