JP2015127179A - Duct device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a duct device for a marine vessel capable of achieving an energy-saving effect.SOLUTION: A duct device 1 comprises: a duct 2 disposed at least a part around a rotation shaft AX of a propeller in a front portion of the propeller installed onto a stern of a hull 100; and a stay 3 for connecting the duct and at least a part of the hull. A cross section of the duct is an airfoil profile type. An angle between a blade chord line of the airfoil and a line parallel to the rotation shaft, and a distance between a middle point of the blade chord line and the rotation shaft are different between a first part of the duct and a second part of the duct which is different from the first part with respect to a circumferential direction of the rotation shaft.

Description

  The present invention relates to a ship duct apparatus.

  In a technical field related to a ship, for example, a ship including a duct device as disclosed in Patent Document 1 is known.

JP 2008-137462 A

  By arranging the duct device at the stern of the hull, the ship can obtain an energy saving effect. A further energy saving effect can be expected by improving the duct device.

  An object of this invention is to provide the ship duct apparatus which can acquire an energy-saving effect.

  According to a first aspect of the present invention, a duct disposed at least at a part around a rotation axis of the propeller is connected in front of a propeller provided at a stern of the hull, and the duct and at least a part of the hull are connected to each other. A cross section of the duct is an airfoil, an angle formed by a chord line of the airfoil and a line parallel to the rotation axis, a midpoint of the chord line, and the rotation axis The distance between the first portion of the duct and the second portion of the duct different from the first portion with respect to the circumferential direction of the rotating shaft is provided.

  In the duct device according to the present invention, at least a part of the duct is disposed above the rotation axis, the first portion includes an upper end portion of the duct, and the second portion is located on a side of the duct. Including the end, the angle of the first portion may be larger than the angle of the second portion, and the distance of the first portion may be smaller than the distance of the second portion.

  In the duct device according to the present invention, the duct has a front end portion that defines an inflow port, and a rear end portion that faces the propeller and defines an outflow port that is different in size and shape from the inflow port. The outflow port is smaller than the inflow port, the inner surface of the upper end portion of the rear end portion protrudes toward the rotation shaft, and the inner surface of the upper end portion of the front end portion does not protrude toward the rotation shaft. May be.

  In the duct device according to the present invention, the stay may have a wing shape in cross section.

  According to a second aspect of the present invention, a duct disposed in at least a part of the periphery of the rotation axis of the propeller in front of a propeller provided at the stern of the hull, and the duct and at least a part of the hull are connected. And a stay having a cross section of the stay.

  In the duct device according to the present invention, the stay may be inclined so that a leading edge of the chord line of the airfoil is disposed above a trailing edge.

  In the duct device according to the present invention, the stay is disposed outside the inner end portion with respect to a radial direction with respect to a rotation axis of the propeller and connected to the duct, and is connected to the duct. And the angle formed by the chord line of the airfoil and the horizontal plane is different between the third portion of the stay and the fourth portion of the stay that is different from the third portion with respect to the radial direction. May be.

  In the duct device according to the present invention, the chord line at the inner end portion of the stay is inclined such that a front edge of the airfoil is disposed above a rear edge, and the outer end portion of the stay The chord line may be inclined so that the leading edge of the airfoil is disposed below the trailing edge.

  In the duct device according to the present invention, the stay includes a first stay and a second stay disposed above a rotation shaft of the propeller, and the first stay and the second stay in the circumferential direction of the rotation shaft. The angle formed by the stay may be smaller than 90 degrees.

  The duct apparatus which concerns on this invention WHEREIN: The said duct may be arrange | positioned so that a part of said rotating shaft may be enclosed above the rotating shaft of the said propeller.

  According to the present invention, an energy saving effect can be obtained.

FIG. 1 is a side view schematically showing an example of a duct device for a ship according to the first embodiment. FIG. 2 is a front view schematically showing an example of a ship duct device according to the first embodiment. FIG. 3 is a perspective view schematically showing an example of a duct device for a ship according to the first embodiment. FIG. 4 is a cross-sectional view showing an example of a duct according to the first embodiment. FIG. 5 is a diagram illustrating an example of a contour of a front end portion and a contour of a rear end portion of a duct according to the first embodiment. FIG. 6 is a cross-sectional view illustrating an example of a stay according to the first embodiment. FIG. 7 is a diagram schematically showing an example of a ship duct device according to the second embodiment. FIG. 8 is a diagram schematically illustrating an example of a duct device for a ship according to the third embodiment. FIG. 9 is a diagram schematically illustrating an example of a duct device for a ship according to the fourth embodiment.

  Hereinafter, embodiments according to the present invention will be described with reference to the drawings, but the present invention is not limited thereto. The requirements of the embodiments described below can be combined as appropriate. Some components may not be used.

<First Embodiment>
A first embodiment will be described. FIG. 1 is a side view schematically showing an example of a ship duct device 1 according to the present embodiment. FIG. 2 is a front view schematically showing an example of the duct device 1 for a ship according to the present embodiment, and corresponds to a view taken along the line AA in FIG. FIG. 3 is a perspective view schematically showing an example of the ship duct apparatus 1 according to the present embodiment.

  As shown in FIG. 1, the ship includes a propeller 101 provided at the stern 100B of the hull 100, a duct device 1 disposed in front of the propeller 101, and a rudder 102 disposed behind the propeller 101. Yes. The duct device 1 is disposed on the stern 100B of the hull 100. Propeller 101 is connected to a power source mounted on hull 100 through shaft 103. The power source includes at least one of an engine such as a diesel engine and a motor. The hull 100 has a stern tube 104, and the shaft 103 is rotatably supported by the stern tube 104. The power source rotates the propeller 101 via the shaft 103. The propeller 101 rotates around the rotation axis AX. As the propeller 101 rotates, the ship sails.

  By the rotation of the propeller 101, the ship advances to the bow side. The bow is arranged in front of the traveling direction of the ship moving forward, and the stern 100B is arranged in the rear. In the following description, the front is simply referred to as “front” as appropriate with respect to the traveling direction of the advancing ship, and the rear is simply referred to as “rear” as appropriate with respect to the traveling direction of the advancing ship. Further, a direction orthogonal to the traveling direction in the horizontal plane is appropriately referred to as a width direction.

  In the following description, a direction parallel to the rotation axis AX is appropriately referred to as an axial direction, a radial direction with respect to the rotation axis AX is appropriately referred to as a radial direction, and a rotation direction around the rotation axis AX is appropriately determined. The circumferential direction is called.

  The duct device 1 includes a duct 2 disposed in front of the propeller 101 and a stay 3 that connects the duct 2 and at least a part of the hull 100. The duct 2 is disposed in front of the propeller 101 at least at a part around the rotation axis AX of the propeller 101. Note that the duct 2 may be referred to as a nozzle 2. The stay 3 may be referred to as a support column 3 or a connecting plate 3. In the present embodiment, the stay 3 connects the duct 2 and the stern tube 104 of the hull 100.

  In the present embodiment, at least a part of the duct 2 is disposed above the rotation axis AX of the propeller 101. In the present embodiment, the duct 2 is disposed above the rotation axis AX of the propeller 101 so as to surround a part of the rotation axis AX. That is, the duct 2 has a semi-cylindrical shape (semi-annular shape). In the following description, the surface of the duct 2 that faces the rotation axis AX in at least a part of the periphery of the rotation axis AX of the propeller 101 is appropriately referred to as the inner surface of the duct 2, and the duct 2 that faces the opposite side of the inner surface of the duct 2. Is referred to as the outer surface of the duct 2 as appropriate.

  The duct 2 has a front end portion 21 and a rear end portion 22. The front end 21 is disposed in front of the rear end 22. The front end portion 21 defines the inflow port 4 into which fluid (seawater or the like) flows. The rear end portion 22 faces the propeller 101. The rear end portion 22 defines the outlet 5 from which the fluid flows out. In the present embodiment, the size of the inlet 4 is different from the size of the outlet 5. In the present embodiment, the outlet 5 is smaller than the inlet 4. Moreover, in this embodiment, the shape of the inflow port 4 and the shape of the outflow port 5 are different.

  As shown in FIGS. 2 and 3, the inner surface of the duct 2 at the upper end portion of the rear end portion 22 protrudes toward the rotation axis AX. That is, the inner surface of the duct 2 at the upper end portion of the rear end portion 22 has a convex portion 22T protruding inward. On the other hand, the inner surface of the duct 2 at the upper end portion of the front end portion 21 does not protrude toward the rotation axis AX.

  Each of the contour of the front end portion 21 and the contour of the rear end portion 22 is symmetrical with respect to the lateral direction. That is, the outline of the front end portion 21 and the outline of the rear end portion 22 are line symmetric with respect to a reference line (symmetric axis) SR that passes through the rotation axis AX and is parallel to the vertical direction.

  FIG. 4 is a sectional view showing an example of the duct 2 according to this embodiment. FIG. 5 is a diagram illustrating an example of the contour of the front end portion 21 and the contour of the rear end portion 22. FIG. 5 shows one contour with respect to the symmetry axis SR.

  As shown in FIG. 4, the cross section of the duct 2 is an airfoil. The airfoil of the duct 2 has an outer shape capable of efficiently obtaining lift by interaction with the fluid. The airfoil (cross-sectional shape) of the duct 2 has a shape that gradually decreases from the front edge portion toward the rear edge portion. In the present embodiment, the outer surface of the airfoil of the duct 2 is linear or convex or concave that is smaller than the convexity of the inner surface. The inner surface of the airfoil of the duct 2 has a curved surface that protrudes inward (rotation axis AX side). In the airfoil of the duct 2, the leading edge 23 at the foremost end of the airfoil, the trailing edge 24 at the rearmost end of the airfoil, a chord line 25 connecting the leading edge 23 and the trailing edge 24, and the upper surface of the airfoil A center line 26 obtained by connecting midpoints to the lower surface in order is defined. The front end 21 includes an airfoil leading edge 23. The trailing end 22 includes an airfoil trailing edge 24.

  In the present embodiment, the duct 2 is arranged such that the distance between the rotation axis AX and the front edge 23 is greater than the distance between the rotation axis AX and the rear edge 24 in the radial direction.

  When the ship advances on the water (on the sea), at least a part of the water flows along the inner surface of the duct 2 via the front edge 23 of the duct 2. According to Bernoulli's theorem, the inner surface of the duct 2 at the front end 21 becomes negative pressure, and lift is generated. Thrust is generated by the axial component of the lift (thrust generated by the duct 2). Moreover, since the output of the power source which moves the propeller 101 is suppressed by the thrust generated by the duct 2, an energy saving effect is obtained.

  In the present embodiment, an angle φ formed by the airfoil chord line 25 of the duct 2 and a line parallel to the rotation axis AX of the propeller 101 is appropriately referred to as an arrangement angle φ.

  In the present embodiment, the distance R between the midpoint 25M of the chord line 25 and the rotation axis AX of the propeller 101 is appropriately referred to as a radial position R with respect to the radial direction of the propeller 101 with respect to the rotation axis AX.

  In the present embodiment, the angle (arrangement angle) φ formed by the airfoil chord line 25 and a line parallel to the rotation axis AX of the propeller 101, the midpoint 25M of the chord line 25, and the rotation axis AX of the propeller 101 Distance (radial position) R between the first portion of the duct 2 and the second portion of the duct 2 different from the first portion in the circumferential direction of the rotation axis AX. That is, in the present embodiment, the arrangement angle φ and the radial position R are different in each of the plurality of portions of the duct 2 in the circumferential direction of the rotation axis AX.

  In the present embodiment, the arrangement angle φ of the upper end portion of the duct 2 arranged immediately above the rotation axis AX is larger than the arrangement angle φ of the side end portion of the duct 2 arranged just beside the rotation axis AX. In the present embodiment, the shape of the duct 2 is determined so that the arrangement angle φ gradually decreases from the upper end portion (0 deg) to the side end portion (90 deg) with respect to the circumferential direction. ing.

  In the present embodiment, the radial position R of the upper end portion of the duct 2 arranged immediately above the rotation axis AX is smaller than the radial position R of the side end portion of the duct 2 arranged just beside the rotation axis AX. In the present embodiment, the shape of the duct 2 is determined so that the radial position R gradually increases from the upper end (0 deg) to the side end (90 deg) of the duct 2 in the circumferential direction. ing.

  More specifically, in the circumferential direction, the radial position R shows a minimum value from 0 deg to 10 deg, and the radial position R gradually increases from 10 deg to 90 deg. When the diameter (outer diameter) of the propeller 101 is Rp, the minimum value of the radial position R may be 0.7 Rp or less. The maximum value of the radial position R is set to Rp or less. The difference between the minimum value and the maximum value of the radial position R may be set to 0.5 Rp or less.

  With respect to the circumferential direction, the arrangement angle φ has a maximum value from 0 deg to 10 deg, and the arrangement angle φ gradually decreases from 10 deg to 90 deg. The minimum value of the arrangement angle φ is set to 0 degree or more.

  Thereby, as shown in FIG.2 and FIG.3, the convex part 22T is provided in the inner surface of the rear-end part 22 of the duct 2, and the semi-annular duct 2 long in a horizontal direction is obtained.

  The velocity component of the fluid (seawater) flow at the stern 100B (in front of the propeller 101) exists not only in the axial direction but also in the circumferential direction and the radial direction. The flow field of the fluid flowing into the duct 2 through the inlet 4 is not uniform. Therefore, the arrangement angle φ and the radial position R of the duct 2 affect the thrust generated by the duct 2. According to the knowledge of the present inventor, it has been found that the thrust of the duct 2 cannot be sufficiently obtained when the arrangement angle φ and the radial position R of the duct 2 are constant in the circumferential direction.

  Therefore, in the present embodiment, the shape of the duct 2 is determined so that the arrangement angle φ and the radial position R are different in each of the plurality of portions of the duct 2 in the circumferential direction of the rotation axis AX. Thereby, the thrust generated by the duct 2 can be maximized, and a greater energy saving effect can be obtained.

  For example, in a large ship, the flow direction angle tends to be large at the 0 deg position (upper end position) and the flow direction angle at the 90 deg position (side end position) in the circumferential direction. Further, the flow velocity tends to increase as the radial position R decreases at the 0 deg position in the circumferential direction, and the flow velocity increases as the radial position R increases at the 90 deg position.

  Therefore, the arrangement angle φ of the upper end portion of the duct 2 is made larger than the arrangement angle φ of the side end portion of the duct 2, and the radial position R of the upper end portion of the duct 2 is made larger than the radial position R of the side end portion of the duct 2. Can also be increased, the thrust of the duct 2 evaluated by the following equations (1), (2), and (3) can be increased.

L = 1/2 · Cl (α) · ρ · S · V2 (1)
D = 1/2 · Cd (α) · ρ · S · V2 (2)
F = L · sin θ−D · cos θ (3)
L: Lift D: Drag F: Thrust (forward component of resultant force)
Cl: Lift coefficient (depends on blade performance; depends on angle of attack α)
Cd: Drag coefficient (depends on blade performance; depends on angle of attack α)
ρ: Fluid specific gravity S: Duct surface area (depending on radial position)
V: Flow velocity (composite flow velocity in the axial direction and radial direction)
θ: Flow direction angle (angle formed by axial flow velocity and radial flow velocity)

  Next, the stay 3 will be described. As shown in FIGS. 1, 2, and 3, the stay 3 includes a front end portion 31 and a rear end portion 32. The front end portion 31 is disposed in front of the rear end portion 32. The rear end portion 32 faces the propeller 101.

  The stay 3 connects the duct 2 and the stern tube 104 of the hull 100. The stay 3 has an inner end portion 38 connected to the outer surface of the stern tube 104 and an outer end portion 39 connected to the inner surface of the duct 2. The outer end portion 39 is disposed outside the inner end portion 38 in the radial direction with respect to the rotation axis AX of the propeller 101.

  The duct device 1 has a pair of stays 3. In the following description, one stay 3 is appropriately referred to as a first stay 301, and the other stay 3 is appropriately referred to as a second stay 302. The first stay 301 is disposed on one side of the rotation axis AX in the lateral direction. The second stay 302 is disposed on the other side of the rotation axis AX in the lateral direction. In the present embodiment, the first stay 301 and the second stay 302 are disposed substantially parallel to the horizontal plane.

  FIG. 6 is a cross-sectional view of the stay 3 according to the present embodiment. As shown in FIG. 6, the cross section of the stay 3 is an airfoil. The airfoil of the stay 3 has an outer shape that allows efficient lift to be obtained by interaction with the fluid. The airfoil (cross-sectional shape) of the stay 3 has a shape that gradually becomes narrower from the front edge portion toward the rear edge portion. In the present embodiment, the upper surface of the airfoil of the stay 3 is linear or convex or concave below the degree of convexity of the inner surface. The lower surface of the airfoil of the stay 3 has a curved surface that protrudes downward. In the airfoil of the stay 3, the front edge 33 of the front end of the airfoil, the rear edge 34 of the rearmost end of the airfoil, the chord line 35 connecting the front edge 33 and the rear edge 34, and the upper surface of the airfoil A center line 36 obtained by connecting the midpoints with the lower surface in order is defined. The front end 31 includes an airfoil leading edge 33. The trailing end 32 includes an airfoil trailing edge 34.

  In the present embodiment, the stay 3 is arranged such that the wing-shaped chord line 35 is inclined. In the present embodiment, the stay 3 is inclined so that the front edge 33 of the airfoil chord line 35 is disposed above the rear edge 34.

  The stay 3 may be arranged such that the chord line 35 is inclined with respect to the horizontal plane. The stay 3 may be arranged such that the chord line 35 is inclined with respect to the water line. The water line includes at least one of a planned water line and a design water line. The stay 3 may be inclined with respect to a predetermined surface including the rotation axis AX such that the front edge 33 is arranged farther from the predetermined surface than the rear edge 34. The predetermined plane including the rotation axis AX may be a horizontal plane or an inclined plane that is inclined with respect to the horizontal plane.

  In the present embodiment, the stay 3 is disposed such that the front edge 33 is disposed above the rear edge 34 and the angle γ formed by the horizontal plane and the chord line 35 is not less than 0 degrees and not more than 10 degrees.

  When the ship advances on the water (on the sea), at least a part of the water flows along the inner surface of the stay 3 via the front edge 33 of the stay 3. According to Bernoulli's theorem, the lower surface of the stay 3 at the front end 31 becomes negative pressure, and lift is generated. A large thrust is generated by the axial component of the lift (thrust generated by the stay 3) and the thrust of the propeller 101. Moreover, since the output of the power source which moves the propeller 101 is suppressed by the thrust generated by the stay 3, an energy saving effect is obtained.

  As described above, according to the present embodiment, the duct 2 is formed such that the arrangement angle φ and the radial position R are different in a plurality of portions in the circumferential direction, so that an energy saving effect can be obtained.

  In the present embodiment, since the cross section of the stay 3 is a wing shape, not only the duct 2 but also the stay 3 generates thrust. Thereby, a higher energy saving effect can be obtained.

  In the present embodiment, the outer end 39 of the stay 3 is connected to the semi-annular duct 2. Thereby, generation | occurrence | production of a blade tip loss is suppressed. When the outer end 39 of the stay 3 and the duct 2 are not connected, a vortex is generated at at least one of the end of the stay 3 and the end of the duct 2, and as a result, the energy saving effect may not be sufficiently exhibited. There is. In this embodiment, since the stay 3 and the duct 2 are connected, the generation of vortices is suppressed. Therefore, a high energy saving effect can be obtained.

Second Embodiment
A second embodiment will be described. In the following description, the same or equivalent components as those in the above-described embodiment are denoted by the same reference numerals, and the description thereof is simplified or omitted.

  FIG. 7 shows an example of a stay 3B of the duct device 1B according to the present embodiment. The cross section of the stay 3B is an airfoil. In the present embodiment, the stay 3B is a symmetric wing in which the shape of the upper surface and the lower surface of the wing shape are symmetric. The stay 3B may be an asymmetric wing in which the shape of the upper surface and the lower surface of the wing shape are asymmetric.

  The stay 3B has an inner end portion 38 connected to the hull 100, and an outer end portion 39 that is disposed outside the inner end portion 38 in the radial direction with respect to the rotation axis AX of the propeller 100 and connected to the duct 2. .

  In the present embodiment, the angle γ formed by the wing chord line 35 of the stay 3B and the horizontal plane is different in each of the plurality of portions of the stay 3B in the radial direction. In the present embodiment, the angle γ of the airfoil chord line 35 of the stay 3B at the inner end 38 is different from the angle γ of the airfoil chord line 35 of the stay 3B at the outer end 39. The stay 3 </ b> B is twisted so that the angle γ gradually changes from the inner end portion 38 toward the outer end portion 39.

  In the present embodiment, the chord line 35 at the inner end 38 of the stay 3B is inclined such that the airfoil leading edge 33 is disposed above the rear edge 34, and at the outer end 39 of the stay 3B. The chord line 39 is inclined such that the airfoil leading edge 33 is disposed below the trailing edge 34.

  The fluid flow field around the duct 2 and the stay 3B is different with respect to the radial direction with respect to the rotation axis AX of the propeller 101. For example, the fluid (seawater) may flow downward in the radial direction and the fluid (seawater) may flow downward in the radial direction. Therefore, the inclination angle γ of the stay 3B affects the thrust generated by the stay 3B. According to the knowledge of the present inventor, it has been found that the thrust of the stay 3B can be further improved by changing the angle γ of the chord line 35 of the stay 3B with respect to the radial direction (inclination angle of the stay 3B) γ with respect to the radial direction. .

  Therefore, in the present embodiment, the shape of the stay 3B is determined so that the inclination angle γ is different in each of the plurality of portions of the stay 3B in the radial direction with respect to the rotation axis AX. Thereby, the thrust generated by the stay 3B can be maximized, and a greater energy saving effect can be obtained.

  Therefore, by adjusting the inclination angle γ of the stay 3B, the thrust of the stay 3B evaluated by the following expressions (4), (5), and (6) can be increased.

L = 1/2 · Cl (α) · ρ · S · V2 (4)
D = 1/2 · Cd (α) · ρ · S · V2 (5)
F = L · sin θ−D · cos θ (6)
L: Lift D: Drag F: Thrust (forward component of resultant force)
Cl: Lift coefficient (depends on blade performance; depends on angle of attack α)
Cd: Drag coefficient (depends on blade performance; depends on angle of attack α)
ρ: Fluid specific gravity S: Stay surface area V: Flow velocity (composite flow velocity in the direction crossing the stay and the main flow direction)
θ: Flow direction angle (angle formed between the flow velocity in the direction crossing the stay and the flow velocity in the main flow direction)

<Third Embodiment>
A third embodiment will be described. In the following description, the same or equivalent components as those in the above-described embodiment are denoted by the same reference numerals, and the description thereof is simplified or omitted.

  FIG. 8 shows an example of a duct device 1C according to the present embodiment. In FIG. 8, the stay 3 includes a first stay 301 and a second stay 302 that are disposed above the rotation axis AX of the propeller 101. With respect to the circumferential direction of the rotation axis AX, an angle formed by the first stay 301 and the second stay 302 is smaller than 90 degrees. In the present embodiment, the outer end 39 connected to the duct 2 is disposed above the inner end 38 connected to the hull 100. Also in this embodiment, an energy saving effect can be obtained.

<Fourth embodiment>
A fourth embodiment will be described. In the following description, the same or equivalent components as those in the above-described embodiment are denoted by the same reference numerals, and the description thereof is simplified or omitted.

  FIG. 9 shows an example of a duct device 1D according to the present embodiment. As shown in FIG. 9, the duct device 1 </ b> D includes a duct 2 </ b> D and a stay 3 </ b> D that connects the duct 2 </ b> D and at least a part of the hull 100. The surface of the connecting portion between the duct 2D and the stay 3D includes a curved surface. That is, in this embodiment, a corner | angular part is not provided in the connection part of duct 2D and stay 3D.

  According to the present embodiment, the blade tip loss can be greatly reduced. Also in the present embodiment, the thrust generated by the stay 3D assists the thrust generated by the duct 2D.

DESCRIPTION OF SYMBOLS 1 Duct apparatus 2 Duct 3 Stay 4 Inlet 5 Outlet 21 Front end part 22 Rear end part 22T Protrusion part 23 Front edge 24 Rear edge 25 Chord line 31 Front end part 32 Rear end part 33 Front edge 34 Rear edge 35 Chord line 38 Inner end 39 Outer end 100 Hull 101 Propeller AX Rotating shaft

Claims (10)

A duct disposed at least in part around the rotation axis of the propeller in front of a propeller provided at the stern of the hull;
A stay connecting the duct and at least a part of the hull;
With
The cross section of the duct is an airfoil,
The angle formed by the chord line of the airfoil and a line parallel to the rotation axis, and the distance between the midpoint of the chord line and the rotation axis, the first portion of the duct, and the rotation axis A duct device that differs in a circumferential direction from a second part of the duct that is different from the first part. At least a part of the duct is disposed above the rotation axis,
The first portion includes an upper end portion of the duct;
The second portion includes a side end of the duct;
The angle of the first portion is greater than the angle of the second portion;
The duct device according to claim 1, wherein the distance of the first portion is smaller than a distance of the second portion. The duct has a front end that defines an inlet, and a rear end that faces the propeller and defines an outlet that is different in size and shape from the inlet.
The outlet is smaller than the inlet;
The inner surface of the upper end portion of the rear end portion protrudes toward the rotating shaft,
The duct device according to claim 2, wherein an inner surface of an upper end portion of the front end portion does not protrude toward the rotation shaft.   The duct device according to any one of claims 1 to 3, wherein a cross section of the stay is an airfoil. A duct disposed at least in part around the rotation axis of the propeller in front of a propeller provided at the stern of the hull;
A stay connecting the duct and at least a part of the hull;
With
The stay has a wing-shaped cross section.   The duct device according to claim 4 or 5, wherein the stay is inclined so that a leading edge of the chord line of the airfoil is disposed above a trailing edge. The stay has an inner end connected to the hull, and an outer end arranged outside the inner end with respect to the radial direction with respect to the rotation axis of the propeller, and connected to the duct,
The angle formed between the chord line of the airfoil and a horizontal plane differs between the third portion of the stay and the fourth portion of the stay that is different from the third portion with respect to the radial direction. The duct apparatus as described in. The chord line at the inner end of the stay is inclined such that the leading edge of the airfoil is disposed above the trailing edge,
The duct device according to claim 7, wherein the chord line at the outer end portion of the stay is inclined so that a front edge of the airfoil is disposed below a rear edge. The stay includes a first stay and a second stay arranged above a rotation shaft of the propeller,
The duct device according to any one of claims 1 to 8, wherein an angle formed by the first stay and the second stay with respect to a circumferential direction of the rotation shaft is smaller than 90 degrees.   The duct device according to any one of claims 1 to 9, wherein the duct is disposed so as to surround a part of the rotation shaft above the rotation shaft of the propeller.

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