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 on a support frame. A support construction formed of vanes may be provided downstream and/or upstream of the propeller. The propeller may be supported from a central hub on a propeller shaft and/or from the periphery of the propeller to the nozzle. An electric motor may be used to drive the propeller shaft directly or through a transmission. Another possibility is to use a rim drive electric motor comprising a rotor on the outer perimeter of the propeller and a stator in the nozzle to drive the propeller.

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 minimum axial distance between the blades of the propeller and the vanes of the support construction should be small so that the vanes are able to efficiently recover the rotational energy created by the blades of the propeller. This minimum axial distance may be in the range of 0.5 to 10%, advantageously in the range of 1 to 5%, of a diameter of the propeller. The vanes should thus be close to the propeller blades in order to be able to recover as much as possible of the rotational flow components produced by the propeller into substantially axial thrust. This will increase the total thrust produced by the propeller.

The support construction may be positioned downstream and/or upstream of the propeller.

The water flow will in case the vanes are positioned upstream of the propeller pass through the support construction to the propeller. The vanes in the support construction will then redirect the incoming water flow into a swirl in an opposite direction of the propeller rotation, whereby energy that is normally lost in wake rotation is recovered. The water flow will in case the vanes are positioned after the propeller pass from the propeller through the support construction. The vanes in the support construction will then redirect the swirls in the water flow from the propeller into substantially axial thrust, whereby energy that is normally lost in wake rotation is recovered.

The format, the position, the angle and the number of the vanes can in both cases be optimized in view of redirecting as much as possible of the rotational components of the water flow into axial thrust.

The direction of each vane may be 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 when the vanes are inclined in relation to the radial direction. 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. The use of inclined vanes may be advantageous especially in case the support construction is positioned downstream of the propeller. The bending forces of the water pulses originating from the propeller blades are much more prominent on a support construction positioned downstream of the propeller.

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 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 a vertical view in the longitudinal direction of a first embodiment of a propulsion unit,

Figure 2 shows a vertical view in the transverse direction from the front of a propulsion unit,

Figure 3 shows a second vertical view in the transverse direction from the aft of the propulsion unit,

Figure 4 shows a vertical view in the longitudinal direction of a second embodiment of the propulsion unit,

Figure 5 shows a support arrangement of the propulsion unit,

Figure 6 shows a cross sectional view of a vane in the propulsion unit,

Figure 7 shows a cross sectional view of the nozzle in the propulsion unit,

Figure 8 shows a cross sectional view of a peripheral support of the propeller in the propulsion unit,

Figure 9 shows a cross sectional view of a blade in a propeller.

DETAILED DESCRIPTION OF THE INVENTION

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

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 25 being concentric with the shaft line X-X. The nozzle 60 may comprise a first end opening 61 and a second end opening 62 opposite to the first end opening 61 . The first end opening 61 forms an upstream opening and the second end opening 62 forms a downstream opening in this embodiment.

The support frame 20 extends downwards from a hull 1 1 of a vessel

10. The support frame 20 may have substantially the form of a letter C. The support frame 20 may comprise an upper portion 21 , an intermediate portion 22, and a lower portion 23.

The upper portion 21 of the support frame 20 may be positioned above the nozzle 60. The intermediate portion 22 of the casing 20 may extend downwards from the upper portion 21 outside the nozzle 60. The intermediate portion 22 may be positioned downstream of the nozzle 60. The lower portion 23 of the support frame 20 may extend into the nozzle 60. A first end 23A of the lower portion 23 may extend to the vicinity of the propeller 40. A longitudinal centre line of the lower portion 23 of the support frame 20 may be concentric with the shaft line X-X. The upper portion 21 and the intermediate portion 22 of the support frame 20 may have at least substantially an air-foil shaped cross section, whereby the upstream edge of the upper portion 21 and of the intermediate portion 22 is formed as a rounded leading edge and the downstream edge of the upper portion 21 and of the intermediate portion 22 is formed as a sharp trailing edge. The lower portion 23 of the casing 20 may have the form of a gondola having a first end 23A and a second end 23B. The first end 23A may form a front end and the second end 23B may form an aft end of the gondola 23. The gondola 23 may have at least substantially an air- foil shaped cross section, whereby the first end 23A is formed as a rounded leading edge and the second end 23B is formed as a sharp trailing edge. The first end 23A of the gondola 23 and the second end 23B of the gondola 23 is connected with an upper surface and a lower surface. The first end 23A of the gondola 23 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 support frame 20 and especially the upper portion 21 and the middle portion 22 of the support frame 20 may also form a rudder of the vessel 10. The upper portion 21 , the intermediate portion 22, and the lower portion 23 of the support frame 20 may be formed of one or more parts. The upper portion 21 , the intermediate portion 22, and the lower portion 23 could be manufactured separately and then finally be welded together into one entity. The lower portion 23 may form a hollow compartment accommodating different equipment. The upper portion 21 and the intermediate portion 22 may also be hollow. It would thus be possible for a technician to enter into the support structure 20 from the top of the upper portion 21 and to climb down through the intermediate portion 22 to the lower portion 23 by a ladder. The technician could then perform maintenance tasks to the equipment in the lower portion 23 of the support frame 20.

The upper end of the upper portion 21 of the support frame 20 may comprise a flange 25 through which the support frame 20 may be attached to a counter flange, which is operatively connected to a slewing arrangement within the vessel 10. The flange 25 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 support frame 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, whereby the support frame 20 and the propulsion unit 100 is turned along with the turning wheel. The support frame 20 is thus rotatable supported at the hull 1 1 of the vessel 10. The support frame 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.

A propeller shaft 25 may be positioned within the lower portion 23 of the support frame 20. The propeller shaft 25 may rotate around the shaft line X-X. The propeller shaft 25 may be rotatably supported with bearings 26, 27 within the lower portion 23 of the casing 20. One end of the propeller shaft 25 may protrude out from the first end 23A of the lower portion 23 of the support frame 20. The propeller shaft 25 may be sealed with a sealing 28 in the opening at the first end 23A of the lower portion 23 of the support frame 20 through which opening the propeller shaft 25 passes from the interior of the lower portion 23 of the support frame 20 to the exterior of the lower portion 23 of the support frame 20. The seal 28 prevents water from penetrating into the lower portion 23 of the support frame 20. The propeller 40 may be attached via a hub 45 to the outer end of the propeller shaft 25. The propeller 40 rotates with the propeller shaft 25. The bearings 26, 27 may be oil lubricated roller bearings.

A first radial plane Y1 passes through an axial X-X middle point of the rotor rim 51 . The first radial plane Y1 is situated outside the first end 23A of the lower portion of the support frame 20.

A second radial plane Y2 passes through an axial X-X middle point between the bearings 26, 27.

The first radial plane Y1 and the second radial plane Y2 may be at an axial X-X distance A1 from each other.

The support construction 50 may support the nozzle 60 on the support frame 20. The upstream end portion 23A of the support frame 20 may extend from the downstream end 62 of the nozzle 60 into a portion of the nozzle 60. The upstream end portion 23A of the support frame 20 may have a substantially cylindrical form. The centre line of the cylinder may be concentric with the shaft line X-X. The upstream end 23A 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 lower portion 23 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 lower portion 23 of the support frame 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. Any disturbing elements such as vanes may thus be omitted upstream of the propeller 40 within the nozzle 60. The nozzle 60 is attached to the lower portion 23 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 support frame 20 and especially the upper portion 21 and the middle portion 22 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 first end opening 61 at the inlet and the second end opening 62 at the outlet 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 annular nozzle 60 may be fixedly attached to the lower portion 23 of the support frame 20 with the support construction 50. The vanes 51 -57 of the support construction 50 may extend between the nozzle 60 and the lower portion 23 of the support frame 20. The vanes 51 -57 may extend inwards from the nozzle 60 to the lower portion 23 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 lower portion 23 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 lower portion 23 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 lower portion 23 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 lower portion 23 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 opening 61 of the central duct 65 to the second end opening 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 a first end opening 61 at the upstream end forming an inlet opening 61 and a second end opening 62 at the downstream end 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 support frame 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 starting from the first end opening 61 is formed as a rounded leading edge and the downstream end starting from the second end opening 62 is formed as a sharp trailing edge. The upstream end of the nozzle 60 and the downstream end of the nozzle 60 is connected with an upper surface and a lower surface.

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 support frame 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 and the outlet end 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 and the outlet end of the nozzle 60. A portion of the vanes 51 -57 could extend outside of the outlet end of the nozzle 60. This would mean that the lower portion 23 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 lower portion 23 of the support frame 20 outside the downstream end of the nozzle 60 and an outer end of the lower portion 23 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 4 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. The uppermost portion of the nozzle 60 may on the other hand be attached to the upper portion 21 of the support frame 20. The form of the upper portion 21 of the support frame 20 may be such that the nozzle 60 fits into the lower surface of the upper portion 21 of the nozzle 20.

The downstream end of the nozzle 60 may be at the same vertical plane as the upstream edge of the middle portion 22 of the middle portion 22 of the support frame 20.

A rim drive electric motor 30 is used to drive the propeller 40. The rime drive electric motor 30 may be an induction motor comprising a rotor rim 31 and a stator 52. The rotor rim 31 is arranged on the outer perimeter of the propeller 40 i.e. on the outer tips of the propeller blades 41 -44. The rotor rim 31 rotates with the propeller 40. The stator 32 is arranged within the nozzle 60. The stator 32 surrounds the rotor rim 31 . The rotor rim 31 may comprise permanent magnets forming a permanent magnet rotor.

The rim drive electric motor 30 generates a high torque, which is beneficial in propulsion applications. The high torque is due to the great diameter D1 of the rotor rim 31 in the rim drive electric motor 30. The torque of an electric motor is proportional to the volume of the electric motor. The volume of the rim drive electric motor 30 is increased by the great diameter D1 of the rim drive electric motor 30. A rim drive electric motor 30 can be designed so that sufficient cooling of the stator 32 directly to the surrounding sea water can be achieved. Also the rotor rim 31 of the rim drive electric motor 30 can be cooled directly to the surrounding sea water.

The rotor rim 31 rotates in an annular groove 66 extending radially outwards from an inner surface of the nozzle 60. A passage P1 is arranged in the annular groove 66 between the rotor rim 31 and the stator 32 allowing water to pass through said passage P1 when sea water is passing through the central duct 65 in the nozzle 60. The sea water flowing in the passage P1 will cool both the rotor rim 31 and the stator 32. The stator 32 of the rim drive electric motor 30 will also be cooled by sea water passing on the outer surface of the nozzle 60. The outer surface of the nozzle 60 is large due to the big diameter of the nozzle 60 and forms therefore a large cooling surface for the stator 32, said large cooling surface being in direct contact with sea water. The cooling of the stator 32 can thus be arranged as a passive cooling directly through the shell of the nozzle 60 to the sea water surrounding the shell of the nozzle 60.

Figure 4 shows a vertical view in the longitudinal direction of a second embodiment of the propulsion unit. This second embodiment differs from the first embodiment in the construction of the support frame 20. The support frame 20 comprises only an upper portion 21 and a lower portion 23 being formed as two separate entities. The uppermost portion of the nozzle 60 is attached to the lower surface of the upper portion 21 of the support frame 20. The lower portion 23 of the support frame 20 is attached only with the support construction 50 to the nozzle 60. This second embodiment makes it possible to use a nozzle 60 that is longer in the axial direction X-X. This second embodiment makes it also possible to use in the axial direction X-X wider vanes 51 -57 in the support construction 50. The area of the vanes 51 -57 may thus be increased, whereby the number of vanes 51 -57 may be reduced. A smaller number of vanes 51 -57 will increase the efficiency of the support construction 50.

Figure 5 shows a support arrangement of the propulsion unit.

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 a2 between the vane 51 - 57 and the radial direction R1 would in such case be different for each group of vanes 51 -57.

Figure 6 shows an axonometric view of a vane in the propulsion unit.

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 A2. 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.

The geometry of the vane 51 -57 in the support structure 50 may be optimized in order to work in interaction together with the propeller blade. The pitch of the vane 51 -57 i.e. the twist of the vane 51 -57 around the vane ^' s 51 - 57 centre line, is not constant over the entire length of the vane 51 -57 in the support structure 50. The pitch varies in accordance with the vane ^' s 51 -57 radius i.e. the distance from the shaft line outwards along the vane 51 -57. The vane ^' s 51 -57 have a twist opposite to the twist of the blades 41 -44 in the propeller 40 in order to redirect the swirls in the flow of the propeller 40.

The ratio of the vanes 51 -57 expanded vane-area to the disc area AE/AO is advantageously in the range of 0.4 to 0.7. The expanded vane-area converts the vane from its helix to a flat plane. The disc area is the area of a disc positioned in an axial centre point of the support structure 50 i.e. the cross sectional area of the central duct 65 at the axial middle point of the support structure 50. Figure 7 shows a cross sectional view of the nozzle of the propulsion unit.

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 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 may be flush with the inner surface of the nozzle 60.

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 A3 in the range of 0.35 to 0.65 times the diameter D1 of the propeller 40.

The propeller 40 may be positioned axially X-X within the nozzle 60 so that an axial X-X distance A4 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.

A minimum axial X-X distance A5 between the blades 41 -44 of the propeller 40 and the vanes 51 -57 of the support construction 50 may be in the range of 0.5 to 10%, advantageously in the range of 1 to 5%, of the diameter D1 of the propeller 40. The minimum axial X-X distance A5 is in this embodiment the minimum axial X-X distance between a point on a trailing edge of the blades 41 -44 of the propeller 40 and a corresponding point on a leading edge of the vanes 51 -57 of the support structure 50 in a situation in which the propeller blade 41 -44 is in a position where said axial X-X distance A5 reaches a minimum. Said axial distance may vary along the radial direction of the support structure 50 and the propeller 40. Said distance may e.g. reach a minimum at the root of the propeller blade and a maximum at the tip of the propeller blade. Said distance may vary linearly or nonlinearly or randomly between said end points.

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:

S

a ⁼ s i ^~ n 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 =—

in where S is the section area of the downstream end 61 of the nozzle

60 and Sin is the section area of the rotor disc, a = ^ {D _a ² - d _a ² ) S _p = ^ (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.

Figure 8 shows a cross sectional view of a peripheral support of the propeller in the propulsion unit. An annular support plate 46 is arranged on the outer perimeter of the propeller 40. The support plate 46 rotates with the propeller 40 within the nozzle 60. The support plate 46 is rotatable supported with bearings 67, 68 within the nozzle 60.

The hub 45 of the propeller 40 is in the figures 1 -7 supported on a propeller shaft 25 so that the hub 45 rotates with the propeller shaft 25. The propeller 40 is on the other hand in figure 8 rotatably supported from the outer perimeter with bearings 67, 68 to the nozzle 60. The propeller shaft 25 and also the hub 45 could be left out in the embodiment shown in figure 8. Another possibility would be to support the propeller 40 from the hub 45 on the propeller shaft 25 and from the outer perimeter with bearings 67, 68 to the nozzle 60. The vanes 51 -57 in the support construction 50 could extend inwards in the duct 65 formed by the nozzle 60. There would not be any need for the middle portion 22 and the lower portion 23 of the support frame 20 in such a solution. The inner ends of the vanes 51 -57 could be left free or attached to each other directly or via a centre part.

Figure 9 shows a cross sectional view of a blade in a propeller. The figure shows the hub 45, the propeller blade 41 and the direction of rotation R10 of the propeller 40. The transverse sweeping of the blade 41 shows an asymmetrical shape when viewing the blade from fore or aft. The propeller blade 41 is a blade of a skew propeller. Aft skew is positive skew, where the blades sweep in the direction opposite to the direction of rotation of the propeller 40. Forwards skew is negative skew, where the blades sweep in the same direction as the rotation of the propeller 40. The propeller 40 in the figure has a positive skew. The propulsion unit 100 may be provided with a skew propeller 40 having a positive skew or a negative skew.

The electric power needed for a steering electric motor or motors within the hull 1 1 of the vessel 10 and to the rime drive electric motor 30 may be produced within the hull 1 1 of the vessel 10. The electric power to the rime drive electric motor 30 may be supplied by cables running from the generator within the interior of the hull 1 1 of the vessel 10 to the nozzle 60. 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 through the rotatable support frame 20 to the nozzle 60.

The axis X-X of rotation of the propeller shaft 25 is directed in the horizontal direction in the embodiment shown in the figures. The axis X-X of rotation of the propeller shaft 25 could, however, be inclined in relation to the horizontal direction. The lower portion 23 i.e. the gondola of the support frame 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 support frame

20 and the axis X-X of rotation of the propeller shaft 25 is advantageously 90 degrees, but it could be less than 90 degrees or more than 90 degrees.

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 support frame 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 support structure 50 is positioned downstream of the propeller 40. The support structure 50 could instead be situated upstream of the propeller 40. The first alternative is an advantageous embodiment in the sense that the efficiency is 1 to 2% higher compared to the second alternative. It is on the other hand easier to control the vibrations of the propulsion unit in the second alternative. There could also be additional supports in the form of vanes on the opposite side of the propeller 40 compared to the support structure 50. These additional supports might on the other hand slightly reduce the efficiency of the propulsion unit 100.

The figures show a situation in which the propeller 40 is a pulling propeller. The propeller 40 pulls the vessel 10 in the forwards direction S1 of the vessel 10. The pulling propeller 40 is positioned at the front end of the propulsion unit 100. The invention could also be used in connection with a pushing propeller 40.

The figures show a situation in which the propeller 40 is driven by a rim drive electric motor 30. This is an advantageous embodiment, but the propeller 40 could instead by driven by an electric motor positioned in the lower portion 23 of the support frame 20. The electric motor would then drive the propeller shaft 25 directly or through a transmission. Another possibility would be to position the electric motor in the middle portion 22 of the support frame 20 or within the vessel 10. Power from the electric motor could be transferred via a vertical shaft to the propeller shaft 25. The vertical shaft could be connected with a cog wheel arrangement to the propeller shaft 25. The electric motor could be positioned vertically or horizontally within the vessel 10.

The propeller 40 in the propulsion unit 100 is advantageously a skew propeller, but also a non-skewed propeller 40 may be used. The diameter D1 of the propeller 40 may be in the order of 5000 mm or more in big vessels. The minimum axial distance A5 between the propeller blades 41 -44 and the vanes 51 -57 in the support construction 50 is 0.5 to 10%, advantageously 1 to 5%, of the diameter D1 of the propeller 40 i.e. in the range of 50 to 250 mm when the diameter D1 of the propeller 40 is 5000 mm. The chord length in the axial X-X direction of the propeller blades 41 -44 of such a propeller 40 may be in the range of 1000 to 1800 mm. The minimum axial distance A5 (50 to 250 mm) calculated as per cents of the axial X-X chord length of the propeller blades 41 -44 would thus be in the range of 5 to 25% of the axial X-X chord length of the propeller blades 41 -44.

The invention and its embodiments are not limited to the examples described above but may vary within the scope of the claims.