JP2012116402A - Ship - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ship that reduces hull resistance during sailing.SOLUTION: A stern 12 is composed of a horizontal part 22 becoming a bottom part on a stern ship's bottom 21, right and left side walls 23, and right and left curved surface parts 24 connecting each end part in the width direction of the horizontal part 22 and the lower part of each side wall 23 to each other. The width Ws of the horizontal part 22 on the stern ship's bottom 21 is set to ≥60% of the width W of the stern 12. A region in the width direction of the horizontal part 22 on the stern ship's bottom 21 is increased so as to accelerate a flow in the vicinity of the stern end, thereby preventing the stern end from being submerged in water in the whole region from a high-speed region to a low-speed region, and consequently, reducing hull resistance.

Description

  The present invention is generally used for passenger ships, ferries, container ships, RO-RO ships (Roll-on / Roll-off Ship), PCC (Pure Car Carrier), PCTC (Pure Car / Truck Carrier), etc. Related to a serious ship.

  In a ship used as a thin high-speed ship such as a passenger ship or a ferry, when navigating in the voyage speed range, the stern speed increases, so the negative pressure at the stern increases, and the stern sinking amount increases. Therefore, from the viewpoint of hull resistance, the stern becomes enlarged and the resistance of the entire hull increases rapidly. Such a tendency is particularly remarkable in a high-speed ship in which the fluid number is a predetermined number (for example, 0.3) or more.

  There exists a thing described in the following patent document 1 as what solves such a problem. The transom stern type stern shape described in Patent Document 1 is the shape of the bottom of the hull center line of the stern part of a general merchant ship having a transom stern, and the flow with a change in flow velocity at a position a certain distance forward from the stern end. An inflection point that should cause a field change is provided, and a bottom surface that is inclined downward to create a downward flow to form a region that accelerates the flow backward from the inflection point is provided. Wave generation can be reduced.

Japanese Patent No. 3490392

  In the above-mentioned conventional transom stern type stern shape, an inflection point is provided in front of a certain distance from the stern end, and a ship bottom inclined downward from the inflection point is provided to reduce stern wave formation. be able to. However, recent ships are further required to improve the performance and operational efficiency during navigation. Therefore, it is important to reduce the hull resistance at the time of sailing, and further reduction of the hull resistance is desired.

  The present invention solves the above-described problems, and an object thereof is to provide a ship that can reduce hull resistance during navigation.

  In order to achieve the above object, the ship of the present invention is configured such that the stern end of the hull is configured by connecting the lower part of the left and right side walls and each end part in the width direction of the ship bottom by a curved part, and the horizontal part of the ship bottom. Is set to 60% or more of the width at the stern end of the hull.

  Therefore, when a ship navigates, the water flow that flows along the stern flows backward along the bottom of the ship, and flows to the horizontal part of the bottom of the ship, so that the hull surface pressure rises and this hull surface pressure pushes the stern upward. Thus, stern settlement is suppressed and hull resistance can be reduced.

  In the ship according to the present invention, the width of the horizontal portion at the bottom of the ship is set to be 60% or more and 95% or less of the width at the stern end of the hull.

  Therefore, the hull resistance can be further reduced by setting the width of the horizontal portion to the optimum value.

  In the ship of the present invention, the stern has a first bottom where the bottom at the center line position in the width direction of the hull is inclined upward, and a position where the first bottom is moved forward by a predetermined distance from the stern end. And a second ship bottom having an angle that is not less than an angle parallel to the planned draft and smaller than an angle of a rearward extension line from the first ship bottom.

  Therefore, when the ship sails, the water flow that flows along the stern flows backward along the first ship bottom, and flows to the second ship bottom, thereby increasing the hull surface pressure, and the hull surface pressure pushes the stern upward. As a result, stern settlement is suppressed and hull resistance can be reduced. Moreover, since the 2nd ship bottom does not incline below, the stern end is hard to be immersed in water, and hull resistance can be reduced also in this point by suppressing generation | occurrence | production of the stern wave generation by the 2nd ship bottom.

  In the ship of the present invention, the second ship bottom is set to be 0 degree or more and 20 degrees or less with respect to the planned draft.

  Therefore, by setting the second bottom to an appropriate angle with respect to the draft, the hull is pushed up by the hull surface pressure and the stern wave generation is suppressed by inundation at the stern end of the second bottom. Resistance can be effectively reduced.

  In the ship of the present invention, the width of the horizontal portion is set to a predetermined ratio of the width of the hull at the second ship bottom.

  Therefore, the water flow that flows along the stern flows to the horizontal part of the second bottom of the ship, and the hull surface pressure rises. This hull surface pressure pushes the stern upward, suppressing the stern sinking and reducing the hull resistance. It can be effectively reduced.

  According to the ship of the present invention, since the width of the horizontal part at the bottom of the stern is set to 60% or more of the width at the stern end of the hull, it is possible to reduce the hull resistance during cruising.

FIG. 1 is a side view showing a stern of a ship according to Embodiment 1 of the present invention. FIG. 2 is a front view illustrating the stern shape of the ship according to the first embodiment. FIG. 3 is a graph showing the required horsepower with respect to the ship speed. FIG. 4 is a side view showing the stern shape of the ship according to the second embodiment of the present invention. FIG. 5 is a plan view illustrating the stern shape of the ship of the second embodiment. FIG. 6 is a side view illustrating the stern shape of the ship according to the third embodiment of the present invention. FIG. 7 is a front view illustrating the stern shape of the ship of the third embodiment. FIG. 8 is a side view showing the stern shape of the ship according to the fourth embodiment of the present invention.

  Exemplary embodiments of a ship according to the present invention will be described below in detail with reference to the accompanying drawings. In addition, this invention is not limited by this Example, Moreover, when there exists multiple Example, what comprises combining each Example is also included.

  1 is a side view showing a stern of a ship according to a first embodiment of the present invention, FIG. 2 is a front view showing a stern shape of the ship according to the first embodiment, and FIG. 3 is a graph showing horsepower with respect to the ship speed. .

  In the ship of the first embodiment, as shown in FIG. 1, the stern 12 in the hull 11 has a substantially horizontal ship bottom 13 extending rearward to form a bearing portion 14. A main shaft 15 is rotatably supported by the bearing portion 14, and a propeller boss 17 having a screw propeller 16 is fixed to a rear end portion of the main shaft 15.

  Further, the ship bottom 13 is smoothly continuous up to above the propeller boss 17, a ladder horn 18 is fixed to the rear of the propeller boss 17, and a rudder 20 is supported by a stern 12 and a rudder column 19 installed on the ladder horn 18. Has been.

  In the ship of Example 1 configured as described above, as shown in FIGS. 1 and 2, the stern of the hull 11, that is, the stern 12, is formed with a stern bottom 21 that smoothly continues from the bottom 13. The stern 12 includes a horizontal portion 22 that is a bottom portion, left and right side walls 23, left and right curved surface portions 24 that connect widthwise ends of the horizontal portion 22 and lower portions of the side walls 23 at the stern bottom 21. It consists of and. In this case, the horizontal portion 22 has a flat or gentle curved surface shape in the front-rear direction and a horizontal flat shape in the left-right (ship width) direction. Each side wall 23 has a flat surface or a gentle curved surface.

  And the width Ws of the horizontal part 22 in the stern bottom 21 is set to 60% or more of the width W in the stern 12 (hull 11). The width Ws of the horizontal portion 22 in the stern bottom 21 is preferably set to 60% or more and 95% or less of the width W of the stern 12 (the hull 11). This limitation takes into account work limitations.

  Therefore, when the ship sails, when the water flow that flows along the stern 12 reaches the horizontal portion 22 of the stern bottom 21, the stern 12 is pushed upward via the horizontal portion 22, and the amount of settlement of the stern 12 is reduced. Is done. Therefore, it is possible to greatly reduce the hull resistance generated when the stern 12 sinks, leading to an improvement in fuel consumption.

  Conventionally, the bottom of the stern end is curved in the width direction or the horizontal area in the width direction is small, so in the area where the stern speed is slow, the stern end is immersed in water, and the wave breaks that occur at the stern As a result, the resistance is greatly deteriorated. In the ship of the first embodiment, it is possible to accelerate the flow in the vicinity of the stern end by increasing the width direction region of the horizontal portion 22 in the stern bottom 21, and the stern end becomes water in the entire region from the high speed region to the low speed region. Hull resistance is reduced with little soaking.

  Accordingly, as shown in FIG. 3, the width direction of the horizontal portion 22 of the stern bottom 21 is different from that of a conventional ship (dotted line) where the stern end bottom is curved in the width direction or the horizontal area in the width direction is small. The ship of Example 1 having a large area (solid line) can reduce the necessary horsepower with respect to the ship speed.

  As described above, in the ship according to the first embodiment, the stern 12 is placed at the stern bottom 21, the horizontal portion 22 serving as the bottom, the left and right side walls 23, the widthwise end portions and the side walls of the horizontal portion 22. 23. The width Ws of the horizontal portion 22 at the stern bottom 21 is set to 60% or more of the width W at the stern 12 (the hull 11).

  Therefore, when the ship navigates, the water flow that flows along the stern 12 flows backward along the stern bottom 21 and flows to the horizontal portion 22 of the stern bottom 21, thereby increasing the hull surface pressure. The stern 12 is pushed upward, the settlement of the stern 12 is suppressed, and the hull resistance can be reduced.

  Moreover, in the ship of Example 1, the width Ws of the horizontal part 22 in the stern bottom 21 is set to 60% or more and 95% or less of the width W in the stern 12 (the hull 11). Therefore, the hull resistance can be further reduced by setting the width of the horizontal portion 22 to the optimum value.

  FIG. 4 is a side view showing the stern shape of the ship according to the second embodiment of the present invention, and FIG. 5 is a plan view showing the stern shape of the ship according to the second embodiment. In addition, the same code | symbol is attached | subjected to the member which has the function similar to the Example mentioned above, and detailed description is abbreviate | omitted.

  In the ship of the second embodiment, as shown in FIGS. 4 and 5, the stern 12 is set in advance from the first ship bottom 31 in which the ship bottom at the center line position in the width direction of the hull 11 is inclined upward and the stern end. A second bottom 32 having an angle that is equal to or greater than an angle parallel to the planned draft S and continuously smaller than the angle of the rearward extension line from the first bottom 31 at a position moved forward by a predetermined distance. Have.

  In this case, it is desirable that the second ship bottom 32 is set to 0 degrees or more and 20 degrees or less with respect to the planned draft S. In addition, the first ship bottom 31 has a substantially flat planar shape or a gentle curved surface shape, while the second ship bottom 32 has a shape that becomes horizontal before and after being parallel to the planned draft S. Furthermore, the continuous part of the 1st ship bottom 31 and the 2nd ship bottom 32 is the inflection position 33 which produces the flow field change accompanying a flow velocity change.

  That is, the ship of the second embodiment is a general merchant ship having a transom stern, and an inflection point (inflection point) at which a flow field change accompanied with a flow velocity change occurs at a position moved forward by a predetermined distance from the stern end. Inflection position) 33 is provided. Then, a first ship bottom 31 that is raised backward by a flat surface or a gentle curved surface is formed so as to form a region with a low flow velocity in front of the inflection point 33. On the other hand, a second bottom 32 is formed that has a predetermined distance from the stern end and is inclined downward to generate a downward flow so as to form a region that accelerates the flow backward from the inflection point 33.

  More specifically, the stern 12 has a symmetrical shape with respect to the center line C in the width direction of the hull 11. The first ship bottom 31 is a flat surface or a curved surface inclined backward from the ship bottom 13 by a predetermined angle θ with respect to the planned draft S. The second bottom 32 is a horizontal plane that continues to the first bottom 31 at an inflection position 33 that has moved forward by a predetermined distance L from the stern end and is parallel to the planned draft S. In this case, since both sides of the stern end are curved and continue to the side of the stern, both sides of the stern end are curved and are continued to the side of the stern so that the inflection position 33 also follows the shape of the stern end. .

  The second ship bottom 32 is within an angle formed by a horizontal line 32a parallel to the planned draft S and an extension line 31a extending rearward from the first ship bottom 31, and this angle is at least 0 degree behind the horizontal line 32a. And an inclination angle below the extension line 31a. In this case, as for predetermined angle (theta), it is preferable to set the upward inclination angle to the back with respect to planned draft S to 20 degrees or less. Further, the inflection position 33 does not need to connect the first ship bottom 31 and the second ship bottom 32 at a predetermined angle, and may be smoothly continuous with a predetermined curved surface on the front and rear. Further, when the first ship bottom 31 has a gently curved shape instead of a planar shape, the extension line 31 a from the first ship bottom 31 is a tangent to the first ship bottom 31 at the inflection position 33.

  Further, the planned draft S is a draft in a state in which a load having a predetermined weight is loaded on the hull 11, and a draft in a state in which a load having a maximum weight allowable in structural strength is loaded on the hull 11 is a strength draft. It is. Therefore, the planned draft S is set so as to have a margin for the strength draft.

  In the ship according to the second embodiment, the stern bottom of the stern 12 includes a first bottom 31 and a second bottom 32. The stern 12 includes a horizontal portion 22, left and right side walls 23, and a curved surface portion 24 (see FIG. 2 above) at the second bottom 32, as in the first embodiment. The width Ws of the horizontal portion 22 at 32 is set to 60% or more of the width W at the stern 12 (the hull 11).

  Accordingly, when the ship sails, the water flow that flows along the stern 12 is deflected downward and backward from the inflection position 33, so that the stern 12 is pushed upward via the second bottom 32, and the stern 12 The amount of settlement is reduced. Therefore, it is possible to greatly reduce the hull resistance generated when the stern 12 sinks, leading to an improvement in fuel consumption.

  Conventionally, since the ship bottom inclined downward is provided, in a region where the boat speed is low, the stern end is in a state of being immersed in water, and the resistance is greatly deteriorated due to the wave collapse occurring at the stern. In the ship of Example 2, it is possible to secure a sufficient clearance from the still water surface by leveling the second ship bottom 32, and the stern end is almost immersed in water in all regions from the high speed region to the low speed region. Hull resistance is reduced.

  That is, when the ship navigates, the water flow that flows along the stern 12 flows from the first bottom 31 that inclines upward to the inflection position 33 side, and from the inflection position 33 to the horizontal portion 22 of the second second bottom 32. The hull surface pressure rises by flowing, and the stern 12 is pushed upward by this hull surface pressure. Therefore, the settlement of the stern 12 is suppressed, and the hull resistance is reduced.

  In this case, when the maximum weight load is loaded on the ship, the draft rises to the strength draft, and the stern may be immersed in the water. Conventionally, the stern bottom is inclined downward, and the stern end is likely to be immersed in water. Therefore, the stern wave is generated by the stern end immersed in water, and the resistance is greatly deteriorated. On the other hand, in the ship of Example 2, since the second ship bottom 32 is horizontal in the front-rear direction and the left-right direction, the second ship bottom 32 is less likely to be immersed in water, and even if immersed in water, the amount is small. The generation of stern waves is reduced, and the deterioration of resistance is suppressed.

  As described above, in the ship according to the second embodiment, the first bottom 31 in which the bottom 13 at the position of the center line C in the width direction of the hull 11 is inclined upward and the predetermined distance L set in advance from the stern end. A second ship bottom 32 that is continuous with the first draft 31 at a position moved forward and parallel to the planned draft S is provided, and the width Ws of the horizontal portion 22 at the second ship bottom 32 is 60% or more of the width W at the stern 12. Is set.

  Accordingly, when the ship navigates, the water flow that flows along the stern 12 flows backward along the first bottom 31 and flows to the horizontal portion 22 of the second bottom 32, thereby increasing the hull surface pressure, and this hull surface. The stern 12 is pushed upward by the pressure, and the settlement of the stern 12 is suppressed, and the hull resistance can be reduced. Further, since the second bottom 32 is not inclined downward to the rear, it is difficult to be immersed in water, and by suppressing the generation of stern wave formation at the stern end of the second bottom 32, the hull resistance can be reduced in this respect as well. it can.

  Moreover, in the ship of Example 2, the angle of the 2nd ship bottom 32 is set to 0 degree or more with respect to the plan draft S, and 20 degrees or less. Accordingly, by setting the second bottom 32 to an appropriate angle with respect to the planned draft S, the stern 12 can be pushed up by the hull surface pressure and the stern wave can be prevented from being generated by the flooding of the stern end of the second bottom 32. The hull resistance can be effectively reduced by the action.

  Moreover, in the ship of Example 2, the 1st ship bottom 31 is made into a flat surface or a gentle curved surface shape, and the 2nd ship bottom 32 is made into the shape which becomes horizontal before and after parallel to the plan draft S. Accordingly, the hull resistance can be further reduced by making the entire ship bottom smooth.

  Moreover, in the ship of Example 2, the continuous part of the 1st ship bottom 31 and the 2nd ship bottom 32 is made into the inflection position 33 which produces the flow field change accompanying a flow velocity change. Therefore, by raising the hull surface pressure on the front side of the inflection position 33, the stern 12 can be pushed up properly by the hull surface pressure.

  FIG. 6 is a side view showing the stern shape of the ship according to the third embodiment of the present invention, and FIG. 7 is a front view showing the stern shape of the ship according to the third embodiment. In addition, the same code | symbol is attached | subjected to the member which has the function similar to the Example mentioned above, and detailed description is abbreviate | omitted.

  In the ship of the third embodiment, as shown in FIGS. 6 and 7, the stern 12 is set in advance from the first ship bottom 31 in which the ship bottom at the center line position in the width direction of the hull 11 is inclined upward and the stern end. A second bottom 41 having an angle that is equal to or greater than an angle that is continuously parallel to the planned draft S at a position that has moved forward by a predetermined distance and that is smaller than an angle of a rearward extension line from the first bottom 31. Have.

More specifically, the first ship bottom 31 is a plane or a curved surface inclined upward by a predetermined angle θ with respect to the planned draft S from the ship bottom 13 to the rear. The second bottom 41 is a plane that continues to the first bottom 31 at an inflection position 33 that has moved forward by a predetermined distance L from the stern end and is inclined upward with respect to the planned draft S by a predetermined angle θ _1. It is. In this case, the predetermined angle θ ₁ of the second ship bottom 41 is smaller than the predetermined angle θ of the first ship bottom 31.

That is, the second ship bottom 41, parallel to the horizontal line 41a in plan draft S, there from the first vessel bottom 31 in the angle between the extension line 31a which extends rearward and has a predetermined angle theta ₁ with respect to the horizontal line 41a It is a plane.

  The stern bottom of the stern 12 is composed of a first bottom 31 and a second bottom 41. The stern 12 includes a horizontal part 42, left and right side walls 43, and a curved part 44 at the second ship bottom 41. The width Ws of the horizontal part 42 in the second ship bottom 41 is equal to the stern 12 (the hull 11). It is set to 60% or more of the width W at.

Therefore, when the ship sails, the water flow that flows along the stern 12 flows from the first bottom 31 that inclines upward to the inflection position 33 side, and then flows from the inflection position 33 to the second bottom 41 that inclines upward. Here, since the predetermined angle θ ₁ of the second ship bottom 41 is smaller than the predetermined angle θ of the first ship bottom 31, the hull surface pressure increases here, and the stern 12 is pushed upward by this hull surface pressure. Therefore, the settlement of the stern 12 is suppressed, and the hull resistance is reduced.

  Moreover, when the maximum weight load is loaded on the ship, the draft rises to the strength draft, and the stern end may be immersed in the water. However, since the second ship bottom 41 is inclined upward from the horizontal, the stern end of the second ship bottom 41 is not soaked in water, and even if it is soaked in water, the amount of the stern wave is small. This reduces the deterioration of resistance.

As described above, in the ship of the third embodiment, the first bottom 31 where the bottom 13 at the position of the center line C in the width direction of the hull 11 is inclined upward and the predetermined distance L set in advance from the stern end is provided. A second ship bottom 41 having a predetermined angle θ ₁ smaller than the angle of the rearward extension line from the first ship bottom 31 continuously to the first ship bottom 31 at a position moved forward, and the horizontal portion 42 of the second ship bottom 41 The width Ws is set to 60% or more of the width W at the stern 12.

  Therefore, when the ship sails, the water flow that flows along the stern 12 flows backward along the first bottom 31 and flows to the horizontal portion 42 of the second bottom 41, so that the hull surface pressure increases, and the hull surface The stern 12 is pushed upward by the pressure, and the settlement of the stern 12 is suppressed, and the hull resistance can be reduced. Further, since the second bottom 41 is not inclined downwardly, it is difficult to be immersed in water, and by suppressing the generation of stern waves by the stern end of the second bottom 41, the hull resistance can also be reduced in this respect. it can.

  FIG. 8 is a side view showing the stern shape of the ship according to the fourth embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the member which has the function similar to the Example mentioned above, and detailed description is abbreviate | omitted.

  In the ship of the fourth embodiment, as shown in FIG. 8, the stern 12 includes a first ship bottom 31 in which the ship bottom in the width direction center line position of the hull 11 is inclined upward and a predetermined distance set in advance from the stern end. A second bottom 32 having an angle that is not less than the angle of the rearward extension line from the first bottom 31 more than the angle that is parallel to the planned draft S continuously from the first bottom 31 at a position that has moved forward only. Yes.

  More specifically, the first ship bottom 31 is a plane or a curved surface inclined upward by a predetermined angle θ with respect to the planned draft S from the ship bottom 13 to the rear. The second ship bottom 32 is a plane that continues to the first ship bottom 31 at the inflection position 33 that has moved forward by a predetermined distance L from the stern end and is parallel to the planned draft S.

  Further, the stern bottom in the stern 12 is composed of a first bottom 31 and a second bottom 32. The stern 12 includes a horizontal portion 22, left and right side walls 23, and a curved surface portion 24 (see FIG. 2 above) at the second bottom 32, as in the first embodiment. The width Ws of the horizontal portion 22 at 32 is set to 60% or more of the width W at the stern 12 (the hull 11).

  Further, the stern 12 is provided with a recess 51 in a region facing the upper side of the second ship bottom 32. The concave portion 51 cuts the rear end portion of the stern 12 vertically from above and substantially horizontally from the rear. In this case, the vertical wall of the recess 51 may be a vertical surface, an inclined surface, or a curved surface, or the bottom wall of the recess 51 may be an inclined surface, a horizontal surface, or a curved surface.

  As described above, in the ship according to the fourth embodiment, the first bottom 31 in which the bottom 13 at the position of the center line C in the width direction of the hull 11 is inclined upward and the predetermined distance L set in advance from the stern end. A second ship bottom 32 parallel to the planned draft S is provided continuously to the first ship bottom 31 at a position moved forward, and the width Ws of the horizontal portion 22 at the second ship bottom 32 is set to 60% or more of the width W at the stern 12. A recessed portion 51 is provided in the hull 11 that is set and faces the upper side of the second bottom 32.

  Therefore, by removing a part that does not affect the propulsion performance of the hull 11, the hull weight can be reduced without reducing the propulsion performance, hull resistance can be reduced, and the manufacturing cost can be reduced. Can do.

In each of the above-described embodiments, the shape of the bottom of the stern at the stern is tilted upward at a predetermined angle θ, leveled in the middle, or angle θ ₁ , but is not limited to this structure. Instead, it may be inclined downwardly in the middle as in the prior art, the stern bottom itself may be horizontally or downwardly inclined, and may have a shape curved upward and downward and curved back and forth. That is, the width of the horizontal portion only needs to be set to a predetermined ratio regardless of the shape of the stern bottom.

  Further, the ship of the present invention is not limited to the single-shaft ship described as each example, but a multi-shaft ship (two or more shafts) or other propulsion equipment-equipped ship (swing type POD propulsion device or azimuth propulsion). The same operational effects can be achieved.

  The present invention enables a reduction in hull resistance during cruising by setting the width of the horizontal part at the bottom of the stern to a predetermined ratio in a ship, and can be applied to any ship. .

DESCRIPTION OF SYMBOLS 11 Hull 12 Stern 13 Bottom 21 Stern bottom 22, 42 Horizontal part 23,43 Side wall 24,44 Curved part 31 1st bottom 32,41 2nd bottom 33 Inflection position (inflection point)
51 recess

Claims (5)

The stern end of the hull is configured by connecting the lower part of the left and right side walls and the end part in the width direction of the ship bottom by a curved surface part,
The width of the horizontal portion at the bottom of the ship is set to 60% or more of the width at the stern end of the hull.
A ship characterized by that.   2. The ship according to claim 1, wherein a width of a horizontal portion at the bottom of the ship is set to be 60% or more and 95% or less of a width at a stern end of the hull.   The stern is continuously drafted continuously to the first bottom at a position where the bottom at the center line in the width direction of the hull is tilted backward and moved forward by a predetermined distance from the stern end. The ship according to claim 1, further comprising a second ship bottom having an angle that is equal to or greater than an angle parallel to the first ship bottom and smaller than an angle of a rearward extension line from the first ship bottom.   The ship according to claim 3, wherein the second ship bottom is set to 0 degrees or more and 20 degrees or less with respect to the planned draft.   The ship according to claim 3 or 4, wherein a width of a horizontal portion is set to a predetermined ratio of a width of the hull at the second ship bottom.

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