Roll-on / roll-off ship equipped with tank for storing liquefied gas

Abstract

To provide a roll-on / roll-off ship, in which a tank for storing liquefied fuel gas is arranged and a size of the tank is determined.SOLUTION: A roll-on / roll-off ship (1) according to the present invention is equipped with: a ship hull (3) comprising a bottom part with double walls; a plurality of intermediate decks including a main cargo-handling deck; at least one cargo handling ramp; a pillar (11) with load bearing extending in a height direction; an engine room; a sealed / insulated membrane tank (2) for storing liquified fuel gas, which is arranged below the main cargo-handling deck to oppose to an inner wall of a bottom part; and cofferdam walls comprising inner skins and outer skins. Each tank wall in a longitudinal direction is fixed to the inner skin of either of the cofferdam walls in the longitudinal direction, and at least one pillar of a first row or at least one pillar of a second row is arranged at one of the cofferdam walls in the longitudinal direction.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to the field of roll-on / roll-off (RO / RO) ships for transporting self-propelled or towed wheeled cargo such as vehicles that are loaded using one or more access ramps. The present invention relates more particularly to the field of roll-on / roll-off vessels comprising a sealed insulated membrane tank for storing liquefied fuel gas at low temperatures. The tank is designed to receive the liquefied gas that serves as fuel for the propulsion of the roll-on / roll-off vessel.

[0002] In one embodiment, the liquefied gas is LNG, a mixture with high methane content stored at atmospheric pressure and a temperature of about −162° C. Other liquefied fuel gases such as ethane, propane, butane, liquefied petroleum gas (LPG) or ethylene may also be considered. [Background technology]

[0003] Roll-on / roll-off vessels for transporting self-propelled or towed wheeled cargo are known in the prior art.

[0004] These vessels have a hull with a bottom and an outer deck spaced apart in height from the bottom, several intermediate decks, in particular a main loading deck and one or more storage decks, arranged between the bottom of the hull and the outer deck, a loading ramp connected to the main loading deck, and load-bearing columns extending in height such that a first end is fixed to the bottom and a second end is fixed, for example, to the outer deck. The load-bearing columns are generally arranged in several columns rows in the longitudinal direction of the vessel. The main loading deck therefore corresponds to a fixed deck onto which the cargo is brought via one or more loading ramps for loading and unloading the cargo.

[0005] These load-bearing columns play a vital role in the rigidity of the vessel's hull because, unlike conventional ships, roll-on / roll-off vessels do not have any bulkheads dividing the inside of the hull, while at the same time ensuring that the hull is rigid. This lack of bulkheads is necessary to allow self-propelled or towed wheeled cargo to travel on the intermediate deck.

[0006] The fuels mainly used by this type of vessel consist of petroleum products such as heavy fuel oil (HFO), whose boiling point is well above ambient temperature, for example between 120 and 600°C. Prior art vessels carry one or more tanks for storing such fuels inside the hull. These tanks do not require any special equipment, since their contents can be stored in liquid form at ambient temperature. Such tanks therefore do not pose any problem as to where they are located within the vessel, being located in areas of the vessel left free, for example at the side edges.

[0007] However, due to increasingly stringent regulations regarding greenhouse gas emissions, especially for maritime transport, these roll-on / roll-off vessels will need to change their propulsion technology.

[0008] Compared to conventional heavy fuel oil, burning LNG results in a 100% reduction in sulfur oxides and particulate matter, an 80% reduction in nitrogen oxides, and a 20% reduction in CO2. Currently, LNG is the most carbon-efficient fuel from a technical, operational, and environmental standpoint. Summary of the Invention

[0009] The idea underlying the present invention is to arrange and dimension tanks for storing liquefied fuel gas on a roll-on / roll-off vessel.

[0010] According to one embodiment, the present invention provides a roll-on / roll-off vessel, comprising: - a hull with a double-walled bottom and an outer deck spaced heightwise from the bottom, the double-walled bottom comprising an inner wall and an outer wall; - a plurality of intermediate decks disposed between the bottom of the hull and the outer deck, the intermediate decks including a main cargo handling deck and one or more storage decks; - load-bearing columns, each having a lower end fixed to the bottom of the hull and extending in height through the intermediate deck for support, the load-bearing columns being arranged in at least a first row of columns and a second row of columns, the load-bearing columns of the same row being spaced apart from each other in the longitudinal direction of the vessel; - a machinery room located within the hull and including a propulsion system; - a sealed, insulated tank for storing liquefied fuel gas and supplying the fuel gas to a propulsion system, the tank having two longitudinal walls spaced apart laterally, the transverse direction being perpendicular to the longitudinal and height directions of the ship; a cofferdam wall comprising two longitudinal cofferdam walls, each cofferdam wall comprising an inner skin and an outer skin spaced apart from the inner skin; Each longitudinal tank wall is fixed to the inner skin of one of the longitudinal cofferdam walls; A roll-on / roll-off vessel is provided, wherein at least one load-bearing pillar of the first row of pillars or the second row of pillars is located in one of the longitudinal cofferdam walls.

[0011] These features allow the location and size of the tank to be adapted to the specific construction of the roll-on / roll-off vessel without requiring major structural changes, including significant structural recalculations. In particular, the location of the tank between the pillars allows the same arrangement of the load-bearing pillars to be maintained. Furthermore, by locating at least one of the pillars adjacent to the tank within the longitudinal cofferdam wall, it is possible to increase or even maximize the lateral dimensions of the tank without changing the arrangement of the pillars within the vessel's hull.

[0012] According to some embodiments, such a vessel may include one or more of the following features:

[0013] According to one embodiment, at least one load-bearing column of the first row of columns is located in one of the longitudinal cofferdam walls and at least one load-bearing column of the second row of columns is located in the other longitudinal cofferdam wall.

[0014] According to one embodiment, the roll-on / roll-off vessel comprises at least one loading ramp connected to the main loading deck.

[0015] According to one embodiment, the sealed, insulated tank is a membrane tank, preferably a tank adapted to store LNG.

[0016] According to one embodiment, the tank has a longitudinal dimension extending in the longitudinal direction, the longitudinal dimension of the tank being adjustable between the machinery room and the front of the vessel depending on the maximum amount of liquefied gas desired.

[0017] According to one embodiment, the main handling deck is fixed and at least one storage deck is height movable to vary the distance between two adjacent intermediate decks for placement of bulky items.

[0018] According to one embodiment, the storage deck, located above or below the main handling deck, is movable in height.

[0019] According to one embodiment, at least one, some, or each load-bearing column extends heightwise through and supports all of the intermediate deck.

[0020] According to one embodiment, at least one, some, or each load-bearing column has an upper end fixed to the outer deck.

[0021] According to one embodiment, the one or more cofferdam walls are made from a metal, for example steel.

[0022] According to one embodiment, the inner and / or outer skins are formed from layers of sheet metal, for example steel.

[0023] According to one embodiment, the load-bearing columns are made from a metal, for example steel.

[0024] According to one embodiment, at least one load-bearing column located in one of the longitudinal cofferdam walls is made from a higher steel grade than the other load-bearing columns.

[0025] Therefore, the temperature within the cofferdam wall adjacent to the tanks can be lower than in other parts of the ship due to its proximity to the tanks for storing liquefied gas. The higher steel grade of this column is better able to offset this temperature difference and retain sufficient mechanical strength.

[0026] The steel grades in this case are those steel grades included in the EN10027-1-2 standard, whose symbol-based steel names are based on non-alloy steels for general use. In this steel name, the first letter refers to the use of the steel, and this letter is followed by a number that represents the yield strength in megapascals. For example, S235 indicates a non-alloy structural steel with a yield strength of 235 MPa. Thus, the term "higher steel grade" in this case means a steel grade with a higher yield strength for the same application. Furthermore, the IGF code ("International Code for the Safety of Ships Using Gas or Other Low Flashpoint Fuels") also uses symbol-based steel names to classify different steel grades. Specifically, in this code, the symbols used for steel grades are letters or pairs of letters, and higher steel grades are designated by the first letter higher in the alphabet, for example steel grade B is higher than steel grade A.

[0027] In another embodiment, at least one load bearing column located in the cofferdam wall may be made from the same steel grade as that of the other load bearing columns.

[0028] According to one embodiment, at least one load-bearing column located in the longitudinal cofferdam wall is made from a steel whose yield strength is equal to or greater than that of the steel of the other load-bearing columns.

[0029] According to one embodiment, at least one load-bearing column of the first row of columns is formed against an inner or outer skin of the longitudinal cofferdam wall.

[0030] By locating the load-bearing columns against the inner skin, it is possible to optimize the lateral dimensions of the tank to the maximum extent without affecting their position, which in this case are subjected to thermal and mechanical stresses that must be taken into account due to their proximity to the tank's structure. Specifically, in this case, the increase in the lateral dimensions is equal to the spacing between the inner and outer skin. On the other hand, if the load-bearing columns are located against the outer skin, they are less exposed to thermal and mechanical stresses arising from the tank, but the increase in the lateral dimensions of the tank is correspondingly reduced.

[0031] According to one embodiment, at least one load-bearing column of the second row of columns is formed against an inner or outer skin of the longitudinal cofferdam wall.

[0032] According to one embodiment, the inner and outer skins of the longitudinal cofferdam walls are provided with laterally projecting stiffeners to stiffen the inner and outer skins.

[0033] The load-bearing columns placed against the inner or outer skin of the longitudinal cofferdam wall also contribute to the stiffness of this skin, and more preferably, the load-bearing columns make it possible to do without some of these reinforcements.

[0034] According to one embodiment, the load-bearing columns have a lateral dimension between 100mm and 400mm, for example 400mm, and the inner and outer skins of the longitudinal cofferdam walls are spaced apart laterally from each other by a distance preferably of at least 900mm, more preferably between 900mm and 1200mm.

[0035] According to one embodiment, the tank is of parallelepiped shape.

[0036] According to one embodiment, the tank comprises an aft tank wall separated from the machinery room by an aft cofferdam wall, a forward tank wall spaced apart in the longitudinal direction of the vessel from the aft tank wall, a bottom tank wall preferably arranged opposite the inner wall of the bottom of the hull, a ceiling tank wall spaced apart in height from the bottom tank wall and two longitudinal tank walls.

[0037] According to one embodiment, the tank is of polyhedral shape, the polyhedron comprising eight or ten faces.

[0038] According to one embodiment, the tank is arranged vertically below the main loading and unloading deck and facing the inner wall of the bottom of the hull.

[0039] Thus, the entire tank is located between the double wall bottom and the main loading deck so that the tank does not interfere with loading and unloading and therefore does not require any modifications to the movement of goods.

[0040] According to one embodiment, the ship includes a tank connection space, a tank valve arranged in the tank connection space, and at least one dome structure, the tank connection space being arranged on a ceiling wall of the tank and below the main loading and unloading deck in the height direction.

[0041] The tank connection space is therefore also located between the double wall bottom and the main loading deck, so that it does not interfere with loading and unloading and therefore does not require any modifications to the movement of goods.

[0042] According to one embodiment, each tank wall comprises a multilayer structure comprising, from the outside to the inside of the tank, a secondary insulating barrier, a secondary sealing membrane arranged opposite the secondary insulating barrier, a primary insulating barrier arranged opposite the secondary sealing membrane and a primary sealing membrane arranged opposite the primary insulating barrier and intended to be in contact with the liquefied gas.

[0043] According to one embodiment, the present invention also provides a transfer system for transferring liquefied fuel gas, comprising a roll-on / roll-off vessel as described above, an insulated pipeline arranged to connect a tank installed within the hull of the roll-on / roll-off vessel to a floating or on-shore storage facility, and a pump for pumping a flow of cryogenic liquid product from the floating or on-shore storage facility via the insulated pipeline to the tank of the roll-on / roll-off vessel.

[0044] According to one embodiment, the present invention also provides a method of loading a roll-on / roll-off vessel as described above, wherein liquefied fuel gas is removed from a floating or onshore storage facility through an insulated pipeline into the tanks of the roll-on / roll-off vessel. [Brief description of the drawings]

[0045] The invention will be better understood and other objects, details, features and advantages will appear more clearly during the following description of some particular embodiments of the invention, given purely by way of non-limiting example with reference to the accompanying drawings, in which:

[0046] [Figure 1] FIG. 1 illustrates a side view of the interior of a roll-on / roll-off vessel according to one embodiment.

[0047] [Diagram 2] FIG. 2 is a view of Detail II of FIG. 1, specifically showing the storage tanks within the hull of the vessel.

[0048] [Diagram 3] FIG. 3 is a partial cross-sectional view along plane III-III of FIG. 1, showing the lateral arrangement of the load-bearing columns relative to the storage tank according to the first embodiment.

[0049] [Figure 4] FIG. 4 is a cross-sectional view along plane IV-IV of FIG. 1, showing the longitudinal arrangement of the load-bearing columns relative to the storage tank according to the first embodiment.

[0050] [Diagram 5] FIG. 5 is a view of detail V of FIG. 4, showing in particular the storage tank and part of the load-bearing column.

[0051] [Figure 6] FIG. 6 shows diagrammatically a roll-on / roll-off vessel including tanks for storing liquefied fuel gas and a terminal for loading the tanks. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0052] A roll-on / roll-off vessel 1 according to various embodiments will now be described with reference to Figures 1 to 6.

[0053] As mentioned above, the roll-on / roll-off vessel 1 has a special structure that allows self-propelled or towed wheeled cargo to move freely between the various decks, and the vessel 1 allows goods to enter and leave the vessel 1 by their own means. This cargo can consist of, for example, automobiles, road transport vehicles and their cargo (tractor trailers, articulated trucks), heavy construction machinery, agricultural equipment such as tractors, or containers attached to handling vehicles such as forklifts or trailers.

[0054] Thus, unlike a normal cargo ship where the cargo is loaded vertically by means of lifting equipment such as a crane, in this case the cargo is loaded / unloaded by moving the ship in and out using a movable loading ramp 10 which connects to a quay at the port or directly to a ramp installed at the quay.

[0055] For this purpose, the roll-on / roll-off vessel 1 - a hull 3 with a double-walled bottom 4 and an outer deck 7 spaced apart from the bottom 4 in the height direction H, - a number of intermediate decks 8, 9 arranged between the bottom 4 of the hull 3 and the outer deck 7, comprising a main loading and unloading deck 8 and one or more storage decks 9; - at least one loading ramp 10 connected to the main loading deck 8; - load-bearing columns 11 extending in height through and supporting the intermediate decks 8, 9; a machinery room 14 located within the hull 3 and equipped with a propulsion system 15; a sealed insulated tank 2 for storing liquefied fuel gas and for supplying the fuel gas to the propulsion system 15.

[0056] The double-walled bottom 4 is made up of an inner wall 5 and an outer wall 6. Thus, the load-bearing columns 11 have their lower ends fixed to the inner wall 5 of the bottom 4 and their upper ends which can be fixed to the outer deck 7.

[0057] The load-bearing columns 11 are arranged in a first row of columns 12 and a second row of columns 13 in the example shown in Figures 5 and 6. The load-bearing columns 11 of one and the same row 12, 13 are spaced apart from each other in the longitudinal direction L of the vessel 1. Furthermore, the two rows 12, 13 are arranged symmetrically in the transverse direction T so as to provide a balanced stiffening of the hull 3 over the entire length of the vessel 1. In other embodiments not shown, the load-bearing columns 11 may be arranged in more than three rows, for example four rows, preferably an even number of rows.

[0058] FIG. 1 shows a roll-on / roll-off vessel 1 according to one design example. Specifically, in this example, the roll-on / roll-off vessel 1 includes 12 intermediate decks, thus including 11 storage decks 9 and one main loading deck 8. The inner wall 5 of the bottom 4 is also used as the storage deck 9 and is generally considered to be the first deck, and each deck is referenced by its number from the lowest deck to the highest deck in the height direction H of the vessel 1. Thus, in this design, the main loading deck 8 is the fifth deck. The intermediate decks 8, 9 and the inner wall 5 are connected to each other by an access ramp 16 or a vertical lift system.

[0059] The structure of the tank 2 and its location and size within the hull 3 of the vessel 1 will now be described in more detail below.

[0060] The tank 2, as can be seen in figure 2, is in this case of parallelepiped shape and comprises several tank walls, namely a rear tank wall 17, a front tank wall 18 opposite the rear tank wall 17, a bottom wall 19, a ceiling wall 20 opposite the bottom wall 19 and two longitudinal walls 21. The bottom wall 19 is arranged opposite the inner wall 5 of the bottom 4.

[0061] Except for the bottom wall 19, the other tank walls 17, 18, 20, 21 are fixed to a cofferdam wall 22 which together with the inner wall 5 of the hull 4 forms the load-bearing structure of the tank 2, as can be seen in Figures 2 to 4. The cofferdam wall 22 consists of an inner skin 23 to which the tank walls 17, 18, 20, 21 are fixed, and an outer skin 24 spaced apart from the inner skin 23. Stiffeners 25 are placed inside the cofferdam wall 22 on the inner skin 23 and the outer skin 24 to stiffen each skin 23, 24.

[0062] The tank 2 is arranged in the hull 3 such that one of the cofferdam walls 22 separates the machinery room 14 from the aft tank wall 17, as shown in Figure 2. The machinery room 14 is in this case arranged opposite the inner wall 5 of the bottom 4 at the aft part of the vessel 1 with respect to the longitudinal direction L of the vessel 1.

[0063] Each tank wall 17-21 comprises a multilayer structure including, from the outside to the inside of the tank, a secondary insulating barrier, a secondary sealing membrane arranged opposite the secondary insulating barrier, a primary insulating barrier arranged opposite the secondary sealing membrane, and a primary sealing membrane arranged opposite the primary insulating barrier and intended to be in contact with the liquefied fuel gas. Examples of such membrane tanks are described in particular in WO 2019239048, WO 14057221, FR 2691520 and FR 2877638. Membrane tanks can be built in particular using the GTT technologies Next1®, Mark V®, Mark III® and NO96® developed by the Applicant.

[0064] As can be seen in Figure 2, the ceiling wall 20 is covered by a tank connection space 26, which is surrounded by the cofferdam wall 22. The tank connection space 26 includes a dome structure 27 through which inter alia a loading pipe 28 passes through the ceiling wall 20 in order to fill the tanks 2 with liquefied fuel gas. This tank connection space 26 is a secure space in which the pipes passing through the ceiling wall 20 are connected to other equipment of the ship, for example tank valves.

[0065] The vessel 1 also has a fuel preparation chamber 29, visible in figures 5 and 6, arranged adjacent to the longitudinal wall 21 of the tank 2 and adjacent to one of the machinery rooms 14. The fuel preparation chamber 29 is equipped in particular with devices for conditioning the fuel gas so as to adapt its pressure and temperature to values ​​suitable for the propulsion system 15.

[0066] Therefore, the tank 2, the cofferdam wall 22 and the tank connection space 26 are dimensioned to be located below the main loading deck 8 as shown in Figure 2. Specifically, in the design example of Figure 2, the highest cofferdam wall 22, i.e., the cofferdam wall located above the tank connection space 26, is located on one of the fourth decks, i.e., the storage decks 9. Therefore, the structure of the tank 2 and the tank equipment and the tank connection space 26 does not affect the design of the main loading deck 8.

[0067] FIG. 3 shows one embodiment regarding the location and size of the tank 2 relative to the load-bearing columns 11 .

[0068] In this figure, one can distinguish the first to fifth decks, the tank 2 and one of the load-bearing columns 11 of the first row of columns. The design is symmetrical in the transverse direction T, so that only half of the cross section of the vessel 1 is shown. Thus, in this design example shown in figures 3 and 4, the second and fourth decks, which are the storage deck 9, are mobile decks in the height direction H, while the third and fifth decks, which are the storage deck 9 and the main loading and unloading deck 8, are fixed decks in the height direction H. The fixed decks are designed to be able to withstand heavier loads than the mobile decks.

[0069] In the embodiment of FIG. 3, one load-bearing column 11 of the first row of columns 12 is located against one of the longitudinal cofferdam walls 22, i.e. against the inner skin 23. The structure of the tank 2 and the cofferdam wall 22 therefore does not influence the design and position of the load-bearing column 11. Furthermore, in this case it is possible to obtain a tank with a maximal increase in lateral dimensions without affecting the position of the load-bearing column 11. The increase in width of the tank 2 is substantially equal to the lateral dimensions of the longitudinal cofferdam wall 22.

[0070] In another embodiment, not shown, one load-bearing column 11 of the first row of columns 12 can be located in one of the longitudinal cofferdam walls 22, but in this case facing the outer skin 24. Thus, as mentioned above, the structure of the tank 2 and the cofferdam wall 22 does not influence the design and location of the load-bearing column 11.

[0071] It can thus be seen that the load-bearing columns 11 of each row 12, 13 are substantially aligned in the longitudinal direction L.

[0072] 4 and 5 show a cross section of the vessel 1 in which all the load bearing columns 11 of each row of columns 12, 13 are visible together with the arrangement of the tanks 2 and the cofferdam walls 22 relative to these load bearing columns 11.

[0073] Specifically, as can be seen in the detailed view of Figure 5, in this embodiment three load-bearing columns 11 in each row of columns 12, 13 are arranged in the longitudinal cofferdam wall 22. The number of load-bearing columns in the cofferdam wall 22 depends on the length of the vessel 1, the total number of columns and the longitudinal length L of the tank 2.

[0074] Referring to Figure 6, a cut-away view of a roll-on / roll-off vessel 1 shows a generally parallelepiped shaped sealed insulated tank 2 fitted to the hull 3 of the vessel 1. As is known, a loading pipeline 73 for filling the vessel can be connected by suitable connectors to an offshore or port terminal which transfers the cargo of LNG to the tank 2.

[0075] FIG. 6 shows an example of a marine terminal with a loading station 75, an underwater pipe 76 and an onshore facility 77. The loading station 75 is a fixed offshore facility with a movable arm 74 and a tower 78 supporting the movable arm 74. The movable arm 74 carries a bundle of insulated flexible pipes 79 that can be connected to a loading pipeline 73. The orientable movable arm 74 can be adjusted to fit any size of vessel. A connecting pipe (not shown) extends inside the tower 78. The loading station 75 allows the loading of the roll-on / roll-off vessel 1 with LNG fuel from an onshore facility 77. The facility comprises a tank 80 for storing liquefied gas and a connecting pipe 81 connected to the loading station 75 by an underwater pipe 76. The underwater pipe 76 allows the transfer of liquefied gas between the loading station 75 and the onshore facility 77 over long distances, for example 5 km, and allows the roll-on / roll-off vessel 1 to be kept at a long distance from the shore during the loading operation.

[0076] To generate the pressure required to transport the liquefied gas, pumps on board the vessel 1 and / or pumps mounted at a shore facility 77 and / or pumps mounted at a loading station 75 are used.

[0077] Although the present invention has been described with reference to some specific embodiments, it is clear that, within the scope of the invention, the invention is in no way limited thereto, but includes all technical equivalents of the described means and combinations thereof.

[0078] Use of the verb "comprise" or "include" and their conjugations does not exclude the presence of elements or other steps in addition to those stated in a claim.

[0079] In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim.

Claims

1. A roll-on / roll-off vessel (1), comprising: a hull (3) comprising a double-walled bottom (4) and an outer deck (7) spaced apart in height (H) from said bottom (4), said double-walled bottom (4) comprising an inner wall (5) and an outer wall (6); - a number of intermediate decks arranged between the bottom (4) of the hull (3) and the outer deck (7), comprising a main handling deck (8) and one or more storage decks (9); - load-bearing columns (11), each having a lower end fixed to the bottom (4) of the hull (3) and extending in the height direction (H) for support through the intermediate deck, said load-bearing columns (11) being arranged in at least a first row of columns (12) and a second row of columns (13), said load-bearing columns (11) of the same row being spaced apart from each other in the longitudinal direction (L) of the vessel; - a machinery room (14) located in said hull (3) and comprising a propulsion system (15), - a sealed, insulated tank (2) for storing liquefied fuel gas and supplying said propulsion system (15), said tank having two longitudinal walls (21) spaced apart from each other in a transverse direction (T), said transverse direction (T) being perpendicular to said longitudinal direction (L) and to said height direction (H) of said ship, a cofferdam wall (22) comprising two longitudinal cofferdam walls (22), each cofferdam wall (22) comprising an inner skin (23) and an outer skin (24) spaced apart from said inner skin (23); Each longitudinal tank wall (21) is fixed to the inner skin (23) of one of the longitudinal cofferdam walls (22); 1. A roll-on / roll-off vessel, wherein at least one load-bearing pillar (11) of said first row of pillars (12) or said second row of pillars (13) is located in one of said longitudinal cofferdam walls (22).

2. 2. The roll-on / roll-off vessel (1) according to claim 1, wherein at least one load-bearing pillar (11) of the first row of pillars (12) is located on one of the longitudinal cofferdam walls (22) and at least one load-bearing pillar (11) of the second row of pillars (13) is located on the other of the longitudinal cofferdam walls (22).

3. 3. The roll-on / roll-off vessel (1) according to claim 1 or claim 2, wherein the at least one load-bearing pillar (11) of the first row of pillars (12) or of the second row of pillars (13) is formed against the inner skin (23) or against the outer skin (24) of the longitudinal cofferdam wall (22).

4. 3. The roll-on / roll-off vessel (1) according to claim 1 or claim 2, wherein the load-bearing columns (11) have a dimension in the transverse direction (T) between 100 mm and 400 mm, and wherein the inner skin (23) and the outer skin (24) of the longitudinal cofferdam wall (22) are spaced apart from each other in the transverse direction (T) by a distance of at least 900 mm.

5. 3. The roll-on / roll-off ship (1) according to claim 1 or 2, wherein the tank (2) is of parallelepiped shape and comprises an aft tank wall (17) separated from the machinery room (14) by an aft cofferdam wall (22), a front tank wall (18) spaced apart from the aft tank wall (17) in the longitudinal direction (L) of the ship, a bottom tank wall (19) arranged opposite the inner wall (5) of the bottom (4) of the hull (3), a ceiling tank wall (20) spaced apart from the bottom tank wall (19) in the height direction (H), and the two longitudinal tank walls.

6. The roll-on / roll-off vessel (1) according to claim 1 or 2, wherein the load-bearing pillars are made of metal.

7. 7. The roll-on / roll-off vessel (1) according to claim 6, wherein the at least one load bearing pillar located in one of the longitudinal cofferdam walls is made from the same or a higher steel grade than that of the other load bearing pillars.

8. 3. The roll-on / roll-off vessel (1) according to claim 1 or claim 2, wherein each load-bearing column extends in said elevation through and supporting all of said intermediate decks.

9. 9. The roll-on / roll-off vessel (1) according to claim 8, wherein each load-bearing pillar has an upper end fixed to the outer deck.

10. 3. The roll-on / roll-off vessel (1) according to claim 1 or claim 2, wherein each tank wall (17, 18, 19, 20, 21) comprises a multi-layer structure comprising, from the outside to the inside of the tank (2), a secondary insulating barrier, a secondary sealing membrane arranged against the secondary insulating barrier, a primary insulating barrier arranged against the secondary sealing membrane, and a primary sealing membrane arranged against the primary insulating barrier and intended to be in contact with the liquefied gas.

11. 1. A transfer system for transferring liquefied fuel gas, comprising: a roll-on / roll-off vessel (1) according to claim 1 or claim 2; an insulated pipeline (73, 79, 76, 81) arranged to connect the tank (2) installed in the hull (3) of the roll-on / roll-off vessel (1) to a floating or onshore storage facility (77); and a pump for pumping a flow of cryogenic liquid product from the floating or onshore storage facility to the tank (2) of the roll-on / roll-off vessel (1) via the insulated pipeline.

12. A method for loading a roll-on / roll-off vessel (1) as described in claim 1 or claim 2, wherein liquefied fuel gas is removed from a floating or on-shore storage facility (77) to the tank (2) of the roll-on / roll-off vessel (1) via the insulated pipeline (73, 79, 76, 81).

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