EP3885243A1

EP3885243A1 - Ballastless cargo vessels

Info

Publication number: EP3885243A1
Application number: EP20382223.4A
Authority: EP
Inventors: Claudio Fernández Marmiesse; Pablo Campos-Ansó Fernández
Original assignee: Ecoeficiencia E Ingenieria SL
Current assignee: Ecoeficiencia E Ingenieria SL
Priority date: 2020-03-24
Filing date: 2020-03-24
Publication date: 2021-09-29

Abstract

Examples refer to a ballastless cargo vessel that comprises a hull having an upper body and lower body, the upper body having a substantially rectangular cross section and the lower body having a substantially V-shaped cross section. The vessel further comprises cargo spaces in correspondence with the upper body and void spaces in correspondence with the lower body. Having a pre-defined parameter that is selected among a maximum draft, a minimum draft and a maximum beam of the vessel, the geometry of the vessel is defined by: a ratio between a width of a flat bottom and a maximum waterplane area of the vessel that ranges between 0 and 0.7, a ratio between a submerged draft of the upper body and a maximum draft of the vessel that ranges between 0 and 0.7, and a midship section coefficient of the vessel that ranges between 0.65 and 0.85.

Description

TECHNICAL FIELD

In general, the present invention relates to ships, and more preferably to cargo vessels, with no ballast systems having an upper body with a substantially rectangular cross section and a lower body with a substantially V-shaped cross section. The ballast tanks (normally located at the bottom and both sides of the ship) storing the ballast water can be eliminated from the ship and then the hull forms are redesigned with the substantially V-shaped body, so that the new design of the vessel is equivalent in buoyancy to the conventional one. The ballast effect concept on the conventional design (with ballast) is replaced by the convenient reduction of buoyant volume of the hull.

STATE OF THE ART

A ship, in particular, a cargo vessel is designed considering the weight of the vessel itself and the weight of a cargo that is to be transported on board. Therefore, when the ship is in no cargo condition or in partial load, the ship floats higher relative to the water surface and may become unstable to traverse waves and side wind and may be susceptible to trim or heel. In addition, the propellers of the ship approach the surface of the water which may cause cavitation damage on them as well as make them work under a regime lower than the recommended, increasing wear of the propeller and the need for maintenance. In order to decrease the degree to which the hull goes up relative to the water surface in no cargo or partial load condition, ships normally integrate a water ballast system comprising tanks containing sea water that maintains the necessary draft to ensure efficient propeller, safe navigation and is used to balance the ship. The ballast water is normally loaded and discharged at different harbours that may be in different countries or continents. Because of improvements in speed of ships, said ships are able to travel between countries in a short time with living aquatic species, in particular, invasive marine species, contained in the ballast water such that when this ballast water is discharged in a place far away from where it was loaded, the release of these living aquatic species may cause environmental problems of disturbing ecosystems on a global scale.
In order to prevent certain species from entering the ballast tanks some ships integrate filtration systems blocking said species while allowing water to enter the ballast tank. Other ships integrate ballast water treatment systems that include heating systems, ultraviolet light systems, de-oxygenation systems, etc., in order to kill or at least reduce the amount of living aquatic species contained in the ballast water. However, all these solutions are inefficient and have high installation and maintenance costs. Moreover, these solutions require large amounts of energy to be operated and thus, require burning more fuel which results in higher emissions.
Other solutions that attempt to release the ballast water, including the species contained therein, at a location near where the ballast water entered the ship have been developed. Some ships, known as a "free-ballast vessels", integrate a group of structural trunks running the full length of vessel. In ballast operations, these trunks can be opened to the sea with an intake opening at the bow and a discharge opening at the stern, being subjected to a flow of water from the intake opening to the discharge opening. In this way, these trunks can be flooded, reducing the buoyancy of the hull and allowing the ship to sink to its desired ballast draft. The diameter of the openings, the diameter of the trunks, or even of the number of available trunks can be varied to modify the amount of ballast water contained within the trunks at any moment depending on the ballast requirement. With flow, the water in these trunks can always be "local" water virtually decreasing ecosystem disturbance. An example of this kind of ship is disclosed in US2003019413A1 (Parsons ). However, this solution is technically complex and adds a great drag on the ship's hull while moving through the water.
In addition, multihull ships without a ballast system are known in the art. This kind of ship does not need to carry ballast water. However, the manufacturing and maintenance costs of this kind of ships is significantly higher than a monohull ship. Besides, due to the particular design of these ships, integrating a hold big enough and in one single piece is difficult and the beam is significatively greater than in monohull ships. Another disadvantage of these ships is that when the multihull ships transport heavy loads at low speeds, the wetted surface area and the drag in seaway significantly increases.
Ships having a V-shaped deadrise that is provided with a high beam are known in the art. In this kind of ship, ballast water may not be needed for achieving an appropriate control of the centre of gravity of the ship under different cargo conditions. Ships with V-shaped deadrise are designed to transport fluid cargos, e.g., gas, oil or other petroleum sub-products, which easily adapt to any kind of hold, having different shapes and geometries, in which they are stored. However, these solutions cannot be applied for transporting cargos, e.g. objects, solid materials, etc., which require specific hull geometries, dimensions, or shapes.
Therefore, it would be desirable to find a solution alternative to ballast water systems that avoids all the drawbacks mentioned above and that ensures a safe and efficient sailing of the ship cargo vessels.

DESCRIPTION OF THE INVENTION

The object of the invention is a ballastless ship, in particular a ballastless cargo vessel, that comprises a hull having a longitudinal upper body and a longitudinal lower body, the lower body being located beneath the upper body. The upper body has a substantially rectangular cross section along the length of the hull and the lower body has a substantially V-shaped cross section along the length of the hull. More particularly, the upper body may have a substantially rectangular cross section along the length of the cargo space, e.g., the hold, of the vessel while the bow section and the stern section of the vessel may have a substantially similar or different cross section. Similarly, the lower body may have a substantially V-shaped cross section along the length of the cargo space, e.g., the hold, of the vessel while the bow section and the stern section of the vessel may have a substantially similar or different cross section. For example, the bow section of the vessel may be a bulbous bow, clipper bow, curved bow, or any other type of bow. Said bow section may be designed to reduce the resistance of the hull cutting through water. On the other hand, the stern section of the vessel may be a square or transom stern, an elliptical stern, fantail stern, merchant stern, or any other type of stern.
Said upper and lower bodies are joined to each other at least by their side walls creating the side shells of the hull. The upper body and the lower body may be further joined to each other by means of inner structural frames, pillars or similar. The height of the upper body relative to the height of the lower body may depend on the difference between the maximum and the minimum displacement of the vessel. For example, the greater the difference between the maximum and the minimum displacement of the vessel, the greater the height of the lower body relative to the height of the upper body. In some examples, the height of the upper body relative to the moulded depth of the vessel may range between 45%-85%. Thus, in such examples, the height of the lower body relative to the moulded depth of the vessel may range between 55%-15%. To compensate said difference between the maximum and the minimum displacement of the vessel, the maximum beam (beam at the upper body) of the vessel may be further modified, such that the greater is this difference the greater the maximum beam of the vessel. Alternatively, the beam and the draft of the vessel may be modified together to compensate said difference.
The substantially V-shaped cross section of the lower body alters the vertical distribution of the hull buoyancy causing a deeper draft of the ship in the light (unloaded) condition than other known ships with different vessel geometries.
The ballastless cargo vessel further comprises at least one cargo space, in other words, at least one volume for transporting the cargo, such as the cargo hold, arranged at least in correspondence with the upper body for at least storing the cargo. This hold may totally occupy the space defined by the upper body or may totally or partially occupy the space defined by the upper body and also partially occupy the space defined by the lower body of the vessel. The cargo space may also protrude from the upper body so as to partially occupy the deck of the ship.
The ballastless cargo vessel also comprises void spaces in correspondence with the lower body. These void spaces act as float tanks for the ship. Part of these void spaces may be further used for storing fuel tanks, pipe systems, or a trim compensation system as described hereinafter, among other systems or elements of the vessel. By way of example, the ratio between the volume of the void spaces and the maximum volumetric displacement of the vessel may range from 0,1 to 0,45, although other ratios may be reached based on the particular vessel design.
The lower body with the V-shaped cross section comprises inclined side walls that may join to each other and to the side walls of the upper body. These inclined side walls may be substantially planar (the inclined side walls may be at a substantially constant angle relative to the waterplane) or may be curved (the inclined side walls may be at a variable angle relative to the waterplane). In any case, the equivalent average slope of the inclined side walls (obtained for an equivalent volume of the lower body having completely planar inclined side walls) may range between 0.5° and 85° relative to the horizontal. In some embodiments, the lower body further comprises a flat bottom (also known as flat bottom wall) located at a central portion of the bottom of the hull and along the length of the hull, and more preferably along the length of the cargo spaces, such that the inclined side walls are formed at both sides of the flat bottom so as the lower body has a substantially truncated V-shaped cross section. This truncated V-shaped cross section of the lower body is substantially similar to an inverted trapezoidal cross section.
The ballastless cargo vessel is defined such that, for a pre-defined parameter, the parameter being selected from a group comprising a maximum draft (T_max), a minimum draft (T_min) and a maximum beam (B_max) of the vessel, the geometry of the vessel is defined by:

i) a ratio (%B_max) between the width of the flat bottom of the vessel and the maximum beam at the waterplane area of the vessel that ranges between 0 and 0.7,
ii) a ratio (%T_max) between the submerged draft of the upper body (in other words, the vertical distance corresponding to the submerged portion of the vertical walls of the upper body) and the maximum draft of the vessel that ranges between 0 and 0.7, and
iii) a midship section coefficient (C_m) of the vessel defined as: $% T_{\max} + (1 - % T_{\max}) \cdot % B_{\max} + \frac{(1 - % T_{\max}) \cdot (1 - % B_{\max})}{2} = = \frac{1 + % T_{\max} + % B_{\max} - % T_{\max} * % B_{\max}}{2} = 1 - \frac{(1 - % T_{\max}) * (1 - % T_{\max})}{2}$
that ranges between 0.65 and 0.85.

As used herein the midship section coefficient of a vessel refers to the ratio between the area of the midship section of the vessel, for a defined draft, and the area of the rectangle that contains said area of the midship section of the vessel, the width of the rectangle corresponding to the moulded beam of the vessel and the height of the rectangle corresponding to the previously defined draft.
Then, the coefficient %B_max that has been defined as the ratio between the width (b) of the flat bottom of the vessel (if the vessel does not have flat bottom this ratio will be zero) and the maximum beam (B_max) of the vessel at the waterplane area of the vessel is: $% B_{\max} = \frac{b}{B_{\max}}$
Similarly, the coefficient %T_max that has been defined as the ratio between the submerged draft (t) of the upper body and the maximum draft of the vessel (T_max) is: $% T_{\max} = \frac{t}{T_{\max}}$
The V-shaped cross section of the lower body maintains sufficient draft and stability in light condition and avoids cavitation damage in the propeller with no need of having a ballast system. It also reduces hull resistance and improves propulsion efficiency. The volume of the void spaces in the lower body ensures that the maximum draft of the vessel is not exceeded (the empty spaces act as a float when the vessel is loaded). The lower body may further have a shape that becomes more pointed in the longitudinal direction shifting the centre of the hull towards the stern of the vessel.
Besides, having an upper body with a substantially rectangular cross section along the entire length of the vessel and avoiding using side ballast tanks, the space occupied by the cargo space (e.g., hold) can be maximized in said upper body (the cargo space can have a width that substantially corresponds to the beam of the vessel), compensating any spatial loss in the lower body due to its V-shaped cross section.
The block coefficient of a ship is defined as the ratio of the underwater volume of the ship to the volume of a parallelepiped block defined by the length between perpendiculars, the breadth (beam) and the depth (draft) of the ship. In some embodiments, this block coefficient of the vessel depends on a value of the angle of the inclined side walls relative to the baseline.
For example, for a predefined B_max and T_max and a constant t and %T_max (only b and %B_max are varied) a higher angle of the inclined side walls relative to the flat bottom implies having a higher block coefficient and vice versa. In other examples, for a predefined B_max and T_max and a constant b and %B_max (only t and %T_max are varied) a higher angle of the inclined side walls relative to the flat bottom implies having a lower block coefficient and vice versa. Besides, the midship section coefficient and the block coefficient of a vessel are related to each other. That is, the lower the midship section coefficient, the lower the block coefficient, and vice versa.
In some embodiments, the block coefficient (C_b) is defined as: $% T_{\max} + (1 - % T_{\max}) \cdot % A_{floatmax} + \frac{(1 - % T_{\max}) \cdot (1 - % A_{floatmax})}{2} = \frac{1 + % T_{\max} + % A_{floatmax} - % T_{\max} * % B_{\max}}{2} = 1 - \frac{(1 - % T_{\max}) * (1 - % A_{floatmax})}{2}$
and ranges between 0.52 and 0.72, wherein %A_floatmax is the ratio between the area of the flat bottom (A_flatbottom) of the lower body of the vessel and the area of the maximum waterline (A_floatmax) of the vessel. The resulting block coefficient (C_b) of the vessel will depend on the difference between the maximum and minimum displacement of the vessel.
Then, the coefficient %A_floatmax that has been defined as the ratio between the area of the flat bottom (A_flatbottom) of the lower body of the vessel (if the vessel does not have flat bottom this ratio will be zero) and the area of the maximum waterline (A_floatmax) of the vessel is: ${% A}_{floatmax} = \frac{A_{flatbottom}}{A_{floatmax}}$
In some embodiments, when the vessel is at its minimum draft (minimum weight), the lower body is at least partially submerged and, when the vessel is at its maximum draft (maximum weight), the lower body is totally submerged and the upper body is partially submerged.
In some embodiments, the at least one cargo space is a hold, and more particularly, a box-type hold. In such embodiments, due to the lack of side ballast tanks in the vessel, the hold may have a width that substantially corresponds to the beam of the vessel along the length of the vessel. Therefore, the hold can maximize space occupancy within the vessel. Then, a reduction in the moulded depth of the hold due to the V-shaped cross section of the lower body can be compensated with the increase in the width of the hold.
For the box-type holds the influence of the transition between the baseline (or the flat bottom if the vessel has it) of the lower body and the side walls of the upper body on the vessel hydrodynamic parameters is especially relevant since it is of interest to reach the maximum value (moulded breadth) with the smallest possible draft, as the box-type hold is to be placed as low as possible within the vessel for stability reasons, as well as for contributing to the maximum draft not being excessive. Therefore, for these particular box-type holds, the inclined side walls of the lower body may have an angle relative to the baseline that is smaller than other type of known holds. For example, for the box-type holds the inclined side walls may be at an angle relative to the baseline that may range from 0.5° to 85°.
In some embodiments, the minimum draft of the vessel depends on the propulsion system of the vessel. In other words, the minimum draft may be the draft required for a proper immersion of the propellers of the propulsion system of the vessel. The minimum draft of the vessel of the vessel may further depend on stability and seakeeping requirements of the ship.
In some embodiments, the ballastless cargo vessel comprises two propellers. In such embodiments, the ballastless cargo vessel may further comprise two propulsion engines such that when the vessel sails with its minimum draft only one of the two propulsion engines is configured to feed the two propellers, and when the vessel sails with a draft higher than the minimum draft each propulsion engine feeds a corresponding propeller of the two propellers. Mainly, there are two clearly differentiated extreme cargo conditions: empty and full load. When the cargo vessels are empty (no cargo), the displacement and draft are small, as well as the drag on the vessel while moving through the water (energy saving). When sailing at full load (maximum deadweight tonnage) the drag of the ballastless cargo vessel will be very similar to the drag in seaway of the conventional cargo ship. This may imply that the difference in power required for the propulsion of the ship in either condition is large. For the no cargo condition, because the draft has been reduced to the minimum necessary for the correct operation of the vessel, one single propulsion engine is used to feed the two propellers. For any other draft higher than the minimum draft, each engine of the two propulsion engines is used to feed one of the two propellers. In some examples, the propulsion engines may be diesel-electric propulsion engines, such as ASD (Azimuth Stern Drive) type propulsion engines with either mechanical (L-Drive, Z-Drive) or electrical transmission, that allow a better control of the power delivered to each one of the propellers. These diesel-electric propulsion engines may be feed by a plurality of generator sets that may be operated based on the power required by the propulsion engines.
In some embodiments, the hull further comprises a trim compensation system having at least two tanks fluidly connected to each other wherein a fluid, e.g., fresh water, stored in the at least two tanks is transported (weight transfer on board) between the at least two tanks to keep the vessel stabilized. This trim compensation system is able to correct heeling and trimming. The size of the tanks and the location of the tanks within the ballastless cargo vessel may be optimized for providing enough torque with as little water as possible. In some examples, there may be at least one tank located in proximity of each one of the side shells (port and starboard) of the hull fluidly connected to each other to correct the heel of the ship and there may be at least one tank located in proximity to the bow and another tank located in proximity to the stern, fluidly connected to each other, to correct the trim of the ship.
The cargo vessel herein described avoids using ballast water systems and thus, eliminates the transport of sea water containing invasive marine species. Therefore, this solution is more effective than current treatment methods in reducing the potential for the introduction of said invasive marine species in other foreign ecosystems. Besides, by avoiding treating the ballast water significant energy savings are achieved. In addition, installation of tanks, pumps, pipes, pipes and other elements of the water ballast system is avoided with the corresponding installation and maintenance cost savings. Another advantage is that the vessel herein described is more efficient since it significantly reduces its drag while moving through the water in its empty condition (less displacement, less wetted surface and lower power required).

BRIEF DESCRIPTION OF THE DRAWINGS

To complete the description and in order to provide for a better understanding of the invention, a set of drawings is provided. Said drawings form an integral part of the description and illustrate an embodiment of the invention, which should not be interpreted as restricting the scope of the invention, but just as an example of how the invention can be carried out.
The drawings comprise the following figures:

Figures 1A-C show different views of a ballastless cargo vessel, according to a particular embodiment of the invention.
Figure 2 shows a cross sectional view of the ballastless cargo vessel of Figure 1 along line A-A.
Figure 3 shows a cross sectional view of a prior art cargo vessel and a cross sectional view of the ballastless cargo vessel, according to a particular embodiment of the invention.
Figure 4A shows a cross sectional view of the ballastless cargo vessel, according to a particular embodiment of the invention, with the parameters that define the ballastless cargo vessel in two dimensions.
Figure 4B shows a cross sectional view of the ballastless cargo vessel of Figure 4A, with the parameters that define the ballastless cargo vessel in three dimensions.

DETAILED DESCRIPTION OF THE INVENTION

Figures 1A-C shows different views of a ballastless cargo vessel 100, according to a particular embodiment of the invention. It should be understood that the ballastless cargo vessel 100 of Figures 1A-C may include additional components and that some of the components described herein may be removed and/or modified without departing from a scope of the described vessel 100. Additionally, implementation of the ballastless cargo vessel 100 is not limited to such embodiment.
Figure 1A shows a bottom perspective view of the ballastless cargo vessel 100. The ballastless cargo vessel 100 comprises an upper body 101 and a lower body 102 along the entire length of the vessel 100. Figures 1B and 1C show a bottom and a side view of the vessel 100, respectively. The upper body 101 of the vessel 100 has a substantially rectangular cross section along its central portion, in particular, along the space occupied by the hold (not shown in this figure). The lower body 102 of the vessel 100 has a substantially truncated V-shaped cross section (or inverted trapezoidal cross section) along the central portion of the vessel 100.
In the bow portion 103 of the vessel 100, the shape of the lower body 102 tapers to a point so that said lower body 102 can be widen at the stern portion 104 (the lower body 102 at the stern portion 104 is the portion of the vessel 100 in which a greater concentration of weights, such as machinery, etc., is located). This helps the vessel 100 to avoid trimming and decrease the drag in the seaway. The geometry of the bow portion 103 of the upper body 101 has been chosen to fit the geometry of the bow portion 103 of the lower body 102 and thus avoid very large "horizontal" surfaces between the upper body 101 and the lower body 102 that increase drag and reduce efficiency. These geometries, that become more pointed in the longitudinal direction, minimize the slamming. At a certain point, the lower body 102 defines a transition surface between the bottom of the vessel 100 and the upper body 101 leaving a space for the propellers to be placed.
While the ballastless cargo vessel 100 in Figures 1A-C shows a bow portion 103 and stern portion 104 having a particular geometry, said bow portion and stern portion may have any other geometry depending on the particular vessel design. In addition, while the ballastless cargo vessel 100 in Figures 1A-C shows a lower body 102 with a substantially truncated V-shaped cross section (or inverted trapezoidal cross section) along its central portion, the lower body 102 may have a V-shaped cross section (not having a flat bottom) along its central portion.
Figure 2 shows a cross sectional view of the ballastless cargo vessel 100 of Figure 1 along line A-A. The upper body 101 of the vessel 100 has a substantially rectangular cross section that is defined by the side shells 105 of the hull and the deck 106 of the vessel 100. The side shells 105 of the upper body 101 are joined by their lower ends to inclined side walls 107 of the lower body 102. These inclined side walls 107 define the transition zone between the flat bottom (or flat bottom wall) 108 located at the bottom of the vessel 100 and the upper body 101. The angle of the inclined side walls 107 relative to the flat bottom 108 determines how fast or slow the underwater volume of the vessel 100 increases or decreases in relation with a variation in the weight of the ship. There is also a direct relationship between this angle and the block coefficient of the vessel 100.
The lower body 102 comprises void spaces 109 that act as floats for the vessel 100. These void spaces 109 are dimensioned such that the air volume in the submerged void spaces 109 is equivalent to the air volume in the submerged ballast tanks, totally or partially empty, in the load condition of a conventional vessel. For example, the ratio between the volume of the void spaces 109 and the maximum volumetric displacement of the vessel 100 may range from 0,1 to 0,45. The vessel 100 further comprises a box-type hold 110 arranged within the upper body 101 for storing the cargo. This hold 110 has a width that substantially corresponds to the beam of the vessel 100 and a length that substantially corresponds to the length of the vessel 100. In particular, the length of the hold 110 may substantially correspond to the length of the central portion of the vessel 100, i.e., excluding the bow portion 103 and the stern portion 104.
While the ballastless cargo vessel 100 of Figure 2 shows a hold 110 arranged in correspondence with the upper body 101 of the vessel 100, the hold 110 may also partially occupy the space contained within the lower body 101 and/or may protrude above the deck line of the vessel 100. Moreover, while the ballastless cargo vessel 100 shows one single hold, in some other embodiments, there may be more than one hold arranged longitudinally along the length of the vessel, more than one hold arranged transversally to the length of the vessels or any combination thereof.
Figure 3 shows a cross sectional view of a conventional cargo vessel 200 (cargo vessel with ballast system) and a cross sectional view of the ballastless cargo vessel 201, according to a particular embodiment of the invention. It should be understood that the ballastless cargo vessel 201 of Figure 3 may include additional components and that some of the components described herein may be removed and/or modified without departing from a scope of the described vessel 201. Additionally, implementation of the ballastless cargo vessel 201 is not limited to such embodiment.
The ballastless cargo vessel 201 of Figure 3 substantially corresponds to the ballastless cargo vessel 100 of Figure 2 but with the hold 202 protruding above the deck line of the vessel 201. While the hold 202 of the ballastless cargo vessel 201 occupies its upper body 203 and slightly protrudes over its deck line leaving the lower body 204 free of the hold 202 to contain the void spaces that will act as a float for the vessel 201, the hold 205 of the conventional cargo vessel 200 substantially occupies the entire vessel 200, except for the space for the machinery, the ballast system, tanks, etc.
In the ballastless cargo vessel 201, due to the lack of side ballast tanks, the hold 202 has a width that substantially corresponds to the beam of the vessel. In this way, the hold 202 is able to maximize space occupancy within the upper body 203.
In such figure, the moulded depth and the beam of the ballastless cargo vessel 201 and of the conventional cargo vessel 200 are substantially similar. However, although the moulded depth is similar, the draft of the ballastless cargo vessel 201 in its full load condition will be higher than the draft of the conventional cargo vessel 200 in its full load condition. This is because the displacement in the full load condition is the same for both vessels 200,201 but the difference between the displacement in full load condition and the displacement in empty condition or in ballast condition is different for both vessels 200, 201. In particular, this difference will be larger for the ballastless cargo vessel 201 and smaller for the conventional cargo vessel 200. If both vessels 200,201 have the same beam (assuming that both vessels have the same length) and draft (the minimum draft for the proper functioning of the vessels) in their empty condition and in ballast condition, the ballastless cargo vessel 201 will have to sink more because it has to compensate the greater difference in displacement between its full load condition and its empty and ballast conditions.
Therefore, assuming that both vessels 200,201 have a substantially similar beam and a substantially similar draft in their empty (for both vessels 200,201) and ballast (only for vessel 201) conditions, the moulded depth of the ballastless cargo vessel 201 should increase as much as the maximum draft of the ballastless cargo vessel 201 increases relative to the maximum draft of the conventional cargo vessel 200 (assuming the same or similar freeboard requirement for both vessels). This greater difference in displacement in the ballastless cargo vessel 201 can also be compensated by increasing the beam instead of the moulded depth or by reaching a compromise between increasing the beam and the moulded depth of the ballastless cargo vessel 201.
While the ballastless cargo vessel 201 in Figure 3 shows a lower body with a substantially truncated V-shaped cross section, the lower body may present a V-shaped cross section (without flat bottom).
Figure 4A shows a cross sectional view of a ballastless cargo vessel 300, according to a particular embodiment of the invention, including the parameters that define the geometry of the vessel 300 in two dimensions (2D). Figure 4B shows a cross sectional view of the ballastless cargo vessel 300 of Figure 4A, including the parameters that define the vessel 300 in three dimensions (3D). The cross-sectional view of the ballastless cargo vessel 300 shown in Figures 4A-B is similar to the cross-sectional view of the vessel 100 of Figure 2.
The ballastless cargo vessels 300 herein described have been designed with a hull's geometry, shape and buoyancy distribution that, in any load condition, the draft of the vessel is always between the minimum draft and the maximum draft of the ship's hull. As used herein, the draft of the ship's hull or the vessel refers to the vertical distance between the waterline and the bottom of the hull, including the thickness of the hull. The minimum draft corresponds to the minimum depth of water a ship can safely navigate while complying with the applicable maritime regulations. The minimum draft is normally reached with no cargo being transported on board. Similarly, the maximum draft of the vessel refers to the maximum depth of water a ship can safely navigate and comply with the applicable maritime regulations and is normally reached with the ship's maximum permissible deadweight, i.e., when it is fully loaded.
The vessel cargo condition that corresponds to the minimum draft is that in which the total weight of the vessel is the lowest possible weight (W_min), also known as the minimum displacement. In this condition the total weight is the sum of the following weights:

Lightweigth (LTD),
Constants (K)= Supplies and consumables + Crew and effects + oils and spare parts + effects on storerooms + miscellaneous), and
10% Consumption (fuels and oils in tanks), such that, $W_{\min} = LTD + K + 10 % Cons .$

Therefore, for the minimum draft the vessel should have a volume (V_min) of the hull underbody that balances this minimum weight (W_min): $V_{\min} = W_{\min} / d; (d = 1, 025 t / m^{3}$
sea water specific weight)
On the other hand, the vessel cargo condition that corresponds to the maximum draft is the one in which the total weight of the vessel is the greatest possible weight (W_max). In this condition the weight of the vessel, also known as the loaded (or maximum) displacement, will be the sum of the following weights:

Lightweigth (LTD), and
Deadweight (DWT)= Cargo+K+100% Consumption, such that, $W_{\max} = LTD + DWT = D$

Therefore, for the maximum draft the vessel should have a volume (V_max) of the hull underbody that balances this weight (W_max): $V_{\max} = W_{\max} / d; (d = 1, 025 t / m^{3})$
The transition between the V_max and the V_min should be made achieving an underbody's volume growth rate directly related with the variation of the flotation area of the vessel, in other words, underbody's volume growth rate increases with the beam growth rate (B(T)) for the draft considered. As used herein, the beam refers to the width of a ship at the widest point as measured at the ship's nominal waterline. This beam growth rate may be limited by some design restrictions such as a predefined maximum draft, a minimum draft and a maximum beam of the vessel, among others.
The relationship between the draft (T) of the vessel and the volume of the hull underbody that balances the corresponding weight (W) can be also expressed as a function of the floating area (Afloat(T)) of the vessel for the draft considered. Then, the condition for the minimum draft (minimum weight) of the vessel can be expressed as a function of the floating area or as a function of the beam as follows: $\int_{0}^{Tmin} Afloat (T) ⅆ T = Vmin = Wmin / d$
$\int_{0}^{Tmin} B (T) ⅆ T = AMmin$
wherein AM_min is the section area defined by the submerged portion of the midship section in the minimum draft condition.
The condition for the maximum draft (maximum weight) of the vessel can be expressed as a function of the floating area or as a function of the beam as follows: $\int_{0}^{Tmax} Afloat (T) ⅆ T = Vmax = Vmax / d$
$\int_{0}^{Tmax} B (T) ⅆ T = {AM}_{\max}$
wherein AM_max is the section area defined by the submerged portion of the midship section in the maximum draft condition.
Therefore, it is necessary to define the functions Afloat(T) and B(T). Said functions can be defined on intervals. In the interval of the functions corresponding to the lower body of the hull, the floating area and the beam grow constantly.
According to Figure 4A, the initial data that define the ballastless cargo vessel (considering that the beam of the vessel grows linearly) are: maximum draft (T_max), minimum draft (T_min), ratio (%B_max) between the width (b) of the flat bottom of the lower body of the vessel and the maximum beam (B_max), ratio (%T_max) between the submerged draft (t) of the upper body (i.e., vertical side dimension of the upper body of the vessel) and the maximum draft (T_max), and maximum beam (B_max). For this particular embodiment, T_max has been considered as the pre-defined parameter, i.e., the T_max of the vessel is used as a restriction for obtaining the midship section coefficient (C_m), the ratio %B_max and the ratio %T_max. Alternatively, the midship section coefficient, the ratio %B_max and the ratio %T_max may be obtained using the maximum beam (B_max) or the minimum draft (T_min) as the pre-defined parameters (restriction) since all these dimensions (maximum draft, minimum draft and maximum beam) are related to each other.
Knowing the maximum and minimum displacement of the vessel and a given maximum draft (restriction), varying the values of %B_max and %T_max between 0 and 0.7, respectively, and establishing that $1 - \frac{(1 - % T_{\max}) * (1 - % B_{\max})}{2} = Cm = (0.65, 0.85)$
all possible solutions can be found for designing the ballastless cargo vessel. Each obtained solution will have a minimum draft and a maximum beam. Then, the lower the %B_max and the higher the %T_max, the lower the midship section coefficient and also the block coefficient of the vessel. In addition, and as a consequence, the midship section coefficient, and also the block coefficient, will be lower the more inclined the side walls of the lower body are. The midship section coefficient and the block coefficient of a vessel are related to each other. That is, the lower the midship section coefficient, the lower the block coefficient and vice versa.
According to Figure 4B, the initial data that define the ballastless cargo vessel (considering that the area of flotation of the vessel grows linearly and the variation of the area of the flotation is due only to a variation of the beam) are: maximum draft (T_max), minimum draft (T_min), ratio (%A_floatmax) between the area of the flat bottom (A_flatbottom) of the lower body of the vessel and the area defined by a maximum waterline of the vessel (A_floatmax), ratio (%T_max) between the vertical side dimension (t) of the upper body of the vessel and the maximum draft (T_max), and maximum beam (B_max). For this particular embodiment, T_max has been considered as the pre-defined parameter, i.e. the T_max of the vessel is used as a restriction for obtaining the block coefficient (C_b) (and also the midship section coefficient (C_m)), the ratio between the area of the flat bottom and the maximum water plane area of the vessel, and the ratio between the submerged draft of the upper body and the maximum draft of the vessel. Alternatively, the ratio (%A_floatmax) and the ratio (%T_max) of the vessel may be obtained using the maximum beam or the minimum draft as the pre-defined parameters (restriction) since all these dimensions (maximum draft, minimum draft and maximum beam) are related to each other.
Knowing the maximum and minimum displacement of the vessel and a given maximum draft (restriction), varying the values of %B_max and %A_floatmax between 0 and 0.7, respectively, and establishing that $1 - \frac{(1 - % T_{\max}) * (1 - % A_{floatmax})}{2} = Cb = (0.52, 0.72)$
all possible solutions can be found for designing the ballastless cargo vessel. Each obtained solution will have a minimum draft and a maximum beam. Then, the lower the %B_max and the higher the %T_max, the lower the block coefficient and also the midship section coefficient of the vessel. In addition, and as a consequence, the block coefficient, and also the midship section coefficient, will be lower the more inclined the side walls of the lower body are. The block coefficient and the midship section coefficient of a vessel are related to each other. That is, the lower the block coefficient, the lower midship section coefficient and vice versa.
The design of the lower body up to the height of the minimum draft (T_min) of the vessel achieves an underbody's volume growth rate that is directly related with the variation of the flotation area of the vessel. In other words, the underbody's volume growth rate increases with the beam growth rate for the draft considered. Thus, the block coefficient (C_bm) for the minimum draft (T_min), equivalent to say the block coefficient of the lower body up to height corresponding to the minimum draft, can be defined as: $C_{bm} = \frac{D - W_{load} - 0, 9 * W_{cons}}{d * L * B * T_{\min}}$
wherein D is the full cargo Displacement (max weight of the vessel), W_load is the weight of the cargo carried in the vessel, W_cons is the weight of the consumptions of the vessel, d=1,025 t/m³ (sea water specific weight), L is the length of the vessel between perpendiculars and B is the moulded beam.
Therefore, the block coefficient of the lower body for the minimum draft is determined based on the main dimensions of the vessel, the minimum necessary draft and the load capacity (DWT) and consumptions of the vessel (autonomy). Then, it is obtained a value of the block coefficient of the lower body that depends on the minimum draft of the vessel and that the vessel design cannot exceed, conditioning the maximum value of the block coefficient of the vessel and thus the minimum value of its maximum draft.
The difference between the maximum volume (V_max) and the minimum volume (V_min) of the vessel is: $V_{\max} - V_{\min} = L * B * (T_{\max} - T_{\min}) * C_{b}^{ʹ}$
wherein C'_b is the block coefficient of the upper body in the area between the maximum draft (T_max) and the minimum draft (T_min) of the vessel. $C_{b}^{ʹ} = \frac{(C_{b} * T_{\max} - C_{bm} * T_{\min})}{(T_{\max} - T_{\min})}$
Since V= W/d, then: $V_{\max} - V_{\min} = \frac{(D - W_{\min})}{d} = L * B * (T_{\max} - T_{\min}) * C_{b}^{ʹ}$
and then, $\begin{matrix} T_{\max} = \frac{(D - W_{\min})}{d * L * B * C_{b}^{ʹ}} + T_{\min} \\ (D - W_{\min}) = W_{load} + 0, 9 * W_{cons} \\ T_{\max} = \frac{(W_{load} + 0, 9 * W_{cons})}{d * L * B * C_{b}^{ʹ}} + T_{\min} \end{matrix}$
So, this means that the maximum draft of the vessel can be determined based on the main dimensions of the vessel, the minimum necessary draft and the cargo capacity (DWT) and consumptions of the vessel (autonomy).
From formulas (1) and (2), it can be obtained: $C_{b} = \frac{V_{\max} * C_{b}^{ʹ}}{V_{\max} + L * B * T_{\min} * (C_{b}^{ʹ} - C_{bm})}$
that provides the block coefficient of the vessel as a function of the block coefficient of the lower body up to its minimum draft and of the block coefficient of the upper body between its minimum draft and its maximum draft.
If the midship section coefficient of the upper body (C'_m) of the vessel is considered to be 1 (this simplification maximizes the value of the block coefficient of the vessel and thus, provides a minimum T_max which means that the maximum beam is reached at the minimum draft or even at a draft that is lower than the minimum draft), the block coefficient of the upper body is equal to the prismatic coefficient of the upper body (C'_p), $C_{b}^{ʹ} = C_{p}^{ʹ} * C_{m}^{ʹ} = C_{p}^{ʹ}$
With the prismatic coefficient of the vessel (C_p) and the prismatic coefficient of the lower body (C_pm), the prismatic coefficient of the upper body (C'_p) can be obtained: ${Cʹ}_{p} * (AM - {AM}_{\min}) = C_{p} * AM - C_{pm} * {AM}_{\min}$
${AM}_{\min} * C_{pm} = AM * C_{p} * \frac{V_{\min}}{V_{\max}}$
$C_{p}^{ʹ} = \frac{C_{p} * (1 - \frac{V_{\min}}{V_{\max}})}{1 - \frac{C_{p} * V_{\min}}{C_{pm} * V_{\max}}}$
wherein AM is the area of the midship section of the vessel in the maximum draft condition (T _max) and AM_min is the area of the midship section of the vessel until the minimum draft (T_min ). Applying the simplification C'_b=C'_p, the block coefficient of the vessel based on the prismatic coefficient of the vessel and on the prismatic coefficient of the lower body can be obtained: $C_{b} = \frac{V_{\max}}{\frac{V_{\max}}{C_{p}} - \frac{V_{\min}}{C_{pm}} + L * B * T_{\min}}$
Then the maximum draft can be derived: $T_{\max} = \frac{V_{\max}}{L * B * C_{b}} = \frac{V_{\max}}{L * B * C_{p}} - \frac{V_{\min}}{L * B * C_{pm}} + T_{\min}$
The rest of parameters of the vessel can be derived, with the restrictions predefined, from theses block coefficient and maximum draft.
The prismatic coefficient of the lower body C_pm is limited and cannot be lower than 1-AM*(1-C_p)/AM_min since C'_p is lower than 1. ${Cʹ}_{p} = 1 \to C_{pm} > 1 - \frac{AM (1 - C_{p})}{{AM}_{\min}} = \frac{1}{1 + \frac{V_{\max}}{V_{\min}} (1 / C_{p} - 1)}$
$C_{pm} (\min) = \frac{1}{1 + \frac{V_{\max}}{V_{\min}} * (1 / C_{p} - 1)}$
Since C_pm has a minimum value that cannot be reduced, and since the block coefficient C_b decreases with the increase of C_pm, the value of C_pm should be as close as possible (taking into account the value of C'_p) to its minimum value (it is required a block coefficient as higher as possible to achieve a maximum draft as lower as possible).
Therefore, the value of the block coefficient has an upper limit that cannot be reached. This maximum value corresponds to a value of the prismatic coefficient of the lower body equal to the minimum value it can have, that is, C_pm = C_pm (min), that makes the value of the prismatic coefficient of the upper body to be equal to 1, C' _p = 1. $C_{b} (\max) = \frac{V_{\max}}{V_{\max} - V_{\min} + {LBT}_{\min}} = \frac{D}{W_{load} + 0, 9 * W_{cons} + d * L * B * T_{\min}}$
So, the maximum draft of the vessel has a lower limit that cannot be reached whose value is: $T_{\max} (\min) = \frac{(V_{\max} - V_{\min})}{L * B} + T_{\min} = \frac{(W_{load} + 0, 9 * W_{cons})}{d * L * B} + T_{\min}$
The main features of the vessel will be within the above described limit values.

By way of example, a table with different parameters of a ballastless cargo vessel, according to a particular embodiment of the invention, a conventional slow seagoing cargo vessel and a standard cargo vessel (both of them incorporating ballast systems), is provided.

	Ballastless Cargo Vessel ranges	Slow Seagoing Cargo Vessel	Standard Vessel	Ballastless Cargo Vessel	Ballastless Cargo Vessel maximum
B/T	1.35-3	2.1-2.3	2.3	1.9	1.4
C_b	0.52-0.72	0.65-0.73	0.74	0.69	0.54
C_m	0.65-0.85	0.97-0.995	0.94	0.79	0.67

The parameters compared in this table are the ratio (B/T) between the beam (B) and the draft (T), the block coefficient (C_b) and the midship section coefficient (C_m) of the vessels. The values of the ratio (B/T), the midship section coefficient (C_m) and the block coefficient (C_b) have been obtained based on the formulas described above. For the definition of the dimensions and proportions shown in the table, it has been considered that the length and the beam remain substantially constant for the ballastless cargo vessel. Thus, the most important dimensions to be defined are the draft and the moulded depth of the ballastless cargo vessel.
The "Ballastless Cargo vessel ranges" column refers to the values between which the ballastless cargo vessel as described herein ranges. The "Slow Seagoing Cargo Vessel" column refers to the values between which a conventional slow seagoing cargo vessel with ballast system ranges. The "Standard Vessel" column refers to the values of a particular conventional cargo vessel with ballast system. The values of the "Slow Seagoing Cargo Vessel" and "Standard Vessel" columns are known from prior art (Ship design: Methodologies of Preliminary Design, Papanikolaou 2014). The "Ballastless Cargo Vessel" column refers to values of a particular ballastless cargo vessel, as herein described, in which in order to arrive to the shown parameters the moulded depth of the vessel has been modified. The values of the "Ballastless Cargo Vessel maximum" column have been obtained for a maximum draft (restriction) of a 150% of the maximum draft of a conventional cargo vessel. In particular, the "Ballastless Cargo Vessel maximum" column shows values ballastless cargo vessel in which only the moulded depth of the vessel has been modified and the lower body has a V-shaped deadrise (in other word, there is no flat bottom in the lower body and the lower body has a triangular cross-section).
The ratio (B/T) of the ballastless cargo vessel as described herein ranges between 1.35-3 when the moulded depth of the vessel is substantially modified instead of the beam, i.e. the maximum draft of the vessel is increased. When the beam is substantially modified and not the moulded depth (reaching a similar maximum draft than a conventional vessel i.e. a vessel with ballast system) the ratio (B/T) ranges between 2-3. The particular value of the ratio (B/T) will depend on the difference of displacements of the vessel due to different loading conditions and the particular geometry of the vessel. Since only the moulded depth, or the beam or both of them could be modified a wide range [1.35-3] for the ratio (B/T) is obtained. Then, the design of the ballastless cargo vessel can be defined to reach a solution in which the ratio (B/T) would be substantially equal to the values of this ratio for the conventional ship (e.g., the standard cargo vessel or the slow seagoing cargo vessel), being the moulded depth and the beam of the ballastless cargo vessel higher than the normal values in a conventional ship with similar characteristics. The values of C_b and C_m are not affected by the value of the ratio (B/T) since they are affected by the value of the product (BxT).
When comparing the values obtained for the ballastless cargo vessel with the values obtained for the conventional or standard vessels, it can be seen how the draft and/or the beam of the ballastless cargo vessel is higher. Thus, the multiplication of the beam and the draft is higher than in conventional vessels (having ballast systems). The block coefficient, and thus, the midship section coefficient, is less than in conventional vessels.
In this text, the term "comprises" and its derivations (such as "comprising", etc.) should not be understood in an excluding sense, that is, these terms should not be interpreted as excluding the possibility that what is described and defined may include further elements, steps, etc. The term "another," as used herein, is defined as at least a second or more. The term "coupled," as used herein, is defined as connected, whether directly without any intervening elements or indirectly with at least one intervening elements, unless otherwise indicated. Two elements can be coupled mechanically, electrically, or communicatively linked through a communication channel, pathway, network, or system.
The invention is obviously not limited to the specific embodiments described herein, but also encompasses any variations that may be considered by any person skilled in the art (for example, as regards the choice of materials, dimensions, components, configuration, etc.), within the general scope of the invention as defined in the claims.

Claims

A ballastless cargo vessel, characterized in that the vessel comprises:
a hull comprising an upper body and a lower body, the upper body having a substantially rectangular cross section along a length of the hull and the lower body having a substantially V-shaped cross section along the length of the hull; and

at least one cargo space arranged at least in correspondence with the upper body for at least storing the cargo and void spaces at least partially in correspondence with the lower body;

wherein the lower body comprises respective inclined side walls that join to side walls of the upper body; and

wherein for a pre-defined parameter, the parameter being selected from a group comprising a maximum draft (T_max), a minimum draft (T_min) and a maximum beam (B_max) of the vessel, a geometry of the vessel is defined by: i) a ratio (%B_max) between a width of a flat bottom and a maximum waterplane area of the vessel that ranges between 0 and 0.7, ii) a ratio (%T_max) between a submerged draft of the upper body and a maximum draft of the vessel that ranges between 0 and 0.7, and iii) a midship section coefficient (C_m) of the vessel defined as: $1 - \frac{(1 - % T_{\max}) * (1 - % B_{\max})}{2}$
that ranges between 0.65 and 0.85.
The vessel according to claim 1, wherein the lower body comprises a flat bottom located at a central portion of a bottom of the hull and along the length of the hull, and the inclined side walls are formed at both sides of the flat bottom so as the lower body has a substantially truncated V-shaped cross section.
The vessel according to any one of the preceding claims, wherein a block coefficient (C_b) of the vessel is defined as: $1 - \frac{(1 - % T_{\max}) * (1 - % A_{floatmax})}{2}$
and ranges between 0.52 and 0.72, wherein %A_floatmax is the ratio between an area of the flat bottom of the lower body and an area defined by a maximum waterline of the vessel.
The vessel according to claim 3, wherein the block coefficient of the vessel depends on a value of the angle of the inclined side walls relative to a baseline of the vessel when any one of the ratios %A_floatmax and %T_max is fixed.
The vessel according to any one of the preceding claims, wherein, when the vessel is at its minimum weight, the lower body is at least partially submerged and, when the vessel is at its maximum weight, the lower body is totally submerged and the upper body is partially submerged.
The vessel according to any one of the preceding claims, wherein the at least one cargo space is a hold, and more preferably a box-type hold.
The vessel according to any one of the preceding claims, wherein the at least one cargo space has a width that substantially corresponds to the beam of the vessel along the length of the vessel.
The vessel according to any one of the preceding claims, wherein the minimum draft of the vessel depends on a propulsion system of the vessel.
The vessel according to any one of the preceding claims, comprising two propellers.
The vessel according to claim 9, comprising two propulsion engines such that when the vessel travels with the minimum draft only one of the two propulsion engines is configured to feed the two propellers and when the vessel travels with a draft higher than the minimum draft each propulsion engine feeds a corresponding propeller of the two propellers.
The vessel according to any one of the preceding claims, wherein the hull comprises a trim compensation system having at least two tanks fluidly connected to each other, wherein a fluid stored in the at least two tanks is transported among the at least two tanks to keep the vessel stabilized.
The vessel according to any one of the preceding claims, wherein the upper body may have the substantially rectangular cross section along a length of the at least one cargo space and the lower body may have the substantially V-shaped cross section along the length of the at least one cargo space of the vessel.