FR3122401A1 - Ro-ro ship comprising a tank for the storage of liquefied gas - Google Patents

Abstract

The invention relates to a ro-ro ship (1) comprising: - a hull (3) comprising a double-walled bottom (4), - a plurality of intermediate decks comprising a main loading/unloading deck (8), - at least one loading/unloading ramp, - supporting pillars (11) extending in the height direction (H), - an engine room, - a sealed and thermally insulating tank (2) with membranes for storing a gas liquefied fuel, in which the tank (2) is located under the main loading/unloading deck (8) and against the internal wall (5) of the bottom (4), - cofferdam walls (22) comprising an internal skin ( 23) and an outer skin (24), in which each longitudinal tank wall is fixed to the inner skin (23) of one of the longitudinal cofferdam walls (22), and in which at least one pillar of the first row or at least one pillar of the second row is located in one of the longitudinal cofferdam walls. Figure for the abstract: Fig. 5

Description

Ro-ro ship comprising a tank for the storage of liquefied gas

The invention relates to the field of ro-ro ships called "Roll on / Roll off" for the transport of towed or self-propelled wheeled freight, such as vehicles, boarding using one or more access ramps. The invention relates more particularly to the field of ro-ro ships comprising a sealed and thermally insulating tank with membranes for the storage of a liquefied fuel gas at low temperature. The tank is intended to receive liquefied gas serving as fuel for the propulsion of the ro-ro ship.

In one embodiment, the liquefied gas is LNG, namely a mixture with a high methane content stored at a temperature of approximately -162°C at atmospheric pressure. Other liquefied combustible gases can also be considered, including ethane, propane, butane, liquefied petroleum gas (LPG) or ethylene.

Technology background

It is known from the prior art of ro-ro ships for transporting towed or self-propelled wheeled freight.

These vessels comprise a hull comprising a bottom and an outer deck spaced from the bottom in a height direction, a plurality of intermediate decks located between the bottom and the outer deck of the hull, in particular a main loading/unloading deck and one or more storage decks, a loading/unloading ramp connected to the main loading/unloading deck, and supporting pillars extending in the height direction such that a first end is fixed to the bottom and a second end is fixed for example to the external bridge. The support pillars are generally arranged in a plurality of rows of pillars in a longitudinal direction of the ship. The main loading/unloading bridge thus corresponds to a fixed bridge on which the freight is conveyed via the loading/unloading ramp(s) for the loading or unloading of the freight.

These load-bearing pillars play a key role in the rigidity of the ship's hull because, unlike a traditional ship, ro-ro ships do not have a partition partitioning the interior of the hull and at the same time stiffening the hull. This lack of partition is necessary to allow towed or self-propelled wheeled freight traffic on the intermediate decks.

These ships mainly use oil derivatives as fuel, such as heavy fuel oil (HFO), which have a boiling point well above the ambient temperature, for example between 120 and 600°C. The ships of the prior art embark in their hull one or more tanks for the storage of such fuel. These tanks do not require any special equipment since their content can be stored in liquid form at room temperature. Thus, these tanks do not present any difficulty for their placement in the ship and are in particular placed in the zones left free of the ship such as the side edges.

However, due to regulatory changes in greenhouse gas emission rules, particularly for maritime transport, there is a need for these ro-ro ships to change propulsion technology.

Compared to that of traditional heavy fuel oil, the combustion of LNG generates reductions of 100% of sulfur oxides and fine particles, 80% of nitrogen oxides and 20% of CO2. Currently, LNG is the most efficient carbon fuel from a technical, operational and environmental point of view.

Summary

An idea underlying the invention is to position and size a liquefied combustible gas storage tank in a ro-ro ship.

According to one embodiment, the invention provides a ro-ro ship comprising:
- a hull comprising a double-walled bottom and an outer deck spaced from the bottom in a height direction, the double-walled bottom comprising an inner wall and an outer wall,
- a plurality of intermediate decks located between the bottom and the outer deck of the hull, the plurality of intermediate decks comprising a main loading/unloading deck and one or more storage decks,
- load-bearing pillars, each load-bearing pillar having a lower end fixed to the bottom of the hull and extending in the height direction so as to cross and support the intermediate decks, the load-bearing pillars being arranged according to at least a first row of pillars and a second row of pillars, the bearing pillars of the same row being spaced from each other in a longitudinal direction of the ship,
- an engine room located in the hull and including a propulsion system
- a sealed and thermally insulating tank for storing a liquefied fuel gas intended to supply the fuel gas to the propulsion system, the tank comprising two longitudinal walls spaced from each other in a transverse direction, the transverse direction being perpendicular to the longitudinal direction and the height direction of the ship,
- cofferdam walls comprising two longitudinal cofferdam walls, each cofferdam wall comprising an internal skin and an external skin spaced from the internal skin,
wherein each longitudinal vessel wall is attached to the inner skin of one of the longitudinal cofferdam walls,
and wherein at least one supporting pillar of the first row of pillars or the second row of pillars is located in one of the longitudinal cofferdam walls.

Thanks to these characteristics, the positioning of the tank and its sizing make it possible to adapt to the particular structure of the ro-ro ship without requiring major structural modification which would involve significant new structural calculations. Indeed, the positioning of the tank between the pillars makes it possible to preserve the arrangement of the bearing pillars. In addition, by positioning at least one of the pillars adjacent to the tank in the longitudinal cofferdam walls, it is possible to increase or even maximize the transverse dimension of the tank without modifying the arrangement of the pillars in the ship's hull.

According to embodiments, such a ship may comprise one or more of the following characteristics.

According to one embodiment, at least one supporting pillar of the first row of pillars is located in one of the longitudinal cofferdam walls and at least one supporting pillar of the second row of pillars is located in the other of the cofferdam walls longitudinal.

According to one embodiment, the ro-ro ship comprises at least one loading/unloading ramp connected to the main loading/unloading deck.

According to one embodiment, the sealed and thermally insulating tank is a membrane tank, preferably a tank being configured for the storage of LNG.

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 engine room and the front of the ship according to the maximum volume of liquefied gas desired.

According to one embodiment, the main loading/unloading bridge is fixed, and at least one storage bridge is movable in the height direction so as to vary the distance between two adjacent intermediate bridges for the placement of bulky goods.

According to one embodiment, the storage bridge located above or below the main loading/unloading bridge is movable in the height direction.

According to one embodiment, at least one, several or each bearing pillar extends in the height direction so as to cross and support all of the intermediate bridges.

According to one embodiment, at least one, several or each supporting pillar has an upper end fixed to the external bridge.

According to one embodiment, the cofferdam wall or walls are made of metal, for example steel.

According to one embodiment, the internal skin and/or the external skin is formed from a layer of sheet metal, for example steel.

According to one embodiment, the bearing pillars are made of metal, for example steel.

According to one embodiment, said at least one bearing pillar located in one of the longitudinal cofferdam walls is made of a steel grade higher than that of the other bearing pillars.

Thus, the temperature in the cofferdam walls bordering the tank can be lower than in the other parts of the ship, due to the proximity to the liquefied gas storage tank. The higher grade of steel for this pillar makes it possible to compensate for this temperature difference in order to maintain sufficient mechanical strength.

We are talking here about a steel grade whose symbolic designation is taken from standard EN10027-1-2 in non-alloy steels for general use. In this designation, the first letter concerns the use of a steel, this letter being followed by a number representing the elastic limit in mega pascals. For example, S235 designates a non-alloy steel for construction with an elastic limit of 235 MPa. Thus, the term "higher steel grade" here means that it is a steel grade having a higher elastic limit in the same use. In addition, the IGF code (”International code of safety for using gases or other low flashpoint fuels”) also uses a symbolic designation to classify different steel grades (“steel grade”). Indeed, in this code, the grades of steel are symbolized by a letter or a couple of letters, a higher grade of steel being designated by a first higher order letter in the alphabet, for example the grade of steel B being superior to steel grade A.

In another embodiment, said at least one bearing pillar located in the cofferdam wall can be made of a steel grade identical to that of the other bearing pillars.

According to one embodiment, said at least one bearing pillar located in the longitudinal cofferdam wall is made of a steel whose elastic limit is greater than or equal to the steel of the other bearing pillars.

According to one embodiment, said at least one bearing pillar of the first row of pillars is formed against the internal skin or the external skin of the longitudinal cofferdam wall.

By positioning the bearing pillars against the internal skin, it is possible to optimize the transverse dimension of the vessel as much as possible without impacting the positioning of the bearing pillars, the bearing pillars being in this case subjected to thermal and mechanical stresses to be taken into account. because of their proximity to the structure of the vessel. Indeed, in this case, the gain in the transverse dimension is equal to the spacing of the internal and external skins. If, on the other hand, the bearing pillars are positioned against the outer skin, these are less subject to thermal and mechanical stresses coming from the tank, but the gain in transverse dimension of the tank is thereby reduced.

According to one embodiment, said at least one bearing pillar of the second row of pillars is formed against the internal skin or the external skin of the longitudinal cofferdam wall.

According to one embodiment, the internal skin and the external skin of the longitudinal cofferdam walls comprise stiffeners projecting in the transverse direction making it possible to stiffen the internal skin and the external skin.

The load-bearing pillars located against the internal skin or the external skin of the longitudinal cofferdam walls also contribute to the rigidity of the latter, more preferably said load-bearing pillars make it possible to dispense with some of these stiffeners.

According to one embodiment, the bearing pillars have a dimension in the transverse direction of between 100 and 400mm, for example 400mm, the internal skin and the external skin of the longitudinal cofferdam walls being preferably spaced from each other in the transverse direction by a distance of at least 900 mm, more preferably between 900 and 1200 mm.

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

According to one embodiment, the tank comprises an aft tank wall separated from the engine room by an aft cofferdam wall, a forward tank wall spaced from the aft tank wall in the longitudinal direction of the vessel, a tank wall bottom preferably located against the inner wall of the bottom of the hull, a ceiling tank wall spaced from the bottom tank wall in the height direction, and the two longitudinal tank walls.

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

According to one embodiment, the tank is located in the height direction under the main loading/unloading deck and against the inner wall of the bottom of the hull.

Thus, the entire tank is located between the double-walled bottom and the main loading/unloading deck so that the tank does not interfere during loading and unloading operations and therefore does not require modifying the movement of goods.

According to one embodiment, the ship comprises a tank connection space, tank valves and at least one dome structure being located in the tank connection space, the tank connection space being located on a wall ceiling of the tank and under the main loading/unloading deck in the height direction.

Thus, the tank connection space is also located between the double-walled bottom and the main loading/unloading bridge so that the latter tank does not interfere during loading and unloading operations and therefore does not require modifying the movement of goods.

According to one embodiment, each vessel wall comprises a multilayer structure comprising, from the exterior towards the interior of the vessel, a secondary thermally insulating barrier, a secondary sealing membrane located against the secondary thermally insulating barrier, a barrier primary thermally insulating barrier located against the secondary sealing membrane and a primary sealing membrane located against the primary thermally insulating barrier and intended to be in contact with the liquefied gas.

According to one embodiment, the invention also provides a transfer system for a liquefied fuel gas, the system comprising an aforementioned ro-ro ship, insulated pipes arranged so as to connect the tank installed in the hull of the ro-ro ship to a floating or onshore storage facility and a pump for driving a flow of cold liquid product through the insulated pipes from the floating or onshore storage facility to the tank of the ro-ro ship.

According to one embodiment, the invention also provides a method for loading an aforesaid ro-ro ship, in which a liquefied fuel gas is routed through insulated pipes from a floating or terrestrial storage installation to the tank of the ro-ro ship.

Brief description of figures

The invention will be better understood, and other aims, details, characteristics and advantages thereof will appear more clearly during the following description of several particular embodiments of the invention, given solely by way of illustration and not limitation. , with reference to the accompanying drawings.

There shows a side view of the interior of a ro-ro ship according to one embodiment.

There is a view of detail II of the , representing in particular the storage tank in the hull of the ship.

There is a partial sectional view according to plan III-III of the , representing the arrangement of a bearing pillar with respect to the storage tank in the transverse direction according to a first embodiment.

There is a sectional view according to plan IV-IV of the , showing the arrangement of a bearing pillar with respect to the storage tank in the longitudinal direction according to the first embodiment.

There is a view of detail V of the , representing in particular the storage tank and part of the load-bearing pillars.

There is a schematic representation of a ro-ro ship comprising a liquefied combustible gas storage tank and a loading terminal for this tank.

There will be described below a ro-ro ship 1 according to different embodiments in relation to Figures 1 to 6.

As presented above, RO/RO type ro-ro ships 1 have a special structure to allow free movement between the different towed or self-propelled wheeled freight bridges, ship 1 allowing the goods to enter ship 1 by their own means and to get out of ship 1 the same way. This freight can be, for example, composed of cars, road transport vehicles of goods and their load (trucks with trailers, semi-trailers), heavy construction machinery, agricultural equipment such as tractors, or even containers. mounted on loading/unloading vehicles such as forklifts or trailers.

Thus, unlike the usual cargo ships where the cargo is loaded vertically by lifting gear such as cranes, the cargo here is loaded and unloaded by rolling it inside in and out of the ship. thanks to a mobile loading/unloading ramp 10 which connects with a ramp installed on the quay of a port or directly on the quay.

To do this, the ro-ro ship 1 comprises:
- a hull 3 comprising a double-walled bottom 4 and an outer deck 7 spaced from the bottom 4 in a direction of height H,
- a plurality of intermediate decks 8, 9 located between the bottom 4 and the outer deck 7 of the hull 2, the plurality of intermediate decks comprising a main loading/unloading deck 8 and one or more storage decks 9,
- at least one loading/unloading ramp 10 connected to the main loading/unloading bridge 8,
- supporting pillars 11 extending in the height direction so as to cross and support the intermediate bridges 8, 9,
- an engine room 14 located in the hull 3 and comprising a propulsion system 15,
- a sealed and thermally insulating tank 2 with membranes for the storage of a liquefied combustible gas intended to supply the combustible gas to the propulsion system 15.

The double-walled bottom 4 is composed of an internal wall 5 and an external wall 6. The support pillars 11 thus have a lower end fixed to the internal wall 5 of the bottom 4 and an upper end which can be fixed to the bridge external 7.

The support pillars 11 are arranged in the example illustrated in Figures 5 and 6 according to a first row of pillars 12 and a second row of pillars 13. The support pillars 11 of the same row 12, 13 are spaced from each other in a longitudinal direction L of the ship 1. In addition, the two rows 12, 13 are arranged symmetrically in the transverse direction T in order to stiffen the hull 3 in a balanced manner and over the entire length of the ship 1. In other embodiments not shown, the support pillars 11 can be arranged in more than two rows, for example four and preferably in an even number of rows.

There illustrates a ro-ro ship 1 according to an example design. Indeed, in this example, the ro-ro ship 1 comprises twelve intermediate decks therefore comprising eleven storage decks 9 and a main loading/unloading deck 8. The internal wall 5 of the bottom 4 is also used as a storage deck 9 and is commonly considered as the first deck, each deck being called by its number, from the lowest deck to the highest deck in the direction of height H of the ship 1. For this design, the main loading/unloading deck 8 is thus the fifth bridge. The intermediate bridges 8, 9 as well as the internal wall 4 are connected to each other by means of access ramps 16 or vertical lift systems.

The structure of the tank 2 as well as its positioning and its dimensioning in the hull 3 of the ship 1 will be described in more detail below.

The tank 2 is here of parallelepipedal shape, as visible on the , and comprises a plurality of vessel walls, namely a rear vessel wall 17, a front vessel wall 18 opposite the rear vessel wall 17, a bottom wall 19, a ceiling wall 20 opposite the bottom 19, and two longitudinal walls 21. The bottom wall 19 is located against the internal wall 5 of the bottom 4.

Apart from the bottom wall 19, the other tank walls 17, 18, 20, 21 are fixed to cofferdam walls 22 which form with the internal wall 5 of the shell 4, the supporting structure of the tank 2, as can be seen in Figures 2 to 4. The cofferdam walls 22 are formed of an internal skin 23 on which the vessel walls 17, 18, 20, 21 are fixed and an external skin 24 spaced from the internal skin 23. Stiffeners 25 are placed inside the cofferdam wall 22 on the internal skin 23 and the external skin 24 in order to stiffen each of the skins 23, 24.

The tank 2 is placed in the hull 3 so that one of the cofferdam walls 22 separates the engine room 14 and the aft tank wall 17, as shown in the . The engine room 14 is here located against the internal wall 5 of the bottom 4 at the rear of the ship 1 with respect to the longitudinal direction L of the ship 1.

Each tank wall 17-21 comprises a multilayer structure comprising, from the outside towards the inside of the tank, a secondary thermally insulating barrier, a secondary sealing membrane located against the secondary thermally insulating barrier, a primary thermally insulating barrier located against the secondary sealing membrane and a primary sealing membrane located against the primary thermally insulating barrier and intended to be in contact with the liquefied combustible gas. By way of example, such membrane tanks are described in particular in patent applications WO2019239048, WO14057221, FR2691520 and FR2877638. Membrane tanks can in particular be built according to the GTT Next1®, Mark V®, Mark III® and NO96® technologies developed by the applicant.

As seen on the , the ceiling wall 20 is surmounted by a tank connection space 26, this tank connection space 26 being surrounded by cofferdam walls 22. The tank connection space 26 comprises in particular a dome structure 27 through which the loading pipe 28 in particular passes through the ceiling wall 20 in order to fill the tank 2 with liquefied combustible gas. This tank connection space 26 is a secure space where the pipes passing through the ceiling wall 20 are connected to the other equipment of the ship, for example to tank valves.

The vessel 1 is also equipped with a fuel preparation room 29, visible in FIGS. 5 and 6, which is located adjacent to one of the longitudinal walls 21 of the tank 2 and to the engine room 14. The fuel preparation room 29 is in particular equipped with a device for conditioning the combustible gas in order to adapt the pressure and the temperature of the combustible gas to values adapted to the propulsion system 15.

The tank 2, the cofferdam walls 22 and the tank connection space 26 are thus dimensioned so as to be located under the main loading/unloading deck 8, as illustrated in . Indeed, in the design example of the , the highest of the cofferdam walls 22, namely the one located above the tank connection space 26, is located at the level of the fourth bridge, that is one of the storage bridges 9. Thus, the structure of the tank 2 and its equipment such as the tank connection space 26 have no impact on the design of the main loading/unloading bridge 8.

There represents an embodiment for the positioning and dimensioning of the tank 2 with respect to the bearing pillars 11.

In this figure, it is possible to distinguish the bridges, from the first to the fifth, the tank 2 as well as one of the supporting pillars 11 of the first row of pillars. Since the design is symmetrical in the transverse direction T, only half of the section of the ship 1 has been represented. Thus, in this design example illustrated in FIGS. 3 and 4, the second bridge and the fourth bridge which are storage bridges 9, are movable bridges in the direction of height H, while the third bridge and the fifth bridge which are respectively a storage bridge 9 and the main loading/unloading bridge 8, are fixed bridges in the height direction H. The fixed bridges are designed so as to be able to support a greater load compared to the mobile bridges.

In the embodiment of the , one of the bearing pillars 11 of the first row of pillars 12 is located in one of the longitudinal cofferdam walls 22, namely against the internal skin 23. Thus, the structure of the tank 2 and the cofferdam walls 22 have no impact on the design and positioning of the bearing pillars 11. In addition, it is possible here to obtain a tank whose transverse dimension is increased to the maximum without impacting the positioning of the bearing pillars 11. The gain in width of the tank 2 is substantially equal to the transverse dimension of the longitudinal cofferdam walls 22.

In another embodiment not illustrated, one of the support pillars 11 of the first row of pillars 12 can be located in one of the longitudinal cofferdam walls 22, but this time against the outer skin 24. Thus, as before , the structure of the tank 2 and the cofferdam walls 22 have no impact on the design and positioning of the supporting pillars 11.

Thus, it can be seen that the bearing pillars 11 of each row 12, 13 are substantially aligned in the longitudinal direction L.

FIGS. 4 and 5 represent a section of the vessel 1 making it possible to illustrate all of the support pillars 11 of each row of pillars 12, 13 as well as the arrangement of the tank 2 and the cofferdam walls 22 with respect to these pillars bearers 11.

Indeed, as visible on the detail view of the , in this embodiment, three supporting pillars 11 of each row of pillars 12, 13 are arranged in the longitudinal cofferdam walls 22. The number of supporting pillars in the cofferdam walls 22 depends on the length of the vessel 1, the number total of pillars, as well as the length of the tank 1 in the longitudinal direction L.

With reference to the , a cutaway view of a ro-ro ship 1 comprising a watertight and thermally insulating tank 2 of generally parallelepipedal shape mounted in the hull 3 of the ship 1. In a manner known per se, loading pipes 73 of the ship can be connected, by means of suitable connectors, at a maritime or port terminal to transfer an LNG cargo to tank 2.

There represents an example of a maritime terminal comprising a loading and unloading station 75, an underwater pipe 76 and an onshore installation 77. The loading station 75 is a fixed offshore installation comprising a mobile arm 74 and a tower 78 which supports the movable arm 74. The movable arm 74 carries a bundle of insulated flexible pipes 79 which can be connected to the loading pipes 73. The adjustable movable arm 74 adapts to all vessel sizes. A connecting pipe, not shown, extends inside the tower 78. The loading station 75 allows the loading of the ro-ro ship 1 with LNG fuel from the shore installation 77. This comprises storage tanks for liquefied gas 80 and connecting pipes 81 connected by the underwater pipe 76 to the loading station 75. The underwater pipe 76 allows the transfer of the liquefied gas between the loading station 75 and the shore installation 77 on a great distance, for example 5 km, which makes it possible to keep the ro-ro ship 1 at a great distance from the coast during loading operations.

To generate the pressure necessary for the transfer of the liquefied gas, pumps on board the ship 1 and/or pumps fitted to the shore installation 77 and/or pumps fitted to the loading station 75 are used.

Although the invention has been described in connection with several particular embodiments, it is obvious that it is in no way limited thereto and that it includes all the technical equivalents of the means described as well as their combinations if these fall within the scope of the invention.

The use of the verb "to comprise", "to understand" or "to include" and of its conjugated forms does not exclude the presence of other elements or other steps than those set out in a claim.

In the claims, any reference sign in parentheses cannot be interpreted as a limitation of the claim.

Claims (12)

Ro-Ro ship (1) comprising:
- a hull (3) comprising a double-walled bottom (4) and an outer deck (7) spaced from the bottom (4) in a direction of height (H), the double-walled bottom (4) comprising an inner wall ( 5) and an outer wall (6),
- a plurality of intermediate decks located between the bottom (4) and the outer deck (7) of the hull (3), the plurality of intermediate decks comprising a main loading/unloading deck (8) and one or more storage decks (9),
- supporting pillars (11), each supporting pillar (11) having a lower end fixed to the bottom (4) of the hull (3) and extending in the height direction (H) so as to cross and support the decks intermediate, the bearing pillars (11) being arranged in at least a first row of pillars (12) and a second row of pillars (13), the bearing pillars (11) of the same row being spaced from each other in a longitudinal direction (L) of the ship,
- an engine room (14) located in the hull (3) and comprising a propulsion system (15),
- a leaktight and thermally insulating tank (2) for storing a liquefied fuel gas intended to supply the fuel gas to the propulsion system (15), the tank (2) comprising two longitudinal walls (21) spaced apart the other in a transverse direction (T), the transverse direction (T) being perpendicular to the longitudinal direction (L) and to the height direction (H) of the ship,
- cofferdam walls (22) comprising two longitudinal cofferdam walls (22), each cofferdam wall (22) comprising an internal skin (23) and an external skin (24) spaced from the internal skin (23),
wherein each longitudinal tank wall (21) is attached to the inner skin (23) of one of the longitudinal cofferdam walls (22),
and wherein at least one bearing pillar (11) of the first row of pillars (12) or the second row of pillars (13) is located in one of the longitudinal cofferdam walls (22). Ro-ro ship (1) according to claim 1, wherein at least one support pillar (11) of the first row of pillars (12) is located in one of the longitudinal cofferdam walls (22) and at least one support pillar ( 11) of the second row of pillars (13) is located in the other of the longitudinal cofferdam walls (22). A ro-ro ship (1) as claimed in claim 1 or claim 2, wherein said at least one bearing pier (11) of the first row of piers (12) or the second row of piers (13) is formed against the inner skin (23) or the outer skin (24) of the longitudinal cofferdam wall (22). Ro-ro ship (1) according to one of Claims 1 to 3, in which the bearing pillars (11) have a dimension in the transverse direction (T) of between 100 and 400 mm, the internal skin (23) and the external skin ( 24) longitudinal cofferdam walls (22) preferably being spaced apart in the transverse direction (T) by a distance of at least 900 mm. Ro-ro ship (1) according to one of Claims 1 to 4, in which the tank (2) is parallelepipedic in shape and comprises an aft tank wall (17) separated from the engine room (14) by a cofferdam wall (22) aft, a forward tank wall (18) spaced from the aft tank wall (17) in the longitudinal direction (L) of the vessel, a bottom tank wall (19) preferably located against the inner wall ( 5) from the bottom (4) of the shell (3), a ceiling tank wall (20) spaced from the bottom tank wall (19) in the height direction (H), and the two longitudinal tank walls . Ro-ro ship (1) according to one of Claims 1 to 5, in which the support pillars are made of metal. Ro-ro ship (1) according to claim 6, wherein said at least one support pillar located in one of the longitudinal cofferdam walls is made of the same or higher grade of steel than the other support pillars. Vessel (1) according to one of Claims 1 to 7, in which each load-bearing pillar extends in the height direction so as to cross and support all of the intermediate decks. Vessel (1) according to claim 8, in which each support pillar has an upper end fixed to the outer deck. Ro-ro ship (1) according to one of claims 1 to 9, in which each tank wall (17, 18, 19, 20, 21) comprises a multilayer structure comprising, from the outside towards the inside of the tank ( 2), a secondary thermally insulating barrier, a secondary sealing membrane located against the secondary thermally insulating barrier, a primary thermally insulating barrier located against the secondary sealing membrane and a primary sealing membrane located against the primary thermally insulating barrier and intended to be in contact with the liquefied gas. Transfer system for a liquefied combustible gas, the system comprising a ro-ro ship (1) according to one of Claims 1 to 10, insulated pipes (73, 79, 76, 81) arranged so as to connect the tank (2) installed in the hull (3) of the ro-ro ship (1) to a floating or onshore storage facility (77) and a pump for driving a flow of cold liquid product through the insulated pipes from the floating or onshore storage facility to the tank (2) of the ro-ro ship (1). Method of loading a ro-ro ship (1) according to one of Claims 1 to 10, in which a liquefied combustible gas is conveyed through insulated pipes (73, 79, 76, 81) from a floating storage installation or land (77) to the tank (2) of the ro-ro ship (1).