JP7513373B2 - Ballast tank - Google Patents

Description

The present invention relates to a ballast tank.

A ballast tank described in Patent Document 1 below is a known technology in this field. This ballast tank has an outer wall, an inner wall, and a side stringer provided between the outer wall and the inner wall. Multiple stages of longitudinals are fixed to each of the outer wall and the inner wall in the longitudinal direction of the hull. The side stringer is also provided with a water drain opening.

Japanese Patent Application Laid-Open No. 11-208569

Therefore, there was a demand for ships with ballast tanks to have a lighter hull structure. At the same time, there was also a demand to maintain the drainage performance of the ballast tank drainage opening structure.

The present invention was made to solve these problems, and aims to provide a ballast tank that can reduce the weight of the ship's hull structure while maintaining its drainage function.

The ballast tank of the present invention is a ballast tank that includes an outer wall, an inner wall, and a side stringer provided between the outer wall and the inner wall, and multiple stages of longitudinals are fixed to each of the outer wall and the inner wall in the longitudinal direction of the hull, and the side stringer is provided with a drainage opening that is provided on both side edges of the side stringer so that it is within the horizontal range of the longitudinals directly above the side stringer in a plan view of the ballast tank, the ballast tank is divided into multiple compartments by multiple side floors in the longitudinal direction of the hull, and within each compartment divided by a pair of side floors, multiple drainage openings are provided on at least one side edge of the side stringer.

In the ballast tank of the present invention, the drain openings are provided on both side edges of the side stringer so that they are within the horizontal range of the longitudinal directly above the side stringer in a plan view of the ballast tank. In this case, the drain openings are configured to be covered by the longitudinal from above, so that when workers walk on the side stringer during shipbuilding or tank inspection, they can be prevented from accidentally putting their legs into the drain opening without providing protective members such as lattices or nets at the drain opening. Here, for example, when one drain opening is provided in one section, the horizontal dimension (ship width direction) of the drain opening is within a certain range, so it is not possible to reduce the horizontal dimension (ship width direction) of the longitudinal to reduce the weight. In contrast, in the ballast tank of the present invention, multiple drain openings are provided on at least one side edge of the side stringer in one section separated by a pair of side floors. In this case, by dividing one large drain opening into multiple drain openings, the horizontal dimension (width of the hull) of each drain opening can be reduced while maintaining drainage performance. In this way, by reducing the horizontal dimension (width of the hull) of each drain opening, it is possible to reduce the dimension of the longitudinal covering the drain opening. Therefore, by reducing the dimension of the longitudinal, the hull structure can be made lighter. As a result, the hull structure can be made lighter while maintaining drainage performance.

The ballast tank of the present invention is vertically divided into at least two compartments by multiple side stringers, and the number of drainage openings provided on one side edge of the side stringer (forming the lower boundary) of the upper compartment may be greater than the number of drainage openings provided on one side edge of the side stringer (forming the lower boundary) of the lower compartment. The upper compartment has a lower required strength due to the low water pressure acting on it. Therefore, by increasing the number of drainage openings in the upper compartment, the longitudinal dimensions can be reduced to accommodate the lower required strength.

In the ballast tank of the present invention, the number of drainage openings provided on the side edge of the outer wall of the side stringer may be greater than the number of drainage openings provided on the side edge of the inner wall. The outer wall does not have loads such as waves acting on it like the inner wall, so the required strength is low. Therefore, by increasing the number of drainage openings on the outer wall side, the longitudinal dimensions can be reduced to accommodate the lower required strength.

The present invention provides a ballast tank that can reduce the weight of the ship's hull structure while maintaining its drainage function.

1 is a schematic side view showing an example of a ship to which a ballast tank according to an embodiment of the present invention is applied. 2 is a cross-sectional view taken along line II-II shown in FIG. FIG. 3 is an enlarged view of a portion III shown in FIG. 2 . 1 is a diagram showing a water drainage opening structure of a ballast tank according to an embodiment of the present invention and a comparative example. FIG. FIG.

A preferred embodiment of the ballast tank of the present invention will be described below with reference to the drawings. In the following description, the terms "forward" and "aft" refer to the direction of travel of the hull, the term "side" refers to the left-right (width) direction of the hull, and the terms "upper" and "lower" refer to the top-lower direction of the hull. The direction in which the hull extends from forward to backward is sometimes referred to as the "hull longitudinal direction D1," and the left-right direction of the hull is sometimes referred to as the "lateral direction D2." In addition, for convenience, the plate thickness of each member may be omitted in the drawings.

Figure 1 is a schematic side view showing an example of a ship to which a ballast tank according to an embodiment of the present invention is applied. Figure 2 is a cross-sectional view taken along line II-II shown in Figure 1. The ship to which the hull structure 1 is applied is a ship that transports petroleum-based liquid cargo such as crude oil or liquid gas, for example, an oil tanker. Note that the ship is not limited to an oil tanker, and may be, for example, a double-hull bulk carrier.

As shown in FIG. 1, the ship 10 has a hull 11 and a propeller 12. The hull 11 has a bow 13 and a stern 14. The bow 13 is located at the front of the hull 11. The stern 14 is located at the rear of the hull 11. The bow 13 has a shape designed to reduce wave-making resistance, for example, when the ship is fully loaded. The propeller 12 propels the hull 11, and is, for example, a screw shaft. The propeller 12 is installed below the waterline SL in the stern 14. In addition, a rudder 15 for adjusting the propulsion direction is installed below the waterline SL in the stern 14.

As shown in FIG. 2, the hull 11 is equipped with a cargo oil tank 16 and a ballast tank 17. The cargo oil tank 16 carries petroleum-based cargo to be transported by the ship 10. The ballast tank 17 stores ballast water in an amount corresponding to the weight of the petroleum-based cargo loaded in the cargo oil tank 16. For example, when the weight of the petroleum-based cargo is small, the ballast tank 17 pumps up seawater W (ballast water) using a ballast pump (not shown) to increase the amount of stored ballast water. On the other hand, when the weight of the loaded petroleum-based cargo is large, the ballast water is discharged into the sea to decrease the amount of stored ballast water. As a result, the weight of the ship 10 as a whole is adjusted to a weight that ensures the safety of the ship 10 and ensures a sufficient draft.

The cargo oil tank 16 is provided inside the hull 11, as shown in FIG. 2. The ceiling surface of the cargo oil tank 16 is formed by the upper deck 18. The sides and lower sides of the cargo oil tank 16 are formed into a double hull by the outer wall 20 and inner wall 30 of the hull 11. In addition, side floors 40 are provided on the sides and lower sides of the cargo oil tank 16, separating the inside of the double hull in the hull longitudinal direction D1 of the hull 11 (see FIG. 1).

As shown in FIG. 2, the ballast tank 17 is provided on the lateral side and below the cargo oil tank 16. In other words, the area surrounded by the outer wall 20 and the inner wall 30 that constitute the double hull of the hull 11 is the ballast tank 17. The ballast tank 17 extends in the vertical direction on the side 11a of the hull 11, and also extends in the lateral direction D2 on the bottom 11b of the hull 11.

Next, the ballast tank 17 will be described in detail with reference to Figure 3. Figure 3 is an enlarged view of part III shown in Figure 2.

As shown in FIG. 3, the ballast tank 17 has an outer wall 20, an inner wall 30, a side floor 40, and a side stringer 50.

The outer wall 20 has a side shell plate 21 and a bottom shell plate 22. The side shell plate 21 extends in the hull longitudinal direction D1 of the hull 11 at the side portion 11a of the hull 11. The bottom shell plate 22 extends in the hull longitudinal direction D1 of the hull 11 at the bottom portion 11b of the hull 11. The inner wall 30 has a longitudinal bulkhead 31 and an inner bottom plate 32. The longitudinal bulkhead 31 extends in the hull longitudinal direction D1 of the hull 11 at the side portion 11a of the hull 11. The inner bottom plate 32 extends in the hull longitudinal direction D1 of the hull 11 at the bottom portion 11b of the hull 11. The inner bottom plate 32 has an inclined surface 32s that slopes upward toward the longitudinal bulkhead 31. The inclined surface 32s of the inner bottom plate 32 and the vertical bulkhead 31 are joined by a joint 33.

As shown in FIG. 3, the side floor 40 and the bottom floor 43 extend in the direction in which the outer wall 20 and the inner wall 30 extend in a cross-sectional view of the hull 11. That is, the side floor 40 extends in the vertical direction in the side part 11a, and the bottom floor 43 extends in the horizontal direction D2 in the bottom part 11b. The side floor 40 separates the side shell 21 and the longitudinal bulkhead 31 in the hull longitudinal direction D1 of the hull 11, and is formed to be passable in the hull longitudinal direction D1 of the hull 11. As a result, the ballast tank 17 is divided into multiple compartments by the multiple side floors 40 in the hull longitudinal direction D1. In FIG. 4(a), each compartment is indicated by "E". The side floor 40 is provided with a communication hole 41 to allow passage in the hull longitudinal direction D1 of the hull 11. The access hole 41 functions as a passageway that can be used by workers to perform maintenance and inspection inside the ballast tank 17. The access hole 41 is formed through the side floor 40. This allows movement between the compartments separated by the side floor 40 through the access hole 41.

The side stringer 50 is provided between the outer wall 20 and the inner wall 30. The side stringer 50 is installed horizontally across the side shell plating 21 and the vertical bulkhead 31 in the ballast tank 17. The side stringer 50 is configured as a vertical beam as a structural member inside the hull. The side stringer 50 is joined to the side shell plating 21 and the vertical bulkhead 31 at both ends, and divides the inside of the ballast tank 17 in a direction intersecting the extension direction of the side floor 40. That is, in the side section 11a, the side stringer 50 divides the inside of the ballast tank 17 in the vertical direction. The side stringer 50 of the side section 11a extends in the hull longitudinal direction D1 of the hull 11 while connecting the side shell plating 21 and the vertical bulkhead 31. The side stringer 50 constitutes a floor member. The side stringer 50 constituting the floor member has a walkway surface on the upper surface. The walkway surface functions as a surface on which workers who pass through the access hole 41 walk during maintenance and inspection of the ballast tank 17. As described above, the ballast tank 17 is vertically divided into at least two sections by the multiple side stringers 50. In this embodiment, the ship side 11a of the ballast tank 17 is divided into two sections, but it may be divided into more sections. The upper section may be referred to as the upper section UE and the lower section as the lower section DE. In FIG. 3, the side stringers 50 and longitudinals 55 of the lower section DE are referred to as "side stringers 50A" and "longis 55A". The side stringers 50 and longitudinals 55 of the upper section UE are referred to as "side stringers 50B" and "longis 55B". However, in the following description, when the configurations of the lower section DE and the upper section UE are described comprehensively, they may be simply referred to as "side stringers 50" and "longis 55".

A number of longitudinal sections 55 are fixed to the side shell 21 and the longitudinal bulkhead 31 as reinforcing members in the hull longitudinal direction D1. The longitudinal sections 55 protrude from the side shell 21 and the longitudinal bulkhead 31 into the ballast tank 17. A pair of the longitudinal sections 55 are installed at a predetermined position in the extension direction of the side floor 40, facing each other in a direction intersecting the extension direction of the side floor 40. That is, in the side section 11a of the hull 11, the longitudinal sections 55 are installed at the same position in the up-down direction. In addition, in the side section 11a of the hull 11, the longitudinal sections 55 face each other in the lateral direction D2. The longitudinal sections 55 are formed, for example, with a substantially T-shaped cross section. The longitudinal sections 55 are installed on the side shell 21 and the longitudinal bulkhead 31 so that the flange surfaces of the substantially T-shaped cross sections face each other.

The water drain opening structure 100 of the ballast tank 17 according to this embodiment will be described with reference to Figures 4(a) and 4(b). Figure 4(a) is a plan view of the water drain opening structure 100 of the ballast tank 17 according to this embodiment, as seen from above. Figure 4(b) is a schematic cross-sectional view of the water drain opening structure 100 of the ballast tank 17 according to this embodiment, as seen from the hull longitudinal direction D1. Note that Figures 4(a) and 4(b) show the configuration near the side stringer 50A of the lower section DE. A structure similar to the water drain opening structure 100 of Figures 4(a) and 4(b) is provided near the side stringer 50B of the upper section UE, and therefore a description thereof will be omitted.

As shown in FIG. 4(a), the ballast tank 17 has a water drain opening structure 100. The water drain opening structure 100 has the above-mentioned side floor 40, side stringer 50A, and longitudinal 55A, and the side stringer 50A has a water drain opening 60. The ballast tank 17 is divided into a plurality of compartments E by a plurality of side floors 40 in the hull longitudinal direction D1. Each compartment E is formed by a space surrounded by a pair of side floors 40 adjacent to each other in the hull longitudinal direction D1, a floor-side side stringer 50A, a ceiling (which may be a side stringer 50B one step above or another ceiling member) facing the side stringer 50A on the upper side, the ship's side shell 21, and the longitudinal bulkhead 31. The ballast tank 17 has a plurality of compartments E arranged in a line in the hull longitudinal direction D1. The ballast tank 17 also has multiple compartments E in the vertical direction (see Figure 3).

The side stringer 50A has a side edge 50Aa on the side of the ship's side shell plating 21 and a side edge 50Ab on the side of the vertical bulkhead 31. That is, as shown in FIG. 3, in the lower section DE, the position indicated by "E1" corresponds to the side edge 50Aa of the side stringer 50A on the side of the ship's side shell plating 21. In the lower section DE, the position indicated by "E2" corresponds to the side edge 50Ab of the side stringer 50A on the vertical bulkhead 31. In the upper section UE, the position indicated by "E3" corresponds to the side edge 50Ba of the side stringer 50B on the side of the ship's side shell plating 21. In the upper section UE, the position indicated by "E4" corresponds to the side edge 50Bb of the side stringer 50B on the vertical bulkhead 31.

As shown in Fig. 4(a) and (b), drainage openings 60 are provided on both side edges 50Aa, 50Ab of the side stringer 50A. The drainage openings 60 are formed by through holes penetrating the side stringer 50A. The drainage openings 60 connect the two spaces separated by the side stringer 50A. Therefore, when draining ballast water from the section E separated by the side stringer 50A, the ballast water passes through the drainage openings 60 and drains into the space below the side stringer 50A. When storing ballast water in the ballast tank 17, the ballast water that fills from the space below the side stringer 50A passes through the drainage openings 60 and is supplied to the space in the section E separated by the side stringer 50A. Note that Fig. 4(a) and (b) only show the ballast tank 17 at one end of the hull in the transverse direction D2, but the ballast tank 17 at the other end has the same configuration.

The drain opening 60 is provided on both side edges 50Aa and 50Ab of the side stringer 50A so as to be within the horizontal range of the longitudinal 55A directly above the side stringer 50A in a plan view of the ballast tank 17. The drain opening 60 provided on the side edge 50Aa is arranged at a position overlapping with the longitudinal 55A fixed to the side shell plating 21 when viewed from the top-bottom direction. In other words, the drain opening 60 provided on the side edge 50Aa is arranged at a position closer to the side shell plating 21 than the tip of the longitudinal 55A fixed to the side shell plating 21, and is arranged so as not to protrude from the tip of the longitudinal 55A toward the longitudinal bulkhead 31. The drain opening 60 provided on the side edge 50Ab is arranged at a position overlapping with the longitudinal 55A fixed to the longitudinal bulkhead 31 when viewed from the top-bottom direction. That is, the water drain opening 60 provided on the side edge 50Ab is positioned closer to the longitudinal bulkhead 31 than the tip of the longitudinal 55A fixed to the longitudinal bulkhead 31, and is positioned so as not to protrude beyond the tip of the longitudinal 55A toward the ship's side shell 21.

With the above-mentioned configuration, the water drain opening 60 is covered from above by the longitudinals 55A. Therefore, when workers walk on the side stringers 50A during shipbuilding or tank inspections, the water drain opening 60 is covered by the longitudinals 55A, preventing the workers from accidentally putting their legs into the water drain opening 60. For this reason, there is no need to provide protective members such as lattices or nets for the water drain opening 60.

In one section E separated by a pair of side floors 40, multiple drainage openings 60 are provided for each of the side edges 50Aa, 50Ab of the side stringer 50A. Here, two drainage openings 60 are provided for each of the side edges 50Aa, 50Ab in one section E. The multiple drainage openings 60 are arranged in different positions in the hull longitudinal direction D1, so that they are arranged side by side in the hull longitudinal direction D1. In this way, by providing multiple drainage openings 60 in one section E, the dimension of each drainage opening 60 in the lateral direction D2 can be reduced. In this case, by reducing the size of the drainage opening 60, which is the object covered by the longitudinal 55A, the dimension of the longitudinal 55A in the lateral direction D2 can also be reduced accordingly, making it possible to reduce weight.

Next, the configuration of the drain opening 60 will be described in more detail with reference to FIG. 5. FIG. 5(a) is an enlarged view showing two drain openings 60 in one section E. As shown in FIG. 5(a), one drain opening 60 in the hull longitudinal direction D1 is designated as "60A", and the other drain opening 60 is designated as "60B". The explanation of the dimensional relationship using FIG. 5(a) applies to both the drain openings 60 at the side edges 50Aa, 50Ab of the lower section DE and the drain openings 60 at the side edges 50Ba, 50Bb of the upper section UE. Therefore, in FIG. 5(a), the side edges 50Aa, 50Ab and the side edges 50Ba, 50Bb are referred to as "side edges 50a, 50b" without distinguishing between them. Also, in FIG. 5(a), the side edges 50a and 50b are shown to have a common configuration. When the side edge 50a is shown, the front and rear relationships are reversed from when the side edge 50b is shown. In the following explanation, the side of the wall 21, 31 in the horizontal direction D2 may be referred to as the "outside in the horizontal direction D2," and the side away from the wall 21, 31 may be referred to as the "inside in the horizontal direction D2."

The drain openings 60A, 60B have an oval shape extending in the hull longitudinal direction D1. Therefore, the drain openings 60A, 60B have an outer end 60a in the lateral direction D2, an inner end 60b, an end 60c on one side in the hull longitudinal direction D1, and an end 60d on the other side. The ends 60a, 60b extend linearly so as to be parallel to the hull longitudinal direction D1. In the following explanation, the dimensional relationship of the drain opening 60A will be explained, but the same relationship is assumed to apply to the drain opening 60B.

If the length of the water drain opening 60A along the hull longitudinal direction D1 is "dimension L1" and the length along the lateral direction D2 is "dimension L2", then "dimension L1 ≧ dimension L2". Furthermore, the ratio of "dimension L2/dimension L1" is limited to a specified range (for example, within a ratio range of 0.5 to 1.0) from the perspective of ensuring strength. In other words, there are restrictions on providing a water drain opening 60A with an extremely small dimension L2.

The distance of the drain opening 60A from the walls 21, 31 is referred to as "dimension L3". Dimension L3 may be set taking into consideration the processing required to secure the side stringer 50 to the walls 21, 31. For example, when the side stringer 50 is secured to the walls 21, 31 by welding, the drain opening 60A must be spaced from the walls 21, 31 to the extent that the welding work is not hindered by the drain opening 60A being too close to the walls 21, 31. Dimension L3 may be larger, the same as, or smaller than dimension L2 of the drain opening 60A. However, it is necessary to ensure strength when determining all dimensions L1 to L6.

The distance of the drain opening 60A from the tip of the longitudinal 55 is defined as "dimension L4". Unlike the above-mentioned dimension L3, dimension L4 has no manufacturing constraints and can be adjusted in relation to the reinforcing performance required of the longitudinal 55. Therefore, dimension L4 may be made smaller in order to shorten the longitudinal 55 in order to reduce the weight of the hull structure. Specifically, dimension L4 may be smaller than dimension L3. When such a dimensional relationship is adopted, the drain opening 60A is positioned in a position closer to the tip of the longitudinal 55 (inner position in the lateral direction D2) in the area overlapping with the longitudinal 55. Dimension 4 may be smaller than dimension L2 of the drain opening 60A. However, in places where the reinforcing performance of the longitudinal 55 is required, dimension L4 may be made larger to some extent by making the length of the longitudinal 55 somewhat longer. Therefore, dimension L4 may be larger than dimension L3 or may be the same as dimension L3. Additionally, dimension L4 may be greater than dimension L2 of drain opening 60A, or may be the same as dimension L2.

In this embodiment, the drain opening 60 is divided into two drain openings 60A, 60B, thereby reducing the dimension L2 of each of the drain openings 60A, 60B. Therefore, the proportion of the dimension of the drain openings 60A, 60B in the horizontal direction D2 of the longitudinal 55 may be less than half, and the relationship "dimension L2 < dimension L3 + dimension L4" may hold. However, the relationship "dimension L2 > dimension L3 + dimension L4" may also hold, or the relationship "dimension L2 = dimension L3 + dimension L4" may also hold.

The distance from the nearest side floor 40 to the water drain opening 60A is referred to as "dimension L5". Dimension L5 may be set taking into consideration the processing required to fix the side floor 40 to the side stringer 50. For example, when fixing the side floor 40 to the side stringer 50 by welding, the water drain opening 60A needs to be spaced away from the side floor 40 to an extent that the welding work is not hindered by the water drain opening 60A being too close to the side floor 40. Dimension L5 may be larger than, the same as, or smaller than dimension L1 of the water drain opening 60A.

The distance between the drain opening 60A and the drain opening 60B is referred to as "dimension L6". From the viewpoint of strength, it is sufficient that dimension L6 has a certain length. Dimension L6 may be larger than, the same as, or smaller than dimension L1 of the drain opening 60A. Dimension L6 may be larger than, the same as, or smaller than dimension L5.

As described above, the same dimensional relationship as that of the drain opening 60A is established for the drain opening 60B. That is, the drain opening 60B has the same shape and dimensions as the drain opening 60A, and the distance from the wall 21, 31 and the tip of the longitudinal 55 is the same as that of the drain opening 60A, and the distance from the nearest side floor 40 is also the same as that of the drain opening 60A. For example, if the drain opening 60A is larger than the drain opening 60B and the end 60b of the drain opening 60A extends further inward in the lateral direction D2 than the end 60b of the drain opening 60B, the dimension of the longitudinal 55 in the lateral direction D2 is set based on the position of the end 60b of the larger drain opening 60A. In this case, the dimension of the longitudinal 55 in the lateral direction D2 becomes excessively large for the small drain opening 60B. Therefore, the positions of the end 60a of the drain opening 60A and the end 60a of the drain opening 60B in the horizontal direction D2 are as nearly as possible in the same position, the areas allocated to the drain openings 60A and 60B are as uniform as possible, and the positions of the end 60b of the drain opening 60A and the end 60b of the drain opening 60B in the horizontal direction D2 are the same. This prevents the dimension L2 of only one of the drain openings 60A and 60B from becoming large, thereby making it possible to reduce the dimension of the longitudinal 55 in the horizontal direction D2. However, the shape and size of the drain opening 60A and the drain opening 60B do not have to be the same, and the positions in the horizontal direction D2 within the side edges 50a and 50b may also be different from each other.

As mentioned above, the drain openings 60 are provided at the locations of "E1", "E2", "E3", and "E4" shown in FIG. 3, but the number of drain openings 60 at the locations of "E1", "E2", "E3", and "E4" may all be the same (for example, two as shown in FIG. 5(a)). However, the number of drain openings 60 at the locations of "E1", "E2", "E3", and "E4" may be different from each other. In other words, since the strength required for the hull differs depending on the position, it is also possible to increase the number of drain openings 60 in order to reduce the weight of the longitudinal 55 in a location where the strength of the longitudinal 55 is excessive for the required strength. For such a location, for example, three drain openings 60A, 60B, and 60C may be provided in one section E as shown in FIG. 5(b). In this case, the dimension L2 in the lateral direction D2 of each drain opening 60A, 60B, and 60C can be made even smaller than in the case of FIG. 5(a). In this case, even if the dimensions L3 and L4 are the same, the dimension of the longitudinal 55 in the lateral direction D2 (= dimension L2 + dimension L3 + dimension L4) is shorter in the configuration of FIG. 5(b) than in the configuration of FIG. 5(a). Note that four or more drainage openings 60 may be provided for one section E.

For example, the water pressure acting on the upper section UE is smaller than that on the lower section DE, so the strength required for the upper section UE is lower than that of the lower section DE. Therefore, the number of water drain openings 60 provided on the side edge 50Ba (at E3) of the side stringer 50B of the upper section UE may be greater than the number of water drain openings 60 provided on the side edge 50Aa (at E1) of the side stringer 50A of the lower section DE. As a result, the length in the lateral direction D2 of the longitudinal 55B on the side of the ship's side shell plating 21 of the upper section UE may be shorter than the length in the lateral direction D2 of the longitudinal 55A of the ship's side shell plating 21 of the lower section DE. In addition, the number of water drain openings 60 provided at the side edge 50Bb (at E4) of the side stringer 50B of the upper section UE may be greater than the number of water drain openings 60 provided at the side edge 50Ab (at E2) of the side stringer 50A of the lower section DE. As a result, the length in the lateral direction D2 of the longitudinal 55B on the vertical bulkhead 31 side of the upper section UE may be shorter than the length in the lateral direction D2 of the longitudinal 55A on the vertical bulkhead 31 side of the lower section DE. Note that FIG. 3 shows a state in which the longitudinal 55B on the vertical bulkhead 31 side of the upper section UE is shorter than the longitudinal 55A on the vertical bulkhead 31 side of the lower section DE. In addition to this, or instead of this, as described above, the longitudinal 55B on the side of the ship's side shell plating 21 of the upper section UE may be shorter than the longitudinal 55A on the side of the ship's side shell plating 21 of the lower section DE.

In addition, while the side shell plating 21 is subjected to loads due to waves, such loads do not act on the longitudinal bulkhead 31. Therefore, the strength required for the longitudinal bulkhead 31 is generally lower than that of the side shell plating 21. Therefore, in the lower section DE, the number of water drain openings 60 provided at the side edge 50Ab (at E2) of the side stringer 50A on the longitudinal bulkhead 31 side may be greater than the number of water drain openings 60 provided at the side edge 50Aa (at E1) on the side shell plating 21 side. As a result, the lateral length D2 of the longitudinal bulkhead 31 side of the lower section DE may be shorter than the lateral length D2 of the longitudinal bulkhead 55A of the side shell plating 21 of the lower section DE. In the upper section UE, the number of drain openings 60 provided at the side edge 50Bb (at E4) of the side stringer 50B on the vertical bulkhead 31 side may be greater than the number of drain openings 60 provided at the side edge 50Ba (at E3) on the side of the ship's side shell plating 21 side. As a result, the length in the lateral direction D2 of the longitudinal 55B on the vertical bulkhead 31 side of the upper section UE may be shorter than the length in the lateral direction D2 of the longitudinal 55B on the ship's side shell plating 21 of the upper section UE. Note that FIG. 3 shows a state in which the longitudinal 55B on the vertical bulkhead 31 side of the upper section UE is shorter than the longitudinal 55B on the ship's side shell plating 21 side of the upper section UE. In addition to this, or instead of this, as described above, the longitudinal 55A on the vertical bulkhead 31 side of the lower section DE may be shorter than the longitudinal 55A on the ship's side shell plating 21 side of the lower section DE.

The manufacturing procedure for the water drain opening structure 100 will be described. However, this is merely an example of the manufacturing procedure, and the procedures for attaching and assembling each member are not particularly limited. First, the plate member constituting the side stringer 50 is formed into the desired shape, and the water drain opening 60 is formed in the plate member. This side stringer 50 is placed between the ship's side shell plate 21 and the longitudinal bulkhead 31, and both ends are fixed to each wall 21, 31 by welding or the like. At this time, the water drain opening 60 is sufficiently separated from each wall 21, 31 so that it does not hinder the welding work. Next, the side floor 40 is provided, and the longitudinals 55 are provided. As a result, the water drain opening 60 is covered from above by the lowest longitudinals 55 in each section E.

Next, the action and effect of the ballast tank 17 according to this embodiment will be explained.

In the ballast tank 17 of this embodiment, the water drain opening 60 is provided on both side edges 50a, 50b of the side stringer 50 so that it is within the horizontal range of the longitudinal 55 directly above the side stringer 50 in a plan view of the ballast tank 17. In this case, the water drain opening 60 is configured to be covered by the longitudinal 55 from above, so that when workers walk on the side stringer 50 during ship construction or tank inspection, it is possible to prevent workers from accidentally putting their legs into the water drain opening 60 without providing protective members such as lattices or nets on the water drain opening 60.

Here, referring to Figures 4(c) and (d), a water drain opening structure according to a comparative example will be described. Figure 4(c) is a plan view of the water drain opening structure 200 of the ballast tank 217 according to the comparative example seen from above. Figure 4(d) is a schematic cross-sectional view of the water drain opening structure 200 of the ballast tank 217 according to the comparative example seen from the hull longitudinal direction D1. That is, Figures 4(a) and 4(b) show the configuration of the ballast tank 217 according to the comparative example at a location corresponding to the vicinity of the side stringer 50A of the lower section DE of Figure 3. In the water drain opening structure 200 according to the comparative example, one large water drain opening 70 is provided on the side edges 50Aa, 50Ab of the side stringer 50A in one section E. We will consider reducing the size of the longitudinal 55A covering the water drain opening 70 in the lateral direction D2 to reduce weight. If the dimensions of the longitudinal 55A are reduced so that the drain opening 70 protrudes from the tip of the longitudinal 55A when viewed from above, the possibility of the worker's legs entering the drain opening 70 increases. If the drain opening 70 is to be moved closer to the walls 21 and 31, it becomes difficult to perform the work of welding and fixing the side stringer 50 to the walls 21 and 31. Therefore, the drain opening 70 cannot be moved closer to the walls 21 and 31 than a certain range. If the entire drain opening 70 is made elongated in the hull longitudinal direction D1 to reduce the dimension in the lateral direction D2, it cannot be made elongated beyond a certain range from the viewpoint of strength. If the area of the drain opening 70 itself is reduced to reduce the dimension in the lateral direction D2, the drainage performance of the drain opening will be reduced. As described above, with the drain opening structure 200 according to the comparative example, it was difficult to reduce the weight of the hull structure while maintaining the drainage function.

In contrast, in the drain opening structure 100 of the ballast tank 17 according to this embodiment, multiple drain openings 60 are provided on the side edges 50a, 50b of the side stringer 50 within one section E separated by a pair of side floors 40. In this case, one large drain opening 70 is divided into multiple drain openings 60. For example, the sizes of the drain openings 60A, 60B are set so that the total area of the two drain openings 60A, 60B is approximately the same as the area of one drain opening 70 (see FIG. 5(a)). In this case, even if "dimension L2/dimension L1" is within a range that satisfies the strength, the absolute value of dimension L2 can be reduced because the area of each drain opening 60A, 60B is reduced. This allows the horizontal dimension D2 of each drain opening 60 to be reduced while maintaining the drainage performance. In this way, by reducing the horizontal dimension of each drain opening, it is possible to reduce the dimension of the longitudinal 55 that covers the drain opening 60. For example, the position of the tip of the longitudinal 55 in the drain opening structure of the comparative example is "SL1" (see FIG. 4(d)). In this embodiment, the dimension of the drain opening 60 in the lateral direction D2 is smaller than the drain opening 70, so if the longitudinal 55 is extended to the SL1 position, the area covering the drain opening 60 with the longitudinal 55 will be excessive. In other words, the entire drain opening 60 can be covered without extending the tip of the longitudinal 55 to the SL1 position, so the longitudinal dimension can be reduced (see FIG. 4(b)). Therefore, by reducing the dimension of the longitudinal 55, the weight of the hull structure can be reduced. As a result, the weight of the hull structure can be reduced while maintaining the drainage function.

In the ballast tank 17 of this embodiment, the ballast tank 17 is vertically divided into at least two sections E by a plurality of side stringers 50, and the number of drainage openings 60 provided on the side edges 50a, 50b of the side stringers 50 of the upper section UE may be greater than the number of drainage openings 60 provided on the side edges 50a, 50b of the side stringers 50 of the lower section DE. The upper section UE generally has a low required strength due to the low water pressure acting thereon. In other words, if the horizontal dimension D2 of the longitudinal 55 of the upper section UE is the same as the horizontal dimension D2 of the longitudinal 55 of the lower section DE, the strength of the upper section UE will be excessive relative to the required strength. Therefore, by increasing the number of drainage openings 60 in the upper section UE, the dimension of the longitudinal 55 can be made smaller than that of the longitudinal 55 of the lower section DE to correspond to the low required strength.

In the ballast tank 17 of this embodiment, the number of drain openings 60 provided on the side edge 50b of the side stringer 50 on the longitudinal bulkhead 31 side may be greater than the number of drain openings 60 provided on the side edge 50a on the side of the ship's side shell plating 21 side. The longitudinal bulkhead 31 is generally required to have a lower strength because it is not subjected to loads such as waves, unlike the ship's side shell plating 21. In other words, if the transverse dimension D2 of the longitudinal 55 relative to the longitudinal bulkhead 31 is the same as the transverse dimension D2 of the longitudinal 55 relative to the ship's side shell plating 21, the strength of the longitudinal bulkhead 31 will be excessive relative to the required strength. Therefore, by increasing the number of drain openings 60 on the longitudinal bulkhead 31 side, the dimension of the longitudinal 55 can be made smaller than that of the longitudinal 55 on the ship's side shell plating 21 side to correspond to the lower required strength.

The present invention is not limited to the above-described embodiments.

For example, the water drain opening structure of the present application does not have to be adopted in all compartments E in the hull longitudinal direction D1 and vertical direction, but may be adopted in at least one compartment E. In other words, some compartments E may have only one water drain opening. Also, within one compartment E, multiple water drain openings 60 may be formed on one of the side edges 50a, 50b, and one water drain opening 70 may be formed on the other side.

The shape of the drainage opening does not have to be an oval, but can be an ellipse, rectangle, or other polygon.

17... ballast tank, 21... ship's side shell, 31... longitudinal bulkhead, 40... side floor, 50... side stringer, 55... longitudinal, 60... water drain opening, 100... water drain opening structure.

Claims (1)

A ballast tank comprising an outer wall, an inner wall, and a side stringer provided between the outer wall and the inner wall,
A number of longitudinal members are fixed to the outer wall and the inner wall in the longitudinal direction of the hull,
The side stringer is provided with a water drain opening,
The water drain openings are provided on both side edges of the side stringers so as to be within a horizontal range of the longitudinal axis directly above the side stringers in a plan view of the ballast tank,
The ballast tank is divided into a plurality of compartments by a plurality of side floors in the longitudinal direction of the hull,
In one section separated by a pair of the side floors, a plurality of the water drain openings are provided in at least one side edge of the side stringer so as to be aligned in the longitudinal direction of the hull,
A distance of the drain opening from one of the outer wall and the inner wall on the side edge side in the plan view is defined as a first dimension;
When the distance from the tip of the longitudinal end of the water drain opening in the plan view is defined as a second dimension,
The second dimension is less than the first dimension.

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