JP2019137323A - Vessel - Google Patents

Abstract

To improve propulsion performance by reducing wave resistance in an attachment unit of a rudder in a vessel.SOLUTION: A vessel includes a hull 10, a pair of right and left propellers 19A, 19B arranged in a stern 12 of the hull 10, and a pair of right and left rudders 20A, 20B arranged behind the pair of right and left propellers 19A, 19B in the stern 12 of the hull 10, and a pair of right and left projection units 31A, 31B projecting below are provided on a bottom 13 to which the pair of right and left rudders 20A, 20B are attached in a vessel width direction Y of the vessel 10 in positions of rotational center lines RCL1, RCL2 of the pair of right and left rudders 20A, 20B in a vessel length direction X of the vessel 10.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a ship provided with two propellers and two rudders.

  In recent years, ships have become larger in size in order to improve transportation efficiency. However, a conventional single-shaft ship equipped with one propeller and one rudder can increase the propeller area because the maximum diameter of the propeller that can be manufactured is limited with respect to the increase in hull resistance. This is not possible, and the propeller efficiency is greatly deteriorated by increasing the load of the propeller. Therefore, a ship equipped with two propellers and two rudders has been proposed.

  Such a ship employs two rudders in order to ensure the maneuverability of the hull, and each rudder is arranged behind the propeller on the left and right sides. In this case, the hull resistance is reduced by making the lower part of the left and right skegs incline outward in the width direction of the hull. The conventional hull has a shape in which the bottom of the ship is inclined upward toward the rear in the longitudinal direction of the hull, and has a height in the vicinity of the planned draft at the position of the rudder shaft. As such a ship, there exists a thing described in the following patent document, for example.

JP 2008-013039 A JP 2012-035785 A

  In a 2-axle vessel with a loaded area where the vicinity of the rudder mounting is submerged, the inward flow that goes around the hull interferes with the rudder placed in the direction of travel, and the propulsion performance is generated by the generation of wave resistance. Getting worse. The cause is due to the rudder arrangement peculiar to the biaxial ship. The hull curved surface of the rudder mounting part has a shape in which the outer side and the stern side are inclined upward, and the flow in the boundary layer near the waterline surface follows the inclination of the hull. It flows from outside to inside. On the other hand, there is a flow in the traveling direction outside the hull boundary layer. Along with these two flows, the flow direction angle of the cross section in the rudder height direction changes abruptly, and it is difficult to make the rudder shape follow the flow, and the rudder shape adopts a shape that matches the mainstream outside the boundary layer. As one of the countermeasures, it is conceivable to make the cross section of the rudder mounting portion horizontal, but in that case, there is a concern that the resistance of the main hull will increase because the stern tail end will be submerged extensively on the water surface. As another countermeasure, the left and right rudders are arranged close to the center in the width direction of the hull, and the rudder is arranged at a position where the rising inclination in the width direction of the hull is gentle to direct the hull surface flow in the propulsion direction. Can be considered. However, the effect is very small, and in the case of a ship provided with a rudder valve on the rudder plate, it is difficult to obtain an energy saving effect because the rudder valve cannot be arranged behind the propeller. As another countermeasure, the rudder may be arranged at an angle, the rudder valve may be located behind the propeller lab, and the mounting part may be located inside the hull. There is concern about increased rudder resistance by increasing the rudder area to ensure performance. Any of these measures greatly deteriorates the propulsion performance due to a contradiction, and the fundamental improvement cannot be expected with the conventional technology.

  This invention solves the subject mentioned above, and it aims at providing the ship which aims at the improvement of propulsion performance by reducing the wave-making resistance in the attaching part of a rudder.

  In order to achieve the above object, a ship of the present invention includes a hull, a pair of left and right propellers disposed at the stern of the hull, and a pair of left and right propellers disposed at the rear of the left and right propellers at the stern of the hull. A left and right projecting to the bottom of the hull to which the pair of left and right rudders are mounted in the width direction of the hull at the position of the rotation center of the pair of left and right rudders in the longitudinal direction of the hull. A pair of convex portions is provided.

  Accordingly, the hull is provided with a pair of left and right convex portions projecting downward at the bottom of the hull to which the pair of left and right rudders in the width direction of the hull is mounted at the position of the rotation center of the pair of left and right rudders in the longitudinal direction of the hull. The water flow that flows from the left port and starboard around the stern flows along the length of the bottom of the convex portion at the mounting portion of the pair of left and right rudders in the hull. For this reason, it is possible to prevent the water flow from interfering with the mounting portions of the pair of left and right rudder, and to prevent the flow to the rear of the hull from being hindered. it can.

  In the ship according to the present invention, the pair of left and right convex portions is disposed at the lowest position in the width direction of the hull at the position of the rotation center of the pair of left and right rudders in the longitudinal direction of the hull. Yes.

  Accordingly, since the pair of left and right convex portions are disposed at the lowest position in the width direction of the hull, the water flow flowing around the stern from the port side and starboard side of the hull can be smoothly flowed backward by the pair of left and right convex portions.

  The ship of the present invention is characterized in that the port side and starboard side of the hull and the pair of left and right convex portions are connected by a smooth curved portion that is continuous without a step.

  Therefore, the port and starboard of the hull and the pair of left and right convex portions are connected by a smooth curved portion that is continuous without a step, and the flow outside the port and starboard of the hull is smoothly flown by the curved portion. It can be led to the convex part and flow backward.

  In the ship of the present invention, the ship bottom is characterized in that a horizontal portion having a horizontal plane shape is provided between the pair of left and right convex portions.

  Therefore, since the horizontal part which makes a horizontal surface shape is provided between the left and right pair of convex parts on the ship bottom, the horizontal part is suppressed from contacting the water surface, and the wave-making resistance can be reduced.

  In the marine vessel of the present invention, the pair of left and right convex portions are provided in an area where at least the pair of left and right rudders are arranged in the longitudinal direction of the hull.

  Accordingly, since the pair of left and right convex portions are provided in the region where the pair of left and right rudders are arranged, the water flow flowing from the port side and the starboard of the hull around the stern is spread over the region where the pair of left and right rudder is arranged by the pair of left and right convex portions. It can flow smoothly backwards.

  The ship according to the present invention is characterized in that the pair of left and right projections are inclined upward or horizontally toward the stern along the longitudinal direction of the hull.

  Accordingly, since the pair of left and right convex portions are inclined upward or horizontally toward the stern along the longitudinal direction of the hull, the water flow flowing through the bottom of the ship can be smoothly flowed backward.

  The ship according to the present invention is characterized in that the pair of left and right convex portions are disposed below the full flooding line.

  Therefore, since the pair of left and right convex portions are arranged below the full flooding line, the water flow flowing around the stern from the port side and starboard side of the hull flows backward along the pair of left and right convex portions. Interference can be suppressed.

  In the ship of the present invention, the distance in the height direction of the hull between the lower end of the pair of left and right convex portions and the center position in the width direction of the ship bottom is set in a range of 2% to 30% of the center position height from the ship bottom. It is characterized by that.

  Therefore, the distance in the height direction of the hull at the center position in the width direction of the bottom of the pair of left and right convex portions is set in the range of 2% to 30% of the center position height from the bottom of the ship. The submerged area at the end can be minimized, and an optimum height that can reduce the rudder resistance can be obtained.

  In the ship of the present invention, the position in the ship length direction of the lower ends of the pair of left and right convex portions is characterized by spreading toward the bow side of the hull.

  Accordingly, since the position in the ship length of the lower ends of the pair of left and right convex portions expands toward the bow side of the hull, the water flow flowing from the port side and starboard side of the hull to the stern end side is guided to the pair of left and right convex portions. Thus, the rudder resistance can be reduced without deteriorating the hull resistance.

  The ship according to the present invention is characterized in that a bow-side spread angle at a position in the ship length direction of the lower ends of the pair of left and right convex portions is set to 15 degrees or less.

  Therefore, the rudder resistance can be effectively reduced because the bow side spreading angle at the position in the ship length of the pair of left and right convex portions at the lower end is set to the optimum angle range.

  According to the ship of the present invention, the propulsion performance can be improved by reducing the wave-making resistance at the rudder mounting portion.

FIG. 1 is a schematic side view of a ship. FIG. 2 is a schematic bottom view of the ship. FIG. 3 is a side view showing the stern of the first embodiment. FIG. 4 is a bottom view showing the stern of the first embodiment. 5 is a cross-sectional view taken along the line VV in FIG. 6 is a cross-sectional view taken along the line VI-VI in FIG. 7 is a sectional view taken along line VII-VII in FIG. FIG. 8 is a side view illustrating a stern modification of the first embodiment. FIG. 9 is a bottom view of the stern in the ship of the second embodiment.

  Hereinafter, preferred embodiments of a ship according to the present invention will be described in detail with reference to the accompanying drawings. In addition, this invention is not limited by this embodiment, and when there are two or more embodiments, what comprises combining each embodiment is also included.

[First Embodiment]
FIG. 1 is a schematic side view of a ship according to the first embodiment, and FIG. 2 is a schematic bottom view of the ship.

  The ship of the first embodiment is a displacement-type merchant ship, such as a large oil tanker (VLCC, ULCC), an LNG ship, an LPG ship, a passenger ship (car ferry), and the like. Moreover, the ship of 1st Embodiment is a biaxial ship provided with two propellers and two rudders.

  As shown in FIGS. 1 and 2, the hull 10 has a bow 11, a stern 12, a ship bottom 13, a port 14, and a starboard 15. In this embodiment, the ship length direction (front-rear direction) of the hull 10 is represented as the X direction, the ship width direction (width direction) as the Y direction, and the ship height direction (up and down direction) as the Z direction. CL represents a center line in the width direction of the hull 10, and WL represents a full load water line of the hull 10. PCL1 and PCL2 represent the rotation center lines of the propellers, and RCL1 and RCL2 represent the rotation center lines of the rudder shafts.

  In the hull 10, an engine room 17 is partitioned by a partition wall 16 on the stern 12 side, and a main engine (for example, a diesel engine) 18 is disposed in the engine room 17. The main engine 18 is drive-coupled with two propellers 19A and 19B that transmit propulsive force. Each propeller 19A, 19B can rotate around a rotation center line PCL1, PCL2 along the ship length direction X.

  Further, the hull 10 is provided with two rudders 20A and 20B for controlling the traveling direction of the hull 10 on the stern 12, and each rudder 20A and 20B has a rotation center line RCL1 and RCL2 along the ship height direction Z. Can pivot to the center.

  Hereinafter, the detailed shape of the stern 12 in the ship of this embodiment is demonstrated. 3 is a side view showing the stern, FIG. 4 is a bottom view showing the stern, FIG. 5 is a sectional view taken along line VV in FIG. 3, FIG. 6 is a sectional view taken along line VI-VI in FIG. It is VII-VII sectional drawing of FIG.

  As shown in FIGS. 3 to 7, the ship of the present embodiment has a pair of left and right in the ship width direction Y at the positions of the rotation center lines RCL1 and RCL2 of the pair of left and right rudders 20A and 20B in the ship length direction X of the hull 10. A pair of left and right convex portions 31A, 31B projecting downward are provided at the position of the bottom 13 where the rudder 20A, 20B is mounted. The pair of left and right convex portions 31A and 31B are disposed below the full flooding line WL in the ship height direction Z.

  The hull 10 is provided with a pair of left and right skegs 32 </ b> A and 32 </ b> B on the stern 12. The pair of left and right propellers 19A and 19B are attached to the rear part of the pair of left and right skegs 32A and 32B, and the pair of left and right rudders 20A and 20B are provided behind the pair of left and right propellers 19A and 19B.

  The pair of left and right convex portions 31A and 31B are located at the positions of the rotation center lines RCL1 and RCL2 of the pair of left and right rudders 20A and 20B in the ship length direction X of the hull 10 and at the position of the pair of left and right rudders 20A and 20B in the ship width direction Y. , And so as to protrude downward from the ship bottom 13. The pair of left and right convex portions 31A and 31B are provided in the region X1 in which at least the pair of left and right rudders 20A and 20B are arranged in the ship length direction X. However, you may provide in the area | region from the bow 11 side (for example, position to the boss | hub part of a pair of left-right propeller 19A, 19B) to the stern 12 from a pair of left-right rudder 20A, 20B.

  That is, as shown in FIG. 1, the ship bottom 13 has a horizontal portion (baseline) 13a and an inclined portion 13b inclined upward from the horizontal portion 13a toward the rear. Therefore, as shown in FIGS. 3 and 5, the inclined portion 13 b of the ship bottom 13 is positioned in front of the pair of left and right propellers 19 </ b> A and 19 </ b> B along the ship width direction Y between the pair of left and right skegs 32 </ b> A and 32 </ b> B. A horizontal portion 13c is provided. Further, as shown in FIGS. 3 and 6, the inclined portion 13b of the ship bottom 13 is located at a position near the pair of left and right propellers 19A and 19B and higher than the horizontal portion 13c between the pair of left and right skegs 32A and 32B. A horizontal portion 13d that is horizontal along the ship width direction Y is provided. And as shown in FIG.3 and FIG.7, the inclination part 13b of the ship bottom 13 is a position of a pair of left and right rudders 20A and 20B, and a pair of left and right convex parts 31A and 31B is located at a position of a pair of left and right skegs 32A and 32B. A horizontal portion 13e that is provided along the ship width direction Y is provided between the pair of left and right convex portions 31A and 31B at a position higher than the horizontal portion 13d.

  Here, the pair of left and right convex portions 31A and 31B has a lower end portion provided horizontally along the ship length direction X, but is not limited to this configuration. For example, the pair of left and right convex portions 31A and 31B may be configured such that the lower end portion is inclined upward along the ship length direction X toward the stern 12 side.

  The pair of left and right convex portions 31A and 31B has a semicircular shape with a curved surface protruding downward, and the curved outer surfaces of the left side 14 and the right side 15 and the curved portions 13f and 13g have no step and are smoothly continuous. Further, the pair of left and right convex portions 31A and 31B are smoothly continuous without a step due to the horizontal portion 13e and the curved portions 13h and 13j. The pair of left and right rudders 20 </ b> A and 20 </ b> B includes a ladder horn 33, a rudder main body 34, and a rudder shaft 35. The ladder horn 33 is fixed to the lower surfaces of the pair of left and right convex portions 31A and 31B, and the rudder main body 34 is rotatably attached to the ladder horn 33 by a rudder shaft 35.

  In addition, although the horizontal part 13e horizontal along the ship width direction Y was provided between left-right paired convex part 31A, 31B, it is not limited to this structure. For example, a curved concave portion that protrudes upward in the ship height direction Z is provided between the pair of left and right convex portions 31A, 31B, or a curved protrusion that projects downward in the boat height direction Z between the pair of left and right convex portions 31A, 31B. A part may be provided.

  The pair of left and right convex portions 31A and 31B are the lowest positions in the ship width direction Y at the positions of the rotation center lines RCL1 and RCL2 of the pair of left and right rudders 20A and 20B in the ship length direction X. Specifically, the distance Z1 in the height direction between the pair of left and right convex portions 31A and 31B and the horizontal portion 13e of the center line CL in the ship width direction Y of the ship bottom 13 is 2 of the center position height Z0 from the ship bottom 13. % To 30%. When the distance Z1 is less than 2%, the effect of the pair of left and right convex portions 31A and 31B becomes insufficient, and wave-making resistance occurs. On the other hand, when the distance Z1 exceeds 30%, the stern 12 has a shape that is lowered downward from the horizontal position toward the rear, and thus hull resistance occurs.

  Note that the mounting configuration of the pair of left and right rudders 20A and 20B with respect to the pair of left and right convex portions 31A and 31B is not limited to the configuration described above. FIG. 8 is a side view illustrating a stern modification.

  As shown in FIG. 8, at the position of the rotation center lines RCL1, RCL2 of the pair of left and right rudders 20A, 20B in the ship length direction X of the hull 10, the bottom 13 on which the pair of left and right rudders 20A, 20B in the ship width direction Y is mounted. A pair of left and right convex portions 41 projecting downward is provided at each position, and the rudder skeg 42 is fixed to each convex portion 41. The rudder horn 33 is fixed to the lower surface of the rudder skeg 42, and the rudder main body 34 is rotatably attached to the rudder horn 33 by a rudder shaft 35.

  Therefore, as shown in FIGS. 3 and 7, when the ship navigates, the water flow W that flows toward the stern 12 along the outer surfaces of the port 14 and starboard 15 of the hull 10 is a pair of left and right rudders 20 a and 20 B in the hull 10. And smoothly flows rearwardly outside the pair of left and right convex portions 31A and 31B. Therefore, this water flow W is suppressed from interfering with the pair of left and right rudder 20A, 20B and its mounting portion, and the flow to the rear of the hull 10 is not hindered.

  As described above, in the ship of the first embodiment, the hull 10, the pair of left and right propellers 19 </ b> A and 19 </ b> B disposed on the stern 12 of the hull 10, and the pair of left and right propellers 19 </ b> A and 19 </ b> B A pair of left and right rudders 20A, 20B arranged at the rear, and at the positions of the rotation center lines RCL1, RCL2 of the pair of left and right rudders 20A, 20B in the ship length direction X of the hull 10, left and right in the width direction Y of the hull 10 A pair of left and right convex portions 31A and 31B projecting downward is provided on the ship bottom 13 to which the pair of rudders 20A and 20B are mounted.

  Accordingly, since the water flow W flowing around the stern 12 from the port 14 and starboard 15 of the hull 10 smoothly flows rearwardly outside the pair of left and right convex portions 31A and 31B, the water flow W is attached to the pair of left and right rudders 30A and 30B. It is possible to improve the propulsion performance by significantly reducing the wave-making resistance without interfering with the parts and without hindering the backward flow of the hull 10.

  In the ship of the first embodiment, the pair of left and right convex portions 31A and 31B are positioned at the rotation center lines RCL1 and RCL2 of the pair of left and right rudders 20A and 20B in the longitudinal direction of the hull 10, and in the ship width direction Y of the hull 10. , Placed in the lowest position. Therefore, the water flow W flowing around the stern 12 from the port 14 and starboard 15 of the hull 10 can be smoothly flowed backward by the pair of left and right convex portions 31A and 31B.

  In the ship of the first embodiment, the port 14 and starboard 15 of the hull 10 and the pair of left and right convex portions 31A and 31B are connected by smooth curved portions 13f and 13g that are continuous without a step. Accordingly, the flow outside the port 14 and starboard 15 of the hull 10 can be smoothly guided to the pair of left and right convex portions 31A and 31B by the curved portions 13f and 13g and flow backward.

  In the ship of the first embodiment, a horizontal portion 13c having a horizontal plane shape is provided between a pair of left and right convex portions 31A and 31B on the bottom 13 of the ship. Therefore, it is suppressed that the horizontal part 13c contacts a water surface, and wave-making resistance can be reduced.

  In the ship of the first embodiment, a pair of left and right convex portions 31A and 31B are provided in an area where at least a pair of left and right rudders 20A and 20B are arranged in the ship length direction X of the hull 10. Therefore, the water flow W flowing around the stern 12 from the port 14 and starboard 15 of the hull 10 can be smoothly flowed backwards over the region where the pair of left and right rudders 20A and 20B are disposed by the pair of left and right convex portions 31A and 31B.

  In the marine vessel of the first embodiment, the pair of left and right convex portions 31A and 31B are inclined upward or horizontally toward the stern 12 along the ship length direction X of the hull 10. Accordingly, the wave resistance can be reduced by smoothly flowing the water flow W flowing through the ship bottom 13 backward.

  In the ship according to the first embodiment, the pair of left and right convex portions 31A and 31B are disposed below the full flooding line. Accordingly, since the water flow W flowing around the stern 12 from the port 14 and starboard 15 of the hull 10 flows backward along the pair of left and right convex portions 31A and 31B, interference between the water flow W and the pair of left and right rudders 20A and 20B is suppressed. can do.

  In the ship of the first embodiment, the distance Z1 in the ship height direction Z of the hull 10 of the center line CL between the pair of left and right convex portions 31A and 31B and the ship bottom 13 is 2% to 30% of the center position height Z0 from the ship bottom 13. % Range is set. Accordingly, it is possible to minimize the submerged area at the end of the stern 12 serving as the hull resistance and to obtain an optimum height that can reduce the rudder resistance.

[Second Embodiment]
FIG. 9 is a side view of the stern in the ship of the second embodiment. In addition, the same code | symbol is attached | subjected to the member which has the same function as embodiment mentioned above, and detailed description is abbreviate | omitted.

  As shown in FIG. 9, the ship of the second embodiment has a pair of left and right rudders 20A in the ship width direction Y at the positions of the rotation center lines RCL1 and RCL2 of the pair of left and right rudders 20A and 20B in the ship length direction X of the hull 10. , 20B is provided with a pair of left and right convex portions 31A, 31B projecting downward. The pair of left and right convex portions 31A and 31B are disposed below the full flooding line WL in the ship height direction Z. The pair of left and right convex portions 31A and 31B are provided in the region X1 in which at least the pair of left and right rudders 20A and 20B are arranged in the ship length direction X.

  The pair of left and right convex portions 31A and 31B have a shape in which the position in the ship length direction at the lower end expands toward the bow 11 side of the hull 10, and the bow side spreading angle is set to 15 degrees or less. That is, the convex center lines NCL1, NCL2 along the pair of left and right convex parts 31A, 31B have a predetermined spread angle with respect to the center line CL of the hull 10. The convex center lines NCL1 and NCL2 are formed so as to extend toward the bow 11 side through the rotation center lines RCL1 and RCL2 of the pair of left and right rudders 20A and 20B. The angles of the convex center lines NCL1 and NCL2 are set to 0 to 15 degrees of the bow 11 side opening, and the angles of the pair of left and right rudders 20A and 20B are parallel to the convex center lines NCL1 and NCL2. Therefore, the inflow vector from the outside of the hull 10 matches the rudder angle, and the resistance of the pair of left and right rudders 20A and 20B is also reduced. In addition, when the angle of the convex part center lines NCL1 and NCL2 exceeds 15 degrees, the rudder 20A and 20B itself becomes resistance, and becomes resistance by inhibiting the flow of the traveling direction vector inside the hull 10.

  As described above, in the ship of the second embodiment, the pair of left and right in the ship width direction Y of the hull 10 at the position of the rotation center lines RCL1 and RCL2 of the pair of left and right rudders 20A and 20B in the ship length direction X of the hull 10. A pair of left and right convex portions 31A and 31B projecting downward is provided on the bottom 13 to which the rudder 20A and 20B are mounted, and a ship length direction position of the lower end of the pair of left and right convex portions 31A and 31B is directed toward the bow 11 side of the hull 10. And spread out.

  Therefore, since the pair of left and right convex portions 31A and 31B are formed to expand toward the bow 11 side of the hull 10, the pair of left and right convex portions 31A and 31B are closed toward the stern 12 side of the hull 10, The shape of the hull 10 from the port 14 and starboard 15 to the stern 12 side is similar to the shape of the pair of left and right convex portions 31A, 31B. Therefore, when the water flow flowing from the port 14 and starboard 15 of the hull 10 toward the stern 12 end is guided to the pair of left and right convex portions 31A and 31B, the rudder resistance can be reduced without deteriorating the hull resistance.

  In the ship of the second embodiment, the bow-side spread angle at the position in the ship length direction at the lower end of the pair of left and right convex portions 31A and 31B is set to 15 degrees or less. Accordingly, the rudder resistance can be effectively reduced.

10 hull 11 bow 12 stern 13 bottom 13a, 13c, 13d, 13e horizontal part 13b inclined part 13f, 13g, 13h, 13j curved part 14 port 15 starboard 19A, 19B propeller 20A, 20B rudder 31A, 31B convex part 32A, 32B 33 Ladder horn 34 Rudder body 35 Rudder shaft X Ship length direction Y Ship width direction Z Ship height direction CL Center line WL Full flooding line PCL1, PCL2 Propeller rotation center line RCL1, RCL2 Rudder shaft rotation center line

Claims (10)

The hull,
A pair of left and right propellers disposed at the stern of the hull;
A pair of left and right rudders disposed behind the pair of left and right propellers at the stern of the hull;
With
A pair of left and right projections projecting downward is provided on the bottom of the hull to which the pair of left and right rudders in the width direction of the hull is mounted at the position of the rotation center of the pair of left and right rudders in the longitudinal direction of the hull. Be
A ship characterized by that.   The pair of left and right convex portions are arranged at the lowest position in the width direction of the hull at the position of the rotation center of the pair of left and right rudders in the longitudinal direction of the hull. Ship.   The ship according to claim 1 or 2, wherein the port side and starboard of the hull and the pair of left and right convex portions are connected by a smooth curved portion that is continuous without a step.   The said ship bottom is provided with the horizontal part which makes a horizontal surface shape between the said left-right paired convex part, The ship as described in any one of Claims 1-3 characterized by the above-mentioned.   The ship according to any one of claims 1 to 4, wherein the pair of left and right protrusions are provided in an area where at least the pair of left and right rudders are disposed in a longitudinal direction of the hull. .   The ship according to any one of claims 1 to 5, wherein the pair of left and right protrusions are inclined upward or horizontally toward the stern along the longitudinal direction of the hull.   The ship according to any one of claims 1 to 6, wherein the pair of left and right protrusions are disposed below the full flooding line.   The distance in the height direction of the hull between the lower end of the pair of left and right convex portions and the center position in the width direction of the ship bottom is set in a range of 2% to 30% of the center position height from the ship bottom. The ship according to any one of claims 1 to 7.   The ship according to any one of claims 1 to 8, wherein a position in a ship length direction of the lower ends of the pair of left and right convex portions is widened toward a bow side of the hull.   The ship according to claim 9, wherein a bow side spread angle at a position in a ship length of the lower ends of the pair of left and right convex portions is set to 15 degrees or less.

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