US20160347417A1

US20160347417A1 - Twin skeg ship

Info

Publication number: US20160347417A1
Application number: US14/911,268
Authority: US
Inventors: Daisuke Matsumoto
Original assignee: Mitsubishi Heavy Industries Ltd
Current assignee: Mitsubishi Heavy Industries Ltd
Priority date: 2014-11-18
Filing date: 2015-02-06
Publication date: 2016-12-01
Also published as: CN105829204A; CN105829204B; JP6422020B2; KR20160075493A; JP2016097686A; WO2016080001A1

Abstract

Provided is a twin skeg ship equipped with a pair of left and right skegs provided at a bottom of a stern, propellers provided behind the pair of left and right skegs; and fins provided in front of the propellers only at inner sides in a ship width direction with respect to the skegs and configured to radially extend from rotational centers of the propellers.

Description

TECHNICAL FIELD

The present invention relates to a twin skeg ship having propeller shafts at a pair of left and right skegs provided on the bottom of a stern.
Priority is claimed on Japanese Patent Applications No. 2014-233257, filed on Nov. 18, 2014, the contents of which are incorporated herein by reference.

BACKGROUND ART

A twin skeg ship in which a pair of left and right skegs are provided on the bottom of a stern to form a tunnel-shaped bottom recess between the left and right skegs and propeller shafts for the pair of left and right skegs are provided is known.
In such a twin skeg ship, various proposals have been presented to improve propulsion performance.
A constitution in which a fin extending in a leftward/rightward direction is provided between left and right skegs is disclosed in, for example, Patent Literature 1. In this constitution, a flow passing through an upper portion of a tunnel, both sides of which are surrounded by the skegs, hits the fin between the left and right skegs, and thereby generates a lift force to improve the propulsion performance using part of the lift force as an advance force.
A constitution in which fins are provided on inner wall surfaces of a pair of left and right skegs is also disclosed in Patent Literature 2. This fin is provided to have an elevation angle with respect to a longitudinal vortex generated between the left and right skegs. According to this constitution, as the longitudinal vortex hits the fin, a lift force having an advance directional component occurs, and thus the propulsion performance is improved by the advance directional component.
A constitution in which a tubular duct having a greater diameter at a bow side than at a stern side is provided in front of a propeller is disclosed in Patent Literature 3. According to this constitution, the tubular duct straightens a flow of the propeller to improve propulsion performance.

CITATION LIST

Patent Literature

[Patent Literature 1]

Japanese Patent No. 5426699

[Patent Literature 2]

Japanese Unexamined Patent Application, First Publication No. 2012-006556

[Patent Literature 3]

Japanese Unexamined Patent Application, First Publication No. 2008-143488

SUMMARY OF INVENTION

Technical Problem

Various proposals have been given to improve the propulsion performance. However, the flow below the bottom is variously changed by a shape of the stern bottom of the hull. As a result, even if such constitutions as disclosed in, for instance, Patent Literatures 1 to 3 are applied, the propulsion performance is not always improved, but may actually be reduced. Thus, further improvement in the propulsion performance is always required.
The present invention is directed to providing a twin skeg ship capable of improving propulsion performance.

Solution to Problem

According to a first aspect of the present invention, a twin skeg ship includes: a pair of left and right skegs provided at a bottom of a stern; propellers provided behind the pair of left and right skegs; and fins provided in front of the propellers only at inner sides in a ship width direction with respect to the skegs and configured to radially extend from rotational centers of the propellers.
In this way, as the fins are provided in front of the propellers only at the inner sides in the ship width direction with respect to the skegs, flows at the inner sides of the skegs in the ship width direction can be strengthened or weakened in front of the propellers by the fins. Thereby, the wake gain can be increased in the left and right propellers.
In the twin skeg ship, flows at the inner sides in the ship width direction with respect to the skegs may be configured to be slower than flows at outer sides in the ship width direction with respect to the skegs.
In the twin skeg ship having this constitution, specific resistance of the fins provided only at the inner sides of the skegs in the ship width direction can be reduced, and as the slow flows at the inner sides of the skegs in the ship width direction are accelerated or decelerated in front of the propellers by the fins, it is possible to effectively increase the wake gains of the propellers to improve the propulsion performance.
In the twin skeg ship, the fins may be configured to strengthen upward flows occurring at the inner sides of the skegs in the ship width direction in front of the propellers in the pair of left and right skegs.
In this way, as the fins are provided in regions in which the upward flows occurring at the inner sides of the skegs in the ship width direction are strengthened, it is possible to effectively increase the wake gains of the propellers to improve the propulsion performance.
In the twin skeg ship, rotating directions of the propellers may be set to be inward directions in which upper portions of the propellers rotate from the outer sides in the ship width direction toward the inner sides in the ship width direction.
According to this constitution, the upward flows that are strengthened by the fins and occur at the inner sides of the skegs in the ship width direction cause strong flows in directions opposite to the rotating directions of the propellers. Therefore, it is possible to effectively increase the wake gains of the propellers to improve the propulsion performance.
In the twin skeg ship, the fins may be configured to weaken upward flows occurring at the inner sides of the skegs in the ship width direction in front of the propellers in the pair of left and right skegs.
In this way, as the fins are provided in regions in which the upward flows occurring at the inner sides of the skegs in the ship width direction are weakened, it is possible to effectively increase the wake gains of the propellers to improve the propulsion performance.
In the twin skeg ship, rotating directions of the propellers may be set to be outward directions in which upper portions of the propellers rotate from the inner sides in the ship width direction toward the outer sides in the ship width direction.
According to this constitution, even when the upper portions of the propellers rotate outward from the inner sides in the ship width direction toward the outer sides in the ship width direction, the flows at the inner sides of the skegs in the ship width direction are weakened in front of the propeller by the fins, and thereby flows in the same directions as the rotating directions of the propellers are weakened, and it is possible to increase the wake gains to improve the propulsion performance in the left and right propellers.
The twin skeg ship may be configured to further include tubular ducts which are provided in front of the propellers while crossing the inner sides of the skegs in the ship width direction and the outer sides of the skegs in the ship width direction and whose outer diameters are gradually reduced from a bow side toward a stern side.
With this constitution, flows directed to the propellers are accelerated by passing through the inside of the ducts. Thereby, since a propulsive force in an advance direction occurs at the ducts, the propulsion performance can be increased.
The twin skeg ship may be configured to further include semi-cylindrical ducts which are in front of the propellers and are provided only at the inner sides in the ship width direction with respect to the skegs and whose outer diameters are gradually reduced from a bow side toward a stern side.
With this constitution, the flows directed to the propellers are accelerated by passing through the inside of the ducts. Thereby, since a propulsive force in an advance direction occurs, the propulsion performance can be increased. Thus, according to the constitution, no ducts are present at the outer sides of the skegs in the ship width direction. Therefore, in comparison with a case in which the ducts are exposed to the outer sides of the skegs in the ship width direction, specific resistance caused by the ducts can be reduced. As a result, a propulsive force caused by the ducts can be increased to more effectively improve the propulsion performance.
In the twin skeg ship, the ducts may be configured to be supported on ends of outer circumferential sides of the fins or on intermediate portions of the fins.

Advantageous Effects of Invention

According to the twin skeg ship of the present invention, the flows at the inner sides in the ship width direction are accelerated or decelerated with respect to the skegs by the fins, and the wake gains of the propellers are increased. Thereby, the propulsion performance can be improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a left side view of a starboard side at a stern portion of a twin skeg ship of a first embodiment of the present invention when viewed from a port side.

FIG. 2 is a rear view of the stern portion of the twin skeg ship when viewed from the rear, and is a view showing cross sections D1-D1, D2-D2, D3-D3, and D4-D4 of FIG. 1.

FIG. 3 is a view showing a result of fully analyzing a flow field immediately in front of a propeller of the port side of a certain twin skeg ship in which a pair of left and right propellers rotate inward when viewed from a stern side.

FIG. 4 is a rear view of the stern portion of the twin skeg ship in a modification of the first embodiment of the present invention when viewed from the rear.

FIG. 5 is a left side view of a starboard side at a stern portion of a twin skeg ship of a second embodiment of the present invention when viewed from a port side.

FIG. 6 is a rear view of the stern portion of the twin skeg ship shown in FIG. 5 when viewed from the rear.

FIG. 7 is a left side view of a starboard side at the stern portion of the twin skeg ship in a modification of the second embodiment of the present invention when viewed from a port side.

FIG. 8 is a rear view of the stern portion of the twin skeg ship shown in FIG. 7 when viewed from the rear.

FIG. 9 is a rear view of a stern portion of a twin skeg ship of a third embodiment of the present invention when viewed from the rear.

FIG. 10 is a rear view of the stern portion of the twin skeg ship in a modification of the third embodiment of the present invention when viewed from the rear.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a twin skeg ship of an embodiment of the present invention will be described based on the drawings.

First Embodiment

FIG. 1 is a left side view of a starboard side at a stern portion of a twin skeg ship of a first embodiment of the present invention when viewed from a port side. FIG. 2 is a rear view of the stern portion of the twin skeg ship when viewed from the rear.
As shown in FIGS. 1 and 2, the twin skeg ship 1 is equipped with skegs 2 and propellers 10.
A stern hull 3 that is a stern 1 b of a hull of the twin skeg ship 1 has inclined surfaces 4 s at which a bottom 4 thereof is gradually inclined upward from the side of a bow (not shown) toward the side of the stern 1 b. Also, the bottom 4 of the stern hull 3 is formed such that a width dimension in a ship width direction is gradually reduced from the side of the bow (not shown) toward the side of the stern 1 b.
The pair of left and right skegs 2 are symmetrically provided on inclined surfaces 4 s of the bottom 4 across an inner side C in the ship width direction at an interval in the ship width direction. The pair of left and right skegs 2 are each provided in a shape that extends downward from the inclined surface 4 s of the bottom 4 of the stern hull 3 to protrude backward from the inclined surface 4 s in a horizontal direction.
A bottom recess 5 surrounded by the pair of left and right skegs 2 and the inclined surfaces 4 s of the bottom 4 is formed below the stern hull 3 by the pair of left and right skegs 2 and the inclined surfaces 4 s of the bottom 4. The bottom recess 5 is formed such that a cross-sectional area thereof is gradually reduced toward the stern 1 b.
Also, rear ends of the skegs 2 are each provided with a tubular bossing 6 protruding backward.
The propellers 10 are provided at the rear ends of the pair of left and right skegs 2. Each of the propellers 10 is connected to a main machine (not shown) provided inside the stern hull 3 via a propeller shaft 12. The propeller shaft 12 is connected to the main machine (not shown) inside the stern hull 3 at one end thereof, extends toward the stern 1 b at the other end 12 b thereof, and protrudes from the inside of the stern hull 3 through the bossing 6 and behind the skeg 2. The propellers 10 are integrally mounted on the other ends 12 b of the propeller shafts 12 protruding behind the skegs 2.
The propeller shafts 12 are driven to rotate about central axes thereof by the main machine (not shown) provided inside the stern hull 3, and thereby the propellers 10 rotate in a predetermined direction to exert a propulsive force of the twin skeg ship 1.
In this embodiment, rotating directions of the propellers 10 provided at the rear ends of the pair of left and right skegs 2 are set to turn in inward directions R2 and R1 in which upper portions of the propellers 10 rotate from the outer sides in the ship width direction toward the inner sides C in the ship width direction.
Fins 20 are provided in front of the pair of left and right propellers 10. A plurality of fins 20 (e.g., three fins in the present embodiment) are provided on an outer circumferential surface of each of the bossings 6, which are provided to protrude backward from the rear ends of the skegs 2 to radially protrude from the rotational center of each of the propellers 10.
In this embodiment, the fins 20 are provided close to the inner sides C in the ship width direction with respect to the pair of left and right skegs 2. That is, the fins 20 are provided to protrude from an outer circumferential surface 6 s of the bossing 6, which is close to the inner side C in the ship width direction, to a space inside the bottom recess 5.
The fins 20 cause flows F1 and F2 in directions opposite to the rotating directions of the propellers 10 located therebehind, that is, in outward directions in which the upper portions of the propellers 10 are directed from the vicinities of the inner sides C in the ship width direction toward the outer sides in the ship width direction.
Incidentally, in the twin skeg ship 1, due to the shape of the bottom 4 of the stern hull 3, the flow velocity in the bottom recess 5 formed between the pair of left and right skegs 2 is slower than flows of outer sides (outer sides in the ship width direction) of the pair of left and right skegs 2.
FIG. 3 is a view showing a result of fully analyzing a flow field immediately in front of the propeller 10 of the port side in the skeg 2 of the port side of the twin skeg ship 1 in which the pair of left and right propellers 10 turn inward at upper sides thereof. In FIG. 3, the directions of arrows indicate directions of flows within planes thereof, the lengths of the arrows indicate magnitudes of the flows, and a circle indicates the radius of rotation of the propeller 10.
As shown in FIG. 3, an upward flow Fs becoming a flow in a direction opposite to a rotating direction R2 of the propeller 10 is generated close to the inner side C in the ship width direction, i.e., within a range of θ=00 to 900 and 90° to 180° with respect to the skeg 2 of the port side.
The fins 20 provided close to the inner side C in the ship width direction with respect to the skeg 2 are provided in a region in which the upward flow Fs occurs in the direction opposite to the rotating direction R2 of the propeller 10.
Thereby, the fins 20 of the port side cause the flow F2 in the outward direction at the upper portion of the propeller 10, which is the direction opposite to the rotating direction of the propeller 10 located therebehind, thereby accelerating and strengthening the upward flow Fs becoming the flow that is in the direction opposite to the rotating direction R2 of the propeller 10 and occurs in front of the propeller 10 of the port side. Also, the fins 20 of the starboard side cause the flow F1 in the outward direction at the upper portion of the propeller 10, which is the direction opposite to the rotating direction of the propeller 10 located therebehind, thereby strengthening the upward flow Fs becoming a flow that is in a direction opposite to the rotating direction R1 of the propeller 10 and occurs in front of the propeller 10 of the starboard side.
The upward flows Fs which occur in front of the left and right propellers 10 and whose directions are opposite to the rotating directions R1 and R2 of the propellers 10 are strengthened by the above fins 20, and thereby the wake gain increases in the left and right propellers 10.
Therefore, according to the twin skeg ship of the first embodiment mentioned above, the fins 20 radially extending only toward the inner sides C in the ship width direction with respect to the skegs 2 are provided in front of the pair of left and right propellers 10. Due to these fins 20, the flows close to the inner sides C in the ship width direction in the skegs 2 can be strengthened in front of the propellers 10. Thereby, since the wake gain can be increased in the left and right propellers 10, it is possible to efficiently collect the flows to improve the propulsion performance.
In particular, in the twin skeg ship 1, the flows Fs close to the inner sides C in the ship width direction with respect to the skegs 2 are slow due to the flows at the outer side in the ship width direction with respect to the skegs 2. In the twin skeg ship 1 having this constitution, specific resistance of the fins 20 can be reduced, and the slow flows Fs at the inner sides C of the skegs 2 in the ship width direction are accelerated in front of the propellers 10 by the fins 20. Thereby, it is possible to effectively increase the wake gain of the propellers 10 to improve the propulsion performance.
Further, the fins 20 are provided in the region in which the upward flows Fs occurring close to the inner sides C of the skegs 2 in the ship width direction are strengthened. Thereby, it is possible to effectively increase the wake gain of the propellers 10 to improve the propulsion performance.
Also, the rotating directions of the propellers 10 are set to be inward directions in which the upper portions of the propellers 10 rotate from the outer sides in the ship width direction toward the inner sides C in the ship width direction. According to this constitution, the upward flows Fs that occur close to the inner sides C of the skegs 2 in the ship width direction are strengthened in front of the propellers 10 by the fins 20, and become the directions opposite to the rotating directions of the propellers 10. Therefore, in the left and right propellers 10 rotating in the inward directions, it is possible to effectively increase the wake gain of the propellers 10 to improve the propulsion performance.
(Modification of the First Embodiment)
FIG. 4 is a rear view of the stern portion of the twin skeg ship in a modification of the first embodiment of the present invention when viewed from the rear.
In the first embodiment, the upper portions of the left and right propellers 10 are designed to rotate in the inward directions, but they are not limited thereto. As shown in FIG. 4, even in the constitution in which the upper portions of the left and right propellers 10 rotate in the outward directions, similar to the above embodiment, the fins 20 may be radially provided close to the inner sides C in the ship width direction with respect to the pair of left and right skegs 2.
According to this constitution, since a flow in the same outward direction in which the propeller 10 rotates can be weakened by the fins 20, it is possible to increase the wake gain to improve the propulsion performance.

Second Embodiment

Next, a second embodiment of the twin skeg ship of the present invention will be described. In the second embodiment described below, since the only difference from the first embodiment is that ducts 30 are also provided, portions that are the same as those of the first embodiment will be given the same symbols, and duplicate description thereof will be omitted.
FIG. 5 is a left side view of a starboard side at a stern portion of the twin skeg ship of the second embodiment of the present invention when viewed from a port side. FIG. 6 is a rear view of the stern portion of the twin skeg ship shown in FIG. 5 when viewed from the rear.
As shown in FIGS. 5 and 6, the twin skeg ship 1 in this embodiment is equipped with, similar to the first embodiment, a pair of left and right skegs 2 and a pair of left and right propellers 10.
Thus, rotating directions of the propellers 10 provided at rear ends of the pair of left and right skegs 2 are set to be inward directions R2 and R1 in which upper portions of the propellers 10 rotate from outer sides in a ship width direction toward inner sides C in the ship width direction.
Fins 20 are provided in front of the pair of left and right propellers 10. The fins 20 are radially provided to protrude from an outer circumferential surface 6 s of a bossing 6 which is close to the inner side C in the ship width direction to a space inside a bottom recess 5.
These fins 20 cause flows F1 and F2 in directions opposite to the rotating directions of the propellers 10 located therebehind, that is, in outward directions in which the upper portions of the propellers 10 are directed from the vicinities of the inner sides C in the ship width direction toward the outer sides in the ship width direction.
Further, in this embodiment, tubular ducts 30 are provided in front of the propellers 10. Each of the ducts 30 is concentrically disposed centering on the bossing 6 in a cylindrical shape formed in a circular shape when viewed from the side of a stern 1 b.
The duct 30 is fixed to ends of outer circumferential sides of a plurality of fins 20 that radially extend from the bossing 6, and thereby is supported on the ends. That is, the duct 30 uses the plurality of fins 20 as support members, and is fixed to the bossing 6.
The duct 30 is formed in a tapered shape such that an outer diameter thereof is gradually reduced from the side of a bow to the side of the stern 1 b. Also, the lengths of the ducts 30 in a ship length direction are set to be the same in a circumferential direction.
According to this constitution, upward flows Fs which occur in front of the propellers 10 and whose directions are opposite to the rotating directions R1 and R2 of the propellers 10 are strengthened by the fins 20 provided close to the inner sides C in the ship width direction with respect to the skegs 2, and thereby a wake gain increases in the left and right propellers 10.
Further, since the outer diameter of the duct 30 is gradually reduced toward the propeller 10 close to the stern 1 b, the flow velocity inside the duct 30 is increased in the vicinity of the stern 1 b. Therefore, a propulsive force in an advance direction occurs in the duct 30.
Therefore, according to the twin skeg ship of the aforementioned second embodiment, similar to the first embodiment, flows close to the inner sides C in the ship width direction in the skegs 2 can be strengthened in front of the propellers 10 by the fins 20 provided in front of the pair of left and right propellers 10. Thereby, it is possible to increase the wake gain in the left and right propellers 10, and to efficiently collect the flows to improve propulsion performance.
Also, the twin skeg ship in this embodiment is equipped with the tubular ducts 30 whose outer diameters are gradually reduced from the side of the bow toward the side of the stern 1 b to cross the vicinities of the inner sides C and the outer sides of the skegs 2 in the ship width direction in front of the propellers 10. The flows passing through the insides of the ducts 30 to thereby flow toward the propellers 10 are accelerated. Thereby, since the propulsive force in the advance direction occurs at the ducts 30, the propulsion performance can be enhanced.
(Modification of the Second Embodiment)
FIG. 7 is a left side view of a starboard side at the stern portion of the twin skeg ship in a modification of the second embodiment of the present invention when viewed from a port side. FIG. 8 is a rear view of the stern portion of the twin skeg ship shown in FIG. 7 when viewed from the rear.
In the second embodiment, as the ducts 30 are fixed to the ends of the outer circumferential sides of the plurality of fins 20, the ducts 30 are designed to have the same diameters as the outer circumferential sides of the plurality of fins 20, but are not limited thereto.
As shown in FIGS. 7 and 8, the ducts 30 may be designed to have smaller diameters than the outer circumferential sides of the plurality of fins 20, and to be fixed by intermediate portions of the plurality of fins 20.
Even in the modification of this second embodiment, similar to the second embodiment, the propulsion performance can be improved.

Third Embodiment

Next, a third embodiment of the twin skeg ship of the present invention will be described. In the third embodiment described below, since the only difference from the second embodiment is the constitutions of ducts 40, the portions that are the same as those of the second embodiment will be given the same symbols, and duplicate description thereof will be omitted.
FIG. 9 is a rear view of the stern portion of the twin skeg ship of the third embodiment of the present invention when viewed from the rear.
As shown in FIG. 9, the twin skeg ship 1 in this embodiment is equipped with, similar to the first and second embodiments, a pair of left and right skegs 2 and a pair of left and right propellers 10.
Thus, rotating directions of the propellers 10 provided at rear ends of the pair of left and right skegs 2 are set to be inward directions R2 and R1 in which upper portions of the propellers 10 rotate from outer sides in a ship width direction toward inner sides C in the ship width direction.
Fins 20 are provided in front of the pair of left and right propellers 10. The fins 20 are radially provided to protrude from an outer circumferential surface 6 s of a bossing 6, which is close to the inner side C in the ship width direction, to a space inside a bottom recess 5.
These fins 20 cause flows F1 and F2 in directions opposite to the rotating directions of the propellers 10 located therebehind, that is, in outward directions in which the upper portions of the propellers 10 are directed from the vicinities of the inner sides C in the ship width direction toward the outer sides in the ship width direction.
Further, in this embodiment, semi-cylindrical ducts 40 are provided in front of the propellers 10. Each of the ducts 40 is concentrically disposed centering on the bossing 6 at the inner side C in the ship width direction in a cylindrical shape formed in a semicircular shape when viewed from the side of a stern 1 b.
The duct 40 is fixed to ends of outer circumferential sides of a plurality of fins 20 that radially extend from the bossing 6, and thereby is supported on the ends. That is, the duct 40 uses the plurality of fins 20 as support members, and is fixed to the bossing 6.
The duct 40 is formed in a tapered shape such that an outer diameter of curvature of an outer circumferential surface thereof is gradually reduced from the side of a bow toward the side of the stern 1 b. Also, the lengths of the ducts 40 in a ship length direction are set to be the same in a circumferential direction.
According to this constitution, upward flows Fs which occur in front of the propellers 10 and whose directions are opposite to the rotating directions R1 and R2 of the propellers 10 are strengthened by the fins 20 provided close to the inner sides C in the ship width direction with respect to the skegs 2, and thereby the wake gain increases in the left and right propellers 10.
Further, since the outer diameter of the duct 40 is gradually reduced toward the propeller 10 close to the stern 1 b, flows at wake sides of the skegs 2 are accelerated close to the inner sides C in the ship width direction with respect to the skegs 2. Therefore, a propulsive force in an advance direction occurs in the duct 40.
Therefore, according to the twin skeg ship of the aforementioned third embodiment, similar to the first and second embodiments, flows close to the inner sides C in the ship width direction in the skegs 2 can be strengthened in front of the propellers 10 by the fins 20 provided in front of the pair of left and right propellers 10. Thereby, it is possible to increase the wake gain in the left and right propellers 10, and to efficiently collect the flows to improve propulsion performance.
Also, the twin skeg ship in this embodiment is equipped with the semi-cylindrical ducts 40 whose outer diameters are gradually reduced from the side of the bow toward the side of the stern 1 b only in the vicinities of the inner sides C of the skegs 2 in the ship width direction in front of the propellers 10. The flows passing through the insides of the ducts 40 to thereby flow toward the propellers 10 are accelerated. Thereby, since the propulsive force in the advance direction occurs at the ducts 40, the propulsion performance can be enhanced.
In addition, according to this constitution, no ducts 40 are present at the outer sides of the skegs 2 in the ship width direction. In comparison with the case in which the ducts 30 are exposed to the outer sides of the skegs 2 in the ship width direction as in the second embodiment, specific resistance caused by the ducts 40 can be reduced. As a result, the propulsive force caused by the ducts 40 can be further increased, and the propulsion performance can be more efficiently improved.
(Modification of the Third Embodiment)
FIG. 10 is a rear view of the stern portion of the twin skeg ship in a modification of the third embodiment of the present invention when viewed from the rear.
In the third embodiment, as the ducts 40 are fixed to the ends of the outer circumferential sides of the plurality of fins 20, the ducts 40 are designed to have the same diameters as the outer circumferential sides of the plurality of fins 20, but are not limited thereto.
As shown in FIG. 10, the ducts 40 may be designed to have smaller diameters than the outer circumferential sides of the plurality of fins 20, and to be fixed by intermediate portions of the plurality of fins 20.
Even in the modification of this third embodiment, similar to the third embodiment, the propulsion performance can be improved.
(Other Modifications)
The prevent invention is not limited to the aforementioned embodiments, and also includes various modifications of the aforementioned embodiments that do not depart from the spirit and scope of the present invention. That is, the specific shapes and constitutions represented in the embodiments are merely examples, and can be appropriately modified.
For example, in each of the embodiments and their modifications, the plurality of fins 20 are radially provided, but there is no limitation on the number installed or the angle at which they are installed.
Also, the ducts 30 and 40 are provided at the outer circumferential portions of the fins 20 in the second and third embodiments, but the ducts 30 and 40 may be separately provided while their positions are shifted from the fins 20 in the ship length direction.

REFERENCE SIGNS LIST

- 1: twin skeg ship
- 1 b: stern
- 2: skeg
- 3: stern hull
- 4: bottom
- 4 s: inclined surface
- 5: bottom recess
- 6: bossing
- 6 s: outer circumferential surface
- 10: propeller
- 12: propeller shaft
- 12 b: other end
- 21
- 20: fin
- 30: duct
- 40: duct
- C: inner side in ship width direction
- R1, R2: rotating direction

Claims

1. A twin skeg ship comprising:

a pair of left and right skegs provided at a bottom of a stern;

propellers provided behind the pair of left and right skegs; and

fins provided in front of the propellers only at inner sides in a ship width direction with respect to the skegs and configured to radially extend from rotational centers of the propellers.

2. The twin skeg ship according to claim 1, wherein flows at the inner sides in the ship width direction with respect to the skegs are slower than flows at outer sides in the ship width direction with respect to the skegs in the pair of left and right skegs.

3. The twin skeg ship according to claim 1, wherein the fins strengthen upward flows occurring at the inner sides of the skegs in the ship width direction in front of the propellers.

4. The twin skeg ship according to claim 1, wherein rotating directions of the propellers are set to be inward directions in which upper portions of the propellers rotate from the outer sides in the ship width direction toward the inner sides in the ship width direction.

5. The twin skeg ship according to claim 1, wherein the fins weaken upward flows occurring at the inner sides of the skegs in the ship width direction in front of the propellers.

6. The twin skeg ship according to claim 1, wherein rotating directions of the propellers are set to be outward directions in which upper portions of the propellers rotate from the inner sides in the ship width direction toward the outer sides in the ship width direction.

7. The twin skeg ship according to claim 1, further comprising tubular ducts which are provided in front of the propellers while crossing the inner sides of the skegs in the ship width direction and the outer sides of the skegs in the ship width direction and whose outer diameters are gradually reduced from a bow side toward a stern side.

8. The twin skeg ship according to claim 1, further comprising semi-cylindrical ducts which are provided in front of the propellers only at the inner sides of the skegs in the ship width direction and whose outer diameters are gradually reduced from a bow side toward a stern side.

9. The twin skeg ship according to claim 7, wherein the ducts are supported on ends of outer circumferential sides of the fins or on intermediate portions of the fins.