GB2156297A - Rudders with wings and method for manufacture thereof - Google Patents

Abstract

A ship's rudder 5 comprises a vertical rudder blade 6 from each side of which a transverse auxiliary wing 7 projects which improves the efficiency with which the rotational energy of the propeller slip stream is converted into a forward propulsive force. <IMAGE>

Description

SPECIFICATION Rudders with wings and method for manufacture thereof The present invention relates to a ship's rudder with wings whose purpose is to produce a saving of energy and to a method of manufacture thereof.

In order to increase the steering efficiency of the rudder of a ship, it is advantageous to locate the rudder in the fast propeller slip stream. For this reason rudders are normally located behind the propeller. In addition to steering the ship, rudders frequently have the subsidiary function of propelling the ship. Thus, when the rudder is impinged on by the propeller slip stream, a lift is developed, the propulsion component of which assists in propelling the ship.

A conventional symmetrical aerofoil shaped rudder for developing a propulsion force will now be described. Figure 1 a view of a propeller 1 from the stern of a ship. In general, the propeller 1 is rotated in the clockwise direction i so that a helical propeller slip stream including rotating streams a to h is formed.

Figure 2 which is a view in the same direction, shows the associated rudder 2 located in the propeller slip stream so that, as shown in Figure 3, oblique streams 3 and 4 impinge against the rudder 2.

In Figure 3, which is a plan view of the rudder, Vu is a vector indicating the stream flowing upwardly from the axis j of the propeller; V, is a vector indicating the stream flowing downwardly; Lu is the lift developed by the flow Vu: L, is the lift developed by the flow V,; T is a thrust ()u indicates the direction in which the lift Lu acts; ando iL indicates the direction in which the lift L, acts. When the rudder angle is t) as shown in Figure 3, a thrust T is produced which equals Lu cos(lu + L,cosB,. Thus, the rudder 2 converts part of the energy of the propeller slip stream into a propulsive force.In other words, the rudder 2 functions as a propulsion device.

However the energy of the propeller slip stream cannot be satisfactorily recovered when only a single rudder blade is located vertically in the propeller slip se.

Another object of the present invention is to provide a method of manufacturing a rudder of the type described in a simple manner yet with a high degree of accuracy.

According to the present invention a rudder comprises a main wing located, in use, behind a propeller and extending substantially vertically and at least one transversely extending auxiliary wing connected to each side of the main wing. In one embodiment of the invention the main wing comprises a rudder blade and a rudder horn which rotatably supports the rudder blade and is located in front of the rudder blade.

The auxiliary wings may be connected to the rudder blade or to the rudder horn.

The wings are preferably connected to the main wing at positions which, in use, are higher than the axis of rotation of the propeller and the auxiliary wings on the port and starboard sides are preferably rotationally offset in opposite senses with respect to the vertical. The wings may extend horizontally from their points of connection with the main wing or they may extend outwardly and upwardly therefrom.

The present invention also embraces a method fabricating a rudder with wings which comprises integrally fabricating by casting the root portion of each auxiliary wing and a rudder horn, fabricating by casting the tip portion of each auxiliary wing, welding the tip portions to respective root portions and thereafter welding steel wing surface plates to the root portions and the tip portions to define the upper and lower wing surfaces of each auxiliary wing.

Further features and details of the present invention will be apparent from the following description of certain specific embodiments which is given by way of example only with reference to Figures 4 to 43 of the accompanying drawings, in which: Figure 4 is a rear view of a first embodiment of the present invention; Figure 5 is an elevation from the right hand side thereof; Figure 6 is an elevation from the left hand side thereof; Figure 7A is an elevation from the right side of a second embodiment of the present invention; Figure 7B is an elevation from the left side thereof; Figure 8A is a rear view of a third embodiment of the present invention; Figure 8B is an elevation from the right side thereof; Figure 9 is a rear view of a fourth embodiment of the present invention;; Figure 10 is a view illustrating the distribution of a ship's wake; Figure 11 is a view illustrating the distribution of the rotating streams of the propeller slip stream in the ship's wake; Figure 12 is a rear view of a fifth embodiment of the present invention; Figure 13 is a side elevation thereof; Figure 14 is a view illustrating the propeller slip stream in the ship's wake; Figure 15A is an elevation from the left side of a sixth embodiment of the present invention; Figure 158 is an elevation from the right side thereof; Figure 16A is a rear view of a seventh embodiment of the present invention; Figure 168 is an elevation from the right side thereof; Figures 17 and 18are views illustrating a stream impinging on a wing and the force acting on the wing;; Figure 19A is an elevation from the right side of an eighth embodiment of the present invention; Figure 19B is an elevation from the left side thereof; Figure 20 is a view illustrating a stream impinging on a wing and the forces acting on the wing of the rudder as shown in Figures 19A and 19B; Figure 21A is an elevation from the right side of a ninth embodiment of the present invention; Figure 21B is an elevation from the left side thereof; Figure 22 is a view illustrating a stream impinging on the wing and the forces acting on the wing of the rudder shown in Figures 21A and 21B; Figure 23 is a rear view of a rudder with horizontal wings; Figure 24 is a rear view of a rudder with inclined or oblique wings which is a tenth embodiment of the present invention; Figure 25 is an enlarged view of part of Figure 23;; Figure 26 is an enlarged view of part of Figure 24; Figure 27 is a sectional view, on enlarged scale, of a wing shown in Figures 23 and 25; Figure 28 is a sectional view, on enlarged scale, of a wing as shown in Figures 24 and 26; Figure 29 is an elevation from the right side of an eleventh embodiment of the present invention; Figure 30 is an elevation from the right side of a twelfth embodiment of the present invention; Figure 31 is an elevation from the right side of a conventional hanging rudder; Figure 32 is a sectional view, on enlarged scale, on the line S-S of Figure 31; Figure 33 is a detailed side elevation of the embodiment of Figure 30; Figure 34 is a sectional view on the line R-R in Figure 33; Figure 35 is a view illustrating the lift developed when the rudder shown in Figure 32 is steered; Figure 36 is a sectional view on the line U-U in Figure 33;; Figure 37 is a schematic elevation from the right side of a hanging rudder; Figure 38 is a sectional view showing the construction of a conventional wing; Figure 39 is a top view, partly in section, of a rudder wing fabricated in accordance with the present invention; Figure 40 is a sectional view, on a reduced scale, on the line Y-Y in Figure 39; Figure 41 is a sectional view, on a reduced scale, on the line Z-Z in Figure 39; Figure 42 is a side elevation of a fourteenth embodiment in accordance with the present invention; and Figure 43 is a sectional view on the line Q-Q in Figure 42.

Figures 4,5 and 6 show first embodiment of the present invention in which a rudder 5 comprises a main vertical wing 6 and horizontal auxiliary wings 7.

The horizontal auxiliary wings 7 develop lifts L5 and Lp due to the oblique streams V5 and Vp produced by the rotary components b and f of the propeller slip stream. The resultant force T'of the fore-and-aft line components of the lifts L5 and Lp is given by T' = Ls cos Hs + Lp cos Hp The resultant force T' provides a further propulsive force which is added to the thrust given by T = Lu cos Hu + L, cos H, The thrust T is developed by the main wing 6 (see Figure 3). Thus the capability of the rudder 5 of recovering the energy of the propeller slip stream is further increased.

Figures 7A and 7B show a second embodiment of the present invention. The horizontal auxiliary wings 8 and 8' are in the form of an airfoil so as to best utilise the oblique streams V5 and Vp. As a result, the lifts L5 and Lp developed by the horizontal auxiliary wings 8 and 8' are increased.

Figures 8A and 8B show a third embodiment of the present invention in which a vertical vortex-preventing plate 9 is attached to the free end of each of the auxiliary horizontal wings 7 so that the wake downstream of the auxiliary horizontal wings 7 is reduced to a minimum. As a result, the energy loss due to such wake is avoided or minimised.

Figure 9 shows a fourth embodiment of the present invention in which in addition to the horizontal auxiliary wings 7, oblique auxiliary wings 10 and 11 are added to each side of the vertical wing 6 which develop thrust from the oblique streams produced by the rotary components a, c, e, and g.

A ship including a rudder as described in the first to fourth embodiments of the present invention has a power consumption which is reduced by 3 to 4% as compared to a ship with a conventional rudder.

In the first to fourth embodiments, it is assumed that the propeller slip stream is uniformly distributed about the rotational axis j of the propeller so that each auxiliary wing is attached at the same height as the axis j.

However, when the propeller slip stream is studied in detail, it is found out that the influence of the ship's wake on the propeller slip stream cannot be neglected. Thus, the influence of the ship's wake on the propeller slip stream must be taken into consideration for a correct analysis of the propeller slip stream. Such consideration permits the propulsive force of the rudder to be further increased.

As described above, the wings are located in the propeller slip stream to recover a proportion of the energy of the propeller slip stream and convert it into a propulsive force. It follows, therefore, that it is preferable to locate them at the place at which the force of the propeller slip stream is a maximum. The magnitude of the rotary force of the propeller slip stream is dependent on the load rate of the propeller, that is to say, the thrust produced by per unit area of the propeller disk. Therefore, the higher the load rate of the propeller, the greater the rotary stream becomes. Furthermore, the propeller load rate is de pendent upon the ship's wake impinging on the surface of the propeller. Moreover, the slower the speed in the fore-and-aft direction of the ship's wake the greater the load rate becomes.As a result, the propeller load rate is greater at those areas at which the component in the direction of the propeller axis of the ship's wake is small so that the velocity of the rotary stream at those areas is greater.

Figure 10 shows the flow velocity distribution in the direction of the propeller axis of the ship's wake impinging on the surface 12 of the propeller. The wake coefficient W is expressed by V -v "" or Vx = (l-W)V5 V X s where V5 is the velocity of the ship, and Vx is the velocity in the direction of the propeller axis of the ship's wake.

In general, as shown in Figure 10, the wake coefficient has a high value in the area above the rotational axis j of the propeller. That is to say, the velocity Vx in the direction of the propeller axis of the ship's wake is reduced.

Figure 11 shows the distribution of the rotary streams a to h of the propeller slip stream after the ship's wake has passed over the propeller surface 12. As in the case of Figure 1, the length of each arrow indicates the velocity. The radius of the propeller is indicated by r. From Figure 11, it may be seen that the rotary streams a, b, e and h are faster in the region in which wake coefficient W is high, as indicated in Figure 10, or in the region in which the velocity Vx in the direction of the propeller axis of the ship's wake is low while the rotary streams c, d, f and g are slower in the region where the wake coefficient W is low.Therefore, in order to recover the rotational energy of the propeller slip stream satisfactorily, it is preferable that the wings are located above the axis j of rotation of the propeller.

Figure 12 and 13 show a fifth embodiment of the present invention. Reference numeral 1 designates a propeller and 5 a rudder. Substantially horizontal wings 7 are attached to both side surfaces 14 of the rudder blade 13 at an optimum position (which is described below) which is spaced by a distance p upwardly from the axis of rotation j of the propeller. The propeller slip stream impinges on the wings 7 to produce a propulsive force. As compared with a conventional rudder without wings,the engine power required for propulsion purposes is reduced. Furthermore, as compared with a rudder with wings (7 in Figure 4) which are attached at the level of the axis j of the propeller rotation, the rotating energy of the high velocity rotary streams b and h above the axis j of the propeller rotation can be recovered so that an increased propulsive force is developed.In Figure 13, the oblique streams which correspond to the rotary streams b and h are indicated by V5 and VH respectively.

Referring now to the optimum height at which the wings should be disposed, the propeller slip stream will not produce rotary streams over a wide area just behind the propeller and the region in which the rotary streams are developed is limited to a cylinder whose cross section corresponds to the propeller surface 12. Figure 14 shows that the wake 15 developed by a ship with a propeller which rotates in the clockwise direction passes the propeller surface 12 thereby imparting rotational energy to the wake 15 and that the propeller slip stream 16 impinges on the rudder in accordance with the present invention.

The propeller slip stream 16 is accelerated by the propeller surface 12 so that it flows helically in the direction indicated by the arrow m in a cylinder whose diameter is slightly smaller than the diameter 2r of the propeller.

Figure 14 shows the regions in which the rotary streams a to h flow. Thus, Figure 14 is a cross-sectional view of the propeller slip stream 16 taken along the rudder 5. The rotary streams are located within the cylinder defined by the propeller surface 12 whose radius is r. As a result, unless the wings 7, which absorb the rotational energy, are located within a circle of radius r, the wings do not function at all. It follows therefore that the width f of the wing 7 is uniquely given by

where p is the distance from the axis j of the propeller rotation of the point of attachment of the wings 7 (Figure 12).

Thus, the width e: of the wings 7 becomes greatest (ç > =r) when they are located at the level of the axis of the propeller rotation and as the position of the wings is moved upwardly from the axis j of the propeller rotation, the length of the wings is reduced. As the length e of the wings 7 is reduced, the area of the wings is decreased so that the lift produced is also decreased. As a result, the thrust which is the component in the direction of the propeller axis of the lift is also decreased. It follows that in order to increase the area of the wings, it is preferable that the wings are located as close as possible to the level of the axis j of the propeller rotation.

For the reasons described above, it is preferable that the magnitude of the rotary streams due to the propeller slip stream which is influenced by the ship's wake impinging on the propeller surface is compared with the surface area of the wings so that the height at which the wings are attached is such that the thrust or propulsion force, which is the component in the direction of the axis of the propeller of the lift, is a maximum.

The optimum installation position described above is therefore, not uniquely determined because the distribution of the ship's wake varies depending on the design of the hull, but it is considered that the optimum installation position is located above the axis j of the propeller rotation and is spaced therefrom by 0.2 to 0.4 times the radius of the propeller.

Figures 15A and 15B show a sixth embodiment of the present invention. The wings 8 and 8' are in the form of aerofoils so that the oblique streams VH and VH are optimally utilised, i.e. the lift developed by the wings 8 and 8' is maximised.

In the sixth embodiment, the power required for propulsion can be reduced by 4 to 5% as compared to a ship with a conventional rudder without wings.

Figures 16A and 16B show a seventh embodiment of the present invention. A vortex preventing plate 9 is attached vertically at the free end of each wing 7 so that the wake downstream of the wings 7 is reduced to a minimum. As a result, the energy loss due to such wake is reduced to a minimum.

The optimum angle of inclination of the wings will now be discussed. As described above with reference to Figure 11, the velocities of the rotary streams vary from one place to another. Thus, as shown in Figure 17, the rotary stream VO varies from one place to another so that the magnitude and direction of the oblique stream V vary. Therefore the wing installation angle must be taken into consideration, depending upon the position at which the wing is installed, in order that the maximum propulsive force may be developed. As shown in Figure 14, the direction of the rotary stream V,, impinging on the right hand wing 7 is opposite to the direction of the rotary stream inpinging on the left hand wing.Thus in the case of the propeller 1 shown in Figure 14 which is rotated in a clockwise direction, the rotary flow V,, is directed downwards on the starboard side, as indicated by the solid lines in Figure 18, and is directed upwards on the port side, as indicated by the broken lines. As a result, the angles of attack are opposite with respect to the horizontal plane. As a result, the starboard and port wings are desirably twisted in opposite directions.

Figures 19A, 19B and 20 show an eighth embodiment based upon the principle described above.

Figure 19A is a side view of the starboard wing 7 when the propeller 1 rotates in the clockwise direction while Figure 19B is a side view of the port wing 7.

When a wing 7 is located in the oblique stream V as shown in Figure 20, the following forces act on it: the lift L produced by the oblique stream V, the drag D, the resultant force L' of the lift L and the drag D and the propulsive component T of the force L'.

When the angle P of the wing 7 with respect to the horizontal plane is varied, the angle of attack a of the wing 7 with respect to the oblique stream V varies so that the propulsive component T of the resultant force L' varies also. The drag D causes the angle a to increase and there is an angle a at which the propulsive component T becomes maximum. Therefore, if the propeller load and the ship's wake 15 (see Figure 14) are predetermined, the magnitude and direction of the oblique stream V can be assumed and the optimum wing installation angle ( can be determined. It should be noted that the wing installation angle on the starboard side may be different from the wing installation angle on the port side.

Figures 21A, 218 and 22 show a ninth embodiment of the present invention. Figure 21A shows the starboard wing when the propeller 1 is rotated in the clockwise direction while Figure 228 shows the port wing. Wings, which are twisted in opposite directions, are attached to both side surfaces of the rudder blade 13. A second method of increasing the propulsive force or thrust of a wing located in an oblique stream is to attach symmetrical wings with a camber, as illustrated in Figure 22. The forces which act on the symmetrical wing as shown in Figure 20 also act on the asymmetrical wing 8 with the camber 17 as shown in Figure 22, but is should be noted that at the same angle of attack cs, the lift L on the latter is increased. As a result, a greater propulsive component T is obtained if the wing 8 is given a camber 17.

Depending upon the directions of the oblique streams V, the asymmetrical wings 8 are attached to the starboard and port surfaces of the rudder blade 13 with opposite cambers 17.

In the ninth embodiment of the present invention described above, the propulsive force or thrust can be increased as compared with the case in which symmetrical horizontal wings are provided having regard to the configuration of the propeller slip stream and the twisting of the wings, and thus a further energy saving can be attained.

In the tenth embodiment the wings are inclined at an angle with respect to the horizontal. As shown in Figure 23, the rotary streams V,, of the propeller slip stream impinge at an angle on the wings 7. The vertical component V,, is the component which is responsible for the lift of the wing 7, but the horizontal component (that is to say, the component directed from the root of the wing to the tip of the wing) does not contribute to the development of the lift.

Thus, in order to maximise the recovery of the energy of the rotary stream V,, the wing 7 is preferably so disposed that the rotary stream V,, impinges on the wing 7 at right angles. In this case the stream V,, will have no ineffective component. Thus, in order to utilise all the rotary stream V,, so as to maximise the lift of the wing 7, the wing 18 is inclined upwardly at an angle" as shown in Figure 24. The angle y of inclination is dependent upon the vertical distance p between the axis j of the propeller rotation and the root of the wing 18. The optimum distance p has been already described in detail with reference to the fifth embodiment. In Figures 23 and 24, reference numeral 12 designates the circle described by the tips of the propeller blades.

Figures 25 and 26 show, on enlarged scale, the wings 7 and 8 which are shown in Figures 23 and 24. In Figure 25, the rotary stream V which impinges at an angle on the wing 7 may be resolved into a vertical component Vv and a horizontal component VH. Thus, Vv = V" V1, cos V;, = V" V,1 sin z where the angle y is the angle between the rotary stream V,, and a vertical plane normal to the wing 7.

Figure 27 is a typical cross-sectional view of the wing which is shown in Figure 23 while Figure 28 is a similar view of the wing which is shown in Figure 24.

In Figures 27 and 28, Vx is the component in the axial direction of the propeller slip stream and the vertical component Vv as shown in Figure 27 corresponds to the vertical component Vv as shown in Fig ure 25. The rotary stream V,, as shown in Figure 28 corresponds to the rotarv stream V,, as shown in Fiqure 26. Therefore, in Figure 17. the resultant V, of the components V:iX and Vv impinges on the wing 7. Figure 28, the resultant V:i2 of the components Vx and V,, impinges on the wing 18. Therefore

Since cos 2 7 < 1, V2 > V1 In order to reduce the drag to a minimum, each wing is installed at the optimum angle of attack a with respect to the oblique stream Vl or V2.The lift of the wings 7 and 18 is in proportion to the square of the velocity of the oblique stream. Since V2 > Vl as described above, the lift L2 in Figure 28 is greater than the lift L1 in Figure 27. The oblique stream V2 has a greater angle of flow than the oblique stream V1.

According to the theory of the wing, the lift is at right angles to the oblique stream Vl or V2 impinging on the wing 7 or 18 so that the lift L2 is inclined by a greater angle than the lift L1 with respect to the vertical.

L2 > L, and the angle of the lift L2 is greater than the angle of the lift L1 so that the fore-and-aft compo nent of the lift, i.e., the propulsive thrust produced by the construction of figure 28 is greater than that of Figure 27. As a result, when the wing is installed above the axis j of the propeller shaft, the propulsive thrust is increased when the wing 18 is inclined upwardly at angle The upward and downward movements of the wings attached to the rudder or the rudder supporting device as a result of vertical motion of the ship in the water will now be discussed. When the vertical motion of the ship becomes more pronounced, the wings tend to jump into the air from the water and then to be immersed again. Such motion of the wings is repeated as the ship moves.When the wings strike against the water, an impact is imparted to them. If the impact is reduced, the stressing of the wings is decreased so that the wings can be made of more light weight construction.

In general, it is well known that a wedge with an obtuse angle can soften the impact more than a wedge with an acute angle. In order to express the magnitude of the impact of a wedge with water, the following well known formula of Van-Karman is used: P 1 ~~~~~~~~~~ 1 pV2 P = ' pV tan B' 2 where P is the impact, p' is the angle between the inclined surface of the wedge and the horizontal plane, V is the velocity at which the wedge strikes the water, and p is the density of water, It is seen that the greater angle p' (that is, a wedge with an acute angle), the less the impact becomes.

The same is true for a rudder with wings in accordance with the present invention. Thus, the impact exerted on the inclined wings as shown in Figure 24 is smaller than the impact exerted on the horizontal wings as shown in Figure 23.

Figure 29 shows the eleventh embodiment of the present invention. Reference numeral 1 designates a propeller and 18, a wing directly joined to the side surface of the rudder blade 13. The root of the wing 18 is spaced upwardly from the axis j of the propeller shaft by a distance p.

Figure 30 shows the twelfth embodiment of the present invention which is similar to the eleventh embodiment except that the wings 18 are securely attached to a rudder supporting member 19. The roots of the wings 18 are spaced upwardly from the axis j of the propeller shaft by a distance p. so that the same effects can be obtained as in the eleventh embodiment. Furthermore, the strength can be advantageously increased because the wing is securely attached to the rudder supporting member 19 which in turn is directly joined to the hull.

Figures 31 and 32 show a conventional hanging rudder in which a rudder blade is attached to a rudder supporting member 22 (referred to as "a rudder horn" in this specification) which supports the rudder blade. Located downstream of the propeller 1 in the propeller slip stream is the rudder blade 20 which is in the form of an aerofoil extending in the fore-and-aft direction and which is enlarged in the direction of the depth of the ship's hull. The rudder blade 20 is rotatably supported by the rudder horn 22 which in turn depends from the stern 21 of the ship. As best shown in Figure 32, the rotatable rudder blade 20 and the rudder horn 22 which support the rudder blade are in the form of airfoils.As described above, the oblique streams V (the velocity in the axial direction is Vx and the peripheral velocity is V5 produced by the propeller slip stream impinge on them so that a lift L is produced. The fore-and-aft component of the lift L is the propulsive thrust T.

Figures 33 and 34 show a construction similar to that of Figure 3 in more detail. Reference numeral 1 designates the propeller; 20, the rudder blade; 21, the ship's stern; and 22, the rudder horn which is securely attached to the stern 21. As shown in Figure 33, the depending portion 23 and the root portion 24 of the rudder horn 22 extend away from the hull. Rearwardly extending gudgeons 25 and 26 are formed integral with the depending portion 23 and the root portion 24 respectively. Vertical shafts extend away from the rudder blade 20 and are rotatably fitted into these gudgeons 25 and 26.

Wings 7 are attached to both the side surfaces of the rudder horn 22, that is to say, upsteam of the major portion of the rudder blade 20. More particularly, the wings 7 are formed integral with the gudgeon 25 and are thus located at a position above the axis j of the propeller shaft (i.e. the upper portion of the figure) where the rotary velocity component of the propeller slip stream is higher (i.e. the rotational energy is high). The wings 7 are in the form of airfoils as is the rudder blade 20.

When the ship moves forward in a straight line, the oblique stream V or the resultant of the axial flow Vx and the peripheral flow V" impinges on each wing 7 as shown in Figures 33 and 34 so that lift L is developed. The fore-and-aft component of the lift L constitutes the propulsive thrust T. Since the wings are situated in a region of the propeller slip stream where the rotational energy is high, A high propulsive thrust T is developed in an efficient manner.

However, when the rudder blade 20 is rotated for steering purposes, the rudder blade 20 and the rudder horn 22 do not maintain their overall airfoil shape as seen in Figure 35. As a result, the direction of the propeller slip stream is changed as indicated by the arrows around the rudder blade 20. Thus, a lift Lr which tends to turn the ship is produced, but no propulsive thrust is obtained.

Figure 36 illustrates that the present invention can substantially overcome the above described problems of the loss of propulsive thrust.

The wings 7 are attached to the rudder horn 22 which is located upstream of the rudder blade 20 so that when the rudder blade 20 is rotated about the gudgeons 25 and 26, as shown in Figure 36, the position of the wings 7 relative to the propeller 1 remains unchanged. As a result, the lift T is still developed and a stable performance is ensured.

Moreover, the wings 7 are attached to the depending portion 25 of the rudder horn 22, which extends directly from the hull which permits the strength of the wings 7 to be increased.

Thus, the present invention is concerned with a rudder which is adapted to develop a high propulsive thrust by effectively utilising the rotational energy of the propeller slip stream by virtue of the provision of auxiliary wings. In order to obtain a satisfactory result, it is desirable that the auxiliary wings be hydrodynamically efficient or have a high lift- to-drag ratio. Such wings are thin and precise airfoils in which the chord line is relatively long and whose thickness is relatively small. The wings must therefore be fabricated with a high degreee of precision and be securely fixed in position. A method of fabricating the rudder will be described below for a construction in which the auxiliary wings 7 are attached to the rudder horn 22, as in Figure 37.

As shown in Figure 38, a flat steel plate 30 is formed into a wing or blade 7 by a rolling process or a hot working process in such a way that the trailing edge 31 of the wing 7 is left open. Transverse wing ribs 32 are disposed within the wing 7 and welded thereto. Subsequently, a circular rod 30 is welded in position to close the open trailing edge 31 of the wing 7.

Such a method can be readily applied in the fabrication of the rudder blade 20 which has a substantial thickness t because the steel plate 30 can be easily formed, but it cannot be applied to a small thinairfoil- shaped wing 7 which is to be attached to a rudder horn 22 as shown in Figure 37 because it is difficult to maintain the desired degree of accuracy of shape. When the fabricated wing 7 is attached to the depending portion 23 of the rudder horn 22, it is difficult to locate it with respect to the rudder horn 22 with the desired degree of accuracy. As a result, the attached wing cannot perform satisfactorily.

The method of fabrication of the present invention was devised to overcome the above and other problems encountered in the known methods of wing fabrication and has as its object the fabrication of a rudder with wings with a high degree of accuracy in which the strength of the fabricated wings and thus their performance is ensured.

One example of the method for fabricating a rudder with wings in accordance with the present invention will be described below.

In Figures 39 and 40, the depending portion 23 of the rudder horn 22 has a through hole 34 through which a shaft (not shown) extends so that the rudder blade, which depends from the ship's stern, may be rotatably supported. The auxiliary wings 7 extend horizontally from the depending portion 23 in the widthwise direction W of the ship.

Each wing 7 comprises a root portion 35 which has predetermined thickness and width and which extends in the widthwise direction W of the ship and a peripheral portion 36 of which one side is defined by the root portion 35 and which extends in the widthwise direction W of the ship to define a frame. The wing also includes a wing surface plate 37 which sandwiches the frame comprising the root portion 35 and the peripheral portion 36, thereby forming the surfaces of the wing 7.

The peripheral portion 36 comprises a leading edge portion 38 on the side of the propeller, a trailing edge portion 39 on the side of the rudder blade and a tip portion 40 which is in opposed relationship with the root portion and interconnects the leading and trailing edge portions 38 and 39. As shown in Figures 39, 40 and 41, beams 43 which are spaced apart by a suitable distance extend between the root portion 35 and the tip portion 40 of the wing 7 to reinforce the wing structure. A backing plate 44 is interposed between the beams 43 and the wing surface plate 37 (especially the upper surface plate) to facilitate welding. In this embodiment, the wing surface plate 37 is formed with spot welding holes 45 along the backing plate 44.

In Figures 40 and 41, reference numeral 46 designates a working stand upon which the wing 7 is assembled.

The fabricating and assembling steps of the wing 7 of the type described will now be explained. As shown in Figures 39, 40 and 41, the depending portion 23 of the rudder horn 22 and the root portion 35 of the wing 7 are first integrally formed by casting.

At the same time, the peripheral portion 36 comprising the leading edge portion 38, the trailing edge portion 39 and the tip portion 40 is cast separately.

The wing surface plate 37 is fabricated into a predetermined shape by rolling a steel plate. Beams 43 and backing plates 44 are cut off from steel plates.

The lower wing surface plate 37 is placed upon the working stand 46 welded together with the depending portion 23 and the peripheral portion 36. The root portion 35 and the peripheral portion 36 are welded together, thereby fabricating the frame. The beams 43 are placed between the root portion 35 and the tip portion 40 and welded to the wing surface plates 37.

Thereafter the backing plates 44 are welded to the beams 43 and the upper wing surface plate 37 is placed over the backing plate 44 and spot welded thereto.

According to the present invention, the depending portion 23 of the rudder horn 22 and the root portion 35 of the wings 7 are cast as a unitary construction and the peripheral portion 36 of the wings 7 is fabricated by casting. As a result, the installation and shape accuracies can be substantially improved and the satisfactory performance of the wing 7 can be ensured. In addition, the strength of the wing may be increased.

The fabrication of the wing 7 is simple because the frames are fabricated by casting so that the number of fabrication steps is reduced.

In addition, the number of moulded parts is reduced to a minimum so that the accuracy in shape can be maintained and the weight of the wing can be considerably reduced as compared with the case in which the whole wing is fabricated by casting.

In this embodiment the upper wing surface plate 37 has been described as being slot welded to the backing plates 44, but it is to be understood that the upper wing surface plate 37 may be divided into a plurality of sections along the backing plates 44 and the divided sections continuously welded to the backing plates 44.

The lower wing surface plate 37 has been described as being welded to the beams 43 when the lower wing surface plate 37 is welded to the root portion 35 and the peripheral portion 36, but it is to be understood that the beams 43 may be previously welded to the wing surface plate 37.

Figures 42 and 43 show another embodiment in which the root portion 35a of the wing 7 can be cast integral with a leading edge portion 48 which has a pivot shaft 47 for supporting the rudder blade 13.

Other constructions are substantially similar to those described above and the same effects as described above can be obtained.

The method in accordance with the present invention for fabricating a rudder with wings has the following features and advantages: Since the supporting shaft of the rudder blade and the root portion of the wing are formed integral by casting, the installation accuracy can be considerably improved. Since the peripheral portion of the wing is also fabricated by casting, the accuracy in shape can be considerably improved. As a result, the performance of the wing can be ensured and the strength of the wing can be improved. The frame of the wing is fabricated by precision casting so that the fabrication can be simplified and the number of fabrication steps reduced.

It is to be understood that the rudder with wings and the method of fabrication thereof according to the present invention are not limited to the above described embodiments and that the present invention may be equally applied to rudders which are located behind twin or multiple screws.

The features and advantages of a rudder in accordance with the present invention may be summarised as follows: The main wing or blade is disposed at right angles to the vertical main shaft so that the rotational energy of the propeller slip stream can be converted into a propulsive thrust in a very effective manner. As a result, the output of the main engine can be reduced or the fuel consumption can be decreased and energy savings acheived. The auxiliary wings can be attached in a simple manner to existing rudders so that the present invention finds wide applicability. The edges of the auxiliary wings and the joints between the main and auxiliary wings are preferably fabricated by casting so that thin auxiliary wings can be fabricated with high degree of accuracy and can be securely attached to the main wing and satisfactory performance of the auxiliary wings can be ensured.

Claims (11)

1. A rudder comprising a main wing located, in use, behind a propeller and extending substantially vertically and at least one transversely extending auxiliary wing connected to each side of the main wing.

2. A rudder as claimed in Claim 1 in which the main wing comprises a rudder blade and a rudder horn which rotatably supports the rudder blade and is located in front of the rudder blade.

3. A rudder as claimed in Claim 2 in which the auxiliary wings are connected directly to the rudder blade.

4. A rudder as claimed in Claim 2 in which the auxiliary wings are connected to the rudder horn.

5. A rudder as claimed in any one of the preceding claims in which the wings are connected to the main wing at positions which, in use, are higher than the axis of rotation of the propeller.

6. A rudder as claimed in any one of the preceding claims in which the auxiliary wings on the port and starboard sides are rotationally offset in opposite senses with respect to the vertical.

7. A rudder as claimed in any one of the preceding claims in which the auxiliary wings extend outwardly and upwardly from their points of connection with the main wing.

8. A rudder as claimed in any one of Claims 1 to 6 in which the main wings extend substantially horizontally from the main wing.

9. A rudder as claimed in Claim 2 or any subsequent claim when dependent thereon in which the rudder horn and the root of each auxiliary wing constitute an integral casting and the tip portion of each auxiliary wing constitutes a respective integral casting welded to its respective root portion, steel wing surface plates being welded to each auxiliary wing and defining the outer surface thereof.

10. A rudder substantially as specifically herein described with reference to Figures 5 and 6 or Figures 7A and 78 or Figures 8A and 8B or Figure 9 or Figures 12 and 13 or Figures 15A and 15B or Figures 16A and 16B or Figures 19A and 19B or Figures 21A and 218 or Figures 24, 25 and 28 or Figures 29 or Figures 30 , 33, 34 and 36 or Figures 42 and 43 of the accompanying drawings.

11. A method of fabricating a rudder as claimed in Claim 3 which comprises integrally fabricating by casting the root portion of each auxiliary wing and the rudder horn, fabricating by casting the tip portion of each auxiliary wing, welding the tip portions to respective root portions and thereafter welding steel wing surface plates to the root portions and the tip portions to define the upper and lower wing surfaces of each auxiliary wing.