Stern energy-saving device and twin-paddle ship

Abstract

The invention relates to the technical field of ships, and particularly discloses a stern energy-saving device and a double-propeller ship, the stern energy-saving device comprises a rudder blade, a propeller shaft, propellers and vortex elimination fins, the cross sectional area of the rudder blade is gradually reduced from top to bottom, the propeller shaft comprises a connecting section and an extending section, the connecting section and the extending section extend in the axial direction of the propeller shaft and are connected, and the connecting section is connected with the extending section. The rudder blade is integrally arranged above the axis of the extending section, the rear end of the extending section extends to the position below the rudder blade, the propeller is fixedly arranged on the connecting section, the vortex eliminating fin is fixedly arranged on the connecting section or the extending section, and the vortex eliminating fin is arranged behind the propeller. According to the stern energy-saving device, the vortex eliminating fin, the propeller shaft extending section extending to the position below the rudder blade and the rudder blade located above the axis of the propeller shaft extending section are matched with one another, so that resistance borne by the rudder blade can be reduced, energy loss caused by trailing vortex is reduced, the ship navigation resistance is reduced, the propelling efficiency of a propeller is improved, and the service life of the propeller is prolonged. And the rapid performance of the ship is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of ships, and in particular to a stern energy-saving device and a double-propeller ship. Background Art

[0002] Common ship appendages mainly include rudder blades, shafts, shaft brackets, bilge keels, etc. For medium- and high-speed twin-propeller ships such as government ships and passenger ships, the resistance of the appendages generally accounts for 10%-40% of the total resistance. The flow field state of the appendages and their mutual interference with the hull and propeller are quite complex.

[0003] In the related art, a rudder blade and a propeller are provided at the stern of a ship. The rudder blade is connected to the bottom plate of the ship. The rudder blade is generally installed directly behind the propeller, and the lower end of the rudder blade extends downward to the longitudinal baseline of the ship. When the ship is sailing, the rudder blade will not only generate greater resistance under the action of the rotating wake of the propeller, but also the force difference between the upper and lower halves is obvious. The resistance of the lower half of the rudder blade is much greater than that of the upper half, and it will also cause adverse effects such as mutual vibration between the rudder blade and the stern structure of the hull. In addition, there is obvious tail vortex energy loss behind the high-speed rotating propeller, which reduces the rapid performance of medium and high-speed ships. Summary of the invention

[0004] The purpose of the present invention is to provide a stern energy-saving device and a double-propeller ship to solve the problem in the related art that the rudder blade is set directly behind the propeller, which not only generates large resistance but also has obvious resistance difference between the upper and lower halves, easily causes vibration and easily forms a wake vortex behind the propeller, thereby reducing the speed of the ship.

[0005] To achieve this object, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a stern energy-saving device, the stern energy-saving device comprising:

[0007] A rudder blade, the rudder blade is used for driving connection with the ship body, and the cross-sectional area of ​​the rudder blade gradually decreases from top to bottom;

[0008] A propeller shaft, the propeller shaft comprising a connecting section and an extending section, the connecting section and the extending section are extended and connected along the axial direction of the propeller shaft, the connecting section can be drivingly connected to the ship body, the rudder blade is integrally arranged above the axis of the extending section, and the rear end of the extending section extends to a position below the rudder blade;

[0009] A propeller and a vortex-eliminating fin, wherein the propeller is fixedly arranged on the connecting section, the vortex-eliminating fin is fixedly arranged on the connecting section or the extending section, and the vortex-eliminating fin is arranged behind the propeller.

[0010] In one of the embodiments, in the axial direction of the propeller shaft, the radial dimension of the extension section gradually decreases from front to back.

[0011] In one embodiment, the propeller includes a hub and a plurality of blades connected to each other, and the plurality of blades are arranged along the circumference of the hub;

[0012] The radial dimension of the front end of the extension section is equal to the radial dimension of the hub, and / or the rear end of the extension section is flush with the rear side edge of the bottom wall of the rudder blade in the front-to-rear direction.

[0013] In one embodiment, the extension section is configured as a cone, the bottom end of the cone is connected to the connecting section, the tip of the cone is flush with the rear side edge of the bottom wall of the rudder blade in the front-to-back direction, and the extension section is an internal hollow structure.

[0014] In one embodiment, the vortex eliminating fin comprises a plurality of fins, the fins are connected to the connecting section or the extending section, and the plurality of fins are arranged along the circumference of the connecting section;

[0015] Among them, the number of the fins is equal to that of the blades, the ratio of the radius of the fin to the radius of the blade is 0.2, and the ratio of the axial distance between the front end of the root of the fin and the rear end of the root of the blade in the axial direction of the propeller shaft to the radius of the blade is 0.1.

[0016] In one embodiment, the rudder blade has a first side wall and a second side wall, the first side wall and the second side wall are arranged opposite to each other in the front-rear direction, and the distance between the first side wall and the second side wall gradually decreases from top to bottom; and / or,

[0017] The rudder blade has a third side wall and a fourth side wall, the third side wall and the fourth side wall are arranged opposite to each other in the left-right direction, and the distance between the third side wall and the fourth side wall gradually decreases from top to bottom.

[0018] In one embodiment, there is a movable spacing between the bottom wall of the rudder blade and the extension section, and the height of the bottom wall of the rudder blade gradually decreases from front to back;

[0019] Wherein, the aspect ratio of the rudder blade is 1.1-1.3.

[0020] In one of the embodiments, the extension section is detachably connected to the connection section, and / or the rudder blade has a connection portion, and the connection portion can be detachably connected to the hull.

[0021] In a second aspect, the present invention provides a double-propeller ship, comprising a hull and a stern energy-saving device according to any of the above-mentioned schemes, wherein the stern energy-saving device is arranged at the stern position of the hull, and the stern energy-saving device is provided in two groups, and the two groups of the stern energy-saving devices are arranged on both sides of the longitudinal baseline of the hull.

[0022] In one embodiment, the rudder blade, the propeller shaft, the vortex-reducing fin and part of the propeller are all located above the longitudinal baseline of the hull.

[0023] The beneficial effects of the present invention are:

[0024] The present invention provides a stern energy-saving device and a double-propeller ship. The stern energy-saving device can reduce the resistance of the rudder blade and the energy loss caused by the tail vortex through the mutual cooperation between the vortex-eliminating fin, the propeller shaft extension section extending to the position below the rudder blade, and the rudder blade located above the axis of the propeller shaft extension section, thereby reducing the navigation resistance of the ship, improving the propulsion efficiency of the propeller, and improving the speed performance of the ship. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The structure of the stern energy saving device in the embodiment of the present invention is shown in FIG. Figure 1 ;

[0026] Figure 2 The structure of the stern energy saving device in the embodiment of the present invention is shown in FIG. Figure 2 ;

[0027] Figure 3 The structure of the stern energy saving device in the embodiment of the present invention is shown in FIG. Figure 3 ;

[0028] Figure 4 Schematic diagram of the connection structure of the propeller, the vortex-eliminating fin and the extension section in an embodiment of the present invention.

[0029] In the figure:

[0030] 1. Rudder blade;

[0031] 2. propeller shaft; 21. connecting section; 22. extension section;

[0032] 3. propeller; 31. hub; 32. blade;

[0033] 4. Vortex elimination fin; 41. Fin;

[0034] 5. Ship body. DETAILED DESCRIPTION

[0035] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

[0036] In the description of the present invention, unless otherwise clearly specified and limited, the terms "connected", "connected", and "fixed" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0037] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0038] In the description of this embodiment, the terms "upper", "lower", "right", etc., directions or positional relationships are based on the directions or positional relationships shown in the drawings, and are only for the convenience of description and simplification of operation, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are only used to distinguish in the description and have no special meaning.

[0039] like Figures 1 to 3As shown, the X direction shown in the figure is a schematic diagram of the front and rear direction of the ship body, the Y direction is a schematic diagram of the left and right direction of the ship body, the Z direction is a schematic diagram of the up and down direction of the ship body, L1 is a schematic diagram of the axial direction of the propeller shaft, and L2 is a schematic diagram of the longitudinal baseline position of the ship body. An embodiment of the first aspect of the present invention provides a stern energy-saving device, which includes a rudder blade 1, a propeller shaft 2, a propeller 3 and a vortex-eliminating fin 4. The rudder blade 1 is used for transmission connection with the ship body 5, that is, the rudder blade 1 can be connected to the drive system of the ship body 5 through the rudder bar. During the travel of the ship, the drive system of the ship body 5 can drive the rudder blade 1 to swing and adjust the angle position of the rudder blade 1. The cross-sectional area of ​​the rudder blade 1 gradually decreases from top to bottom, that is, in the vertical up and down direction, the cross-sectional area of ​​the rudder blade 1 gradually decreases.

[0040] The propeller shaft 2 includes a connecting section 21 and an extension section 22, which are arranged to extend along the axial direction of the propeller shaft 2 and are connected to each other. The connecting section 21 can be connected to the hull 5 by transmission, that is, the connecting section 21 can be mounted on the bottom of the hull 5, and the end of the connecting section 21 can be connected to the driving system of the hull 5 by transmission, and the driving system of the hull 5 can drive the connecting section 21 to rotate along the axis of the propeller shaft 2. The rudder blade 1 is arranged above the axis of the extension section 22 as a whole, and the rear end of the extension section 22 extends to the position below the rudder blade 1. The propeller 3 and the vortex-eliminating fin 4 are fixedly arranged at the connecting section 21, and the vortex-eliminating fin 4 is arranged behind the propeller 3.

[0041] With such an arrangement, when the propeller 3 is working, the tail vortex formed at the rear of the middle part thereof by the rotation moves backward along the axial direction of the propeller shaft 2 to the position of the vortex-eliminating fin 4. The vortex generated by the vortex-eliminating fin 4 as it rotates with the propeller shaft 2 can offset the tail vortex, and the intensity of the tail vortex behind the propeller 3 is weakened. The entire flow field can become smooth, thereby reducing the pressure behind the propeller 3. Compared with the rudder blade 1 being arranged directly behind the propeller 3, the lower end of the rudder blade 1 is located at the longitudinal baseline L2 of the hull 5. Due to the uneven distribution of the wake velocity in the vertical direction, there is a large difference in the forces on the rudder blade 1 above and below the axis of the propeller shaft 2. The force on the rudder blade 1 below the axis of the propeller shaft 2 accounts for more than half of the total resistance of the rudder blade 1. In this embodiment, while the water flow pressure behind the propeller 3 is reduced, the rudder blade 1 is arranged as a whole above the axis of the extension section 22, the area of ​​the rudder blade 1 is significantly reduced, and the water flow below the axis of the propeller shaft 2 is difficult to exert resistance on the propeller blade 32, and the force exerted by the water flow above the axis of the propeller shaft 2 on the rudder blade 1 is less different, which not only reduces the wet surface area of ​​the rudder blade 1, but also greatly reduces the water pressure and resistance of the rudder blade 1. The rear end of the extension section 22 of the propeller shaft 2 extends to the lower position of the rudder blade 1, so that the tail vortex formed at the rear end of the extension section 22 during the rotation process can be shifted to the lower or rear position of the rudder blade 1, reducing the resistance exerted by the tail vortex from the rear end of the extension section 22 on the rudder blade 1. This embodiment can reduce the resistance on the rudder blade 1 and reduce the energy loss caused by the tail vortex through the mutual cooperation between the vortex elimination fin 4, the extension section 22 extending to the lower position of the rudder blade 1, and the rudder blade 1 located above the axis of the extension section 22, thereby reducing the navigation resistance of the ship, improving the propulsion efficiency of the propeller 3, and improving the rapid performance of the ship. It solves the problem in the related art that the rudder blade is set directly behind the propeller, which not only generates a large resistance but also has a significant difference in resistance between the upper and lower halves, is easy to cause vibration, and a tail vortex is easy to form behind the propeller, reducing the speed of the ship.

[0042] In this embodiment, in the front-to-back direction, part or all of the rudder blade 1 is located above the extension section 22, that is, the rear end of the extension section 22 is flush with the rear side of the bottom wall of the rudder blade 1 in the front-to-back direction, or the rear end of the extension section 22 can also be retracted in the front-to-back direction to the rear side of the bottom wall of the rudder blade 1. The propeller shaft 2 is tilted in the up-down direction, and the height of the front end of the propeller shaft 2 is higher than the height of the rear end of the propeller shaft 2, which is convenient for the transmission connection between the propeller shaft 2 and the ship body 5, and also convenient for the installation of the propeller 3, so that the propeller 3 forms a certain downward tilt angle, and the vortex generated by the rotation of the propeller 3 can generate both forward propulsion force for the ship body 5 and upward lifting force for the ship body 5.

[0043] like Figure 1 and Figure 4As shown, in some embodiments, in the axial direction of the propeller shaft 2, the radial dimension of the extension section 22 gradually decreases from front to rear, so that the vortex generated by the rotation of the extension section 22 gradually decreases, and the dimension is smallest at the rear end of the extension section 22, thereby reducing the strength of the tail vortex formed at the rear end of the extension section 22, thereby reducing the resistance of the vortex or tail vortex generated by the rotation of the extension section 22 to the rudder blade 1.

[0044] like Figure 1 and Figure 4 As shown, in some embodiments, the propeller 3 includes a hub 31 and a plurality of blades 32 connected to each other, the plurality of blades 32 are arranged along the circumference of the hub 31, the plurality of blades 32 are fixedly connected to the hub 31, and then the hub 31 is fixedly connected to the connecting section 21 by bolts or clamping, etc., for easy installation.

[0045] Optionally, the radial dimension of the front end of the extension section 22 is equal to the radial dimension of the hub 31, and the size transition between the extension section 22 and the hub 31 is smoother, thereby reducing the formation of a tail vortex due to the size difference between the hub 31 and the extension section 22, and reducing the resistance of the rudder blade 1.

[0046] Optionally, the rear end of the extension section 22 is flush with the rear side edge of the bottom wall of the rudder blade 1 in the front-to-rear direction, so as to facilitate the shifting of the tail vortex formed at the rear end of the extension section 22 to the rear of the rear side edge of the bottom wall of the rudder blade 1, thereby reducing the resistance of the tail vortex on the rudder blade 1.

[0047] like Figure 1 and Figure 4 As shown, in some embodiments, the extension section 22 is configured as a cone, the bottom end of the cone is connected to the connecting section 21, and the tip of the cone is flush with the rear side edge of the bottom wall of the rudder blade 1 in the front-to-back direction, so as to reduce the size of the rear end of the extension section 22 as much as possible, reduce the strength of the tail vortex, and further reduce the resistance of the tail vortex on the rudder blade 1. Optionally, the extension section 22 is an internal hollow structure, that is, the extension section 22 is a cavity inside, which reduces the weight of the extension section 22 and the overall weight of the propeller shaft 2, and reduces the energy loss of the hull drive. The extension section 22 is a rear end suspended rotation structure of the propeller shaft 2, which reduces its weight and can also reduce the vibration amplitude of the propeller shaft 2 during long-distance transmission, so that the rotation of the propeller shaft 2 is more stable, and the rotation of the propeller 3 and the swinging process of the rudder blade 1 are also more stable.

[0048] like Figure 1 and Figure 4As shown, in some embodiments, the vortex elimination fin 4 includes a plurality of fins 41, the fins 41 are connected to the connecting section 21 or the extension section 22, and the plurality of fins 41 are arranged along the circumference of the propeller shaft 2. The number of fins 41 is equal to that of the blades 32, and the ratio of the radius of the fins 41 to the radius of the blades 32 is 0.2, that is, the radius of the fins 41 is much smaller than the radius of the blades 32, and the fins 41 only offset the wake generated at the root of the blades 32, reducing the impact on the driving performance of the blades 32. The ratio of the axial distance between the root front end of the fin 41 and the root rear end of the blade 32 in the axial direction of the propeller shaft 2 to the radius of the blade 32 is 0.1, so as to provide a certain conversion spacing for the water flow flowing out of the root of the blade 32, so that the fins 41 and the blades 32 can form vortices independently and then interact with each other, and the vortex elimination effect is good.

[0049] In this embodiment, optionally, a plurality of fins 41 are evenly arranged in the circumferential direction of the connecting section 21, and the spacing between any two adjacent fins 41 is equal. The pitch angle of the fin 41 has a certain difference from the root pitch angle of the blade 32, for example, -10° to 10°, and the fin 41 has a reverse bevel angle, for example, the reverse bevel angle can be selected to be 20° to 60°, and the angle of the reverse bevel angle can vary with the number of fin blades. The fin 41 is located between two adjacent blades 32 to improve the vortex elimination effect.

[0050] like Figures 1 to 3 As shown, in some embodiments, the rudder blade 1 has a first side wall and a second side wall, the first side wall and the second side wall are arranged opposite to each other in the front-rear direction, and the distance between the first side wall and the second side wall gradually decreases from top to bottom, thereby reducing the area of ​​the rudder blade 1 in the left-right direction, and the size of the lower section of the rudder blade 1 is smaller than that of the upper end, thereby further reducing the wet surface area of ​​the rudder blade 1.

[0051] Optionally, the rudder blade 1 has a third side wall and a fourth side wall, the third side wall and the fourth side wall are arranged opposite to each other in the left-right direction, the distance between the third side wall and the fourth side wall gradually decreases from top to bottom, the area of ​​the rudder blade 1 in the front-back direction is reduced, the size of the lower section of the rudder blade 1 is smaller than the size of the upper section, further reducing the wet surface area of ​​the rudder blade 1. The rudder blade 1 of this embodiment can adopt an airfoil profile to further reduce the resistance. For example, the rudder blade 1 can adopt a NACA airfoil profile (NACA, National Advisory Committee for Aeronautics).

[0052] like Figures 1 to 3As shown, in some embodiments, there is an active spacing between the bottom wall of the rudder blade 1 and the extension section 22 to avoid position interference between the rudder blade 1 and the extension section 22 during the rotation of the rudder blade 1. The height of the bottom wall of the rudder blade 1 is gradually reduced from front to back, so that the extension change trend of the bottom wall of the rudder blade 1 in the front-to-back direction is adapted to the extension change trend of the surface of the extension section 22. While avoiding interference, the active spacing between the bottom wall of the rudder blade 1 and the surface of the extension section 22 is reduced, and the resistance of the rudder blade 1 is reduced. Optionally, on the same axial section of the extension section 22, the distance of the active spacing between the surface of the extension section 22 and the bottom wall of the rudder blade 1 is equal.

[0053] In some embodiments, the aspect ratio of the rudder blade 1 is 1.1-1.3, which can reduce the pressure difference on both sides of the rudder blade 1, thereby reducing the rudder pressure, improving the control flexibility of the rudder blade 1, and improving the rudder efficiency.

[0054] like Figures 1 to 3 As shown, in some embodiments, the extension section 22 is detachably connected to the connecting section 21, and / or the rudder blade 1 has a connecting portion, which can be detachably connected to the hull 5. The connection method between the extension section 22 and the connecting section 21 and the connection method between the connecting portion and the hull 5 can be but is not limited to threaded connection, snap-on connection or magnetic connection. According to different driving or resistance requirements, the extension section 22 and the rudder blade 1 can be replaced with different sizes, which is not only convenient for maintenance and replacement, but also can form different drag reduction effects.

[0055] like Figures 1 to 3 As shown, an embodiment of the second aspect of the present invention provides a double-propeller ship, comprising a hull 5 and a stern energy-saving device in any of the above-mentioned schemes, the stern energy-saving device being arranged at the stern position of the hull 5, and two groups of stern energy-saving devices being arranged, and the two groups of stern energy-saving devices being arranged on both sides of the longitudinal baseline L2 of the hull 5. For medium and high-speed double-propeller ships, even if the rudder blade 1 is arranged as a whole above the axis of the extension section 22, the stable operating performance of the rudder blade 1 can be guaranteed. By arranging two stern energy-saving devices, the double-propeller ship can reduce the resistance of the rudder blade 1, reduce the energy loss caused by the wake vortex, reduce the navigation resistance of the ship, improve the propulsion efficiency of the propeller 3, and improve the speed performance of the ship.

[0056] In some embodiments, the rudder blade 1, propeller shaft 2, vortex-breaking fin 4 and part of the propeller 3 are all located above the longitudinal baseline L2 of the hull 5 to further reduce the wet surface area of ​​the rudder blade 1 and the resistance experienced by the rudder blade 1 and the hull 5.

[0057] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, various obvious changes, readjustments and substitutions can be made without departing from the protection scope of the present invention. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A stern energy-saving device, characterized in that: The stern energy-saving device comprises: A rudder blade (1), the rudder blade (1) being used for transmission connection with the ship body (5), the cross-sectional area of ​​the rudder blade (1) gradually decreasing from top to bottom; A propeller shaft (2), the propeller shaft (2) comprising a connecting section (21) and an extending section (22), the connecting section (21) and the extending section (22) extending along the axial direction of the propeller shaft (2) and connected to each other, the connecting section (21) being capable of being transmission-connected to the ship body (5), the rudder blade (1) being integrally arranged above the axis of the extending section (22), and the rear end of the extending section (22) extending to a position below the rudder blade (1); A propeller (3) and a vortex-eliminating fin (4), wherein the propeller (3) is fixedly arranged on the connecting section (21), the vortex-eliminating fin (4) is fixedly arranged on the connecting section (21) or the extending section (22), and the vortex-eliminating fin (4) is arranged behind the propeller (3).

2. The stern energy saving device according to claim 1, characterized in that: In the axial direction of the propeller shaft (2), the radial dimension of the extension section (22) gradually decreases from front to back.

3. The stern energy saving device according to claim 2, characterized in that: The propeller (3) comprises a hub (31) and a plurality of blades (32) connected to each other, wherein the plurality of blades (32) are arranged along the circumference of the hub (31); The radial dimension of the front end of the extension section (22) is equal to the radial dimension of the hub (31), and / or the rear end of the extension section (22) is flush with the rear side edge of the bottom wall of the rudder blade (1) in the front-to-rear direction.

4. The stern energy saving device according to claim 3, characterized in that: The extension section (22) is configured as a cone, the bottom end of the cone is connected to the connecting section (21), the tip of the cone is flush with the rear side edge of the bottom wall of the rudder blade (1) in the front-to-back direction, and the extension section (22) is an internal hollow structure.

5. The stern energy saving device according to claim 3, characterized in that: The vortex-eliminating fin (4) comprises a plurality of fins (41), wherein the fins (41) are connected to the connecting section (21) or the extending section (22), and the plurality of fins (41) are arranged along the circumference of the propeller shaft (2); The number of the fins (41) and the blades (32) is equal, the ratio of the radius of the fins (41) to the radius of the blades (32) is 0.2, and the ratio of the axial distance between the root front end of the fins (41) and the root rear end of the blades (32) in the axial direction of the propeller shaft (2) to the radius of the blades (32) is 0.

1.

6. The stern energy saving device according to claim 1, characterized in that: The rudder blade (1) comprises a first side wall and a second side wall, the first side wall and the second side wall are arranged opposite to each other in the front-rear direction, and the distance between the first side wall and the second side wall gradually decreases from top to bottom; and / or, The rudder blade (1) has a third side wall and a fourth side wall, the third side wall and the fourth side wall are arranged opposite to each other in the left-right direction, and the distance between the third side wall and the fourth side wall gradually decreases from top to bottom.

7. The stern energy saving device according to claim 1, characterized in that: There is a movable spacing between the bottom wall of the rudder blade (1) and the extension section (22), and the height of the bottom wall of the rudder blade (1) gradually decreases from front to back; Wherein, the aspect ratio of the rudder blade (1) is 1.1-1.

3.

8. The stern energy saving device according to claim 1, characterized in that: The extension section (22) is detachably connected to the connection section (21), and / or the rudder blade (1) has a connection portion, and the connection portion can be detachably connected to the hull (5).

9. A double-paddle boat, characterized in that: It comprises a hull (5) and the stern energy-saving device according to any one of claims 1 to 8, wherein the stern energy-saving device is arranged at the stern position of the hull (5), and there are two groups of the stern energy-saving devices, which are arranged on both sides of the longitudinal baseline of the hull (5).

10. The double-screw boat according to claim 9, characterized in that: The rudder blade (1), the propeller shaft (2), the vortex-eliminating fin (4) and part of the propeller (3) are all located above the longitudinal baseline of the hull (5).

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