The present disclosure pertains to the field of propulsion systems for vessels. The present disclosure relates to a fin, a propulsion unit and a vessel having a forward fin sweep.

BACKGROUND

The field of propulsion systems for vessels is concerned with converting energy output from a vessel’s prime mover into forward motion. Depending on the type of vessel and service provided by the vessel, fuel costs may represent as much as 50-60% of total ship operating costs. A screw propeller is the mainly used propulsion device on vessels today. Maximum achievable open-water efficiencies by modern screw propellers are about 70%. For commercial shipping, it is desirable to improve the efficiency of the propulsion system, to avoid wasting the energy provided by the prime mover.

SUMMARY

Accordingly, there is a need for a propulsion system, which mitigates, alleviates, or addresses the shortcomings existing and provides a more efficient propulsion of a vessel.

Disclosed is a fin for a propulsion unit. The fin extends from a proximal end to a distal end along a fin axis. The fin comprises a profiled surface with a leading edge and a trailing edge and a chord extending between the leading edge and the trailing edge. The fin, e.g. the leading edge and/or the trailing edge of the fin, has a forward sweep.

Disclosed is a propulsion unit for propelling a vessel in a forward direction. The propulsion unit comprises a body and a first fin. The first fin is a fin according to this disclosure.

Disclosed is a vessel comprising a propulsion unit according to this disclosure. The body of the propulsion unit is arranged at or embedded in a keel of the vessel. The first fin is configured to perform a pitch and heave motion in relation to the keel of the vessel. The keel may extend along a centerline, such as a longitudinal centerline, of the vessel. The longitudinal centerline extends between the fore and the aft of the vessel.

It is an advantage of the present disclosure that the efficiency of the propulsion unit can be increased by providing the fin, such as the leading edge of the fin, with a forward sweep. By providing the fin, such as the leading edge of the fin, with a forward sweep, a flow of water will follow the fin towards the center of the vessel when the fin is arranged on a propulsion unit for propelling the vessel, which may prevent vortices to be generated at the tip of the fin. Thereby, stalling of the flow of water over the fin can be delayed, which in turn increases the efficiency of the fin, the propulsion unit, and the vessel. Thereby lift- induced drag otherwise caused by the vortices around the tip of the fin may be reduced. Reducing the lift-induced drag improves a lift-to-drag ratio of the fin in turn increasing efficiency of the fin. Furthermore, by providing the fin with a forward sweep, the drag of the fin may be reduced e.g. compared to using winglets used on fins to reduce the vortices around the fin tip. The forward swept wing also has the benefit that it is easier to implement than adding winglets and/or end plates to the fin.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present disclosure will become readily apparent to those skilled in the art by the following detailed description of exemplary embodiments thereof with reference to the attached drawings, in which:

Fig. 1 illustrates a perspective view of a vessel comprising a propulsion unit with fins according to one or more examples of this disclosure,

Fig. 2 illustrates a bottom-up view of a vessel comprising a propulsion unit with fins according to one or more examples of this disclosure,

Fig. 3 illustrates a bottom-up view of an example vessel comprising a propulsion unit with fins having a convex leading edge according to one or more examples of this disclosure, Fig. 4 illustrates a bottom-up view of an example vessel comprising a propulsion unit with fins having a straight leading edge according to one or more examples of this disclosure, and

Fig. 5 illustrates a bottom-up view of an example vessel comprising a propulsion unit with a fin having a concave leading edge according to one or more examples of this disclosure.

DETAILED DESCRIPTION

Various exemplary embodiments and details are described hereinafter, with reference to the figures when relevant. It should be noted that the figures may or may not be drawn to scale and that elements of similar structures or functions are represented by like reference numerals throughout the figures. It should also be noted that the figures are only intended to facilitate the description of the embodiments. They are not intended as an exhaustive description of the disclosure or as a limitation on the scope of the disclosure. In addition, an illustrated embodiment needs not have all the aspects or advantages shown. An aspect or an advantage described in conjunction with a particular embodiment is not necessarily limited to that embodiment and can be practiced in any other embodiments even if not so illustrated, or if not so explicitly described.

The figures are schematic and simplified for clarity, and they merely show details which aid understanding the disclosure, while other details have been left out. Throughout, the same reference numerals are used for identical or corresponding parts.

The current disclosure relates to a forward swept fin for a propulsion unit for propelling a vessel. A fin for a propulsion unit for propelling a vessel, such as a ship, is disclosed. The fin extends from a proximal end to a distal end along a fin axis. The proximal end of the fin herein means the end of the fin being configured to be arranged at the body of the propulsion unit, such as towards a keel of the vessel when the propulsion unit is arranged in or at the keel. The distal end of the fin herein means the end of the fin being configured to be furthest away from the body of the propulsion unit, such as the free end of the fin. The fin comprises a profiled surface with a leading edge configured to be arranged in a fore direction of a vessel when the fin is arranged on a vessel, and a trailing edge configured to be arranged in an aft direction, such as a backward direction, when the fin is arranged on a vessel. The fin comprises a chord extending between the leading edge and the trailing edge. The fin, such as the leading edge of the fin, has a forward sweep. Having a forward sweep herein means that a distal part of the fin, such as a distal part of leading edge, is arranged anterior, such as arranged forward of or in front of, a proximal part of the fin, such as a proximal part of the leading edge, when the fin is arranged on a vessel. Forward of or in front of herein means closer to a bow of the vessel.

Consequently, the proximal part of the leading edge is arranged aft of the distal part of the leading edge, such as closer to a stern of the vessel, when the fin is arranged on the vessel. The fin may have a fin axis, such as a center axis, extending centrally through the fin from the proximal end of the fin to the distal end of the fin. The fin axis may be an imaginary axis.

It is an advantage of the present disclosure that the efficiency of the fin is increased by providing the fin, such as the leading edge of the fin, with a forward sweep. By providing the fin, such as the leading edge of the fin, with a forward sweep, the flow of water will follow the fin towards the center of the vessel when the fin is arranged on a propulsion unit for propelling the vessel, which may prevent vortices to be generated at the tip of the fin. Thereby, stalling of the flow of water over the fin can be delayed, which increases the efficiency of the fin, the propulsion unit, and the vessel. Furthermore, by providing the fin with a forward sweep, the drag of the fin may be reduced compared to using winglets commonly used on fins to reduce the vortices around the fin tip.

In one or more example fins, the leading edge, such as at least a part of the leading edge or the entire leading edge, is concave. The leading edge being concave can herein be seen as the leading edge curving in, such as towards a center axis of the fin, between the distal end and the proximal end of the fin.

In one or more example fins, the leading edge, such as at least a part of the leading edge or the entire leading edge, is straight. The leading edge being straight can herein be seen as the leading edge extending in a straight line between the distal end and the proximal end of the fin, such as neither curving in (concave) nor out (convex) between the distal end and the proximal end of the fin.

In one or more example fins, the leading edge, such as at least a part of the leading edge or the entire leading edge, is convex. The leading edge being convex can herein be seen as the leading edge curving out, such as away from a center of the fin, between the distal end and the proximal end of the fin.

In one or more example fins, the trailing edge, such as at least a part of the trailing edge or the entire trailing edge, is concave. The trailing edge being concave can herein be seen as the trailing edge curving in, such as towards a center axis of the fin, between the distal end and the proximal end of the fin.

In one or more example fins, the trailing edge, such as at least a part of the trailing edge or the entire trailing edge, is straight. The trailing edge being straight can herein be seen as the trailing edge extending in a straight line between the distal end and the proximal end of the fin, such as neither curving in nor out between the distal end and the proximal end of the fin.

In one or more example fins, the trailing edge, such as at least a part of the trailing edge or the entire trailing edge, is convex. The trailing edge being convex can herein be seen as the trailing edge curving out, such as away from a center of the fin, between the distal end and the proximal end of the fin. In one or more example fins, the leading edge, such as at least a part of the leading edge or the entire leading edge, is concave, and the trailing edge, such as a part of the trailing edge or the entire trailing edge, is convex, concave or straight.

In one or more example fins, the leading edge, such as at least a part of the leading edge or the entire leading edge, is convex, and the trailing edge, such as a part of the trailing edge or the entire trailing edge, is convex, concave or straight.

In one or more example fins, the leading edge, such as at least a part of the leading edge or the entire leading edge, is straight, and the trailing edge, such as a part of the trailing edge or the entire trailing edge, is convex, concave or straight.

In one or more example fins, the leading edge comprises a first part being concave and a second part being straight. The first part may be arranged between the distal end and the second part.

In one or more example fins, the fin has a length, which may also be referred to as a span of the fin, such as a distance from the proximal end of the fin to the distal end of the fin, in the range from 3 m to 50 m, such as in the range from 10 m to 40 m, such as in the range of 20 m to 30 m, such as in the range of 22 m to 25 m. In one or more examples, the length of the fin is in a range from 0.2W to 0.45W, where W is the width of the vessel.

The length of the fin may, e.g. for smaller vessels, be in the range from 0.10 m to 3 m, such as in the range from 0.20 m to 1 m, e.g. 0.25 m to 0.5 m.

In one or more example fins, the chord, such as a maximum chord distance from the leading edge of the fin to the distal end of the fin, is in the range from 1 m to 10 m. In one or more examples, the cord may be in a range from 0.1 m to 1 m, such as in the range from 0.20 m to 0.5 m.

A propulsion unit for propelling a vessel in a forward direction is disclosed. The forward direction can herein be seen as a direction extending from a stern of the vessel to a bow of the vessel, such as parallel to a keel of the vessel. The propulsion unit comprises a body and a first fin. The first fin is a fin according to this disclosure, such as a fin comprising a leading edge having a forward sweep. In one or more example propulsion units, the propulsion unit comprises a second fin. The second fin may be a fin according to this disclosure, such as a fin comprising a leading edge having a forward sweep. In one or more example propulsion units, the first fin, such as the length and/or span of the first fin, is arranged in a first fin direction forming a first fin angle with the forward direction. The first fin direction can be seen as a direction from the proximal end to the distal end of the first fin, e.g. parallel to a fin axis of the first fin. The fin axis can herein be seen as a center axis of the fin extending from the proximal end to the distal end of the fin. In one or more examples, the first fin angle may be in the range from 45 degrees to 85 degrees, such as in the range from 45 degrees to 55 degrees, such as in the range from 55 degrees to 65 degrees, such as in the range from 65 degrees to 75 degrees, such as in the range from 75 degrees to 85 degrees. In one or more examples, the first fin angle is less than 85 degrees, such as 75 degrees. In one or more examples, the first fin angle may be in the range from 15 degrees to 45 degrees.

In one or more example propulsion units, the second fin, such as the length and/or span of the second fin, is arranged in a second fin direction forming a second fin angle with the forward direction. The second fin direction can be seen as a direction from the proximal end to the distal end of the second fin, e.g. parallel to a fin axis of the second fin. The fin axis can herein be seen as a center axis of the fin extending from the proximal end to the distal end of the fin. In one or more examples, the second fin angle may be in the range from 45 degrees to 85 degrees, such as in the range from 45 degrees to 55 degrees, such as in the range from 55 degrees to 65 degrees, such as in the range from 65 degrees to 75 degrees, such as in the range from 75 degrees to 85 degrees. In one or more examples, the second fin angle is less than 85 degrees, such as 75 degrees. In one or more examples, the second fin angle may be in the range from 15 degrees to 45 degrees.

In one or more example propulsion units, the first fin and the second fin are interconnected by a fin frame and/or integrated in a single fin. When the first fin and the second fin are integrated in a single fin, the fin ends are the respective distal ends of the first fin and second fin, and the center region of the single fin is the respective proximal ends of the first fin and second fin.

In one or more example propulsion units, an angle between the first fin direction and the second fin direction is in the range from 120 degrees to 170 degrees.

In one or more example propulsion units, the propulsion unit comprises an actuator assembly configured to generate a heave motion and/or pitch motion of the first fin in relation to the body. The actuator assembly may be connected to the fin via at least one actuating rod. The actuator assembly may be configured to operate with an oscillating pattern, thereby generating an oscillating heave and/or pitch motion of the fin. The heave and/or the pitch motion of the fin may be generated in relation to the body, such as in relation to the body of the propulsion unit.

A vessel comprising a propulsion unit according to this disclosure is disclosed. The body, such as the body of the propulsion unit, is arranged at or embedded in a keel of the vessel. The first fin and/or the second fin is/are configured to perform a pitch and/or a heave motion in relation to the keel of the vessel.

Fig. 1 illustrates a perspective view of a vessel 100 according to one or more examples disclosed herein. The example vessel 100 comprises a keel 102 and a propulsion unit 4 for propelling the vessel in a forward direction FDIR. The propulsion unit 4 comprises a body 14, and two fins 2, such as a first fin 2A and a second fin 2B. The body 14 is arranged at or embedded in the keel 102 of the vessel 100. The body 14 may be fixedly arranged in relation to the keel 102 of the vessel 100. The propulsion unit comprises an actuator assembly 12 configured to generate a heave motion and/or a pitch motion of the first fin 2A and/or the second fin 2B in relation to the body 14. The first fin 2A and/or the second fin 2B is/are thus configured to perform a pitch and/or heave motion in relation to the keel 102 of the vessel 100. The pitch and/or heave motion of the first fin 2A and/or the second fin 2B generates a propulsion force propelling the vessel 100 in the forward direction FDIR. The first fin 2A and/or the second fin 2B, extend from a proximal end 6 to a distal end 8 of the fin along a fin axis, such as a span of the fin. The fins 2; 2A, 2B comprise a profiled surface with a leading edge 10, a trailing edge 12 and a chord extending between the leading edge 10 and the trailing edge 12. The fins 2A, 2B, such as the leading edge 10, each has a forward sweep, i.e. a distal part 10A of the leading edge 10 is arranged anterior of the proximal part 10B of the leading edge 10 of the respective fins 2A, 2B. Arranged anterior herein means that the distal part 10A of the leading edge 10 is arranged forward of the proximal part 10B of the leading edge 10, when the fin is arranged on the vessel. Forward of herein means closer to the bow of the vessel 100. Consequently, the proximal part 10B of the leading edge 10 is arranged aft of the distal part 10A of the leading edge 10, such as closer to a stern 101 of the vessel 100, when the respective fin 2; 2A, 2B is arranged on the vessel 100.

Fig. 2 illustrates a bottom-up view of the vessel 100 according to one or more examples disclosed herein. The example vessel 100 comprises the keel 102 and the propulsion unit 4 for propelling the vessel in the forward direction FDIR. The propulsion unit 4 comprises a body 14, and two fins 2, such as a first fin 2A and a second fin 2B. The first fin 2A and the second fin 2B may be arranged on opposite sides of the keel 102. The first fin 2A and the second fin 2B can thus have a mirrored or symmetric arrangement around the keel 102. The body 14 is arranged at or embedded in the keel 102 of the vessel 100. The body 14 may be fixedly arranged in relation to the keel 102 of the vessel 100. The propulsion unit 4 comprises an actuator assembly 12 configured to generate a heave motion and/or a pitch motion of the first fin 2A and/or the second fin 2B in relation to the body 14. The first fin 2A and/or the second fin 2B, extend from a proximal end 6 to a distal end 8 of the fin 2; 2A, 2B along a fin axis, such as a span of the fin 2; 2A, 2B. The fins 2; 2A, 2B comprise a profiled surface with a leading edge 10, a trailing edge 12 and a chord extending between the leading edge 10 and the trailing edge 12. The fins 2A, 2B, such as the leading edge 10, each has a forward sweep, i.e. a distal part 10A of the leading edge 10 is arranged anterior of the proximal part 10B of the leading edge 10 of the respective fins 2A, 2B.

Fig. 3 illustrates a bottom-up view of an example vessel 100A comprising a propulsion unit 4 having an example first fin 2C and/or an example second fin 2D according to one or more examples herein. The fins 2; 2C, 2D have a forward fin sweep. The first fin 2C is arranged in a first fin direction DF_1 forming a first fin angle VF1 with the forward direction FDIR. The first fin direction DF_1 is a direction from the proximal end 6 to the distal end 8 of the first fin 2C, parallel to a fin axis of the first fin 2C. The first fin angle VF1 is in the range from 45 degrees to 85 degrees, such as in the range from 45 degrees to 55 degrees, such as in the range from 55 degrees to 65 degrees, such as in the range from 65 degrees to 75 degrees, such as in the range from 75 degrees to 85 degrees. In one or more examples, the first fin angle VF1 is 75 degrees. The second fin 2D is arranged in a second fin direction DF_2 forming a second fin angle VF2 with the forward direction FDIR. The second fin direction DF_2 is a direction from the proximal end 6 to the distal end 8 of the second fin 2D, parallel to a fin axis of the second fin 2D. The second fin angle VF2 (not shown) is in the range from 45 degrees to 85 degrees, such as in the range from 45 degrees to 55 degrees, such as in the range from 55 degrees to 65 degrees, such as in the range from 65 degrees to 75 degrees, such as in the range from 75 degrees to 85 degrees. In one or more examples, the second fin angle VF2 is 75 degrees. The first fin 2C and the second fin 2D comprise respective convex leading edges 10, such as leading edges 10 being at least partially convex or entirely convex. The leading edge 10 being convex can herein be seen as the leading edge 10 curving out, such as away from the fin axis of the fin 2; 2C, 2D between the distal end 8 and the proximal end 6 of the fin 2; 2C, 2D. In other words, a distance from the fin axis to the leading edge 10 may be shorter towards the distal part 10A and the proximal part 10B than at a center of the leading edge 10. Correspondingly, the distance from the fin axis to the leading edge 10 may be longer at the center 10C of the leading edge 10 than towards the distal end 10A and the proximal end 10B. In the example shown in Fig. 3, the trailing edge 12 of the fin 2; 2C, 2D is convex, such as curving out, such as away from the fin axis of the fin 2; 2C, 2D, between the distal end 8 and the proximal end 6 of the fin 2; 2C, 2D. However, the trailing edge 12 may, in one or more example fins, be straight or concave.

Fig. 4 illustrates a bottom-up view of an example vessel 100B comprising a propulsion unit 4 having an example first fin 2E and/or an example second fin 2F according to one or more examples herein. The fins 2; 2E, 2F have a forward fin sweep. The first fin 2E is arranged in the first fin direction DF_1 forming the first fin angle VF1 with the forward direction FDIR. The first fin direction DF_1 is a direction from the proximal end 6 to the distal end 8 of the first fin 2E, parallel to the fin axis of the first fin 2E. The first fin angle VF1 is in the range from 45 degrees to 85 degrees, such as in the range from 45 degrees to 55 degrees, such as in the range from 55 degrees to 65 degrees, such as in the range from 65 degrees to 75 degrees, such as in the range from 75 degrees to 85 degrees. In one or more examples, the first fin angle VF1 is 75 degrees. The second fin 2F is arranged in a second fin direction DF_2 forming a second fin angle VF2 with the forward direction FDIR. The second fin direction DF_2 is a direction from the proximal end 6 to the distal end 8 of the second fin 2D, parallel to a fin axis of the second fin 2D. The second fin angle VF2 (not shown) is in the range from 45 degrees to 85 degrees, such as in the range from 45 degrees to 55 degrees, such as in the range from 55 degrees to 65 degrees, such as in the range from 65 degrees to 75 degrees, such as in the range from 75 degrees to 85 degrees. In one or more examples, the second fin angle VF2 is 75 degrees. The first fin 2E and a second fin 2F comprise respective leading edges 10 being straight, such as being at least partially straight or entirely straight. The leading edge 10 being straight can herein be seen as the leading edge 10 extending in a straight line between the distal end 8 and the proximal end 6 of the fin 2; 2E, 2F. In the example shown in Fig. 4, the trailing edge 12 of the fin 2; 2E, 2F is straight, such as being at least partially straight or entirely straight. However, the trailing edge 12 may, in one or more example fins, be convex or concave, such as at least partially convex or concave, or entirely convex or concave. Fig. 5 illustrates a bottom-up view of an example vessel 100C comprising a propulsion unit 4 having an example first fin 2G and/or an example second fin 2H according to one or more examples herein. The fins 2; 2G, 2H have a forward fin sweep. The first fin 2G is arranged in a first fin direction DF_1 forming a first fin angle VF1 with the forward direction FDIR. The first fin direction DF_1 is a direction from the proximal end 6 to the distal end 8 of the first fin 2G, parallel to the fin axis of the first fin 2G. The first fin angle VF1 is in the range from 45 degrees to 85 degrees, such as in the range from 45 degrees to 55 degrees, such as in the range from 55 degrees to 65 degrees, such as in the range from 65 degrees to 75 degrees, such as in the range from 75 degrees to 85 degrees. In one or more examples, the first fin angle VF1 is 75 degrees. The second fin 2H is arranged in a second fin direction DF_2 forming a second fin angle VF2 with the forward direction FDIR. The second fin direction DF_2 is a direction from the proximal end 6 to the distal end 8 of the second fin 2H, parallel to a fin axis of the second fin 2H. The second fin angle VF2 (not shown) is in the range from 45 degrees to 85 degrees, such as in the range from 45 degrees to 55 degrees, such as in the range from 55 degrees to 65 degrees, such as in the range from 65 degrees to 75 degrees, such as in the range from 75 degrees to 85 degrees. In one or more examples, the second fin angle VF2 is 75 degrees. The first fin 2G and the second fin 2H comprise respective concave leading edges 10, such as leading edges 10 being at least partially concave or entirely concave. The leading edge 10 being concave can herein be seen as the leading edge 10 curving in, such as towards the fin axis of the fin 2; 2G, 2H between the distal end 8 and the proximal end 6 of the fin 2; 2G, 2H. In other words, a distance from the fin axis to the leading edge 10 may be longer towards the distal part 10A and the proximal part 10B than at the center of the leading edge 10. Correspondingly, the distance from the fin axis to the leading edge 10 may be shorter at the center 10C of the leading edge 10 than towards the distal end 10A and the proximal end 10B. In the example shown in Fig. 5, the trailing edge 12 of the fin 2; 2G, 2H is concave, such as curving in, such as towards the fin axis of the fin 2; 2G, 2H, between the distal end 8 and the proximal end 6 of the fin 2; 2G, 2H. However, the trailing edge 12 may, in one or more example fins, be straight or convex.

It shall be noted that the features mentioned in the embodiments described in Figs. 1 -2 are not restricted to these specific embodiments. Any features relating to the propulsion unit, the vessel, and/or the fins and the components comprised therein and mentioned in relation to the vessel of Figs. 1 -2, such as dimensions of the fins an/or arrangements of the fins, are thus also applicable to the vessel, propulsion units and/or fins described in relation to Figs. 3-5, and vice versa.

It shall further be noted that a vertical axis, when referred to herein, relates to an imaginary line running vertically through the ship and through its center of gravity, a transverse axis or lateral axis is an imaginary line running horizontally across the ship and through the center of gravity and a longitudinal axis is an imaginary line running horizontally through the length of the ship through its center of gravity and parallel to a waterline. Similarly, when referred to herein, a vertical plane relates to an imaginary plane running vertically through the width of the ship, a transverse plane or lateral plane is an imaginary plane running horizontally across the ship and a longitudinal plane is an imaginary plane running vertically through the length of the ship.

Embodiments of products (fin, propulsion unit, and vessel) according to the disclosure are set out in the following items:

Item 1 . A fin (2, 2A, 2B, 2C, 2D, 2E, 2F, 2G, 2H) for a propulsion unit (4), the fin extending from a proximal end (6) to a distal end (8) along a fin axis, the fin comprising a profiled surface with a leading edge (10) and a trailing edge (12) and a chord extending between the leading edge and the trailing edge, wherein the fin, such as the leading edge (10) and/or the trailing edge (12) has a forward sweep.

Item 2. The fin (2, 2A, 2B, 2C, 2D, 2E, 2F, 2G, 2H) according to Item 1 , wherein a distal part (10A) of the leading edge is arranged anterior of a proximal part (1 OB) of the leading edge.

Item 3. The fin (2, 2A, 2B, 20, 2D, 2E, 2F, 2G, 2H) according to any one of the preceding Items, wherein a distal part of the trailing edge (12) is arranged anterior of a proximal part of the trailing edge (12).

Item 4. The fin (2, 2A, 2B, 2C, 2D, 2E, 2F, 2G, 2H) according to any one of the preceding Items, wherein a distal part of the trailing edge (12) is arranged anterior of a proximal part (1 OB) of the leading edge (10).

Item 5. The fin (2, 2A, 2B, 20, 2D, 2E, 2F, 2G, 2H) according to any one of the preceding Items, wherein the leading edge is concave or at least partly concave. Item 6. The fin (2, 2A, 2B, 2C, 2D, 2E, 2F, 2G, 2H) according to any one of the preceding Items, wherein the leading edge is straight or at least partly straight.

Item 7. The fin (2, 2A, 2B, 2C, 2D, 2E, 2F, 2G, 2H) according to any one of the preceding Items, wherein the trailing edge is convex or at least partly convex.

Item 8. The fin (2, 2A, 2B, 2C, 2D, 2E, 2F, 2G, 2H) according to any one of the preceding Items, wherein the fin has a length in the range from 3 m to 50 m or in the range from 0.5 m to 3 m.

Item 9. A propulsion unit (4) for propelling a vessel (100) in a forward direction (FDIR), the propulsion unit (4) comprising a body (14) and a first fin (2A, 2C, 2E, 2G), wherein the first fin (2A, 20, 2E, 2G) is a fin according to any of Items 1 -6.

Item 10. The propulsion unit (4) according to Item 9, the propulsion unit (4) comprising a second fin (2B, 2D, 2G, 2H), wherein the second fin (2B, 2D, 2G, 2H) is a fin according to any of Items 1-6.

Item 11 . The propulsion unit (4) according to any one of Items 9-10, the first fin (2A, 2C, 2E, 2G) arranged in a first fin direction (DF_1) forming a first fin angle (VF1 ) with the forward direction, wherein the first fin angle is in the range from 45 degrees to 85 degrees.

Item 12. The propulsion unit (4) according to any one of Items 9-11 , the second fin (2B, 2D, 2G, 2H), arranged in a second fin direction (DF_2) forming a second fin angle (VF2) with the forward direction, wherein the second fin angle is in the range from 45 degrees to 85 degrees.

Item 13. The propulsion unit (4) according to any one of Items 9-12, the propulsion unit comprising an actuator assembly (16) configured to generate a heave motion of the first fin (2A, 2C, 2E, 2G) and/or the second fin (2B, 2D, 2G, 2H) in relation to the body (14).

Item 14. A vessel (100) comprising a propulsion unit (4) according to any one of Items 9- 13, wherein the body (14) is arranged at or embedded in a keel (102) of the vessel (100) and wherein the first fin (2A, 2C, 2E, 2G) is configured to perform a pitch and heave motion in relation to the keel (102) of the vessel (100)

Item 15. A vessel according to Item 14, wherein the second fin (2B, 2D, 2G, 2H) is configured to perform a pitch and heave motion in relation to the keel (102) of the vessel (100). The use of the terms “first”, “second”, “third” and “fourth”, “primary”, “secondary”, “tertiary” etc. does not imply any particular order but are included to identify individual elements. Moreover, the use of the terms “first”, “second”, “third” and “fourth”, “primary”, “secondary”, “tertiary” etc. does not denote any order or importance, but rather the terms “first”, “second”, “third” and “fourth”, “primary”, “secondary”, “tertiary” etc. are used to distinguish one element from another. Note that the words “first”, “second”, “third” and “fourth”, “primary”, “secondary”, “tertiary” etc. are used here and elsewhere for labelling purposes only and are not intended to denote any specific spatial or temporal ordering. Furthermore, the labelling of a first element does not imply the presence of a second element and vice versa.

It is to be noted that the word "comprising" does not necessarily exclude the presence of other elements or steps than those listed.

It is to be noted that the words "a" or "an" preceding an element do not exclude the presence of a plurality of such elements.

Although features have been shown and described, it will be understood that they are not intended to limit the claimed disclosure, and it will be made obvious to those skilled in the art that various changes and modifications may be made without departing from the scope of the claimed disclosure. The specification and drawings are, accordingly, to be regarded in an illustrative rather than restrictive sense. The claimed disclosure is intended to cover all alternatives, modifications, and equivalents.

LIST OF REFERENCES

2 fin

2A, 2C, 2E, 2G first fin

2B, 2D, 2F, 2H second fin

4 propulsion unit

6 proximal end

8 distal end

10 leading edge

10A distal part of leading edge

10B proximal part of leading edge

12 trailing edge

14 body

16 actuator assembly

100 vessel

102 keel

FDIR forward direction

DF_1 first fin direction

DF_2 second fin direction

VF1 first fin angle

VF2 second fin angle