Rectifier and oar

Abstract

Provided are: a rectifier that facilitates operation of an oar; and an oar that comprises the rectifier.　Provided are long and narrow rectifiers 1 that are fixed to a blade 100 of an oar 200 and rectify the flow of water, the rectifiers 1 being characterized by protruding from a front surface 101 of the blade 100 and being fixed so that the tip side thereof is inclined upward. Provided also are rectifiers 2 that are characterized by protruding from a rear surface 102 of the blade 100, and are fixed so that the tip side thereof is inclined downward. Furthermore, in a longitudinal cross section, the projection length L1 from the blade 100 most protrude on the lower side than the middle, and is greatest in the middle and gradually decreases toward both outer sides in the longitudinal direction. An upper surface 11 formed on the upper side is inclined with respect to the blade 100 and has an arch shape projecting upward as seen in the vertical direction of the blade 100.

Description

Commutator and Oar

[0001] The present invention relates to a commutator and an oar.

[0002] An oar for boat racing includes an elongated cylindrical shaft, a blade fixed to the tip of the shaft, a handle fixed to the base end of the shaft, and a sleeve externally inserted on the base end side of the shaft (see Patent Document 1). The sleeve is inserted into a low lock (oar lock, oar receiver) on the boat (hull) side and supported by the low lock. Then, the rower holds the handle and operates the oar with the low lock as a fulcrum.

[0003] Japanese Patent Application Laid-Open No. 2019-137205

[0004] However, it may be difficult to operate the oar depending on the skill of the rower and the condition of the water surface.

[0005] Therefore, an object of the present invention is to provide a commutator and an oar provided with the commutator that make it easy to operate the oar.

[0006] As a means for solving the above problems, the present invention is an elongated commutator fixed to the blade of an oar for rectifying the flow of water, which protrudes from the surface of the blade and is fixed with the tip side inclined upward.

[0007] According to such a configuration, since the commutator protrudes from the surface (front surface) of the blade and the tip side is fixed with an upward inclination, when catching, the water that enters (enters) from the tip side to the surface side of the blade pushes the commutator and the blade vertically upward. As a result, when catching, the blade is less likely to sink into the water, and it becomes easier to operate the oar.

[0008] As a means for solving the above problems, the present invention is an elongated commutator fixed to the blade of an oar for rectifying the flow of water, which protrudes from the back surface of the blade and is fixed with the tip side inclined downward.

[0009] With this configuration, the commutator protrudes from the back (back) of the blade, and its tip is fixed at a downward inclination. As a result, at the finish, water entering the back of the blade from the base pushes the commutator and blade vertically upward. This makes it less likely for the blade to sink in the water at the finish, making it easier to operate the oar. In other words, it makes it less likely for the oar to sink. This case of water entering the back of the blade and pushing up the commutator occurs, for example, in crew boats (eights, quadruple sculls, coxed fours, etc.) when the oar (blade) operation is slower than the water flow corresponding to the boat speed, and the water pushes against the back of the blade.

[0010] Furthermore, in the vertical cross-section, the most protruding part may be located below the middle.

[0011] Here, the longitudinal section refers to the cross-section of the commutator in the vertical direction (longitudinal direction) when the width direction of the blade to which the commutator is fixed is defined as the vertical direction (longitudinal direction). With this configuration, in the longitudinal section of the commutator, it protrudes most below the middle, so the angle between the lower surface below the most protruding position and the front / back surface of the blade is greater than the angle between the upper surface above the most protruding position and the front / back surface of the blade.

[0012] As described above, the angle between the bottom surface and the front / back surface of the blade is large. Therefore, when the commutator is fixed to the front surface of the blade, water entering from the tip side to the front surface of the blade during a catch easily pushes the commutator and blade vertically upward. Also, when the commutator is fixed to the back surface, water entering from the base side to the back surface of the blade during a finish easily pushes the commutator and blade vertically upward.

[0013] Furthermore, in the longitudinal direction, the protruding length from the blade may be greatest in the middle and gradually shorter towards both sides, and the upper surface formed on the upper side may be oblique to the blade and have an upwardly projecting arc shape when viewed in the vertical direction of the blade.

[0014] With this configuration, in the longitudinal direction, the protrusion length from the blade is greatest in the middle and gradually decreases towards both sides, and the upper surface formed on the upper side is oblique to the blade and has an upwardly projecting arc shape when viewed vertically from the blade, so that water entering the front / back side of the blade can easily flow in an arc shape along the arc-shaped upper surface.

[0015] As a result, in the direction of water flow entering the front / back side of the blade, the water that has passed over the top surface of the curved shape flows diagonally downward on the downstream side of the top surface of the curved shape, making it easier to push down the existing water. In this way, the water that has passed over the top surface of the curved shape pushes down the existing water, and as a counterforce (reaction force), it becomes easier to push the commutator and blade vertically upward.

[0016] Furthermore, if the upper surface of the most protruding point in the longitudinal cross-section is a roughly straight slope, water that has gone over the most protruding point will flow more easily along the roughly straight slope of the upper surface, making it less likely for vortices (Karman vortices) to be generated. As a result, the blade will experience less resistance from the water. Moreover, when the blade is forward (feathered) with the blade nearly horizontal to the water surface, the water and air will collide with the straight slope of the upper surface, reducing water and air resistance and making it less likely for the boat to decelerate when moving forward.

[0017] As a means to solve the aforementioned problems, the present invention provides an oar characterized by comprising a blade and a commutator fixed to the blade.

[0018] This configuration makes it easier to operate the oars.

[0019] According to the present invention, it is possible to provide a commutator that makes oars easier to operate, and oars equipped with a commutator.

[0020] This is a plan view of the single scull and oar according to this embodiment, showing the catch stage. This is a plan view of the single scull and oar according to this embodiment, showing the middle stage. This is a plan view of the single scull and oar according to this embodiment, showing the finish stage. This is a surface view (front view) of the blade according to this embodiment, showing the catch stage. This is a surface view (front view) of the blade according to this embodiment, showing the middle stage. This is a surface view (front view) of the blade according to this embodiment, showing the finish stage. This is a back view (rear view) of the blade according to this embodiment, showing the finish stage. This is a perspective view of the commutator according to this embodiment. This is a plan view of the commutator according to this embodiment. This is a cross-sectional view taken along the line X1-X1 in Figure 4. This is a cross-sectional view taken along the line X2-X2 in Figure 7. This is a graph showing the water flow velocity on the surface side of the blade.

[0021] One embodiment of the present invention will be described with reference to Figures 1 to 12. Here, we will describe the bow-side oar 200 (scull oar) of a single scull 300 (boat) for competition. The same applies to the stroke-side oar. Facing forward in the direction of travel of the single scull 300 (upper side of the paper in Figures 1 to 3), the left side is the stroke side and the right side is the bow side. The rower sits facing backward in the seat 320, which will be described later.

[0022] ≪Single Scull≫ As shown in Figures 1 to 3, the single scull 300 comprises a single scull body 310, a seat 320, and a row lock 330 (oar holder). The single scull body 310 is an elongated hull, and its cross-section in the width direction is approximately semi-circular. The seat 320 is slidably mounted in the longitudinal direction (front-to-back direction) of the single scull body 310.

[0023] The row lock 330 is rotatably mounted on the tip of a rigger (not shown) that extends to the left and right sides, respectively, at approximately the midpoint of the single scull body 310. The row lock 330 is a U-shaped member that supports the oar 200 from below. That is, the row lock 330 supports the sleeve 230 of the oar 200, and when the rower operates the oar 200, the row lock 330 becomes the point of action between the single scull 300 and the oar 200.

[0024] ≪Oar≫ The oar 200 comprises a slender, cylindrical shaft 210, a blade 100 fixed to the tip of the shaft 210, a handle 220 fixed to the base end of the shaft 210, a sleeve 230 externally fitted to the base end of the shaft 210, three commutators 1 (see Figure 4) fixed to the surface 101 of the blade 100, and one commutator 2 (see Figure 7) fixed to the back surface 102 of the blade 100. Note that commutators 1 and 2 have the same shape. Here, the axis of the oar 200 corresponds to the axis O2 of the shaft 210 (see Figure 4).

[0025] The shaft 210 and blade 100 are made of, for example, CFRP (Carbon Fiber Reinforced Plastic) and have appropriate elasticity. The handle 220 is the part that the rower grips to operate the oar 200. The sleeve 230 is a cylindrical part that is supported by the row lock 330. When the rower grips and operates the handle 220, the oar 200 rotates around the row lock 330 (sleeve 230) as a pivot point.

[0026] <Blade> As shown in Figures 4 to 7, the blade 100 is a water-scraping member and is a wide, thin plate extending in the direction of the axis O2 of the shaft 210. Here, the blade 100 according to this embodiment is asymmetrical with respect to the axis O2 of the shaft 210. That is, when the width direction of the blade 100 is the vertical direction (when the blade 100 is perpendicular to the water surface S1), it is offset vertically downward so that the portion that scrapes water is larger.

[0027] <Commutators> Commutator 1 stabilizes the movement of the blade 100 by rectifying the water flow on the surface 101 of the blade 100. Commutator 2 stabilizes the movement of the blade 100 by rectifying the water flow on the back surface 102 of the blade 100.

[0028] <Commutators - Surface Side> Referring to Figures 4 to 6 and 8 to 10, three commutators 1 that protrude from and are fixed to the surface 101 of the blade 100 will be described. The commutators 1 are, for example, bonded to the surface 101 with an adhesive. The commutators 1 are elongated resin members that extend in the direction of the axis O3. The resins are, for example, TPU (Thermoplastic Polyurethane) resin, ABS (Acrylonitrile Butadiene Styrene) resin, and PLA (Poly-Lactic Acid) resin.

[0029] The two commutators 1, 1 are positioned on the outer side (towards the tip) of the blade 100 in the longitudinal direction, and in two stages in the width direction (height direction). One commutator 1 is positioned on the inner side (towards the base) of the blade 100 in the longitudinal direction, and between the two outer commutators 1, 1 in the width direction. When the blade 100 is perpendicular to the water surface S1, the width direction of the blade 100 becomes the height direction.

[0030] Each commutator 1 is fixed to the surface 101 with its tip inclined upward, that is, with its base inclined downward, when the width direction of the blade 100 is vertical. In other words, when the shaft 210 enters the water at a predetermined angle θ1 (10 to 20°, preferably 15°) with respect to the water surface S1 (see Figure 4), the width direction of the blade 100 is vertical, and the blade 100 is positioned at a predetermined depth D1 (3 to 15 cm) below the water surface S1, the axis O3 of the commutator 1 is inclined upward at its tip (outside) with respect to the axis O2 of the shaft 210. The angle θ2 between the axis O3 and the horizontal plane S2 (see Figure 8) is, for example, 10 to 20°.

[0031] In a longitudinal cross-sectional view, the commutator 1 is approximately triangular with its surface side protruding (see Figure 10). The longitudinal cross-sectional view is a cross-sectional view perpendicular to the axis O3. In the longitudinal cross-sectional view, the commutator 1 protrudes most below the middle. That is, the protruding portion 30 (top) of the commutator 1 is below the middle in the vertical direction (height direction, width direction). The surface of the protruding portion 30 is chamfered and has an "R shape". The upper surface 11 on the upper side of the protruding portion 30 is a concave curved surface that is slightly recessed toward the blade 100 (surface 101), so that water flows laminarly at the boundary between the upper surface 11 and the surface 101, and vortices are less likely to be generated. The lower surface 21 on the lower side of the protruding portion 30 is also a concave curved surface that is slightly recessed toward the blade 100 (surface 101). However, the upper surface 11 and the lower surface 21 may also be configured as straight slopes.

[0032] The projection length L1 of the projection 30 is greatest in the center in the direction of the axis O3 (the longitudinal direction of the commutator 1) and gradually shortens as it approaches both outer sides (see Figure 9). The upper surface 11 formed on the upper side of the projection 30 is oblique to the surface 101 of the blade 100 (see Figure 10) and is an upwardly projecting arc shape when viewed vertically from the blade 100 (view perpendicular to the plane of the paper in Figure 4). In addition, the upper edge 12 of the commutator 1 in a front view (view vertically from the blade 100) is an upwardly projecting arc shape (see Figure 8). Furthermore, the lower edge 22 of the commutator 1 in a front view is an upwardly projecting arc shape (see Figure 8).

[0033] The angle θ3 between the upper surface 11 and the surface 101 is, for example, 20 to 50° (preferably 30 to 40°) (see Figure 10). The angle θ4 between the lower surface 21 and the surface 101 is, for example, 50 to 70° (preferably 55 to 65°). That is, the upper surface 11 is a gentle slope with respect to the surface 101, and the lower surface 21 is a steep slope with respect to the surface 101.

[0034] <Commutator - Back Side> Next, with reference to Figures 7 and 11, a commutator 2, which protrudes from and is fixed to the back surface 102 of the blade 100, will be described. The differences between commutator 2 and commutator 1 will be explained.

[0035] The commutator 2 is an elongated member extending in the direction of the axis O4. The commutator 2 is positioned inward (towards the base end) of the blade 100 in the longitudinal direction and in the upper position in the width direction (height direction).

[0036] The commutator 2 is fixed to the back surface 102 with its tip inclined downward, that is, with its base inclined upward, when the width direction of the blade 100 is vertical. That is, when the shaft 210 enters the water at a predetermined angle θ1 (10 to 20°, preferably 15°) with respect to the water surface S1 (see Figure 7), the width direction of the blade 100 is vertical, and the blade 100 is positioned at a predetermined depth D1 below the water surface S1, the axis O2 of the shaft 210 and the axis O4 of the commutator 2 are approximately parallel, and the base (inner) side is inclined upward. The angle θ5 between the axis O4 and the horizontal plane S2 is, for example, 10 to 20° (preferably 15°).

[0037] In a longitudinal section view, the commutator 2 is roughly triangular with its back side protruding (see Figure 11). A longitudinal section view is a cross-sectional view perpendicular to the axis O4. In a longitudinal section view, the commutator 1 protrudes most below the middle. That is, the protruding portion 30 (top) of the commutator 2 is below the middle in the vertical direction (height direction, width direction). The surface of the protruding portion 30 is chamfered and has an "R shape". The upper surface 11 on the upper side of the protruding portion 30 and the lower surface 21 on the lower side of the protruding portion 30 are roughly in a straight line.

[0038] The upper surface 11 formed above the protruding portion 30 is oblique to the back surface 102 of the blade 100 (see Figure 7), and in a vertical view of the blade 100 (view perpendicular to the plane of the paper in Figure 7), it is an upwardly projecting arc shape. Furthermore, in a front view (vertical view of the blade 100), the upper edge of the commutator 2 is an upwardly projecting arc shape (see Figure 7). In addition, in a front view (vertical view of the blade 100), the lower edge of the commutator 2 is an upwardly projecting arc shape (see Figure 7).

[0039] ≪Effects of the Commutator and Oars≫ Next, we will explain the effects of commutator 1, commutator 2, and oar 200. When a rower sits on the seat 320, grips the handle 220, and operates the oar 200, the single scull 300 moves forward along the straight target line O1 (see Figures 1 to 3). Specifically, the single scull 300 moves forward by repeating the catch phase (see Figures 1 and 4), middle phase (see Figures 2 and 5), fish (finish) phase (see Figures 3, 6, and 7), and forward phase.

[0040] <Catch Phase> The catch phase is the stage in which the rower, with their legs bent and leaning forward, moves the seat 320 backward (Figure 1), and raises the handle 220 to lower the blade 100 into the water, allowing the blade 100 to grip the water. Subsequently, the rower extends their legs while still leaning forward and pulls the handle 220. Using the position where the blade 100 grips the water as a pivot point and the oar lock 330 as the point of application, the single scull 300 moves forward along the target line O1 (see Figure 1, arrow A1). In other words, the single scull 300 moves forward as the oar 200 rotates with the position where the blade 100 grips the water as a nearly fixed point.

[0041] Here, since the length of the oar 200 is constant, as the single scull 300 moves forward, the blade 100 is pushed further outward (towards the bow side) in the water (see Figure 1, arrow A11). As a result, water flows from the outside to the inside on the surface 101 and back surface 102 of the blade 100 (see Figures 4 and 8, arrow A21).

[0042] Then, water flowing from the outside to the inside collides with the inclined lower surface 21 of the commutator 1, generating a force that pushes the commutator 1 and the blade 100 vertically upward (see Figures 4 and 8, arrow A22). In this way, a force that pushes the commutator 1 and the blade 100 vertically upward is generated immediately after the catch, making it difficult for the blade 100 to sink and making it easier to operate the oar 200.

[0043] Incidentally, as the process progresses from the catch stage, the flow velocity of water on the front surface 101 and the back surface 102 of the blade 100 gradually decreases (see FIG. 12). In FIG. 12, with respect to the front surface 101 of the blade 100, the flow velocity of water towards the inside is taken as minus (negative), and the flow velocity of water towards the outside is taken as plus (positive).

[0044] A part of the water gets over the protruding portion 30 of the commutator 1 and flows into the upper surface 11 side (see FIGS. 4 and 8, arrow A23). At this time, since the upper surface 11 is a gentle linear slope, the water that has got over flows in a laminar flow along the upper surface 11. Thus, since the water that has got over flows in a laminar flow (see FIG. 10, arrow A23), it becomes difficult for water vortices to occur, and it becomes easier for the blade 100 to move without being resisted by the vortices. Here, it is also possible to form a plurality of grooves / ribs on the upper surface 11, for example, along its inclination direction, so that the water that has got over the protruding portion 30 can flow more easily in a laminar flow.

[0045] Further, the water flowing from the outside towards the inside flows in an arc shape along the arcuate upper surface 11 (see FIGS. 4 and 8, arrow A24). Then, in the flow direction of the water flowing in this arc shape, downstream of the arcuate upper surface 11, the water that has passed through the arcuate upper surface 11 heads obliquely downward and pushes down the existing water.

[0046] Thus, since the water that has passed through the arcuate upper surface 11 pushes down the existing water, as its resistance force (reaction force), the commutator 1 and the blade 100 are pushed upward vertically. That is, immediately after the catch, a lift force that pushes the commutator 1 and the blade 100 upward vertically is generated, so that it becomes difficult for the blade 100 to sink and it becomes easier to operate the oar 200. The same applies to the back surface 102 side of the blade 100. Since the water that has passed through along the arcuate upper surface 11 of the commutator 2 pushes down the existing water, as its resistance force (reaction force), the commutator 1 and the blade 100 are pushed upward vertically.

[0047] <Middle stage> The middle stage is the stage when the singleskull 300 progresses and the angle formed by the singleskull 300 and the oar 200 becomes 90° (see FIGS. 2 and 5). When it reaches the middle stage, the flow velocity of water on the front surface 101 and the back surface 102 of the blade 100 becomes substantially 0 (see FIG. 12).

[0048] Thereafter, when the rower pulls the handle 220 while arching the upper body, the single scull 300 further advances along the target line O1 with the position where the blade 100 grabs the water as the fulcrum and the low lock 330 as the point of application (see arrow A2 in FIG. 2).

[0049] Here, since the length of the oar 200 is constant, as the single scull 300 advances from the middle stage, the blade 100 is gradually withdrawn inward (toward the single scull 300 side) in the water. (See arrow A12 in FIG. 2). Then, water flows from the inside to the outside on the front surface 101 and the back surface 102 of the blade 100 (see arrow A31 in FIG. 6). Note that as it progresses from the middle stage, the flow velocity of the water on the front surface 101 and the back surface 102 of the blade 100 gradually increases (see FIG. 12).

[0050] <Finishing stage> The finishing stage is the stage where, after the rower bends the arm and pulls the handle 220 while arching the upper body, the handle 220 is lowered to raise the blade 100 out of the water.

[0051] Here, in the finishing stage, on the front surface 101 of the blade 100, water flowing from the inside to the outside collides with the inclined upper surface 11 of the fairing 1, generating a force that pushes the fairing 1 and the blade 100 vertically downward (see arrow A32 in FIG. 6). Thus, in the finishing stage, since a force that pushes the blade 100 vertically downward is generated, it becomes difficult for the blade 100 to rise above the water early, and it becomes easier to push the water until the end with the blade 100.

[0052] Also, the water flowing from the inside to the outside flows in an arc along the arcuate upper surface 11 (see arrow A34 in FIG. 6). Then, in the flow direction of this water flowing in an arc, downstream of the arcuate upper surface 11, the water after flowing through the arcuate upper surface 11 goes obliquely downward and pushes down the existing water.

[0053] In this way, the water that has passed over the bow-shaped upper surface 11 pushes down the existing water, and as a reaction force, the commutator 1 and blade 100 are pushed vertically upward. That is, in the fish phase, a lift force is generated that pushes the commutator 1 and blade 100 vertically upward, making it difficult for the blade 100 to sink and easier to operate the oars 200. The same applies to the back surface 102 side of the blade 100, where the water that has passed over the bow-shaped upper surface 11 of the commutator 2 (see Figure 7, arrow A44) pushes down the existing water, and as a reaction force, the commutator 2 and blade 100 are pushed vertically upward.

[0054] Furthermore, if the operation of the oars 200 is delayed relative to the boat speed of the single scull 300, the water will push the underside 102 of the blade 100 toward the rear. That is, the water flowing outward along the underside 102 of the blade 100 (see Figure 7, arrow A41) collides with the inclined lower surface 21 of the commutator 2, generating a force that pushes the commutator 2 and the blade 100 vertically upward (see Figure 7, arrow A42). As a result of this vertically upward force, the blade 100 becomes more likely to come out of the water, making it less likely to "slip" (a phenomenon known as "harakiri"), and making it easier to operate the oars 200.

[0055] Some of the water flows over the protruding portion 30 of the commutator 2 and into the upper surface 11 (see Figure 11, arrow A43). At this time, since the upper surface 11 is a gently sloping straight surface, the water that has flowed over flows along the upper surface 11 in a laminar flow. In this way, the water that has flowed over flows in a laminar flow (see Figure 11, arrow A43), making it difficult for water vortices to form, so the blade 100 can move more easily without being resisted by vortices.

[0056] <Forward Phase> The forward phase is the stage in which the rower leans their upper body forward, then bends their legs and extends the handle 220 and seat 320, moving towards the next catch. In the forward phase, in order to reduce the air resistance on the blade 100, the handle 220 is rotated by approximately 90° so that the surface 101 faces vertically upward. That is, in the forward phase, with the underside 102 facing the water surface S1 side (vertically downward), the blade 100 moves in an arc so as to move forward in the direction of travel.

[0057] In this forward phase, the front of the commutator 2 fixed to the back surface 102 on the vertically downward side of the blade 100 becomes the upper surface 11 of a gentle slope. Therefore, even if the blade 100 collides with the water surface S1 due to, for example, rough water, the upper surface 11, which is the main impact surface, is a gentle slope, making it easier for water to pass through the commutator 2 (see Figure 11, arrow A51), and reducing the impact on the blade 100. As the impact on the blade 100 is reduced in this way, the oar 200 becomes easier to operate.

[0058] <Modifications> Although one embodiment of the present invention has been described above, the present invention is not limited thereto, and may be modified as follows, for example.

[0059] In the above-described embodiment, a configuration was illustrated in which the commutator 1 and commutator 2 are separate components from the blade 100 and are bonded together with an adhesive. However, other configurations are also possible, for example, in which the commutator 1 and / or commutator 2 are made of CFRP (Carbon Fiber Reinforced Plastic) and are integrally molded with the blade 100.

[0060] In the above-described embodiment, a configuration in which three commutators 1 are fixed to the surface 101 of the blade 100 was illustrated, but the number of commutators 1 is not limited to this. Also, a configuration in which two commutators 1 are arranged in two stages at the tip end and one commutator 1 is arranged at the base end was illustrated, but the arrangement of the commutators 1 can be freely changed. The same applies to the commutators 2 on the back surface 102 of the blade 100.

[0061] In the above-described embodiment, a configuration in which the upper surface 11 and lower surface 21 of commutators 1 and 2 are straight inclined surfaces was illustrated in the longitudinal section. However, other configurations, such as convex or concave surfaces, are also possible.

[0062] In the above-described embodiment, the commutators 1 and 2 were shown to protrude most below the middle in the vertical cross-section, but other configurations are also possible, for example, in which they protrude most above the middle.

[0063] In the embodiments described above, the present invention was illustrated as being applied to the bow-side oar (skull oar) of a single scull (boat). However, it may also be applied to the stroke-side oar of a single scull (boat). Furthermore, the present invention may be applied to the skull oar and sweep oar of a crew boat (double scull, quadruple scull, coxed four, eight, etc.).

[0064] 1, 2 Commutator 11 Top surface 21 Bottom surface 30 Protrusion 100 Blade 101 Front surface 102 Back surface 200 Oar

Claims

1. A slender commutator fixed to the blade of an oar to straighten the flow of water, characterized in that it protrudes from the surface of the blade and its tip is fixed at an upward inclination.

2. A slender commutator fixed to the blade of an oar to straighten the flow of water, characterized in that it protrudes from the back surface of the blade and its tip is fixed at an angle downward.

3. The commutator according to claim 1 or 2, characterized in that, in a longitudinal cross-section, it protrudes most significantly below the middle.

4. The commutator according to claim 3, characterized in that, in the longitudinal direction, the protrusion length from the blade is greatest in the middle and gradually decreases toward both outer sides, and the upper surface formed on the upper side is oblique to the blade and has an upwardly projecting arc shape when viewed in the vertical direction of the blade.

5. An oar comprising a blade and a commutator according to claim 1 or claim 2 fixed to the blade.

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