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Title:
A PROPULSION UNIT
Document Type and Number:
WIPO Patent Application WO/2018/083370
Kind Code:
A1
Abstract:
The propulsion unit comprises a support frame (20), a propeller (40) rotating around a shaft line (X-X), and a nozzle (60) surrounding the propeller and comprising an upstream end (61) and a downstream end (62). A support construction (50) is positioned downstream of the propeller for supporting the nozzle on an end portion (22A) of the support frame. The support construction comprises vanes (51-57) extending between the nozzle and the end portion of the support frame. The direction of each vane (51-57) is inclined in relation to a radial direction being defined by a radius extending perpendicularly from the shaft line to the nozzle.

Inventors:
HANNUNIEMI JUHO (FI)
KOCK JUHO (FI)
Application Number:
PCT/FI2016/050776
Publication Date:
May 11, 2018
Filing Date:
November 03, 2016
Export Citation:
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Assignee:
ABB OY (FI)
International Classes:
B63H5/14; B63H5/15; B63H11/117
Domestic Patent References:
WO2010093305A12010-08-19
WO1999014113A11999-03-25
Foreign References:
EP2944560A12015-11-18
Attorney, Agent or Firm:
KOLSTER OY AB (FI)
Download PDF:
Claims:
CLAIMS

1 . A propulsion unit (100) comprising:

a support frame (20),

a propeller (40) rotating around a shaft line (X-X),

a nozzle (60) surrounding the propeller (40), the nozzle (60) comprising an upstream end (61 ) and a downstream end (62) opposite to the upstream end (61 ),

a support construction (50) downstream of the propeller (40) for supporting the nozzle (60) on the support frame (20), the support construction (50) comprising vanes (51 -57) extending between the nozzle (60) and an end portion (22A) of the support frame (20),

characterized in that:

the direction of each vane (51 -57) is inclined in relation to a radial direction (R1 ), said radial direction (R1 ) being defined by a radius extending perpendicularly from the shaft line (X-X) to the nozzle (60).

2. The propulsion unit according to claim 1 , characterized in that the vanes (51 -57) of the support construction (50) extend inwards from the nozzle (60) to the end portion (22A) of the support frame (20).

3. The propulsion unit according to claim 1 or 2, characterized in that an angle (a2) between the direction of the vane (51 -57) and the radial direction (R1 ) is in the range of 10 to 50 degrees.

4. The propulsion unit according to claim 1 or 2, characterized in that an angle (a2) between the vane (51 -57) and the radial direction (R1 ) is in the range of 15 to 35 degrees.

5. The propulsion unit according to any one of claims 1 to 4, characterized in that the angle (a2) between the vane (51 -57) and the radial direction (R1 ) is the same for each vane (51 -57).

6. The propulsion unit according to any one of claims 1 to 4, characterized in that the angle (a2) between the vane (51 -57) and the radial direction (R1 ) varies for each vane (51 -57) or for groups of vanes (51 -57).

7. The propulsion unit according to any one of claims 1 to 6, characterized in that the vanes (51 -57) are configured to redirect rotational flow components of the water flow produced by the propeller (40) into axial thrust.

8. The propulsion unit according to any one of claims 1 to 7, characterized in that the vanes (51 -57) are configured to compensate for the rotational effect caused by the propeller (40) on the water flow so that the water flow downstream of the vanes (51 -57) is returned to an at least substantially axial thrust.

9. The propulsion unit according to any one of claims 1 to 8, characterized in that the end portion (22A) of the support frame (20) expends from the downstream end (62) of the nozzle (60) into a portion of the nozzle (60).

10. The propulsion unit according to claim 9, characterized in that the vanes (51 -57) are situated fully within the nozzle (60).

1 1 . The propulsion unit according to any one of claims 1 to 10, characterized in that the propeller (40) is situated fully within the nozzle (60).

12. The propulsion unit according to any one of claims 1 to 1 1 , characterized in that the number of vanes (51 -57) in the support construction (50) is greater than the number of blades (41 -44) in the propeller (40).

13. The propulsion unit according to any one of claims 1 to 12, characterized in that the support frame (20) is formed of a casing (20) comprising an upper portion (21 ) and a lower portion (22), the upper portion (21 ) forming a support arm for the lower portion (22), at least a major portion of the upper portion (21 ) being positioned downstream of the nozzle (60) and extending from the lower portion (22) to a distance above the uppermost point of the nozzle (60), an upstream end portion (22A) of the lower portion (22) of the support frame (20) forming the end portion (22A) of the support frame (20), a propeller shaft (31 ) being positioned within said lower portion (22) of the support frame (20), the propeller shaft (31 ) forming the shaft line (X-X) and extending through an opening at an upstream end of the lower portion (22) of the support frame (20) to the propeller (40).

14. The propulsion unit according to claim 13, characterized in that the nozzle (60) is only attached to the lower portion (22) of the casing (20) with the support construction (50), whereby a downstream end (62) of the nozzle (60) is at an axial (X-X) distance from an upstream edge (21 A) of the upper portion (21 ) of the support frame (20).

15. A vessel, characterized in that the vessel comprises a propulsion unit according to any one of claims 1 to 14.

Description:
A PROPULSION UNIT

FIELD OF THE INVENTION

The present invention relates to a propulsion unit.

BACKGROUND ART

Propulsion units comprising a propeller surrounded by a nozzle are used in many applications. The nozzle may be supported with a support construction on a frame part either downstream or upstream of the propeller. A third possibility is that the nozzle is supported with a support construction on a frame part downstream and upstream of the propeller. The support construction may be formed of vanes extending between the nozzle and the frame part. The direction of the vanes coincides with the radial direction.

Especially vanes situated downstream of the propeller are subjected to a heavy bending moment each time a propeller blade passes the vane. The pulse of water hitting the vane will also cause vibrations to the propulsion unit and thereby to the vessel using the propulsion unit.

BRIEF DESCRIPTION OF THE INVENTION

An object of the present invention is to achieve an improved propulsion unit.

The propulsion unit according to the invention is defined in claim 1 . The fact that the direction of each vane is inclined in relation to a radial direction being defined by a radius extending perpendicularly from the shaft line to the nozzle results in several advantages.

The bending moment acting on the vanes may be reduced with this arrangement. The pulse of water hitting the side surface of the vane each time when a propeller blade passes the vane is reduced. This is due to the fact that the pulse of water originating from the propeller blade does not hit the side surface of the vane simultaneously along the whole chord length of the vane when the vane is inclined in relation to the radial direction. The pulse of water originating from the propeller blade will be distributed along the vane during a certain time interval when the propeller blade passes the inclined vane. The peak of the water pulse is reduced and the width of the water pulse is increased. A maximum bending moment at the root of the vane will thus be reduced. A part of the bending moment acting at the root of the vane is transformed into compressive stress and into tensile stress in the inclined vane.

This will also reduce the vibrations caused by the pulses of water striking the vanes. A reduction of vibrations is naturally a major advantage in a vessel using the propulsion unit.

The thickness of the vanes may be reduced due to the reduced bending moment acting on the vanes. A thinner profile of the vane will increase the efficiency of the vane. The reduction in thickness of the vane may compensate for the slightly reduced efficiency of the vane due to the inclined position of the vane.

The support construction of the nozzle is positioned downstream of the propeller. This means that the spiral shaped flow produced by the propeller will pass through the support construction. The format, the position, the angle and the number of the vanes can be optimized in view of redirecting as much as possible of the rotational components of the propeller flow into axial thrust.

The terms upstream and downstream are in this application used in relation to the forward driving direction of the vessel. When the vessel travels in the forward direction, water passes into the nozzle from the upstream end of the nozzle and water passes out from the nozzle from the downstream end of the nozzle.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described in greater detail by means of preferred embodiments with reference to the attached drawings, in which:

Figure 1 shows an axonometric view of a propulsion unit,

Figure 2 shows a vertical view in the longitudinal direction of the propulsion unit of figure 1 ,

Figure 3 shows a vertical view in the transverse direction from the front of the propulsion unit of figure 1 ,

Figure 4 shows a second vertical view in the transverse direction from the aft of the propulsion unit of figure 1 ,

Figure 5 shows a horizontal view in the longitudinal direction from below of the propulsion unit of figure 1 ,

Figure 6 shows a horizontal view in the longitudinal direction from above of the propulsion unit of figure 1 , Figure 7 shows a support arrangement of the propulsion unit of figure 1 ,

Figure 8 shows a cross sectional view of a vane in the propulsion unit of figure 1 ,

Figure 9 shows a cross sectional view of the nozzle of the propulsion unit of figure 1 .

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 shows an axonometric view of a propulsion unit, figure 2 shows a vertical view in the longitudinal direction of the propulsion unit of figure 1 , figure 3 shows a vertical view in the transverse direction from the front of the propulsion unit of figure 1 , and figure 4 shows a second vertical view in the transverse direction from the aft of the propulsion unit of figure 1 .

The propulsion unit 100 comprises a support frame 20, a propeller 40, a nozzle 60 surrounding the propeller 40, and a support construction 50 supporting the nozzle 60 on the support frame 20. The propeller 40 rotates around a shaft line X-X: The propeller 40 may be attached to a propeller shaft 31 being concentric with the shaft line X-X. The nozzle 60 comprises an upstream end 61 and a downstream end 62 opposite to the upstream end 61 .

The support construction 50 supports the nozzle 60 on the support frame 20. An end portion 22A of the support frame 20 may be concentric with the shaft line X-X. The end portion 22A may extend from the downstream end 62 of the nozzle 60 into a portion of the nozzle 60. The end portion 22A of the support frame 20 may have a generally cylindrical form. The centre line of the cylinder may be concentric with the shaft line X-X. The first end 22A of the support frame 20 may extend into the vicinity of the propeller 40. The support construction 50 comprises vanes 51 -57 extending between the nozzle 60 and the end portion 22A of the support frame 20. The vanes 51 -57 may extend between an inner perimeter of the nozzle 60 and an outer perimeter of the end portion 22A of the support frame 20.

The support frame 20 may be formed of a casing 20 extending downwards from a hull 1 1 of a vessel 10. The casing 20 may be hollow. The casing 20 may comprise an upper portion 21 and a lower portion 22. The upper portion 21 of the casing 20 may form a support arm for the lower portion 22 of the casing 20. At least a major portion of the upper portion 21 of the casing 20 is positioned downstream of the nozzle 60 and extends from the lower portion 22 of the casing 20 to a distance above an uppermost point of the nozzle 60. The upper portion 21 may have at least substantially an air-foil shaped cross section, whereby the upstream edge of the upper portion 21 is formed as a rounded leading edge and the downstream edge of the upper portion 21 is formed as a sharp trailing edge. The lower portion 22 of the casing 20 may have the form of a gondola having a first end 22A and a second end 22B. The first end 22A may form a front end and the second end 22B may form an aft end of the gondola 22. The first end 22A of the gondola 22 forms the end portion 22A of the support frame 20. There may be a small rudder portion 22C extending downwards from the second end 22B of the gondola 22. The gondola 22 may have at least substantially an air-foil shaped cross section, whereby the first end 22A is formed as a rounded leading edge and the second end 22B is formed as a sharp trailing edge. The first end 22A of the gondola 22 and the second end 22B of the gondola 22 is connected with an upper surface and a lower surface. The first end 22A of the gondola 22 is directed towards the forward direction S1 of the vessel 10 when the vessel 10 is driven forwards. This means that the propeller 40 is a pulling propeller 40 pulling the vessel 10 in the forward direction S1 .

The casing 20 and especially the upper portion 21 of the casing 20 may also form a rudder of the vessel 10. The upper portion 21 and the lower portion 22 of the casing 20 may formed of one or more parts. The upper portion 22 and the lower portion 22 could be manufactured separately and then finally be welded together into one entity. The lower portion 22 may form a hollow compartment accommodating different equipment. The upper portion 21 is also hollow. It is thus possible for a technician to enter into the casing 20 from the top of the upper portion 21 and to climb down to the lower portion 22 by a ladder. The technician can then perform maintenance tasks to the equipment in the lower portion 22 of the casing 20.

The upper end of the upper portion 21 of the casing 20 may comprise a flange 23 through which the casing 20 may be attached to a counter flange, which is operatively connected to a slewing arrangement within the vessel 10. The flange 23 may be circular. The slewing arrangement may comprise a turning wheel supported by a slewing bearing. A slewing seal may be positioned below the slewing bearing in order to seal the rotating casing 20 towards the hull 1 1 of the vessel 10. The counter flange may be operatively connected to the turning wheel within the hull 1 1 of the vessel 10. The turning wheel may be driven by one or more electric motors connected via a cog arrangement to the cogs of the turning wheel. The one or more electric motors turn the turning wheel and thereby also the casing 20 and the propulsion unit 100 attached to the casing 20. The casing 20 is thus rotatable supported at the hull 1 1 of the vessel 10. The casing 20 can be rotated 360 degrees around a substantially vertical centre axis Y-Y in relation to the hull 1 1 of the vessel 10.

The propeller 40 may be attached via a hub 45 to the outer end of the propeller shaft 31 . An electric motor 30 may be positioned within the casing 20 in the lower portion 22 of the casing 20. The propeller shaft 31 may pass through the electric motor 30. The electric motor 30 rotates the propeller shaft 31 and thereby also the propeller 40 attached to the outer end of the propeller shaft 31 . The propeller shaft 31 rotates around the shaft line X-X. The propeller shaft 31 may be rotatably supported with bearings (not shown in the figures) within the lower portion 22 of the casing 20. The propeller shaft 31 may further be sealed in the opening at the upstream end 22A of the lower portion 22 of the casing 20 through which opening the propeller shaft 31 passes from the interior of the casing 20 to the exterior of the casing 20.

The propeller 40 may comprise at least three blades 41 -44, advantageously 3 to 7 blades 41 -44. The blades 41 -44 may extend in the radial direction. The water may enter the blades 41 -44 of the propeller 40 within the nozzle 60 directly without any disturbing elements positioned upstream of the propeller 40. There are thus no disturbing elements such as vanes upstream of the propeller 40 within the nozzle 60. The nozzle 60 is attached to the end portion 22A of the support frame 20 only through the vanes 51 -57. The blades 41 -44 of the propeller 40 may be dimensioned according to normal marine propeller dimensioning processes. The blade 41 - 44 geometry of the propeller 40 may be optimized for the freely incoming three dimensional water flow taking into account the downstream equipment such as the casing 20 and especially the upper portion 21 of the support frame 20. The propeller blades 41 -44 may comprise a base portion being attached to a cylindrical middle portion, or rotor disk. The base portion may be slightly tilted from the rotation axis of the propeller 40. The blades 41 -44 may have a twisted form such that at a tip of the propeller blade, the rear end is radially further away from the base of the blade than at the front end of the blade.

The propeller 40 may be fully within the nozzle 60 i.e. within the inlet end 61 and the outlet end 62 of the nozzle 60. The increase in thrust would be reduced if the propeller 40 would be positioned partly or wholly outside the nozzle 60.

The propeller 40 may be positioned axially X-X within the nozzle 60 so that an axial X-X distance L2 between a radial centre plane of the propeller 40 and a radial plane in the upstream end 61 of the nozzle 60 is in the range of 0.15 to 0.45 times the diameter D1 of the propeller 40.

The propeller 40 has a diameter D1 measured from a circle passing through the radial outer edges of the blades 41 -44 of the propeller 40. The outer edges of the blades 41 -44 are flush with the inner surface of the nozzle 60.

The nozzle 60 is fixedly attached to the end portion 22A of the support frame 20 i.e. to the upstream end portion 22A of the lower portion 22 of the casing 20 with the support construction 50. The vanes 51 -57 of the support construction 50 may extend between the nozzle 60 and the end portion 22A of the support frame 20. The vanes 51 -57 may extend inwards from the nozzle 60 to the end portion 22A of the support frame 20. The direction inwards means towards the shaft line X-X. The vanes 51 -57 may extend from an inner perimeter of the nozzle 60 to an outer perimeter of the end portion 22A of the support frame 20. The ends of the vanes 51 -57 may be flush with the inner perimeter of the nozzle 60 and/or with the outer perimeter of the end portion 22 of the support frame 20. The other possibility is that the ends of the vanes 51 -57 are inserted or embedded in the nozzle 60 and/or in the end portion 22 of the support frame 20. There are at least three vanes 51 - 57, advantageously 2 to 7 vanes 51 -57 supporting the nozzle 60 at the end portion 22A of the support frame 20. The vanes 51 -57 are positioned downstream of the propeller 40. The rotating propeller 40 causes water to flow through the central duct 65 from the first end 61 of the central duct 65 to the second end 62 of the central duct 65 in a second direction S2, which is opposed to the first direction S1 i.e. the driving direction of the vessel 10. The thrust produced by the propeller 40 is amplified by the nozzle 60. The propeller 40 is thus pulling the vessel in the forward direction S1 of the vessel 10.

The nozzle 60 surrounds an outer perimeter of the propeller 40 blades 41 -44. The nozzle 60 may be coaxial with the shaft line X-X i.e. the longitudinal centre line of the nozzle 60 may coincide with the shaft line X-X. The nozzle 60 has an upstream end 61 forming an inlet opening 61 and a downstream end 62 forming an outlet opening 62, whereby a central duct 65 is formed between the inlet opening 61 and the outlet opening 62 of the nozzle 60. The central duct 65 forms an axial flow path for water flowing through the interior of the nozzle 60. The shape of the nozzle 60 may be designed for minimal self-induced drag and for maximal thrust. The length, the thickness and the position of the nozzle 60 in relation to the casing 20 may be optimized.

The nozzle 60 may be formed generally as a cylinder or as a cone frustum having open ends. The nozzle 60 may be annular and/or rotationally symmetrical and/or rotationally asymmetrical. The upper portion and the lower portion of the nozzle 60 may thus have a different cross section. The wall of the nozzle 60 may have at least a substantially air-foil shaped cross section, whereby the upstream end 61 is formed as a rounded leading edge and the downstream end 62 is formed as a sharp trailing edge. The upstream end 61 of the nozzle 60 and the downstream end 62 of the wall of the nozzle 60 is connected with an upper surface and a lower surface. The cross-sectional free water area of the nozzle 60 at the inlet opening 61 of the nozzle 60 and the cross-sectional free water area of the nozzle 60 at the outlet opening 62 of the nozzle 60 may be in the range of 1 .00 to 1 .50.

The nozzle 60 may have an axial length L1 in the range of 0.35 to 0.65 times the diameter D1 of the propeller 40.

The support construction 50 comprises vanes 51 -57 extending between the nozzle 60 and the end portion 22A of the support frame 20. The vanes 51 -57 receive the spiral shaped water flow from the blades 41 -44 of the propeller 40 as the vanes 51 -57 are positioned downstream of the propeller 40 in the driving direction S1 of the vessel 10. The vanes 51 -57 recover the rotational energy created by the blades 41 -44 of the propeller 40. The vanes 51 -57 redirect the rotational flow component of the spiral shaped water flow into the axial direction. This will increase the thrust produced by the propeller 40. The sectional shape of the vanes 51 -57 is designed to minimize self- induced drag. Each vane 51 -57 is designed by taking into account the incoming three dimensional water flow produced by the propeller 40. The impact of the casing 20, which is positioned downstream from the vanes 51 -57 is also taken into consideration when designing the vanes 51 -57.

The vanes 51 -57 in the support construction 50 are optimized for redirecting rotational flow components of the flow produced by the propeller 40 into axial thrust. The optimization is done by calculating the flow field produced by the propeller 40 just before the support construction 50. The calculation can be done by computational fluid dynamics (CFD) or by a simple panel method. When the flow field is known, then the optimal angle distribution in the radial direction of the vanes 51 -57 in relation to the incoming flow is determined so that the ratio between the extra thrust that the vanes 51 -57 produce and the self-induced drag that the vanes 51 -57 produce is maximized. The ratio between the thickness and the length of each vane 51 -57 is determined by the strength of the vanes 51 -57. The vanes 51 -57 carry and supply the thrust and the hydrodynamic loads produced by the propeller 40.

The vanes 51 -57 of the support construction 50 may be fully within the nozzle 60 i.e. within the inlet end 61 and the outlet end 62 of the nozzle 60. This is advantageous in order to be able to redirect as much as possible of the rotational flow of the propeller 40 into axial thrust downstream of the propeller 40. The nozzle 60 forms a restricted perimeter for the water flow downstream of the propeller 40, whereby the whole water flow of the propeller 40 has to pass across the full axial width of the vanes 51 -57 of the support structure 50. The vanes 51 -57 of the support construction 50 may extend in a radial plane being perpendicular to the shaft line X-X.

The vanes 51 -57 in the support construction 50 may on the other hand also be partly within the nozzle 60 i.e. within the inlet end 61 and the outlet end 62 of the nozzle 60. A portion of the vanes 51 -57 could be outside of the outlet end 62 of the nozzle 60. This would mean that the end portion 22A of the support frame 20 would not necessary need to extend into the nozzle 60. An inner end of the vanes 51 -57 of the support construction 50 could be attached to the end portion 22A of the support frame 20 outside the downstream end 62 of the nozzle 60 and an outer end of the end portion 22A of the support construction 50 could be attached to the nozzle 60 within the nozzle 60. The vanes 51 -57 of the support construction 50 would thus be inclined in relation to a radial plane being perpendicular to the shaft line X-X.

The vanes 51 -57 may be equally distributed along the inner perimeter of the nozzle 60. The vanes 51 -57 may on the other hand be unequally distributed along the inner perimeter of the nozzle 60. This unequal distribution of the vanes 51 -57 along the inner perimeter of the nozzle 60 may be done according to any pattern.

The number of vanes 51 -57 in the support structure 50 may be greater than the number of blades 41 -44 in the propeller 40. There may be 3 to 5 blades in the propeller 40. There may be 5 to 1 1 vanes 51 -57 in the support structure 50. There may in one advantageous embodiment be 4 blades in the propeller and 7 vanes in the support structure 50. In case the number of blades 41 -44 in the propeller 40 is even, the number of vanes 51 -57 in the support structure 50 should be uneven and vice a versa.

The nozzle 60 may be supported on the support frame 20 only through the vanes 51 -57 of the support structure 50. An additional support 59 may, however be arranged between the nozzle 60 and the upper portion 21 of the casing 20. The additional support 59 may extend outwards from the nozzle 60 to the upper portion 21 of the casing 20.

The downstream end 62 of the nozzle 60 may be at an axial distance from the upstream edge of the upper portion 21 of the support frame 20. The upstream edge of the upper portion 21 of the support frame 20 may start with a substantially vertically upwards directed edge portion from the lower portion 22 of the support frame 20 downstream of the downstream end 62 of the nozzle 60. The substantially vertically upwards directed edge portion may continue as an inclined edge portion extending above the upper edge of the nozzle 60. The inclined edge portion of the upper portion 21 of the support frame 20 starts from a point at an axial distance from the downstream end 62 of the nozzle 60 and extends to a point above the upper edge of the nozzle 60 at a substantially axial middle point of the nozzle 60.

Figure 5 shows a horizontal view in the longitudinal direction from below of the propulsion unit of figure 1 and figure 6 shows a horizontal view in the longitudinal direction from above of the propulsion unit of figure 1 .

The gondola form of the lower portion 22 of the casing 20 is clearly seen from the figures. The upper portion 21 of the casing 20 supports the casing 20 at the hull 1 1 of the vessel 10. The upper portion 21 of the casing 20 has an upstream edge 21 A and a downstream edge 21 B.

Figure 7 shows a support arrangement of the propulsion unit of figure 1 .

The figure shows only a single vane 51 extending between the frame part 22A and the nozzle 60. The radial direction R1 is also shown in the figure. The figure shows that the direction of the vane 51 is inclined by an acute angle o2 in relation to the radial direction R1 . The radial direction R1 may be defined by a radius extending perpendicularly from the shaft line X-X to the nozzle 60.

The angle o2 between the direction of the vane 51 -57 and the radial direction R1 may be in the range of 10 to 50 degrees, advantageously in the range of 15 to 35 degrees, and still more advantageously in the range of 16 to 22 degrees.

The angle o2 between the vane 51 -57 and the radial direction R1 may be the same for each vane 51 -57. This is advantageous in view of the manufacturing of the vanes 51 -57, especially when the vanes 51 -57 are manufacture by casting. A change in the angle o2 between the vane 51 -57 and the radial direction R1 means that the form, the twist, the position etc. of the vane 51 -57 has to be changed.

The angle o2 between the vane 51 -57 and the radial direction R1 could, however, also be individual for each vane 51 -57. This may be an option in a situation where the vanes 51 -57 are manufactured from plates by forming and welding. The angle o2 for each vane 51 -57 would still be within the above specified ranges.

The vanes 51 -57 could also be grouped into two or more groups so that the angle o2 between the vane 51 -57 and the radial direction R1 is the same for all vanes 51 -57 within the group. The angle o2 between the vane 51 - 57 and the radial direction R1 would in such case be different for each group of vanes 51 -57.

Figure 8 shows an axonometric view of a vane in the propulsion unit of figure 1 .

The vane 51 in the support structure 50 may have an at least substantially air-foil shaped cross section, whereby the upstream end 51 A is formed as a rounded leading edge and the downstream end 51 B is formed as a sharp trailing edge. The upstream end 51 A and the downstream end 51 B is connected with an upper surface and a lower surface. The vane 51 has a height H1 and a chord length L3. A centre plane P1 passes in the height direction through the chord length line at the lower surface and at the upper surface of the vane 51 . The plane of the vane 51 may have a variable twist in relation to the centre plane P1 along the length of the vane 51 . The twist of the vane 51 may adapted to the twist of the blades 41 -44 of the propeller 40. The twist of the vane 51 in relation to the twist of the blades 41 -44 of the propeller 40 may produce a substantially opposite rotation force to the water flow leaving the blades 41 -44 of the propeller 40. The idea with the vanes 51 -57 is thus to turn the rotational component of the water flow downstream of the propeller 40 into axial thrust. The profile of the cross section of the vane 51 -57 may be a NACA profile.

Figure 9 shows a cross sectional view of the nozzle of the propulsion unit of figure 1 .

The figure shows the propeller shaft 31 , the shaft line X-X, the propeller 40, the propeller hub 45, a radial centre plane 46 of the propeller 40, the support construction 50 the end portion 22A of the support frame 20, the nozzle 60, the upstream end 61 of the nozzle 60, and the downstream end of the nozzle 60.

The figure shows further:

Da, which is the diameter of the upstream end 61 of the nozzle 60, da, which is the diameter of the hub 45 at the upstream end 61 of the nozzle 60,

Dp, which is the diameter of the downstream end 62 of the nozzle 60,

dp, which is the diameter of the end portion 22A of the support frame 20 at the downstream end 62 of the nozzle 60,

Din, which is the diameter of the nozzle 60 at the axial middle point of the propeller 40,

din, which is the diameter of the hub 45 at the axial middle point of the propeller 40.

The following definitions are made:

where Sa is the section area of the upstream end 61 of the nozzle 60 and Sin is the section area of the rotor disc, β =— where Sp is the section area of the downstream end 61 of the nozzle 60 and Sin is the section area of the rotor disc,

{D a 2 - d¾ (Dj - dj) The thrust of the propeller 40 is maximized when a is within the range of 1 .15 to 1 .35, advantageously within the range of 1 .20 to 1 .30.

The efficiency of the propeller 40 is maximized when β is within the range of 1 .00 to 1 .10.

The electric power needed for a steering electric motor or motors within the hull 1 1 of the vessel 10 and to a driving electric motor 30 within the casing 20 may be produced within the hull 1 1 of the vessel 10. The electric power may be produced by one or more generators connected to a combustion engine. The electric power to a driving electric motor 30 within the casing 20 may be supplied by cables running from the generator within the interior of the hull 1 1 of the vessel 10 to the casing 20. A slip ring arrangement may be used in connection with the turning wheel within the hull 1 1 of the vessel 10 in order to transfer electric power from the stationary hull 1 1 to the rotatable casing 20.

The centre axis X-X of the propeller shaft 31 is directed in the horizontal direction in the embodiment shown in the figures. The centre axis X- X of the propeller shaft 31 could, however, be inclined in relation to the horizontal direction. The lower portion 22 i.e. the gondola of the casing 20 would thus be inclined in relation to the horizontal direction. This might in some circumstances result in hydrodynamic advantages.

The angle a1 between the axis Y-Y of rotation of the casing 20 and the shaft line X-X is advantageously 90 degrees, but it could be less than 90 degrees or more than 90 degrees.

The use of the propulsion unit is naturally not restricted to the arrangements shown in the figures.

The figures show a support frame 20 in the form of a casing 20 being rotatable attached to a hull 1 1 of the vessel 10. The casing 20 could naturally also be fixedly attached to the hull 1 1 of the vessel 10 instead of being rotatable attached to the hull 1 1 of the vessel 10.

The figures show a situation in which the driving motor 30 in the form of an electric motor 30 is situated horizontally in the lower portion 22 of the casing 20. The driving motor 30 may, however, be positioned vertically in the upper portion 21 of the casing 20. An additional shaft would then be needed extending vertically downwards from the driving motor 30 to the propeller shaft 31 . The two shafts would then be operatively connected with a cogwheel arrangement. The driving motor 30 would then drive the propeller 40 via the two perpendicular shafts.

Another possibility would be to position the driving motor 30 within the hull 1 1 of the vessel 10. An additional shaft would then be needed extending vertically downwards from the driving motor 30 from the interior of the hull 1 1 of the vessel 10 to the propeller shaft 31 . The two shafts would then be operatively connected with a cogwheel arrangement. The driving motor 30 would then drive the propeller 40 via the two perpendicular shafts.

The propulsion unit could further be used in connection with a vessel 10 provided with a prime mover 30 within the hull 1 1 of the vessel 10. The propeller shaft 31 would then extend from the interior of the hull 1 1 of the vessel 10 through an opening at an aft end of the hull 1 1 of the vessel 10 to the propeller 40. The prime mover 30 within the hull 1 1 of the vessel 10 would then drive the propeller 40. The support frame 20 would not be in the form of a casing 20 extending downwards from the hull 1 1 of the vessel 10 as shown in the figures. The propeller shaft 31 would protrude directly out from an aft end of the hull 1 1 of the vessel 10. The support frame 20 could be formed of a stationary rudder part extending downwards from the hull 1 1 of the vessel 10. A stationary shaft could be provided on a lower end of the stationary rudder part. The stationary shaft would form an essentially cylindrical frame portion 22A protruding into the nozzle 60 from the downstream end 62 of the nozzle 60. The support structure 50 would then extend between the cylindrical frame portion 22A forming the stationary shaft and the inner perimeter of the nozzle 60. The prime mover 30 may be a combustion engine or an electric engine. The propeller 40 would in this solution push the vessel 10 in the forward direction S1 .

The vessel could naturally be provided with one or more shaft lines, each shaft line extending from the interior of the hull 1 1 of the vessel 10 through an opening at an aft end of the hull 1 1 of the vessel 10 to the propeller 40. One or several or all of the shaft lines could be provided with the propulsion unit according to the invention. The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.