WO2012052030A2

WO2012052030A2 - Rudder for a vessel

Info

Publication number: WO2012052030A2
Application number: PCT/DK2011/050396
Authority: WO
Inventors: Levi Heinesen
Original assignee: Levi Heinesen
Priority date: 2010-10-18
Filing date: 2011-10-18
Publication date: 2012-04-26
Also published as: KR20140031837A; DK179481B9; EP2630029B1; ES2531211T3; DK201200412A; WO2012052030A3; EP2630029A2; PL2630029T3; DK179481B1

Abstract

The present invention relates to a rudder (2) for a craft (1). The rudder (2) comprises a rudder blade (3) and a rudder stock (4), which is adapted to be connected to a craft (1) rotatable around a first axis of rotation (5). The rudder blade (3) is connected to the rudder stock (4) by a first arm (6), which is fixed to the rudder stock (4) so that the rudder blade (3) is rotatable around a second axis of rotation (7), which is parallel to and not coincident with the first axis of rotation (5). A second arm (8) provides a third axis of rotation (9), which is parallel to and fixedly positioned in relation to the first axis of rotation (5) as the rudder blade (3) is displaceable in relation to and rotatable around the second axis of rotation (7) and/or the third axis of rotation (9).

Description

Rudder for a vessel

The present invention relates to a rudder for a craft, particularly a marine craft.

The rudder according to the invention comprises a rudder blade and a rudder stock, which is adapted to be connected to a craft, rotatable around a first axis of rotation.

A rudder as the above-mentioned, the rudder blade of which is hinged at its front edge to a stern, is for instance known from GB 488 043 A. The rudder blade thus rotates substantially around its front edge when the rudder blade is rotated by the rudder stock. Hence, the rotational axis of the rudder blade is coincident with the rotational axis of the rudder stock. The rudder blade is positioned relatively close to and on level with a propeller of a craft.

Another example of a rudder of the above-mentioned type is disclosed in GB 373 656 A, wherein a rudder blade is rotatably connected by its front edge to a stern. Here too, the rudder blade rotates around its front edge when the rudder stock is rotated, and here too, the rudder blade is positioned next to the propeller of the craft.

Yet another example of a rudder of the above-mentioned type is disclosed in US 3,159,132, wherein a rudder for a smaller craft is described. Here, a rudder blade is fixed to a rudder stock in such a way that the rudder blade rotates around its front edge when the rudder stock is rotated. Here too, the rudder blade is positioned next to the propeller of the craft.

With the above-mentioned type of rudder, the rudder blade will, when it is rotated from its neutral position into an angled position, lead to that the craft is not responding very fast or precisely to the performed rotation of the rudder blade. This makes maneuvering the craft difficult, especial- ly in areas where it is crucial to be able to perform fast and precise changes in course, such as in harbour areas, in waters with much water-borne traffic or many rocks, icebergs or other obstacles.

Another problem with rudders of the above-mentioned type is that the rudder stock, the rudder blade and their journaling is exposed to large torque loads when the rudder blade is moved into an angled position. This is due to the journaling of the rudder blade at its front edge that makes the full length of the rudder blade contribute to the torque load. This necessitates a robust and strong construction, which results in a heavy rudder construction that increases the weight of the craft and causes a poor fuel economy for the craft and/or reduces the loading capacity.

Furthermore, it is required that the control means of the craft for setting the angular displacement of the rudder blade are able to overcome the large torques acting on the journaling of the rudder blade in order to be able to control the angular displacement of the rudder blade. Therefore, rudders of the above-mentioned type necessitate powerful hydraulic systems or other kinds of powerful devices for controlling the rudder blade, which increases the weight of the craft and possibly the complexity of the construction.

Previous attempts have been made to mitigate some of the above- mentioned problems by providing a rudder, the rudder stock of which is jour- naled in the rudder blade in a distance from the front edge of the rudder blade. An example of such a rudder is for instance found in DE 38 14 943 Al .

Based on the above, it is an object of the present invention to provide a rudder that provides the craft on which it is mounted with better maneuverability, including reducing the turning radius of the craft at both high and low speeds, while a more lightweight rudder construction is provided that can increase the loading capacity of the craft and/or improve its fuel economy.

Based on the above, a rudder of the initially mentioned kind is provided, the rudder being characterized in that the rudder blade is connected to the rudder stock by a first arm, which is fixed to the rudder stock, so that the rudder blade is rotatabie around a second axis of rotation, which is parallel to and not coincident with the first axis of rotation, and by a second arm, which provides a third axis of rotation, which is parallel to and fixedly positioned in relation to the first axis of rotation, as the rudder blade is displaceable in re- lation to and rotatabie around the second axis of rotation and/or the third axis of rotation.

It is understood that the term "arm" comprises an arm in the meaning : the straight distance between two points in which forces act; in this case, for the first arm, the straight distance between the first axis of rotation and the second axis of rotation, and for the second arm, the straight distance between the first axis of rotation and the third axis of rotation. The skilled person will understand that these arms can in practice be provided by a number of various elements, such as for instance an arm- or rod-shaped element or other differently shaped elements, of which further examples will be given below.

As the front edge of the rudder blade according to the invention is not directly hinged to the rudder stock, a rotation of the rudder stock causes the front edge of the rudder blade to move to one side, while the aft edge of the rudder stock is moved to the opposite side, as the rudder blade is always retained at the third axis of rotation in relation to the first axis of rotation. In this way, when the rudder blade is mounted next to a propeller of a craft, the rudder blade captures water flow from both sides of the propeller when the rudder blade is put into an angled position rather than just from one side of the propeller. Hereby a higher degree of maneuverability is obtained.

Furthermore, the fact that the rudder blade is journaled both at the second axis of rotation and at the third axis of rotation causes the torque loads on each of the two journalings to be smaller than the load on the jour- naling of a rudder of the above-mentioned type of known rudder. This allows for a slimmer and more lightweight construction, which increases the loading capacity and/or the fuel economy of the craft.

Furthermore, the construction of the rudder has the effect that the more angled a position the rudder blade is put into, the closer to the rudder stock the rudder blade is pulled and thus closer to the propeller of the craft, on which the rudder is intended to be mounted. This has the effect that the rudder blade can more efficiently capture a larger part of the water flow from the propeller, since the closer the rudder blade is to the propeller, the smaller a portion of the flow gets past the rudder blade unaffected.

Furthermore, this rudder construction has the effect that the more angled a position the rudder blade is put into, the larger a portion of the rud- der blade will be at one side of a central plane compared to the other side of the central plane. This asymmetric positioning in angled positions enables the provision of a relatively long fin at the aft edge of the rudder blade. Hereby is obtained the possibility of affecting the propeller flow in very large width at large angular displacements of the rudder. This provides for the possibility of a very high degree of maneuverability at both high and low speed of the craft. At low speed the craft is thus provided with the possibility of substantially rotating around its own axis by the aft propeller alone. This has previously only been possible by use of lateral propellers on the craft.

In an embodiment of the rudder, the second axis of rotation and/or the third axis of rotation is within the rudder blade. To have one or both of these axes within the rudder blade reduces the presence of protrusions that can create disturbing whirls and undesirable resistance.

In an embodiment of the rudder, the shortest distance between the first axis of rotation and the third axis of rotation is larger than the shortest distance between the first axis of rotation and the second axis of rotation. This provides for a particularly advantageous pattern of movement of the rudder blade as a function of the rotation of the rudder stock.

In an embodiment of the rudder, the first axis of rotation, seen in an intended direction of flow of a water flow past the rudder blade in a neutral position of the rudder blade, is positioned in front of the second axis of rotation, preferably in front of a front edge of the rudder blade, and the second axis of rotation, seen in the same direction, is positioned in front of the third axis of rotation, which is preferably positioned in front of an aft edge of the rudder blade, seen in the same direction. This provides for a particularly ad- vantageous pattern of movement of the rudder blade as a function of the rotation of the rudder stock.

In an embodiment of the rudder, the first arm comprises a first rod- shaped element extending at least between the first axis of rotation and the second axis of rotation, and/or the second arm comprises a second rod- shaped element extending at least between the first axis of rotation and the third axis of rotation and preferably further being adapted to extend between the first axis of rotation and the craft as a rudder heel. A rod-shaped element will create little undesirable turbulence around the rudder blade. The second rod-shaped element furthermore extending as a rudder heel provides stability and strength to the whole rudder construction, as the rudder is then not just fastened to the craft at the rudder stock, but also furthermore at the second arm as a rudder heel.

In an embodiment of the rudder, the third axis of rotation is provided as a gu/deway comprising a pin, which is provided on the second arm so that the longitudinal axis of the pin is parallel to and coincident with the third axis of rotation, and an oblong recess provided in the rudder blade so that the rudder blade is rotatable and displaceable in relation to the second arm as the oblong recess is displaced and/or rotated around the pin. This is a way to implement the third axis of rotation that provides little undesirable turbulence around the rudder blade. This is due to the fact that those parts being in mutual engagement are within the rudder blade, as the pin is completely or partially within the recess in the rudder blade.

In an embodiment of the rudder, the rudder comprises a fin hingedly connected to the rudder blade so that the fin is rotatable in relation to the rudder blade around a fourth axis of rotation, which is parallel to at least the first axis of rotation, and the fin is connected to the second arm by a third arm, which is fixed to the fin so that the fin is rotatable around a fifth axis of rotation, which is not coincident with the fourth axis of rotation, and the fifth axis of rotation is preferably positioned between the third axis of rotation and the fourth axis of rotation, seen in the intended direction of flow of a water flow past the rudder blade in a neutral position of the rudder blade, as the second arm preferably extends past the third axis of rotation in a direction away from the first axis of rotation. This connection between the fin and the other elements of the rudder enables the fin to be put into an angled position which, together with the corresponding angled position of the rudder blade, renders the craft on which the rudder is mounted most maneuverable. For instance, an angular displacement of the fin of more than 90° in relation to neutral position of the fin is enabled, which has the effect that the craft will be able to turn around its own axis without use of lateral propellers.

In an embodiment of the rudder, a rotation of the rudder stock of substantially 7° in relation to neutral position results in a rotation of the rudder blade of substantially 5°-30°, preferably of 10°-25°, in relation to neutral position and preferably in a rotation of the fin of substantially 20°-40°, preferably of 25°-35°, in relation to neutral position, and a rotation of the rudder stock of substantially 15° in relation to neutral position results in a rotation of the rudder blade of substantially 20°-40°, preferably of 25°-35°, in relation to neutral position and preferably in a rotation of the fin of substantially 50°- 70°, preferably of 55°-65°, in relation to neutral position, and a rotation of the rudder stock of substantially 40° in relation to neutral position results in a rotation of the rudder blade of substantially 35°-55°, preferably of 40°-50°, in relation to neutral position and preferably in a rotation of the fin of substantially 95°-115°, preferably of 100°-110°, in relation to neutral position. These correlated angles provide the craft on which the rudder is mounted with good maneuverability at both high and low speed. By rotating the rudder stock by 40°, the fin is put into a position angled by more than 90° and positioned substantially on one side of the central plane, while the rudder blade is substantially positioned on the other side of the central plane. This implies that the direction of flow of a large part of the water flow is redirected to a greater or lesser extent, whereby the turning radius of the craft on which the rudder is intended to be mounted is reduced considerably. At low speed this will enable the craft to almost turn on the spot.

In an embodiment of the rudder, the rudder blade is adapted to be positioned substantially next to a propeller of a craft, preferably next to an aft propeller of a craft, preferably with the first axis of rotation and the third axis of rotation being in line next to the center of the propeller. The water flow across the rudder is greatest directly next to the propeller, and the largest compressive and tensile forces acting on the rudder blade are generated at this position in relation to the propeller of the craft. Thus, this position gives the most efficient utilization of the rudder blade and thus the best ma- neuverability of the craft.

In an embodiment of the rudder, the front edge of the rudder blade in neutral position of the rudder blade is positioned in a distance from the first axis of rotation, and/or the aft edge of the rudder blade is in neutral position of the rudder blade positioned in a distance from the third axis of rota- tion. The distance between the front edge of the rudder blade and the first axis of rotation in neutral position of the rudder blade is preferably just a little larger than the radius of the rudder stock so that the front edge of the rudder blade is close the rudder stock in neutral position of the rudder blade, but is still able to pass by the rudder stock when the rudder blade is put into an angled position. The short distance between the front edge of the rudder blade and the rudder stock in neutral position of the rudder blade is advantageous as this construction creates little undesirable turbulence in neutral position of the rudder blade and allows for an influence on the water flow in a large width in angled positions of the rudder blade. The aft edge of the rud- der blade is preferably positioned behind the third axis of rotation seen in the direction of flow, and the distance between the aft edge of the rudder blade and the third axis of rotation in neutral position of the rudder blade is preferably between ¼ and ¾ of the length of the rudder blade. Hereby is obtained that the front portion of the rudder blade in an angled position captures an appropriate quantity of the water flow from one side of the propeller, while the rear portion of the rudder blade in an angled position captures an appropriate quantity of the water flow from the other side of the propeller.

In the following, embodiments of the rudder for a craft according to the invention will be described in closer detail with reference to the accompa- nying figures, where

Fig. 1 is a schematic representation of a first embodiment of the rudder according to the invention seen from the side, the rudder blade being in neutral position and mounted on a craft,

Fig. 2 is a schematic representation of the rudder according to the first embodiment seen from above, the rudder blade being in neutral position,

Fig. 3 is a schematic representation of the rudder according to the first embodiment seen from above, the rudder blade being in a slightly angled position,

Fig. 4 is a schematic representation of the rudder according to the first embodiment seen from above, the rudder blade being in a more angled position than shown in Fig. 3,

Fig. 5 is a schematic representation of the rudder according to the first embodiment seen from above, the rudder blade being in an even more angled position than shown in Fig. 4,

Fig. 6 is a schematic representation of the rudder according to a second embodiment seen from the side, the rudder blade being in neutral position and mounted on a craft,

Fig. 7 is a schematic representation of the rudder according to the second embodiment seen from above, the rudder blade being in neutral posi- tion, and

Fig. 8 is a schematic representation of the rudder according to the second embodiment seen from above, the rudder blade being in an angled position.

Similar features in the figures are denoted with the same reference signs. For the sake of lucidity, the rudder is depicted transparent in the fig- ures 2 to 5 and 7 to 8 so that the mutual relations between the individual elements of the rudder are clearly visible.

In this specification, the term "neutral position" of the rudder blade denotes the position in which the second arm is parallel to and within a longi- tudinal central plane of the rudder blade. When the rudder is mounted on a craft this position will usually be parallel to an upright, longitudinal central plane of the craft.

The "central plane" is the upright, longitudinal plane, within which the longitudinal central plane of the rudder blade substantially is in neutral position.

The term "angled position" denotes all those positions of the rudder blade, wherein the longitudinal central plane of the rudder blade is not parallel to and does not contain the second arm. When the rudder is mounted on a craft this will mean all those positions of the rudder blade, wherein the longi- tudinal central plane of the rudder blade is not parallel to the upright longitudinal plane of the craft, i.e. those positions of the rudder blade where it is rotated to the starboard or the port side.

The term "the angular displacement of the rudder blade" denotes the angle between the longitudinal central plane of the rudder blade in the neu- tral position of the rudder blade and in an angled position of the rudder blade.

The term "the length of the rudder blade" denotes the distance along the longitudinal central plane of the rudder blade from a front edge of the rudder blade to an aft edge of the rudder blade.

The term "the height of the rudder blade" denotes the distance along the longitudinal central plane of the rudder blade from an upper edge of the rudder blade to a lower edge of the rudder blade.

The term "neutral position of the fin" denotes the position of the fin, wherein its upright longitudinal plane is substantially coincident with the upright longitudinal plane of the rudder blade in its neutral position.

Depending on the further design of the rudder blade, the front edge, aft edge, upper edge and/or lower edge may be shaped as faces rather than actual edges. Thus, it is understood that "front edge", "aft edge", "upper edge" and/or "lower edge" may be configured as faces.

The term "next to" denotes that the rudder blade is directly behind the propeller seen in the general direction of flow of a water flow from the propeller in operation.

In Fig. 1 an embodiment of the rudder 2 according to the invention is shown. The rudder 2 is mounted on a craft 1, of which only its stern is indi- cated in Fig. 1. The rudder 2 comprises a rudder blade 3 and a rudder stock 4. The rudder stock 4 is seen to be connected to the craft 1 rotatably around a first axis of rotation 5. The rudder stock 4 is rotated by means of control means on or in the craft, such as a steering wheel, a control stick, a joystick or other means (not depicted). Although the aft propeller of the craft 1 is not depicted in the figures 1 to 5, the rudder blade 3 is adapted to be placed substantially next to the aft propeller of the craft. However, it is conceivable that the rudder blade is placed next to other types of propellers of a craft than the aft propeller, such as for instance lateral propellers or front propellers. The rudder blade may also be mounted at other locations than next to the propel- ler(s) of the craft or on crafts without propellers, such as sailboats or crafts that are propelled by oars or the like.

The rudder stock 4 is positioned outside of the rudder blade 3. The rudder blade 3 is connected to the rudder stock 4 by two first arms 6, each of which being fixed to the rudder stock 4. Hence, the two first arms 6 are not moveable in relation to the rudder stock 4. The two first arms 6 are rotatably connected to the rudder blade 3 so that the rudder blade 3 is rotatable around a second axis of rotation 7, which is parallel to and not coincident with the first axis of rotation 5.

It is seen that both of the first arms 6 are shaped as rod-shaped elements 12 extending between the first axis of rotation 5 and the second axis of rotation 7, i.e. between the rudder stock 4 and the journaling 23 of the first arms 6 in the rudder blade 3. It is understood that the first arms do not necessarily have to be rod-shaped but may take other shapes, such as for instance crescent-shaped or curved. They could also be protrusions on the rudder stock or variations in its diameter, such as tooth-shaped, disc-shaped, cylinder-shaped or polygonal protrusions on the rudder stock, as long as the first arms provide a distance between the first axis of rotation 5 and the second axis of rotation 7. Irrespective of their shape, the first arms 6 do not need to be parallel as long as they provide a second axis of rotation 7 that is parallel to but not coincident with the first axis of rotation 5. Although the depicted embodiment of the rudder 2 is provided with two first arms 6, it is understood that just one first arm, or even more first arms, may be provided. In the latter case, if one or more first arms are to be placed between the two first arms 6 depicted in the embodiment in Fig. 1, it may be necessary with a shape of the first arms 6 that allow movement of the rudder blade to the sides so that the one or more arms placed there does not impede movement of the rudder blade 3. Alternatively, notches or recesses in the rudder blade may be provided allowing the first arms to pass through the rudder blade during its movement to the sides.

In the embodiment of Fig. 1, a second arm 8 is furthermore provided, which provides a third axis of rotation 9, which is parallel to and fixedly positioned in relation to the first axis of rotation 5. It is understood that the "second arm" should be read in the sense given above, i.e. the straight distance between two points in which forces act. In the depicted embodiment, the second arm 8 is implemented partly by a rod-shaped element 13 at the lower edge of the rudder blade 3 and partly by a sort of suspension at the upper edge of the rudder blade 3. Embodiments of the rudder where the second arm 8 is provided solely by a suspension or by one or more rod- shaped elements 13 are conceivable.

The rudder blade 3 is displaceable in relation to and rotatable around the third axis of rotation 9, which is provided as a guideway 15. In the following, the guideway 15 at the lower edge of the rudder blade will be described in more detail. It is understood that something similar applies for the guide- way 15 provided at the upper edge of the rudder blade. The guideway 15 comprises a pin 16, which is provided at the second arm 8 so that the longitudinal axis 17 of the pin 16 is parallel to and coincident with the third axis of rotation 9. As is best seen in Figs 2 to 5, the guideway 15 furthermore comprises an oblong recess 18 provided in a lower (upper, respectively) face of the rudder blade 3 in such a way that the rudder blade 3 is rotatable and dis- placeable in relation to the second rod-shaped element 13, as the oblong recess 18 is displaced and rotated around the pin 16 by rotation of the rudder blade 3.

The slidable and rotatable journaling of the rudder blade at the third axis of rotation may be configured in other ways. For instance, the pin may be provided in the rudder blade rather than in the second rod-shaped ele- ment 13, and the oblong recess may correspondingly be provided in the second rod-shaped element 13 rather than in the rudder blade. Other alternative solutions are conceivable, such as a fork-shaped pin being provided at the second rod-shaped element 13 rotatable in relation thereto, between the two fork legs of which the rudder blade is displaceable.

In the depicted embodiment, the rod-shaped element 13 extends between the third axis of rotation 9 and the craft 1 as a rudder heel 14. It is understood that the rod-shaped element 13 does not necessarily have to extend all the way to the craft as a rudder heel. The rod-shaped element may just extend between the first axis of rotation and the third axis of rotation. In that case, it will be expedient with an upper construction that is strong enough for the rudder to be suspended from it at the craft. Also, it is understood that there may be provided two rod-shaped elements 13; one above and one below the rudder blade.

As is best seen from the figures 2 to 5, the third axis of rotation 9 is within the rudder blade 3. The shortest distance ai-₃ between the first axis of rotation 5 and the third axis of rotation 9 is seen to be larger than the shortest distance ai_-2 between the first axis of rotation 5 and the second axis of rotation 7.

As is seen from Fig. 2, the first axis of rotation 5, seen in the direction of flow r_s of a water flow past the rudder blade 3 in a neutral position of the rudder blade 3, is placed in front of the second axis of rotation 7 and in front of a front edge 10 of the rudder blade 3. The second axis of rotation 7, seen in the same direction, is placed in front of the third axis of rotation 9, which is placed in front of an aft edge 11 of the rudder blade 3 seen in the same direction.

With regard to the distance between the front edge 10 of the rudder blade 3 and the first axis of rotation 5 in neutral position of the rudder blade 3, it is only slightly larger than the radius of the rudder stock 4 so that the front edge 10 of the rudder blade 3 is close to the rudder stock 4 in neutral position of the rudder blade 3 but is still able to pass the rudder stock 4, when the rudder blade 3 is put into an angled position. In the depicted embodiment, the distance between the aft edge 11 of the rudder blade 3 and the third axis of rotation 9 in neutral position of the rudder blade 3 make up 4/10-5/10 of the length of the rudder blade 3. Embodiments of the rudder where these distances are different from the above-described are conceivable.

The rudder 2 is provided with a fin 19, which is hingedly connected to the rudder blade 3 so that the fin 19 is rotatable in relation to the rudder blade 3 around a fourth axis of rotation 20, which is parallel to at least the first axis of rotation 5. The fin 19 is connected to the second arm 8 by a third arm 21. The third arm 21 is fixed to the fin 19 along a lower edge of the fin 19 and is rotatably connected to the second arm 8 so that the fin 19 is rotatable around a fifth axis of rotation 22, which is not coincident with the fourth axis of rotation 20. In the depicted embodiment, the fifth axis of rotation 22 is not coincident with any of the other axes of rotation 5, 7, 9, 20. In the depicted embodiment, the second arm 8 extends in the direction r_s from the first axis of rotation 5 past the third axis of rotation 9 and towards the fourth axis of rotation 20. Hence, the fifth axis of rotation 22 is between the third axis of rotation 9 and the fourth axis of rotation 20, as the third arm 21 is journaled there in the second arm 8. The third arm 21 is provided in the shape of a cornered, rod-shaped element, whose first leg 21a extends along a length of the fin 19, and whose second leg 21b extends parallel to and coincident with the fifth axis of rotation 22. It is understood, as also men- tioned in relation to the provision of the second arm, that also a third arm at the upper edge of the rudder blade may be provided depending on the further construction and suspension of the rudder. It is furthermore understood that the third arm may take on other shapes in other embodiments of the rudder, as it was also mentioned in connection with the first arms. Embodi- ments of the rudder with no fin are conceivable.

As best seen in Fig. 1, the length of the rudder blade 3 makes up approximately ¾ of the total length of rudder blade 3 and fin 19, and the fin 19 makes up the remaining ¹A. It is understood that this relation may vary for different embodiments of the invention. Hence, the rudder blade may make up between Vz and all of the total length of the rudder blade and fin altogether, and the fin correspondingly between Vz and none of the total length of rudder blade and fin.

The rudder is intended for use with a wide range of different types and sizes of crafts and is intended to be adapted by scaling of its dimensions. Hence, the height of the rudder blade and fin will typically be between 20 cm and 15 m, the length of the rudder blade between 20 cm and 7 m, and the length of the fin between 5 cm and 3 m. The dimensions in the lower regions of the ranges will be suitable for smaller crafts, such as dinghies, while the dimensions in the upper regions of the ranges will be suitable for larger crafts, such as cruisers, tankers and container carriers.

Notwithstanding the absolute dimensions of the rudder, it is advantageous with a particular correlation between a given rotation of the rudder stock and the resulting rotation of the rudder blade and the fin, which correlation is obtained by an appropriate mutual positioning of the first, second, third, fourth and fifth axis of rotation. As is seen from the figures, the distance between the first and the second axis of rotation make up approximately 2/5 of the distance between the first and the fourth axis of rotation, while the distance between the first and the third axis of rotation make up approximately 3/5 of the distance between the first and the fourth axis of rotation, and the distance between the first and the fifth axis of rotation make up approximately 4/5 of the distance between the first and the fourth axis of rotation. It is understood that the above-mentioned advantages of the rudder will be obtained within certain ranges of these relative mutual distances. Hence, the distance between the first and the second axis of rotation may vary between 1/5 and 3/5 of the distance between the first and the fourth axis of rotation, the distance between the first and the third axis of rotation between 2/5 and 4/5 of the distance between the first and the fourth axis of rotation, and the distance between the first and the fifth axis of rotation between 3/5 and 9/10 of the distance between the first and the fourth axis of rotation.

Figures 2 to 5 exemplify a correlation between the angular displacement v_s of the rudder stock 4 and the resulting angular displacement v_b of the rudder blade 3 and angular displacement v_f of the fin 19. Figures 2 to 5 show the rudder 2 in positions of increasing angular displacement of the rud- der blade 3 and the fin 19. In Fig. 2 the rudder blade 3 and the fin 19 are depicted in their neutral positions, where the angular displacement of rudder stock v_s, rudder blade v and fin v_f is zero. In Fig. 3 the rudder stock 4 has been rotated by v_s=7° clockwise out of the neutral position. As is seen, it has resulted in a rotation of the rudder blade 3 in relation to neutral position of v_b = about 17° and in a rotation of the fin 19 in relation to neutral position of v_f = about 32°. In Fig. 4 the rudder stock 4 has been rotated by v_s=15° clockwise out of the neutral position. This has resulted in a rotation of the rudder blade 3 in relation to neutral position of v_b = about 30° and in a rotation of the fin 19 in relation to neutral position of v_f = about 58°. In Fig. 5 the rudder stock 4 has been rotated by v_s=40° clockwise out of the neutral position. As is seen, it has resulted in a rotation of the rudder blade 3 in relation to neutral position of v_b = about 44° and in a rotation of the fin 19 in relation to neutral position of v_f = about 106°. The skilled person will understand that an angular displacement of the rudder stock resulting in differently angled posi- tions of rudder blade and fin than the above-mentioned will be acceptable and still at least to some degree provide the above-mentioned advantages with regard to better maneuverability, reduction of turning radius etc. Particularly for embodiments of the rudder where no fin is provided it may be desirable to have larger angular displacements of the rudder blade at smaller angular displacements of the rudder stock than exemplified above.

Figures 6 to 8 show another embodiment of the rudder 2 according to the invention. The rudder 2 is seen to be of a broadly similar construction as the rudder according to the first embodiment. Hence, in the following, focus will be on the differences.

As is seen, the rudder blade 3 according to the second embodiment is rotatable around and displaceable in relation to the second axis of rotation 7 and rotatable around the third axis of rotation 9. Embodiments of the rudder, where the rudder blade is rotatable around and displaceable in relation to the second axis of rotation as well as the third axis of rotation are also conceivable.

Furthermore, the rudder 2 according to the second embodiment is seen to be fastened to the craft 1 solely by the rudder stock 4 and the rudder heel 14. It is understood that the rudder according to the second embodiment also may be fastened to the craft in the same way as the first embodi- ment and vice versa. List of reference signs:

1 Craft

2 Rudder

3 Rudder blade

4 Rudder stock

5 First axis of rotation

6 First arm

7 Second axis of rotation

8 Second arm

9 Third axis of rotation

10 Front edge of rudder blade

11 Aft edge of rudder blade

12 First rod-shaped element

13 Second rod-shaped element

14 Rudder heel

15 Guideway

16 Pin

17 Longitudinal axis of pin

18 Oblong recess

19 Fin

20 Fourth axis of rotation

21 Third arm

21a First leg of third arm

21b Second leg of third arm

22 Fifth axis of rotation

Journaling of first arm in rudder blade ai-3 Shortest distance between first and third axis of rotation a_1-2 Shortest distance between first and second axis of rotation r_s Direction of flow

v_s Angular displacement of rudder stock

v_b Angular displacement of rudder blade

v_f Angular displacement of fin

Claims

C L A I M S

1. A rudder (2) for a craft (1), which rudder (2) comprises a rudder blade (3) and a rudder stock (4), which is adapted to be connected to a craft, (1) rotatable around a first axis of rotation (5),

c h a r a c t e r i z e d b y

the rudder blade (3) is connected to the rudder stock (4) by a first arm (6), which is fixed to the rudder stock (4) so that the rudder blade (3) is rotatable around a second axis of rotation (7), which is parallel to and not coincident with the first axis of rotation (5), and

by a second arm (8) providing a third axis of rotation (9), which is parallel to and fixedly positioned in relation to the first axis of rotation (5) as the rudder blade (3) is displaceable in relation to and rotatable around the second axis of rotation (7) and/or the third axis of rotation (9).

2. A rudder (2) according to claim 1, wherein the second axis of ro- tation (7) and/or the third axis of rotation (9) is within the rudder blade (3).

3. A rudder (2) according to claim 1 or 2, wherein the shortest distance (ai_-3) between the first axis of rotation (5) and the third axis of rotation (9) is larger than the shortest distance (a_1-2) between the first axis of rotation (5) and the second axis of rotation (7),

4. A rudder (2) according to any of the preceding claims, wherein the first axis of rotation (5), seen in an intended direction of flow (r_s) of a water flow past the rudder blade (3) in a neutral position of the rudder blade (3), is positioned in front of the second axis of rotation (7), preferably in front of a front edge (10) of the rudder blade (3), and wherein the second axis of rota- tion (7), seen in the same direction, is positioned in front of the third axis of rotation (9), which is preferably positioned in front of an aft edge (11) of the rudder blade (3), seen in the same direction.

5. A rudder (2) according to any of the preceding claims, wherein the first arm (6) comprises a first rod-shaped element (12) extending at least between the first axis of rotation (5) and the second axis of rotation (7),

and/or wherein the second arm (8) comprises a second rod-shaped element (13) extending at least between the first axis of rotation (5) and the third axis of rotation (9) and preferably further being adapted to extend between the first axis of rotation (5) and the craft (1) as a rudder heel (14).

6. A rudder (2) according to any of the preceding claims, wherein the third axis of rotation (9) is provided as a guideway (15) comprising

a pin (16) provided on the second arm (8) so that the longitudinal axis (17) of the pin (16) is parallel to and coincident with the third axis of rotation (9), and

an oblong recess (18) provided in the rudder blade (3) so that the rudder blade (3) is rotatable and displaceable in relation to the second arm (8) as the oblong recess (18) is displaced and/or rotates around the pin (16).

7. A rudder (2) according to any of the previous claims, wherein the rudder (2) comprises a rudder fin (19) hingedly connected to the rudder blade (3) so that the fin (19) is rotatable in relation to the rudder blade (3) around a fourth axis of rotation (20), which is parallel to at least the first axis of rotation (5), and

wherein the fin (19) is connected to the second arm (8) by a third arm (21), which is fixed to the fin (19) so that the fin (19) is rotatable around a fifth axis of rotation (22), which is not coincident with the fourth axis of rotation (20), and

wherein the fifth axis of rotation (22) is preferably positioned between the third axis of rotation (9) and the fourth axis of rotation (20), seen in the intended direction of flow (r_s) of a water flow past the rudder blade (3) in a neutral position of the rudder blade (3), as the second arm (8) preferably extends past the third axis of rotation (9) in a direction away from the first axis of rotation (5).

8. A rudder (2) according to any of the preceding claims, wherein a rotation of the rudder stock (4) of substantially 7° in relation to neutral posi- tion results in a rotation of the rudder blade (3) of substantially 5°-30°, preferably of 10°-25°, in relation to neutral position and preferably in a rotation of the fin (19) of substantially 20°-40°, preferably of 25°-35°, in relation to neutral position, and

wherein a rotation of the rudder stock (4) of substantially 15° in re- lation to neutral position results in a rotation of the rudder blade (3) of substantially 20°-40°, preferably of 25°-35°, in relation to neutral position and preferably in a rotation of the fin (19) of substantially 50°-70°, preferably of 55°-65°, in relation to neutral position, and

wherein a rotation of the rudder stock (4) of substantially 40° in re- lation to neutral position results in a rotation of the rudder blade (3) of sub- stantially 35°-55°, preferably of 40°-50°, in relation to neutral position and preferably in a rotation of the fin (19) of substantially 95°-115°, preferably of 100°-110°, in relation to neutral position.

9. A rudder (2) according to any of the preceding claims, wherein the rudder blade (3) is adapted to be positioned substantially next to a propeller of a craft (1), preferably next to an aft propeller of a craft (1), preferably with the first axis of rotation (5) and the third axis of rotation (9) being in line next to the center of the propeller.

10. A rudder (2) according to any of the preceding claims, wherein the front edge (10) of the rudder blade (3) in neutral position of the rudder blade (3) is positioned in a distance from the first axis of rotation (5), and/or wherein the aft edge (11) of the rudder blade (3) in neutral position of the rudder blade (3) is positioned in a distance from the third axis of rotation (9).