Method for controlling the trim of a transport ship without seawater ballast

Abstract

This invention relates to a method for controlling the trim of a transport ship without seawater ballast (1), having a width l measured along a transverse axis (y'y) of the ship (1), said ship (1) having an empty weight Pv of 20% to 60% of its total weight PT, taking into account a given maximum loading weight capacity PTC, according to the formula: PT = Pv + PTC, at least one first and one second closed liquid tanks (3' or 3"), not communicating with the sea, whose total weight PRT, when completely filled with a liquid of density equal to 1, makes up 2% to 8%, preferably 3% to 6%, of said empty weight Pv, said tanks (3', 3") being in communication, via at least one pipe, in order to transfer liquid from one to the other, and being spaced apart from one another by a distance d, considering the respective geometric centre of each of said tanks (3', 3") to be at least 1 / 2 when the tanks (3', 3") are positioned opposite one another essentially along the transverse axis (y'y): d ≥ 1 / 2.

Description

Field of invention

[0001] The invention relates to a ship not having seawater ballast. The present invention relates more particularly to a ship capable of transporting a very large quantity of goods, such as a ship having Liquefied Natural Gas tanks, hereinafter referred to as LNG or a ship having tanks for transporting liquefied gas (LG) such as for example ethylene, methane, ethane or liquefied petroleum gas LPG, and therefore having a very significant drop in its draft when it sails empty, almost without load, or with a reduced load and on the other hand such a ship, which by the nature of the goods that it can specifically transport, systematically makes a return trip without said goods. State of the art

[0002] Worldwide, a large number of merchant ships use seawater ballast tanks that are filled, or partially filled, to maintain optimum seaworthiness under all circumstances. The main function of these seawater ballast tanks is to push the ship into the water, in other words, to increase its draft or raise its waterline (the level of seawater reached on the ship's hull).

[0003] Indeed, generally speaking, seawater ballast tanks are necessary to obtain a sufficient draft for the complete immersion of the propulsion propeller (or propellers) and to avoid a planing effect of the propeller. Normal cargo ships have a relatively shallow draft when they are not carrying goods and are not ballasted. This phenomenon of reduced draft (or lowering of the waterline) is all the more marked when the weight of the ship when empty represents a relatively small percentage of its total loading capacity, expressed in weight, that is to say the total weight of the ship once loaded to its maximum capacity.

[0004] The expression "unladen weight of a vessel", in the context of the present invention, means the weight of the vessel without any cargo and any device other than those necessary for its operation, i.e. with a little fuel. Taking into account the relative weights, it will be considered here that the unladen weight of the vessel means that the latter only contains or includes a negligible quantity of fuel.

[0005] Without the use of ballast tanks, the propeller is generally not sufficiently submerged and the draft at the bow of the vessel is extremely low due to the weight of the vessel's equipment, which is mainly located at the stern of the vessel. Under these conditions, navigation in a port area or leaving the port and traveling on the high seas is not permitted because the safety relative to the seaworthiness of the vessel is not acceptable.

[0006] Therefore, in order to meet these navigability conditions, a considerable quantity of sea water is transported between different regions of the globe by these cargo ships.

[0007] Again, this obligation to use seawater ballast to restore satisfactory seaworthiness conditions when the vessel is no longer carrying goods (the expression "unladen" may be used in the following) is particularly relevant when these vessels have a very substantial loading capacity, so that, when unladen, these vessels have a much too shallow draught (or a waterline too low on the hull) given their dimensions, in length, height and width.

[0008] Furthermore, for example in the case of a long LNG carrier, the arrangement of the elements necessary for navigation such as the navigation tower, the engine(s) and other elements necessary for the operation of the vessel are located at the rear of the vessel and the tanks intended for LNG storage are located at the front of the vessel. Consequently, when the LNG storage tanks are empty, an imbalance between the elements necessary for the operation of the vessel and the tanks gives the vessel an inclined trim so that the bow of the vessel is raised relative to the stern. This elevation of the bow can cause a significant portion of the bow, for example a portion of the bulbous bow, to protrude from the water, degrading the stability of the vessel and the navigation conditions of the vessel, for example during maneuvers entering a port.

[0009] From a technical point of view, the use of seawater ballast involves very substantial technological and operational investments. In addition, the operation of the vessel can be impaired over time because these seawater ballasts bring a considerable amount of waste forming, over time, a layer of sediment at the bottom of the ballast tanks. It should also be noted that this large quantity of ballast considerably slows the speed of the vessel, which reduces its seakeeping capabilities when sea conditions are poor, particularly due to very poor weather.

[0010] Furthermore, entry into certain port areas requires the presence of a pilot authorized to carry out approach and docking maneuvers because they know the safe channel that the ship must follow. These temporary pilots of the ship board via a launch, a small boat or similar positioned alongside the ship. However, if the waterline of a ship without ballast, typically with a lower V-shaped hull, is too low, the launch or similar can be crushed by the sides of the ship, by these movements in the event of heavy seas.

[0011] From an environmental perspective, the transport of ballast water leads to the transfer of local aquatic organisms and pathogens from one geographical area to another due to the release of at least part of the ballast water in exchange for loading the cargo. As a result, serious ecological problems arise in maritime areas near major ports in some countries. This has recently led to a change in international regulations regarding the treatment of ballast water, requiring that it undergo decontamination and / or sterilization prior to its release. Such equipment is now mandatory for all ships equipped with seawater ballast tanks.

[0012] Documents WO 03010044 and WO 2012083687 are known, which respectively disclose a complex system for managing seawater to give it a flow velocity between the bow and stern of the ship in order to obtain the same ballasting conditions with a reduced volume of seawater and a ballast-free ship having a lower V-shaped hull instead of a flat bottom. Documents CN 201980382, CN 201932341 and CN 201932335 also disclose a modification of the geometry of the hull and the interior space of the ship dedicated to cargo so as to avoid seawater ballast.

[0013] Document WO 2014087008 discloses a vessel having a system for transferring water and oxygen between various tanks on board the vessel.

[0014] None of these technical achievements discloses an effective solution to enable, or even improve, the navigability of ballast-free transport vessels when they are operating empty.

[0015] Document CN 2739094 Y discloses a vessel equipped with a forward tank and a rear tank, or a left side tank and a right side tank. Liquid is transferred between these tanks in order to change the trim of the vessel.

[0016] Document FR 1 032 510 A discloses a ship equipped with several ballast tanks intended to be filled when the ship is unloaded, all the ballast tanks communicating directly with the others.

[0017] GB 2 343 434 A discloses a vessel provided with means for monitoring the vessel's trim and means for adjusting the quantity and / or distribution of liquid between the vessel's ballast tanks in accordance with the vessel's trim.

[0018] Document GB 2 044 201 A discloses a ship fitted with several ballast tanks where ballasting results in all the tanks being filled with sea water simultaneously.

[0019] Document FR 2 309 393 A1 discloses a modification to the geometry of the ship's hull to avoid filling the ship's ballast tanks.

[0020] Document KR 10-2014-0046878 A discloses a vessel having a forward tank and a rear tank. Liquid is transferred between these tanks to alter the vessel's trim. Brief description of the invention

[0021] The present invention seeks to address the problems and drawbacks of existing ships without seawater ballast by improving, or even simply allowing, the navigability of such ships in the open sea or when approaching, and within, port areas. More specifically, but not exclusively, the present invention seeks to provide a solution for ships capable of transporting a particularly large quantity or volume of cargo, such as ships transporting LNG, the phenomena of reduced draft, tilting of the ship's trim or lowering of the waterline becoming critical for the navigability of such ships.

[0022] The applicant discovered, after various studies and analyses, a technically simple solution to implement, making it possible to ensure navigability, when empty, equivalent or almost equivalent to ships with seawater ballast while avoiding or eliminating all the disadvantages inherent in these ballast systems.

[0023] Thus, the present invention relates to several methods for controlling the trim of a transport vessel without seawater ballast, having a length L considered along the longitudinal axis x'x of the vessel and a width ℓ considered along a transverse axis y'y of the vessel and comprising a lower hull, a cross-section of which is in the form of a trapezium comprising a part forming a flat bottom of the vessel from which extend respectively two sides of identical inclination, said vessel having an empty weight P v of between 20% and 60% of its total weight PT , taking into account a given maximum loading weight capacity P TC, according to the formula: P T = P v + P TC .

[0024] Such a lower hull, the cross-section of which is in the form of a trapezium, makes it possible to increase the draft of the vessel compared to other hull section shapes, for example compared to a rectangular hull section shape such as that present on certain LNG carriers.

[0025] According to a first variant of the invention, the ship comprises at least one front liquid tank and one closed rear liquid tank, not communicating with the sea, said reservoirs being in communication, via at least one conduit, for the transfer of liquid from one to the other, said reservoirs being positioned opposite each other essentially along the longitudinal axis (x'x) and distant from each other by a distance d, considering the respective geometric center of each of said reservoirs, where d ≥ L / 4.

[0026] A method of controlling the trim of such a vessel comprises the step of transferring a liquid into the forward tank when the vessel's cargo has a weight less than P TC / 10 to straighten the vessel's waterline, the liquid being pure water or water loaded with minerals and having a mass between 0.95 kg and 1.05 kg per liter, and the total weight P RT of said tanks, when completely filled with the liquid, representing between 2% and 8%, preferably between 3% and 6%, of the aforementioned empty weight P v , said ship further comprising a mooring tank, this mooring tank being independent of the front tank and the rear tank, the ship further comprising a seawater supply line for the mooring tank and a drain line for the mooring tank, said mooring tank being arranged at the front of the ship, the method further comprising the step of, if the ship is not carrying a load and has an inclined trim,transferring seawater into the mooring tank via the supply line to further straighten the vessel's waterline when the vessel enters or navigates a port area or when the vessel enters a dry dock.

[0027] According to a second variant of the invention, the ship comprises at least a first liquid tank and a second closed liquid tank, not communicating with the sea, said tanks being in communication, via at least one conduit, for the transfer of liquid from one to the other, said tanks being positioned opposite each other essentially along the transverse axis (y'y) and separated from each other by a distance d, considering the respective geometric center of each of said tanks, where d ≥ l / 2.

[0028] A method of controlling the trim of such a vessel comprises the step of transferring a liquid into one of the first tank and the second tank in order to heel the vessel, the liquid being pure water or water loaded with minerals and having a mass between 0.95 kg and 1.05 kg per liter, and the total weight P RT of said tanks (3', 3"), when fully filled with the liquid, representing between 2% and 8%, preferably between 3% and 6%, of the aforementioned empty weight P v .

[0029] The cross-section, for which the lower hull has a trapezoidal shape, is located, along the longitudinal axis x'x, classically between 20% and 70%, considered from the rear of the ship, of the length L of said ship.

[0030] The term "lower hull" means the lower part of the vessel, when the latter is or is in normal operation (typically navigation at sea), considered from the location where the two side walls of the hull extend along an inclined plane, above designated by the term "flank", and no longer vertically. In other words, the lower hull is here considered as the lower part of the vessel extending, from the flat bottom, to the two opposite ends of the two sides of identical inclination: for the sake of understanding, in particular the Figure 5a attached indicates that lower part of the vessel referred to herein as the "lower hull" (part of the vessel below the hull line referenced 20). Hull line 20 designates the upper limit of the inclined side walls and extends parallel to the flat bottom of the vessel.

[0031] The expression "liquid with a density equal to 1" means water, pure or slightly loaded, for example, with minerals, whose mass is approximately equal to one (1) kilogram per liter (between 0.95 kg and 1.05 kg) or one (1) tonne per cubic meter (m 3 < ).

[0032] Thanks to the invention, we now have a ship that can transport large quantities of goods, typically a ship specifically designed for the transport of LNG, with improved seaworthiness properties, requiring less energy expenditure for the same journey (due to a lower draft than conventional ships in the empty state) and avoiding the additional equipment costs imposed for ships with seawater ballast due to the absence of ecological disadvantages and the need to respect local ecosystems.

[0033] Furthermore, when the present invention is applied to a methane carrier or a liquefied gas carrier, two examples of ships for which the invention is particularly suitable, advantages induced by this solution are possible: ease of installation of one or more sumps at the bottom of the storage tanks due to the V-shaped geometry of the lower hull; decompartmentalization of the “cofferdam(s), possibly double hull spaces (not occupied by ballast water), between two storage tanks due to the absence of seawater ballast tanks generally located nearby, ambient air possibly being considered as a heat transfer fluid, instead of or in addition to the current heating systems of said cofferdam(s), intended to maintain the steel walls at a relatively high temperature, above or close to zero degrees Celsius; a reduction in the number of storage tanks and the associated handling system (reduction in the number of pumps, valves, detection systems, etc.), that is to say the need for compartmentalization of the ship, due to the ship's better buoyancy properties (and therefore an increased ability to reach a port in the event of breaches that could cause it to sink) in the absence of seawater ballast, typically making it possible to go from three (3) or four (4) tanks to only two (2) tanks, or even a single tank. This reduction in the number of tanks improves the overall thermal performance of the transport vessel, thanks in particular to three points which are: a significant reduction in the surface area to be thermally insulated, a significant reduction in the calories required for the heating system (typically at the level of the cofferdams), and finally the absence of seawater ballast induces a significant reduction in the calories penetrating the hull.

[0034] Other advantageous features are detailed below: according to a preferred embodiment of the first variant, the front tank is located in the first third, preferably in the first quarter, front of the ship and the rear tank is located in the last third, preferably in the last quarter, rear of the ship; advantageously, the ship comprises a third tank, located between in an area comprised between 40% and 60% of the length L of the ship, the communication for the transfer of liquid between the front tank and the rear tank preferably being carried out via said third tank; according to a preferred embodiment of the second variant, one of the tanks is located in the first third, preferably in the first quarter, lateral of the ship and the other tank is located in the last third, preferably in the last quarter, lateral of the ship;advantageously, the ship comprises a set of valves for managing the arrival, or not, of the liquid and its flow rate in each of the tanks, at least one pump for transferring the liquid from one of the tanks to another tank and means for introducing the liquid into at least one of the tanks; according to one possibility, in the first variant, the mooring tank is located in the first third, preferably in the first quarter, forward of the ship; ;

[0035] This mooring tank is used when the vessel is at berth, in particular to modify or rectify the trim of the vessel during loading / unloading. This mooring tank is not intended to be filled while the vessel is moving or only when it is moving in the port or port area, so it is not similar to seawater ballast.

[0036] Preferably, the aforementioned communication conduit has its outlet orifice located above the empty waterline of the vessel so that it is very easy to empty this tank.

[0037] Furthermore, according to a preferred embodiment, the filling is carried out via a conduit or an inlet located at the level of the upper wall of said mooring tank.

[0038] In the case of an LNG carrier type vessel not carrying a load and having an inclined trim, such a mooring tank is particularly useful since it allows the trim of the vessel to be restored when the vessel enters or navigates in the port area or enters a dry dock for repair or maintenance. Indeed, such a mooring tank allows the trim of the vessel to be restored and therefore for the hull line to be parallel to the water surface. In particular, in the case of a vessel in dry dock, if the vessel has an inclined trim when the water present in the dry dock is removed, the weight of the vessel will initially rest entirely on the same part of the hull, in this case the stern containing the functional equipment of the vessel in the case of an LNG carrier type vessel, which can lead to damage to the hull due to the significant weight of the vessel resting on a localized portion of the hull.Restoring the ship's trim allows, when removing the water present in the dry dock, for the ship to rest uniformly on the dry dock and thus present a balanced distribution of support on the hull of the ship, avoiding damage to the hull.

[0039] Furthermore, such a mooring tank does not generate any ecological risks since it is filled and emptied locally, i.e. in the same port area, to correct the trim of the ship. Thus, it does not present any risk of contamination of the water in one port area by water from another port area. preferably, the ship has an empty weight P v of between 30% and 50% of its total weight PT; advantageously, the ship comprises at least one sealed and insulating tank, said tank comprising two successive sealing barriers, one primary in contact with a product contained in the tank and the other secondary arranged between the primary barrier and a supporting structure, preferably constituted by at least part of the walls of the ship, these two sealing barriers being alternated with two thermally insulating barriers or a single thermally insulating barrier arranged between the primary barrier and the supporting structure.

[0040] Such tanks are conventionally designated as integrated tanks according to the International Maritime Organization (IMO) code, such as for example MARK III ®< type tanks. according to another possibility, the ship comprises at least one sealed and insulating tank, said tank comprising a sealing barrier and a thermally insulating barrier. This type of structure is more particularly illustrated by the so-called independent tanks according to the IMO code, such as for example type C tanks. in these last two hypotheses, preferably, the tank contains a Liquefied Natural Gas (LNG) or a Liquefied Gas (LG); Advantageously, at least part of the space surrounding the tank is open;

[0041] The expression "open-plan space" means that the volume between two adjoining tanks or between the tank and another part of the ship (these spaces being known to those skilled in the art as a cofferdam) are open or unenclosed spaces, allowing the circulation, for example, of ambient air from or to said volumes and adjacent volumes. when the vessel is not carrying any cargo, the inclination of the aforementioned sides is such that the ends of these sides are at most 0.8 metres above the water level, preferably at most 1 metre above the water level (the sea or ocean constituting the water level here).

[0042] A transport vessel without seawater ballast is also described, having a length L considered along the longitudinal axis x'x of the vessel and a width ℓ considered along a transverse axis y'y of the vessel and comprising a lower hull whose cross-section is in the form of a trapezium comprising a part forming a flat bottom of the vessel from which extend respectively two sides of identical inclination, said vessel having an empty weight P v of between 20% and 60% of its total weight PT , taking into account a given maximum loading weight capacity P TC, according to the formula: P T = P v + P TC .

[0043] In this embodiment, the two upper ends of the sides are presented, when the ship contains no cargo and preferably when the liquid in the tanks has been transferred so as to straighten the trim of the ship, at a height h above the water level of at most one (1) meter, preferably at most half (0.5) meter.

[0044] A transport vessel without seawater ballast is also described, the vessel having a length L considered along the longitudinal axis (x'x) of the vessel and a width ℓ considered along a transverse axis (y'y) of the vessel and comprising a lower hull of which a transverse section is in the form of a trapezium comprising a part forming a flat bottom of the vessel from which extend respectively two sides of identical inclination, said vessel having an empty weight P v of between 20% and 60% of its total weight PT , taking into account a given maximum loading weight capacity P TC, according to the formula: P T = P v + P TC said vessel comprising at least one mooring tank, the vessel further comprising a liquid supply line for the mooring tank and a drain line for the mooring tank, said mooring tank being arranged at the front of the vessel so that a transfer of liquid into the mooring tank via the supply line allows the trim of the vessel to be straightened.

[0045] All of the embodiments or executions described above may be included in this particular embodiment above.

[0046] Advantageously, the two sides have an inclination angle of between 10° and 45°, preferably between 15° and 35°. Description of the attached figures

[0047] The following description is given solely for illustrative and non-limiting purposes with reference to the attached figures, in which: there Figure 1 illustrates, in schematic section, a ballastless vessel according to an embodiment of the present invention; Figure 2 illustrates, in schematic section, a ballastless vessel according to another embodiment of the present invention; Figure 3 illustrates a diagram of the operation of the liquid transfer circuit between the four tanks present in the ship according to one embodiment of the invention; Figure 4 is a cross-sectional view of a vessel according to one embodiment of the invention; Figures 5a and 5b schematically illustrate respectively a ship according to the invention and this same ship undergoing a strong transverse wind, this ship being placed in a dry dock; the Figure 6is a sectional view of a portion of the hull of a ship according to an embodiment of the invention in which the waterlines are illustrated when the ship contains a partial or full load and when the same ship is empty, without load. Figure 7 is a sectional view of a vessel having a mooring tank. Detailed description of the invention

[0048] There Figure 1 shows an embodiment of a ship 1 according to the invention and the ship 1 chosen to illustrate the invention does not transport goods / cargo or a small quantity thereof.

[0049] In this embodiment, this ship 1 comprises two liquid tanks 2, 3, one 2 located in the front part (bow) and the other 3 located in the rear part (stern), these two liquid tanks 2, 3 communicating with each other so as to allow a transfer of liquid from one to the other. More specifically, the front tank 2 is placed in the first forward quarter of the ship 1, considering the length L of the ship, from the front end 5 of the ship 1 to the rear end 6 of the ship 1. Similarly, in this embodiment, the rear tank 3 is located in the last rear quarter of the ship 1. It may be envisaged that the front liquid tank 2 is located in the first forward part representing the first 12.5% ​​(1 / 8) of the length L of the ship 1 and / or that the rear liquid tank 3 is located in the last rear part representing the last 12.5% ​​(1 / 8) of the length L of the ship 1.

[0050] As can be seen on the Figure 1 , the ship 1 chosen to illustrate the invention conventionally comprises a navigation tower 11, conventionally called the castle, and equipment 10, conventionally called the chimney, located essentially at the rear of the ship 1 so that the ship 1 is inclined towards the rear, along the longitudinal axis x'x, in other words the hull line 20 of the ship 1 has an inclination relative to the surface of the sea 9, represented here along the longitudinal axis x'x.

[0051] This inclination of the ship 1 is particularly significant in the case of ships 1 of great length intended to transport a heavy load, the navigation tower 11 and the equipment 10 being located at the rear of the ship 1 and the front of the ship 1 being reserved for the storage of goods. For example, in the case of a ship 1 of the LNG carrier type, tanks intended to store the LNG are arranged along the entire length of the ship 1 at the front of the tower. Thus, when the ship is not transporting LNG, the front of the ship 1 has a weight significantly lower than the weight of the rear of the ship 1 so that the inclination of the ship 1 relative to sea level is significant. This inclination can cause a significant portion of the front portion of the hull and in particular at least a portion of the bulbous bow to emerge, thus degrading the navigation conditions of the ship.

[0052] In this example, if it is chosen to send all or almost all of the liquid into the forward tank 2, then the hull line 20 of the ship 1 has no inclination, or little inclination, relative to the sea surface, as represented by the waterline 109 on the Figure 1 or by waterline 209 on the Figure 2 . In other words, the transfer of the liquid into the forward tank makes it possible to straighten the trim of the vessel 1 by reducing the inclination of the vessel 1 relative to the surface of the sea, typically reducing the inclination between the hull line 20 and the waterline 109.

[0053] Additionally, the ship 1 may include a mooring tank 12 shown in broken lines on the Figure 1. This mooring tank 12 is located at the front of the ship 1. Such a mooring tank is dedicated to correcting the trim of the ship 1 when empty, in particular to facilitate maneuvers in a port area and to ensure a homogeneous distribution of the weight of the ship when the ship 1 is dry-docked. This mooring tank 12 is filled with liquid in order to further weigh down the front of the ship 1 and thus correct the trim of the ship 1 by balancing the rear of the ship 1 comprising the equipment 11 and the castle 10 and the empty storage area located at the front of the ship 1. Typically, such a mooring tank 12 is filled with seawater when the ship is not carrying a load and makes it possible to obtain a waterline 209 substantially parallel to the hull line 20.Such a docking tank is preferably independent of the front 2 and rear 3 tanks, that is to say that the liquid used for the operation of the front 2 and rear 3 tanks does not communicate with the liquid used to operate the docking tank 12.

[0054] This mooring tank 12 being limited to use in the port area, it can be filled with sea water to facilitate maneuvers in the port area and emptied when the ship 1 must leave the port area. Thus, such a mooring tank 12 dedicated to navigation in a port area does not present any risks for the ecosystem since the sea water used to fill the mooring tank 12 is drawn and then discharged in the same geographical area. In addition, when the ship 1 enters dry dock, a hull line 20 substantially horizontal (i.e. parallel to the water level in the dry dock) allows a good distribution of the weight of the ship 1 over the entire length of the hull when the dry dock is emptied of its water to rest the ship 1 on the bottom of the dry dock.

[0055] There Figure 2illustrates another embodiment of the ship 1. In this case, the ship 1 has three liquid tanks 2, 3, 4, i.e. the two front 2 and rear 3 liquid tanks present in the ship 1 shown in the Figure 1 to which a central tank 4 has been added, this central tank 4 being in communication with the other two tanks 2, 3, for the transfer of liquid from one to the other. The central tank 4 is located substantially in the middle of the ship 1, along its longitudinal axis x'x, typically in an area between 30% and 70% of the length L of the ship 1, considered from the front end 5 or rear end 6 of the ship 1 along the longitudinal axis x'x, preferably in an area between 40% and 60% of the length L of the ship 1.

[0056] According to one possibility offered by the invention, the transfer of liquid between the front 2 and rear 3 tanks is preferably carried out via this central tank 4. According to another possibility, the transfer of liquid between the front 2 and rear 3 tanks is carried out, or can be carried out, independently of this central tank 4.

[0057] As we can see on this Figure 2 , the distribution of the liquid between these three tanks, front 2, rear 3 and central 4, is such that the hull line 20 of the ship 1 extends approximately parallel to the plane of the sea / ocean (local water level). In this case, the hull line 20 of the ship 1 is merged on the Figure 2 with waterline 209.

[0058] There Figure 3schematically illustrates an embodiment of the invention in which the ship has or comprises four tanks, a front tank 2, a central tank 4 and two rear tanks 3', 3" arranged offset from each other along the transverse axis y'y. Such an embodiment, with these two rear tanks 3', 3" laterally offset, is shown more clearly on the Figure 4 where only these two rear tanks 3', 3" are represented.

[0059] As can be seen on the Figure 3, each of the tanks 2, 3', 3" and 4 has at least one filling / emptying conduit 30 and one liquid transfer conduit 40. The filling / emptying conduit 30 makes it possible to fill or empty the tank in question, independently of the other tanks with which they communicate, while the transfer conduit 40 makes it possible to transport liquid from or to this tank, respectively to at least partially empty this tank and at least partially fill another tank and to at least partially fill this tank and at least partially empty another tank. Of course, the network of liquid transfer conduits 40, connecting the different tanks together, as shown in the Figure 3, is only an example of such a network and any arrangement or arrangement of these transfer conduits 40 may be provided as long as this network meets the objective of allowing or authorizing the circulation of liquid between at least two reservoirs 2, 3', 3", 4. The network of liquid transfer conduits 40 comprises at least one pump 60, preferably a plurality of pumps 60 and possibly as many as there are reservoirs 2, 3', 3", 4, capable of at least partially emptying a reservoir 2, 3', 3" or 4 to transfer the liquid it contains to another reservoir 2, 3', 3" or 4. Of course, a plurality of valves, remotely controlled like the pump 60, are provided in this network of liquid transfer conduits 40 in order to send the liquid to the appropriate / desired reservoir.

[0060] The plurality of liquid tanks 2, 3', 3", 4 and the possibility of transferring liquid from at least one to another of these tanks 2, 3', 3", 4 are intended to allow in the first place to vary the inclination of the ship 1, or the hull line 20 of the ship 1 so that the latter is conventionally parallel to the longitudinal axis x'x or to the plane of extension of the surface of the sea / ocean. A second objective of these tanks 2, 3', 3", 4 and of the possibility of transferring liquid between at least two tanks aims to lower the waterline of the ship 1 or to increase its draft but only up to the minimum level required to allow or facilitate its maneuverability, as well as in particular when boarding a captain in order to steer the ship for its entry into a port or a particular port area.

[0061] In the embodiment illustrated in the Figure 4, the ship 1 has at least two tanks 3', 3" arranged offset from each other along the transverse axis y'y. More precisely, a first tank 3' is located in the first third, preferably in the first quarter, along the width ℓ of the ship, along the transverse axis y'y, while the second tank 3" is located in the last third, preferably in the last quarter, always along the width ℓ of the ship 1.

[0062] In this figure, the starboard tank 3" is shown filled, approximately to two-thirds (2 / 3) of its maximum volumetric / mass capacity, while the port tank 3' is empty. Thus, due to this difference or weight gradient, the ship 1 lists to one side, in other words the hull line 20 of the ship 1, here extending parallel to the transverse axis y'y, has a (non-zero) inclination or angle relative to the plane of the sea / ocean surface 50 (local water level).In doing so, by the action of transferring liquid between these two tanks 3', 3", the hull line 20 of the ship 1 is here flush with the level of the sea / ocean 50 to starboard so that a launch or the like, not shown in the attached figures, can come and position itself adjacent to the ship 1 to deliver a captain capable of directing the ship for its approach and its entry into a port or a difficult port area, without this launch or the like risking being crushed or damaged by the sides 21 of the hull of the ship 1 when the sea conditions are capricious.Indeed, thanks to the invention, the possible transfer of liquid from two tanks 3', 3" positioned offset or at a distance along a transverse axis y'y of the ship 1 (i.e. along its width) makes it possible to heel the ship as required, in particular when a smaller boat is alongside it so as not to risk crushing / damaging it by its inclined sides 21 located clearly above the level of the sea / ocean 50 (due to the absence of cargo / loading on the ship 1).

[0063] THE Figures 5a and 5b illustrate one of the design choices of the vessel 1 according to the invention, which led to its particular characteristics and dimensions. Thus, when the vessel 1 is in dry dock, in particular to undergo an overhaul and possible repairs, it is imperative that it does not risk capsizing when a strong crosswind (along the transverse axis y'y) occurs, as illustrated in the Figure 5b. Indeed, due to the absence of seawater ballast, the ship 1 according to the invention has a lower hull of trapezoidal shape, in particular a lower flat part 22 at the two ends of which extend respectively two inclined sides 21. Taking into account the length L and the height of the ship 1, the lower flat part 22 of the ship 1 is determined to be sufficiently large so that the ship 1 can resist, taking into account its empty weight, a lateral wind exerting a maximum force (the value of which is determined by international standards or regulations).Thus, the width of the flat part 22 of the ship 1 according to the invention is a function of its length L, its height and its empty weight such that said ship 1 can withstand an extreme force (quantified by regulation for the safety of maintenance operations in dry dock) directed laterally, along the y'y axis or parallel to this axis, such that the ship 1 does not tip over when it is in dry dock, resting on the flat part 22 of its lower hull.

[0064] There Figure 6illustrates a complementary aspect of the ship 1 according to the invention. In this figure, a half-hull of the ship 1 (of width 1 / 2) is shown in vertical section. The design of a ship 1 without sea water ballast according to the invention aims here firstly to provide that, when the ship 1 is empty (without cargo / goods), the waterline 44 of the ship 1 is close to the hull line 20 of the ship 1, that is to say the zone from which the inclined sides 21 extending from the lower hull end. The difference between the waterline 44 of the ship 1 when empty and the hull line 20 of the ship 1 must at most be equal to 1 meter, preferably less than 50 cm (centimeter), or even very preferably less than 30 cm. It is noted that, in this Figure 6, a waterline 45 of the ship 1 is also shown when it is loaded, that is to say when it is transporting cargo and / or goods. Furthermore, the two sides have an inclination of angle α between 10° and 45°, preferably between 15° and 35°.

[0065] These requirements for the construction of the lower V-shaped hull of the ship 1 without seawater ballast concerning the low height h are provided in particular, but not exclusively, to avoid damaging or breaking a small boat coming alongside the ship when the sea or ocean is rough.

[0066] There Figure 7 illustrates a functional schematic sectional view of a vessel having a mooring tank 12 as illustrated in the Figure 1. As explained above, such a mooring tank 12 is located at the front of the ship in order to balance the ship 1 and allow it to present a horizontal trim, that is to say a hull line 20 parallel to the water level.

[0067] On this Figure 7, the waterline of the ship when empty, that is to say when it is not carrying a load, is illustrated at number 109 when the mooring tank 12 is empty and at number 209 when it is full. The mooring tank 12 is connected on the one hand to a supply line 13 and, on the other hand, to a drain line 14. The supply line opens into the upper part of the mooring tank 12 in order to fill said mooring tank 12, for example by means of a pump (not shown) drawing sea water from the port area to fill the mooring tank 12. The drain line 14 is arranged in the bottom of the mooring tank 12 in order to allow emptying of the mooring tank 12. This drain line 14 opens directly onto a side of the ship 1, for example above the hull line 20, in order to discharge the contents of the mooring tank 12 into the sea.

Claims

1. A method for controlling the trim of a transport ship (1) without seawater ballast, the ship having a length L along the longitudinal axis (x'x) of the ship (1) and a width ℓ along a transverse axis (y'y) of the ship (1) and including a lower hull a cross section of which takes the form of a trapezium comprising a part forming a flat bottom (22) of the ship (1) from which respectively extend two flanks (21) of identical inclination, said ship (1) having an unladen weight Pv between 20% and 60% inclusive of its total weight PT, allowing for a given maximum load weight PTC, according to the formula: P T = P v + P TC said ship including at least one bow closed liquid tank (2) and one stern closed liquid tank (3) not communicating with the sea, said tanks (2, 3) being in communication via at least one line for the transfer of liquid from one to the other, said tanks (2, 3) being positioned facing one another essentially along the longitudinal axis (x'x) and at a distance d from one another, considering the respective geometric center of each of said tanks (2, 3), where d ≥ L / 4, the method including the step of transferring liquid into the bow tank (2) when the load of the ship has a weight less than PTC / 10 to straighten the waterline of the ship, the liquid being either pure water or water slightly charged with minerals, the mass of which is established between 0.95 kg and 1.05 kg per liter. the total weight PRT of said tanks (2, 3) when entirely filled with the liquid representing between 2% and 8%, preferably between 3% and 6%, of said total unladen weight PV, the ship (1) further including a mooring tank (12), that mooring tank (12) being independent of the bow tank (2) and of the stern tank (3), the ship (1) further including a line (13) for supplying sea water to the mooring tank (12) and a line (14) for draining the mooring tank (12), said mooring tank (12) being at the bow of the ship (1), the method further including the step of transferring sea water into the mooring tank (12) via the supply line (13) in order to straighten further the waterline of the ship (1) if the ship transports no load and has an inclined trim when the ship enters or sails in a port zone or enters a dry dock.

2. The method for controlling the trim of a ship (1) as claimed in claim 1 in which the step of transferring the liquid into the bow tank (2) is carried out until the bow tank (2) is filled.

3. The method for controlling the trim of a ship (1) as claimed in claim 1 or 2, characterized in that the mooring tank (12) is situated in the first bow third, preferably in the first bow quarter, of the ship (1).

4. The method for controlling the trim of a ship (1) as claimed in any one of claims 1 to 3, characterized in that the supply line (13) discharges into an upper part of the mooring tank (12).

5. The method for controlling the trim of a ship (1) as claimed in any one of claims 1 to 4, characterized in that the drain line (14) discharges on a flank of the ship (1) and above a Plimsoll line (20) of the ship (1).

6. The method for controlling the trim of a ship (1) as claimed in any one of claims 1 to 5, characterized in that the bow tank (2) is situated in the first bow third, preferably in the first bow quarter, of the ship and the stern tank (3) is situated in the last stern third, preferably in the last stern quarter, of the ship (1).

7. The method for controlling the trim of a ship (1) as claimed in any one of claims 1 to 6, characterized in that the ship (1) includes a third tank (4), situated in a zone between 40% and 60% inclusive of the length L of the ship (1), the communication for the transfer of the liquid between the bow tank (2) and the stern tank (3) preferably being effected via said third tank (4).

8. A method for controlling the trim of a transport ship (1) without seawater ballast (1), the ship having a length L along the longitudinal axis (x'x) of the ship (1) and a width ℓ along a transverse axis (y'y) of the ship (1) and including a lower hull a cross section of which takes the form of a trapezium comprising a part forming a flat bottom (22) of the ship (1) from which respectively extend two flanks (21) of identical inclination, said ship (1) having an unladen weight Pv between 20% and 60% inclusive of its total weight PT, allowing for a given maximum load weight PTC, according to the formula: P T = P v + P TC said ship including at least one first closed liquid tank (3') and one second closed liquid tank (3") not communicating with the sea, said tanks (3', 3") being in communication via at least one line for the transfer of liquid from one to the other, said tanks (3', 3") being positioned facing one another essentially along the transverse axis (y'y) and at a distance d from one another, considering the respective geometric center of each of said tanks (3', 3"), where d ≥ l / 2 the method including the step of transferring a liquid into either the first tank (3') or the second tank (3") in order to cause the ship (1) to heel, the liquid being either pure water or water slightly charged with minerals, the mass of which is established between 0.95 kg and 1.05 kg per liter, the total weight PRT of said tanks (3', 3") when entirely filled with the liquid representing between 2% and 8%, preferably between 3% and 6%, of said total unladen weight PV.

9. The method for controlling the trim of a ship (1) as claimed in claim 8, in which the step of transferring the liquid into either the first tank (3') or the second tank (3") is carried out until an upper limit of a flank (21) of the lower hull of the ship (1) is flush with the level of the water.

10. The method for controlling the trim of a ship (1) as claimed in claim 8 or 9, in which the step of transferring the liquid into either the first tank (3') or the second tank (3") is carried out until said first tank (3') or said second tank (3") is filled.

11. The method for controlling the trim of a ship (1) as claimed in any one of claims 8 to 10, characterized in that one of the tanks (3' or 3") is situated in the first lateral third, preferably in the first lateral quarter, of the ship and the other tank (3' or 3") is situated in the last lateral third, preferably in the last lateral quarter, of the ship (1).

12. The method for controlling the trim of a ship (1) as claimed in any one of claims 8 to 11, characterized in that it further comprises the step of selecting a side of the ship (1) having one of said flanks (21), and in that the step of transferring the liquid into one of the first tank (3') and the second tank (3") is carried out to cause the ship to heel towards said side of the ship (1).

13. The method for controlling the trim of a ship (1) as claimed in any one of the preceding claims, characterized in that the ship (1) includes a set of valves for managing the arrival or non-arrival of the liquid and its flow rate in each of the tanks (2, 3, 3', 3", 4), at least one pump for transferring the liquid from one of the tanks (2, 3, 3', 3" or 4) to another tank (2, 3, 3', 3" or 4) and means (30, 40) for introducing the liquid into at least one of the tanks (2, 3, 3', 3", 4).

14. The method for controlling the trim of a ship (1) as claimed in any one of the preceding claims, characterized in that said ship (1) has an unladen weight Pv between 30% and 50% inclusive of its total weight PT.

15. The method for controlling the trim of a ship (1) as claimed in any one of the preceding claims, characterized in that said ship (1) includes at least one sealed and insulating tank, said tank including two successive sealing barriers, a primary one in contact with a product contained in the tank and a secondary one disposed between the primary barrier and a support structure preferably consisting of at least a part of the walls of the ship (1), these two sealing barriers alternating with two thermally insulating barriers or a single thermally insulating barrier disposed between the primary barrier and the support structure.

16. The method for controlling the trim of a ship (1) as claimed in any one of the preceding claims, characterized in that said ship (1) includes at least one sealed and insulating tank, said tank including a sealing barrier and a thermally insulating barrier.

17. The method for controlling the trim of a ship (1) as claimed in claim 15 or 16, characterized in that the tank contains liquified natural gas (LNG) or liquified gas (LG).

18. The method for controlling the trim of a ship (1) as claimed in any one of claims 15 to 17, characterized in that at least a part of the space surrounding the tank is uncompartmented.

19. The method for controlling the trim of a ship (1) as claimed in any one of the preceding claims, characterized in that when the ship (1) carries no load the inclination of said flanks (21) is such that the extremities of those flanks (21) are situated at a height of at most one meter above the level of the water (50), preferably at a height of at most 0.5 meter above the level of the water (50).

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