SHIP PROPULSION DEVICE

Abstract

 An appendage 4 for reducing a hub vortex due to rotation of a propeller 2 is arranged on a front edge of a rudder 3 behind the propeller 2 at a height position of the propeller 2. A distance L1 between the front edge of the rudder 3 and a blade center of the propeller 2 is 30-60% inclusive of a diameter D of the propeller 2. A distance L2 between a front edge of the appendage 4 and a rear end of the propeller 2 is within a range of 50-300 mm.

Description

Technical Field

[0001] The present invention relates to a propulsion device for a ship.

Background Art

[0002] Conventionally known is a propulsion device for a ship using a propeller comprising appendages on a rudder behind the propeller for reducing a hub vortex generating along with rotations of the propeller to improve propulsion efficiency. For example, undermentioned Patent Literature 1 discloses an enhanced propulsion device for a ship comprising a bulb and a pair of left and right fins on a front edge of a rudder behind a propeller at a position axially of the propeller. Undermentioned Patent Literature 2 discloses a two-propeller-two-rudder twin skeg ship with a bulb and a fin on a rudder behind a propeller at portside and at starboard side, respectively.

Citation List

Patent Literature

[0003] 

Patent Literature 1: JPH 11-139395A

Patent Literature 2: JP 2015-166218A

Summary of Invention

Technical Problems

[0004] Appendages such as a bulb and a fin may be arranged behind a propeller using a rudder as a support irrespective of usage and kind of a ship, provided that the ship has the rudder behind the propeller. For example, similar appendages may be arranged on a rudder of a ship such as an ice breaking ship or an ice-resistant ship.

[0005] However, in the ice breaking ship or the ice-resistant ship, the rudder requires to be arranged in a spaced-away relationship from the propeller in comparison with an ordinary ship, which is for prevention of any ice flowing to a rear of a hull from being wedged between the propeller and the rudder to hinder rotations of the propeller.

[0006] Thus, arrangement of appendages similar to those in an ordinary ship on the rudder of the ice breaking ship or the ice-resistant ship would result in a wide distance between the appendages and the propeller, failing in obtaining a hub-vortex reducing effect in a level obtainable in various ships. During navigation on icy sea, a great hub vortex generates on the propeller of the ice breaking ship or the ice-resistant ship in Bollard condition due to resistance of ice. Reduction of the great hub vortex is desirable for suppression of power of the propeller; however, such great hub vortex cannot be effectively suppressed in the conventional ice breaking ship or ice-resistant ship because of the arrangement of the appendages in the spaced-away relationship from the propeller as mentioned in the above. In navigation not only on icy sea but on calm sea, only a limited suppressive effect can be obtained on the hub vortex because of the arrangement of the rudder and the propeller in the spaced-away relationship. Thus, in a ship such as an ice breaking ship or an ice-resistant ship, the arrangement of the rudder and the propeller in the spaced-away relationship has been a factor of hindered enhancement in propulsion efficiency.

[0007] The invention was made in view of the above and has its object to provide a propulsion device for a ship capable of enhancing propulsion efficiency in the ship with a propeller and a rudder arranged in a spaced-away relationship.

Solution to Problems

[0008] The invention is directed to a propulsion device for a ship comprising an appendage on a front edge of a rudder behind a propeller at a height position of said propeller for reducing a hub vortex due to rotation of the propeller, a distance between the front edge of said rudder and a blade center of said propeller being 30-60% inclusive of a diameter of said propeller, a distance between a front edge of said appendage and a rear end of said propeller being within a range of 50-300 mm.

[0009] It is preferable in the propulsion device for the ship according to the invention that the appendage is in the form of a spindle having a circular cross-section in a direction perpendicular to a central axis thereof along a hull and having a rear portion with diameters gradually reduced toward a rear end.

[0010] It is preferable in the propulsion device for the ship according to the invention that the appendage has a maximum diameter which is 10-40% inclusive of the diameter of the propeller and has a length along the hull which is 40-70% inclusive of the diameter of said propeller.

[0011] The propulsion device for the ship according to the invention may be applied to an ice-breaking ship or an ice-resistant ship.

Advantageous Effects of Invention

[0012] A propulsion device for a ship according to the invention can exhibit an excellent effect that propulsion efficiency of a propeller can be enhanced in the ship with the propeller and a rudder arranged in a spaced-away relationship.

Brief Description of Drawings

[0013] 

Fig. 1 is a view showing an embodiment of a propulsion device for a ship according to the invention;

Fig. 2 is a view showing a further embodiment of the propulsion device for the ship according to the invention; and

Fig. 3 is a view showing a still further embodiment of the propulsion device for the ship according to the invention.

Description of Embodiments

[0014] Embodiments of the invention will be described in conjunction with attached drawings.

[0015] Fig. 1 shows an embodiment of a propulsion device for a ship according to the invention. In a ship 1 which is an ice-breaking ship or an ice-resistant ship, a propeller 2 is arranged at a stern and a rudder 3 is arranged behind the propeller 2. The rudder 3 has a front edge on which arranged is an appendage 4 at a height position of the propeller 2 to reduce a hub vortex due to rotation of the propeller 2.

[0016] In the ship 1 which is the ice-breaking ship or the ice-resistant ship, the propeller 2 and the rudder 3 are arranged in a spaced-away relationship as shown in Fig. 1 in comparison with an ordinary ship. In the embodiment, the appendage 4 for reduction of the hub vortex due to the rotation of the propeller 2 is arranged on the front edge of the rudder 3 to protrude greatly toward the propeller 2.

[0017] In the embodiment illustrated, the appendage 4 is in the form of a spindle having a circular cross-section in a direction perpendicular to a central axis thereof along a hull and having a rear portion with diameters gradually reduced toward a rear end. The central axis of the appendage is set to be aligned with an axis of the propeller 2.

[0018] Arrangement of the rudder 3 and the appendage 4 relative to the propeller 2 will be described. As mentioned in the above, the rudder 3 is arranged behind the propeller 2 and a distance L1 between the front edge of the rudder 3 and a blade center of the propeller 2 is set to be as long as about 44% of a diameter D of the propeller 2. Such spaced-away arrangement of the rudder 3 from the propeller 2 prevents ice flowing to the stern from being wedged between the propeller 2 and the rudder 3 to hinder rotations of the propeller 2.

[0019] The appendage 4 is set to have a length along the hull which is about 56% of the diameter D of the propeller 2 and a diameter which is about 25% of the diameter D of the propeller 2. The appendage 4 with such dimensions protrudes from the front edge of the rudder 3 toward a rear end of the propeller 2 to provide a distance L2 between a front end of the appendage 4 and the rear end of the propeller 2 being as short as about 100 mm. Thus, in the embodiment, the propeller 2 is spaced away from the rudder 3 while the appendage 4 is arranged behind and close to the propeller 2 to effectively reduce the hub vortex due to the rotation of the propeller 2.

[0020] In this connection, if the distance L1 between the front edge of the rudder 3 and the blade center of the propeller 2 were too short, a risk of ice being wedged between the propeller 2 and the rudder 3 would increase; if too long, the rudder 3 would not function well. Thus, the distance L1 is preferably set into 30-60% inclusive, more preferably 40-50% inclusive, of the diameter D of the propeller 2. On the other hand, if the distance L2 between the front edge of the appendage 4 and the rear end of the propeller 2 were too long, the hub vortex would not be satisfactorily suppressed and there would be a fear of ice being wedged between the propeller 2 and the appendage 4; thus, it is desirable that the distance L2 is as short as possible to an extent that the appendage 4 and the propeller 2 do not interfere with each other. Thus, preferably the distance L2 is set to be within a range of 50-300 mm or so.

[0021] In order to effectively reduce the hub vortex due to the rotation of the propeller 2, it is preferable that the appendage 4 has a maximum diameter near the front end thereof which is set into 10-40% inclusive, more preferably 20-30% inclusive, of the diameter D of the propeller 2. It is preferable that the appendage 4 has the length along the hull which is set into 40-70% inclusive, more preferably 50-60% inclusive, of the diameter D of the propeller 2.

[0022] It has been revealed in model tests conducted by the applicant that power of the propeller is reduced by 2-3% or so in calm water and by 1% or so in icy water when arranged behind the propeller 2 is the appendage 4 with the diameter set into about 25% of the diameter D of the propeller 2 and with the length set into about 56% of the diameter D of the propeller 2 as mentioned in the above in the above-mentioned arrangement (the front edge of the rudder 4 being arranged away from the blade center of the propeller 2 by 44% of the diameter D of the propeller 2, the front end of the appendage 4 being 100 mm behind of the rear end of the propeller 2).

[0023] In place of the appendage 4 with the above-mentioned shape and arranged on the front edge of the rudder 3, appendages 5 may be provided which are in the form of oppositely protruding fins as shown in Fig. 2. Alternatively, the appendages 5 as shown in Fig. 2 may be provided in addition to the appendage 4 as shown in Fig. 1. An appendage or appendages in any shape may be arranged on the rudder 3 behind the propeller 2 so as to reduce the hub vortex.

[0024] Fig. 1 illustrates the case where the appendage 4 protrudes greatly toward the forehand propeller 2. Alternatively and in an opposite manner, a boss cap of the propeller 6 may protrude greatly toward the backward appendage 7 as shown in Fig. 3. In the embodiment shown in Fig. 3, the distance L1 between the blade center of the propeller 6 and the front edge of the rudder 3 is set to be long similarly to the embodiment shown in Fig. 1. However, contrarily to Fig. 1, the propeller 6 is extended toward the appendage 7 to make short the distance L2 between the rear end of the propeller 6 and the front end of the appendage 7.

[0025] As mentioned in the above, in the embodiment, the appendage 4 is arranged on the front edge of the rudder 3 behind the propeller 2 at the height position of the propeller 2 so as to reduce the hub vortex due to the rotation of the propeller 2, the distance L1 between the front edge of the rudder 3 and the blade center of the propeller 2 being 30-60% inclusive of the diameter D of the propeller 2, the distance L2 between the front end of the appendage 4 and the rear end of the propeller 2 being within the range of 50-300 mm of the diameter D of the propeller 2. Thus, even in the ship 1 with the propeller 2 and the rudder 3 in the spaced-away relationship, the hub vortex due to the rotation of the propeller 2 can be effectively reduced.

[0026] In the embodiment, it is preferable that the appendage 4 is in the form of a spindle having a circular cross-section in a direction perpendicular to the central axis thereof along the hull and having a rear portion with diameters gradually reduced toward a rear end, which can more effectively reduce the hub vortex due to the rotation of the propeller 2.

[0027] In the embodiment, preferably the appendage 4 has a maximum diameter being 10-40% inclusive of the diameter D of the propeller 2 and has a length along the hull being 40-70% inclusive of the diameter D of the propeller 2, which can especially effectively reduce the hub vortex due to the rotation of the propeller 2.

[0028] Thus, in accordance with the above-mentioned embodiments, propulsion efficiency of a propeller can be enhanced in a ship with the propeller and a rudder arranged in a spaced-away relationship.

[0029] It is to be understood that a propulsion device for a ship according to the invention is not limited to the above embodiments and that various changes and modifications may be made without departing from the scope of the invention.

Reference Signs List

[0030] 

1

ship (ice breaking ship or ice-resistant ship)

2

propeller

3

rudder

4

appendage

5

appendage

6

propeller

7

appendage

D

diameter

L1

distance

L2

distance

Claims

1. A propulsion device for a ship (1) comprising an appendage (4;5) on a front edge of a rudder (3) behind a propeller (2) at a height position of said propeller (2) for reducing a hub vortex due to rotation of the propeller (2), a distance (L1) between the front edge of said rudder (3) and a blade center of said propeller (2) being 30-60% inclusive of a diameter of said propeller (2), a distance (L2) between a front edge of said appendage (4;5) and a rear end of said propeller (2) being within a range of 50-300 mm.

2. The propulsion device for the ship (1) as claimed in claim 1 wherein said appendage (4) is in the form of a spindle having a circular cross-section in a direction perpendicular to a central axis thereof along a hull and having a rear portion with diameters gradually reduced toward a rear end.

3. The propulsion device for the ship (1) as claimed in claim 2 wherein said appendage (4) has a maximum diameter which is 10-40% inclusive of the diameter of said propeller (2) and has a length along the hull which is 40-70% inclusive of the diameter of said propeller (2).

4. The propulsion device for the ship (1) as claimed in any of claims 1-3 applied to an ice-breaking ship or an ice-resistant ship.

Drawing