NL2018880B1

NL2018880B1 - Improved thruster for propelling a watercraft

Info

Publication number: NL2018880B1
Application number: NL2018880A
Authority: NL
Inventors: Breuers-Dressler Jan; Christian Eberhard Yannick; Weinrich Bernd
Original assignee: Veth Propulsion B V
Priority date: 2017-05-09
Filing date: 2017-05-09
Publication date: 2018-11-15

Abstract

Thruster for propelling a watercraft, comprising - a first propeller arranged on a propeller shaft to be rotated during operation of the thruster so as to be capable of causing a waterflow downstream the first propeller; - a motor for driving the propeller shaft, comprising a rotatable output shaft; - a drive arrangement coupling the propeller shaft to the output shaft of the motor, the drive arrangement comprising a rotatable drive shaft and a coupling arrangement arranged between the drive shaft and the output shaft of the motor for coupling the drive shaft to the output shaft of the motor, the drive shaft extending in substantially the same direction as the output shaft of the motor, and the propeller shaft being perpendicular to both the drive shaft and the output shaft of the motor; and - a housing arrangement arranged downstream the first propeller, the housing arrangement comprising a gearbox portion for accommodating the propeller shaft and other components including gearing components, an end of the drive shaft extending into the gearbox portion, and a tube-shaped housing portion accommodating and surrounding a part of the drive shaft, connecting to the gearbox portion at one side thereof; wherein the tube-shaped housing portion comprises a housing tip portion facing away the first propeller, the tip portion locating at substantially one side of a plane extending through the centreline of both the propeller shaft and the drive shaft, at which side the first propeller is moving in a first quadrant wherein a blade of the first propeller is moving away from the motor.

Description

IMPROVED THRUSTER FOR PROPELLING A WATERCRAFT FIELD OF THE INVENTION

The invention relates to a thruster for propelling a watercraft such as a ship, a boat, or a submarine. The invention furthermore relates to a watercraft comprising at least one thruster.

BACKGROUND OF THE INVENTION A thruster for propelling a watercraft is a well-known device. One watercraft may be equipped with more than one thruster. In general, a thruster comprises a wet portion and a dry portion, i.e. a portion that is intended to extend from a watercraft into the water under normal circumstances of the watercraft floating on/in water, and a portion that is intended to be accessible from the interior of the watercraft and not to be contacted by water. Typically, the wet portion comprises at least one propeller arranged on a propeller shaft to be rotated during operation of the thruster, and a housing arrangement comprising a gearbox portion for accommodating the propeller shaft and other components including gearing components, and a more or less elongated tubeshaped housing portion connecting to the gearbox portion at one side thereof, which serves for accommodating and surrounding a part of a drive shaft that is used for driving the propeller shaft. An end of the drive shaft extends into the gearbox portion, and the propeller shaft is coupled to the drive shaft through suitable gearing as present in the gearbox portion, extending perpendicular to the drive shaft and the output shaft of the motor. Optionally, the thruster is provided with a hollow cylindrical component that is designed to function as a nozzle, at a position for surrounding the at least one propeller. The dry portion comprises a motor for driving the propeller shaft through the drive shaft, the drive shaft being coupled to an output shaft of the motor through a coupling arrangement, and foundation components for supporting the motor and other components of the dry portion, and providing a basis from which components of the wet portion and components located at the interface of the dry portion and the wet portion are suspended. Furthermore, in order to prevent water from reaching the dry portion, the dry portion is closed at a side thereof facing the wet portion, by means of suitable sheeting, for example, and a watertight sealing arrangement is located at the interface of the dry portion and the wet portion.

In the following, for the sake of clarity, the direction in which the drive shaft and the output shaft of the motor normally extend will be referred to as vertical direction, and the direction in which the propeller shaft normally extends will be referred to as horizontal direction, which should not be understood such as to mean that the invention is limited to situations in which the respective shafts have an exact vertical and horizontal orientation. Furthermore, indications such as “lower” and “higher” or “upper” as used in this text are to be understood so as to refer to a normal, operational orientation of a thruster in which the gearbox portion and the at least one propeller are situated at the lowest level, and in which the motor and the foundation components are situated at the highest level, without limiting the invention to such orientation.

In a watercraft that is equipped with one or more thrusters, each thruster is fixedly attached to the watercraft at a suitable position on the watercraft’s hull, and each thruster has a function in realizing movement of the watercraft. Operating a thruster involves having the motor of the thruster in an active state, as a result of which the output shaft of the motor, the drive shaft, and the propeller shaft and the propeller associated with the propeller shaft are rotated. Due to the interaction of the rotating propeller with the water surrounding it, a movement of the propeller in a direction in which the propeller shaft extends is realized, and as a result of the thruster being fixedly attached to the watercraft, the entire watercraft is moved. Normally, the thrusters are arranged on a longitudinal centerline of the watercraft and/or in pairs, at opposite sides of the longitudinal centerline, in a symmetrical fashion. Thrusters comprising a single propeller are known, but it is also a practical option for thrusters to comprise two propellers, particularly contra-rotating propellers, in which case the gearbox portion is designed to support two propellers and to accommodate two propeller shafts and suitable gearing for coupling each of the propeller shafts to the drive shaft.

It is to be noted that a thruster is an assembly of the components as mentioned in the foregoing, particularly a number of stationary components and a number of movable/rotatable components, and furthermore comprises additional components such as oil tubes or bearings of the drive shaft and the propeller shaft, which will not be further deliberated on here.

In the field of thrusters suitable for use with a watercraft, a type of thrusters known as azimuth thrusters is known. An azimuth thruster has a steering function besides a propelling function, so that in a watercraft that is equipped with one or more azimuth thrusters, a rudder can be omitted. Generally speaking, an azimuth thruster comprises an azimuth arrangement for setting an angular position of the propeller shaft with respect to stationary components of the thruster. It is known for the azimuth arrangement to comprise a slewing bearing including an outer ring that is coupled to the tube-shaped housing portion and the gearbox portion in such a way that the tubeshaped housing portion and the gearbox portion rotate along with the ring when the angular position of the ring is adjusted. For the purpose of rotating the outer ring of the slewing bearing to any desired angular position, the azimuth arrangement furthermore comprises at least one motor-driven pinion engaging with the ring. The azimuth arrangement comes with a system for processing steering input, i.e. input relating to a desired direction of movement of the watercraft, and controlling operation of the motor(s) for driving the at least one pinion so that an appropriate angular position of the outer ring of the slewing bearing is set at any time, and thereby an appropriate angular position of the tube-shaped housing portion, the gearbox portion and the propeller shaft accommodated by the gearbox portion. Such a device is in general well known in the field of application.

It is a drawback of such a thruster that the portion that is intended to extend from a watercraft into the water under normal circumstances of the watercraft floating on/in water, causes a resistance to the ongoing watercraft propelling in the water, resulting in a loss of power and thus a low efficiency of the drive system of the watercraft.

It is an object of the invention to reduce the loss of power and to improve the efficiency of the drive system of the watercraft. WO2011/110226 discloses a thruster comprising a shank with a trailing edge, wherein in one embodiment the trailing edge from top to bottom curves away from a vertical plane defined by the propeller shaft. EP2281743 discloses a thruster comprising a strut with a trailing edge, wherein in one embodiment the trailing edge from top to bottom curves away from a vertical plane defined by the propeller shaft. DE4440738 discloses a thruster, but does not appear to describe a change in the cross-section wherein the trailing edge curves closer to the plane from top down.

SUMMARY OF THE INVENTION

The invention provides a thruster for propelling a watercraft, comprising - a first propeller arranged on a propeller shaft to be rotated during operation of the thruster so as to be capable of causing a waterflow downstream the first propeller; - a motor for driving the propeller shaft, comprising a rotatable output shaft; - a drive arrangement coupling the propeller shaft to the output shaft of the motor, the drive arrangement comprising a rotatable drive shaft and a coupling arrangement arranged between the drive shaft and the output shaft of the motor for coupling the drive shaft to the output shaft of the motor, the drive shaft extending in substantially the same direction as the output shaft of the motor, and the propeller shaft being perpendicular to both the drive shaft and the output shaft of the motor; and - a housing arrangement arranged downstream the first propeller, the housing arrangement comprising a gearbox portion for accommodating the propeller shaft and other components including gearing components, an end of the drive shaft extending into the gearbox portion, and a tube-shaped housing portion accommodating and surrounding a part of the drive shaft, connecting to the gearbox portion at one side thereof; wherein the tube-shaped housing portion comprises a housing tip portion facing away the first propeller, the tip portion locating at substantially one side of a plane extending through the centreline of both the propeller shaft and the drive shaft, at which side the first propeller is moving in a first quadrant wherein a blade of the first propeller is moving away from the motor, and wherein the tip portion extends from a first end facing the gearbox portion to a second end facing the motor, the tip portion of the first end being nearer to the plane than the tip portion of the second end..

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to a thruster for propelling a watercraft according to claim 1. In this way, a part of the waterflow generated by the first propeller, which part of the waterflow is actually passing along the tube-shaped housing portion downwardly protruding from the hull of the watercraft, is capable of being guided along the skin of the housing portion and of being released at the tip portion thereof with a limited amount of eddies and vortices caused by the waterflow leaving the tip portion of the tube-shaped housing portion. The limited amount of eddies and vortices results in a low resistance the propeller causes when operating in the water and thus contribute to an improved performance. The limited amount of eddies and vortices further results in a limited amount of contact noise causing acoustic noise and vibrations to be noticed inside the watercraft.

According to the invention, the tip portion extends from a first end facing the gearbox portion to a second end facing the motor, the tip portion of the first end being nearer to the plane than the tip portion of the second end. In this way, the waterflow passing the housing portion at the second end side is capable of being guided along the housing portion during a longer time than the waterflow passing the housing portion at the first end side thereof, which is advantageously since the torque exerted on the water, and thus the speed of the waterflow passing the housing portion at the second end side is larger than the waterflow passing the housing portion at the first end side thereof.

In an embodiment, the tip portion, when considered in a view along the plane, is extending from the first end to the second end according to a continuous increment curve. In this way, the tip portion is shaped in a way to allow a gradually increasing twist over the length of the tip portion extending from the first end to the second end thereof so as to cause an improved release of waterflow keeping occurrence of eddies and vortices low. The more away, radially from the first end of the tip portion, the larger the torque generated by the first propeller, the more the waterflow is accelerated, locally. When this locally more accelerated water passes along the tip portion at the second end thereof, the waterflow needs to be guided along it during a longer time for a minimum loss due to waterflow release at the tip portion.

In an embodiment, the tip portion, when considered in a view along the plane, is extending from the first end to the second end according to a continuous increment curve proportional with a distance to the first end of the tip portion. In this way, the tip portion is shaped in a progressive way to allow a progressively increasing twist over the length of the tip portion extending from the first end to the second end thereof so as to cause a further improved release of waterflow keeping occurrence of eddies and vortices even lower. The progressively increasing twist is proportional with the progressing increasing torque generated by the first propeller, considered from the first end to the second end of the housing portion.

In an embodiment, the first end of the tip portion is spaced apart from the plane over a first distance in a range of 5 - 25 mm, preferably in a range of 10 - 20 mm, most preferably 15 mm, and wherein the second end of the tip portion is spaced apart from the plane over a second distance in a range of 15 - 45 mm, preferably in a range of 25 - 40 mm, most preferably 33 mm. In this way, the tip portion forms a fin having an optimal deflection with respect of the plane, causing a reduced amount of eddies and vortices caused by the waterflow leaving the tip portion of the tube-shaped housing portion. The reduced amount of eddies and vortices further result in a reduced amount of contact noise causing acoustic noise and vibrations to be noticed inside the watercraft.

In an embodiment, a cross section of the tube-shaped housing portion transverse to the centreline of the drive shaft is having a drop-shaped form, the dropshaped form preferably divided in a shorter circumferential side at the one side at which the first propeller is capable of moving in the first quadrant, so as to cause the waterflow guiding shorter at the shorter circumferential side. In this way, an optimal release of the waterflow becomes possible at the tip portion of the housing portion when the waterflow leaves the housing portion.

In an embodiment, a first cross section of the housing portion at the gearbox portion side, transverse to the centreline of the drive shaft forms a first outer shape, and a second cross section of the housing portion at the motor side, transverse to the centreline of the drive shaft forms a second outer shape, wherein the first cross section and the second cross section are substantially identical in shape but twisted with respect of each other along a centreline parallel to the drive shaft at a twist angle so as to allow the waterflow to be released by the tube-shaped housing portion with a reduced resistance. In this way, an optimal release of the waterflow becomes possible at the tip portion of the housing portion when the waterflow leaves the housing portion.

In an embodiment, the tip portion is having, from the first end to the second end, a flat strip-shaped surface forming direct edges at both sides of the surface so as to allow the waterflow to go straight when it passes along the tip portion of the tubeshaped housing. In this way, the edges facilitate waterflow to become detached from the skin of the tube-shaped housing in order to prevent the waterflow from taking the forms of eddies and vortices, or at least minimize or suppress these.

In an embodiment, the flat strip-shaped surface is having a width dimension extending between the direct edges at both sides of the surface, wherein the width is in a range of 6 - 20 mm, preferably 9-17 mm, most preferably between 11-14 mm. In this way, the waterflow is guided along the tube-shaped housing with a minimum resistance when the waterflow releases.

In an embodiment, the tip portion, when considered in a view transverse to the plane, is extending from the first end to the second end according to a continuous increment curve. In this way, the tip portion is shaped in a way to allow a gradually increasing tip over the length of the tip portion extending from the first end to the second end thereof so as to cause an improved release of waterflow keeping occurrence of eddies and vortices low. The more away, radially from the first end of the tip portion, the larger the torque generated by the first propeller, the more the waterflow is accelerated, locally. When this locally more accelerated water passes along the tip portion at the second end thereof, the waterflow needs to be guided along it during a longer time for a minimum loss due to waterflow release at the tip portion.

In an embodiment, the tip portion, when considered in a view transverse to the plane, is extending from the first end to the second end according to a continuous increment curve proportional with a distance to the first end of the tip portion. In this way, the tip portion is shaped in a progressive way to allow a progressively increasing tip over the length of the tip portion extending from the first end to the second end thereof so as to cause a further improved release of waterflow keeping occurrence of eddies and vortices even lower. The progressively increasing tip is proportional with the progressing increasing torque generated by the first propeller, considered from the first end to the second end of the housing portion.

In an embodiment, the tip portion, when considered in a view transverse to the plane, is extending from the first end to the second end according to a curved line with a distance to the first end of the tip portion. In this way, the tip portion forms a fin having an optimal extension considered from the centreline of the drive shaft, causing a reduced amount of eddies and vortices caused by the waterflow leaving the tip portion of the tube-shaped housing portion. The reduced amount of eddies and vortices further result in a reduced amount of contact noise causing acoustic noise and vibrations to be noticed inside the watercraft.

In an embodiment, the thruster further comprises: - a second propeller arranged on the propeller shaft to be rotated during operation of the thruster so as to be capable of causing a further waterflow downstream the second propeller, wherein the second propeller is arranged downstream of the tube-shaped housing portion; - the motor being adapted for driving the propeller shaft; - the drive arrangement being adapted for coupling the propeller shaft to the output shaft of the motor, the propeller shaft being perpendicular to both the drive shaft and the output shaft of the motor; and - the housing arrangement being adapted for comprising the gearbox portion for accommodating the propeller shaft. In this way, the power of the drive arrangement is enlarged by means of the second propeller, the second propeller taking advantage from the waterflow flowing from the first propeller along the tube-shaped housing portion including the tip portion capable to condition the waterflow and to direct it in such a way that the loss of speed of the waterflow due to release at the tip portion of the housing portion is reduced so that the second propeller receives the waterflow tailored to be processed by the second propeller.

In an embodiment, a tip of a blade of the first propeller is capable of rotating along a first circumscribed circle and a tip of a blade of the second propeller is capable of rotating along a second circumscribed circle, the diameter of which second circumscribed circle being smaller than the diameter of the first circumscribed circle. In this way, the second propeller is capable of taking the most effective part of the waterflow to almost such an extent that an adversely effect of the tube-shaped housing portion protruding downward from the hull of the watercraft into the waterflow, is hardly perceptible or at least reduced to a minimum.

In a further aspect of the invention, a watercraft is provided including a thruster according to any embodiments described above.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the invention, the drawings show aspects of one or more embodiments of the invention. However, it should be understood that the present invention is not limited to the precise arrangements and instrumentalities shown in the drawings, wherein:

Figure 1 shows a sectional view of the thruster according to the invention;

Figure 2 shows a sectional view of a tube-shaped housing portion of the thruster according to figure 1; and

Figure 3 shows a cross sectional view of the tube-shaped housing portion of the thruster according to figure 1 or 2.

It should be noted that items which have the same reference numbers in different figures, have the same structural features and the same functions, or are the same signals. Where the function and/or structure of such item has been explained, there is no necessity for repeated explanation thereof in the detailed description.

DETAILED DESCRIPTION OF THE DRAWINGS

The orientation of the thruster and the various components thereof as shown in the figures is related to the normal, operational orientation of the thruster. It is emphasized that indications such as “vertical”, “horizontal”, “lower” and “higher” or “upper” as used in the present description with reference to the figures are to be understood in the context of that normal, operational orientation, and not such as to be limiting to the scope of the invention in any way.

Figures 1-3 relate to a thruster 1 according to a preferred embodiment of the invention. In conformity with the general description of a thruster as provided in the foregoing, it is noted that the thruster 1 is designed to be used for propelling a watercraft in a direction S, wherein the direction S is indicated by an arrow pointing from the second propeller 12 to the first propeller 11, and to be fixedly attached to a watercraft at a suitable position on the watercraft’s hull, with an upper, dry portion 2 positioned inside the watercraft’s hull and a lower, wet portion 3 extending downwardly from the watercraft’s hull.

At a lowest level, the thruster 1 comprises two contra-rotating propellers 11, 12 for realizing (part of) the propulsion that is needed for moving a watercraft. As can be seen in figure 1, the propellers 11, 12 are arranged on respective propeller shafts 13, 14, at two sides of a gearbox portion 15 accommodating a number of components besides the propeller shafts 13, 14, such as gearing components 16 and bearings 17. The propeller shafts 13, 14 extend in substantially the same direction and at the same vertical level, one propeller shaft 13 extending from a central position inside the gearbox portion 15 to a first side of the gearbox portion 15, and the other propeller shaft 14 extending from the central position inside the gearbox portion 15 to a second, opposite side of the gearbox portion 15.

For the purpose of rotating the propeller shafts 13, 14 during operation, the thruster 1 is equipped with a motor 20. In this example, the motor 20 is a permanent magnet motor of which only the stator body 21 and the output shaft 22 are shown in figure 1. For the sake of clarity, other components which are known to be part of a permanent magnet motor, such as a rotor body and windings arranged thereon, are not shown. In such a case, the motor 20 is a gearless motor so that the motor 20 and the propeller shaft form a so called L-drive. Alternatively, the motor includes a gearbox in which the shaft of the motor is transverse to the output shaft 22 of the motor, so that the motor and the propeller shaft form a so called Z-drive.

The thruster 1 furthermore comprises a drive arrangement coupling the propeller shafts 13, 14 to the output shaft 22 of the motor 20, the drive arrangement comprising a rotatable drive shaft 31 and a coupling arrangement 32 arranged between the drive shaft 31 and the output shaft 22 of the motor 20 for coupling the drive shaft 31 to the output shaft 22 of the motor 20 at a highest end thereof. The drive shaft 31 extends in substantially the same direction as the output shaft 22 of the motor 20, namely in a substantially vertical direction, whereas the respective propeller shafts 13, 14 are perpendicular to both the drive shaft 31 and the output shaft 22 of the motor 20, i.e. extend in a substantially horizontal direction.

As explained in the foregoing, the gearbox portion 15 serves for accommodating the propeller shafts 13, 14 and other components 16, 17. A lower end 33 of the drive shaft 31 extends into the gearbox portion 15, engaging with respective gears for imposing rotary movement on the respective propeller shafts 13, 14 during operation of the thruster 1. A major part of the drive shaft 31 is accommodated in and surrounded by a steering tube 34, or, in other words, a tube-shaped housing portion 34, that connects to the gearbox portion 15 at a lower side thereof, and that preferably constitutes one integral housing arrangement in combination with the gearbox portion 15. Suitable bearings 35, 36 are arranged between the interior surface of the steering tube 34 and the drive shaft 31.

Advantageously, in order for the thruster 1 to be useful for determining a direction of movement of a watercraft once installed on the watercraft, the thruster 1 may be equipped with an azimuth arrangement. Within the framework of the invention, it is not essential that the thruster 1 has this added functionality of performing a steering action on a watercraft. When the thruster 1 comprises an azimuth arrangement, as is the case in the shown example, the azimuth arrangement is used for setting an angular position of the respective propeller shafts 13, 14 in the thruster 1, i.e. with respect to stationary components of the thruster 1. Thus, when an azimuth arrangement is present in the thruster 1, it is possible to vary the direction in which the propeller shafts 13, 14 extend in the horizontal plane with respect to the stationary components of the thruster 1 and consequently, when the thruster 1 is mounted on a watercraft, to the watercraft. In particular, the azimuth arrangement is configured and arranged to vary the horizontal angular position of the propeller shaft 13, 14 by varying the horizontal angular position of the assembly of the gearbox portion 15 and the steering tube 34. To this end, the azimuth arrangement comprises a slewing bearing including an outer ring 41 and an inner ring 42 about which the outer ring 41 is rotatable, and a steering flange 50, the outer ring 41 being supported on and fixedly connected to the steering flange 50, and the inner ring 42 being fixedly connected to a thruster foundation 61.

Various components of the thruster 1, such as the gearbox portion 15, the steering tube 34, the sleeve-shaped portion 53 of the steering flange 50 and the thruster foundation 61 have a function in covering rotating components and preventing water from reaching the components positioned inside. The thruster 1 is provided with two sealing arrangements 71, 72, one sealing arrangement 71 being arranged at the interface of the dry portion 2 and the wet portion 3 of the thruster 1, and the other sealing arrangement 72 being arranged between the steering flange 50 and the coupling arrangement 32.

The thruster 1 is operated by having the motor 20 in an active condition, i.e. a condition in which the output shaft 22 of the motor 20 rotates. The rotary movement of the output shaft 22 of the motor 20 is transmitted all the way down to the propeller shafts 13, 14 and the propellers 11, 12 through the coupling arrangement 32, the drive shaft 31 and the gears as present in the gearbox portion 15 and engaged by the lower end 33 of the drive shaft 31.

According to the invention, the housing arrangement is arranged downstream the first propeller 11 and the tube-shaped housing portion 34 comprises a housing tip portion 37 facing away the first propeller 11. The tip portion 37 locating at substantially one side of a plane extending through the centreline of both the propeller shaft 13 and the drive shaft 31, at which side the first propeller 11 is moving in a first quadrant wherein a blade of the first propeller 11 is moving away from the motor 20. The tip portion 37 extends from a first end 38 facing the gearbox portion 15 to a second end 39 facing the motor 20. According to the invention, the tip portion 37 of the first end 38 is nearer to the plane than the tip portion 37 of the second end 39.

Figure 2 shows a cross sectional side view of the tube-shaped housing portion 34 along the plane, the view indicating a contour or a curve of the tip portion 37 of the tube-shaped housing portion 34 to allow a minimum amount of eddies and vortices so as to reduce the resistance the tube-shaped housing portion 34 is causing when it is being moved through the water behind the first propeller 11 while the tube-shaped housing portion 34 is in the track or wake of the first propeller 11. In most cases, a height dimension of the tube-shaped housing portion 34 extending between the first end 38 to the second end 39, is in a range of 400 - 2500 mm. In this example, the height dimension is 800 mm.

Figure 3A - 3F show cross sectional top views of cross sections respectively depicted in figure 2 by the centerlines IIIA-IIIA up to IIIF-IIIF respectively. In case the height dimension H (depicted in figure 2) of the tube-shaped housing portion 34 is 800 mm, the first end 38 of the tip portion 37 is spaced apart from the plane over a first distance D1 in a range of 5 - 25 mm, preferably in a range of 10 - 20 mm, most preferably 15 mm. The second end 39 of the tip portion 37 is spaced apart from the plane over a second distance D2 in a range of 15 - 45 mm, preferably in a range of 25 - 40 mm, most preferably 33 mm.

The tip portion 37 is having, from the first end 38 to the second end 39, a flat strip-shaped surface 30 forming direct edges at both sides of the surface so as to allow the waterflow to go straight when it passes along the tip portion 37 of the tube-shaped housing 34. In this example, the flat strip-shaped surface 30 is having a width dimension extending between the direct edges at both sides of the surface, wherein the width is in a range of 6 - 20 mm, preferably 9-17 mm, most preferably between 11 -14 mm.

In the example according to figures 1 - 3, the thruster 1 is arranged to drive both the first and the second propeller 11, 12, the first propeller 11 driven in a rotational direction which is opposite a rotational direction of the second propeller 12. It is not essential however, that the tube-shaped housing portion 34 of the thruster 1 according to the invention requires the second propeller 12 to be equipped. The occurrence of eddies and vortices causing a loss of power is reduced by the design of the tip portion 37 of the tube-shaped housing portion 34 in case the first propeller 11 is placed upstream the tube-shaped housing portion 34. So in obtaining the goal to reduce the loss of power, the presence of the second propeller 12 is, thus, not essential. A thruster 1 being equipped with the second propeller 12, wherein the second propeller 12 is arranged downstream the tube-shaped housing portion 34, is, however, very advantageous since the waterflow to be received by the second propeller 12 is perfectly prepared by means of, or rather, even though the tube-shaped housing portion 34 and the first propeller 11 are arranged and operating upstream the second propeller 12. The tip portion 37 of the tube-shaped housing portion 34 is designed to arrange a conditioned waterflow wherein the eddies and vortices are minimized as much as possible so as to cause an optimized waterflow to be processed by the second propeller 12.

It will be clear to a person skilled in the art that the scope of the invention is not limited to the examples discussed in the foregoing, but that several amendments and modifications thereof are possible without deviating from the scope of the invention as defined in the attached claims. While the invention has been illustrated and described in detail in the figures and the description, such illustration and description are to be considered illustrative or exemplary only, and not restrictive.

The various components of the thruster 1 according to the invention can be made of any suitable materials, including metal materials and plastic materials.

The compact design of the dry portion 2 of the thruster 1 according to the invention can be combined with any suitable design of the wet portion 3 of the thruster 1. For example, the wet portion 3 may have a larger length when compared to the dry portion 2 than illustrated in the figures, wherein it is possible that a generally cone-shaped arrangement known per se is applied, which may serve for providing bearing support to the slewing bearing in case the thruster 1 is an azimuth thruster.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments.

In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb “comprise” and its conjugates does not exclude the presence of elements or steps other than those stated in a claim. The article “a” or “an” preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

A propulsion device (1) for propelling a vessel, comprising: a first propeller (11) mounted on a propeller shaft (13) intended to be rotated during operation of the propeller device (1) so that it is capable of causing a water flow downstream of the first screw (11); a motor (20) for driving the propeller shaft (13), which comprises a rotatable output shaft (22); a drive assembly that couples the propeller shaft (13) to the output shaft (22) of the motor (20), the drive assembly comprising a rotatable drive shaft (31) and a coupling assembly (32) arranged between the drive shaft (31) and the output shaft (22) of the motor (20) for coupling the drive shaft (31) to the output shaft (22) of the motor (20), the drive shaft (31) extending substantially in the same direction as the output shaft shaft (22) of the motor (20), and wherein the propeller shaft (13) is perpendicular to both the drive shaft (31) and the output shaft (22) of the motor (20); and a housing assembly arranged downstream of the first screw (11), the housing assembly comprising a transmission portion (15) for accommodating the propeller shaft (13) and other components including transmission components (16), an end (33) of the drive shaft (31) extending into the transmission portion (15), and a tubular housing portion (34) that accommodates and surrounds a portion of the drive shaft (31) that communicates on one side thereof with the transmission portion (15); the tubular housing portion (34) including a housing tip portion (37) facing away from the first screw (11), the tip portion (37) being located on substantially one side of a plane extending through the axis of both the screw axis (13) as the drive shaft (31), on which side the first screw (11) moves in a first quadrant with a blade moving away from the first screw (11) away from the motor (20); characterized in that the tip section (37) extends from a first end (38) facing the transmission section (15) to a second end (39) facing the motor (20), the tip section ( 37) from the first end (38) is closer to the plane than the tip portion (37) of the second end (39).

Propulsion device (1) according to claim 1, wherein the tip section (37), when viewed in a viewing direction along the plane, extends from the first end (38) to the second end (39) according to a continuous increase curve.

Propulsion device (1) according to claim 1 or 2, wherein the tip section (37), when viewed in a viewing direction along the plane, extends from the first end (38) to the second end (39) according to a continuous increase curve which is proportional to the distance to the first end (38) of the tip section (37).

Propulsion device (1) according to one of the preceding claims, wherein the first end (38) of the tip section (37) is spaced apart from the surface over a first distance (D1) in a range of 5-25 mm, with preferably in a range of 10-20 mm, most preferably of 15 mm, and wherein the second end (39) of the tip section (37) is spaced from the plane by a second distance (D2) in a range of 15-45 mm, preferably in a range of 25 - 40 mm, most preferably 33 mm.

Propulsion device (1) according to one of the preceding claims, wherein a cross-section of the tubular housing portion (34) has a drop-shaped shape transverse to the axis of the drive shaft (31), the drop-shaped shape preferably being divided into a shorter peripheral edge on the one hand with the first screw (11) being able to move in the first quadrant, thereby causing the water flow guide to be shorter on the shorter peripheral side.

Propulsion device (1) according to one of the preceding claims, wherein: a first cross-section of the housing portion (34) forms a first outer shape at the side of the transmission portion (15), transversely of the axis of the drive shaft (31), and a second cross-section of the housing portion (34) at the motor side (2), forming a second outer shape transversely to the axis of the drive shaft (31), the first cross-section and the second cross-section being substantially identical in shape but turned are relative to each other along a axis parallel to the drive shaft (31) at an angle of rotation so as to allow the water flow to be released with minimal resistance through the tubular housing portion (34).

Propulsion device (1) according to one of the preceding claims, wherein the tip section (37), from the first end (38) to the second end (39), has a flat strip-shaped surface that forms direct edges on both sides of the surface so as to allow the water stream to straighten as it passes through the tip portion (37) of the tubular housing (34).

Propulsion device (1) according to claim 7, wherein the strip-shaped surface (30) has a width that extends between the direct edges on both sides of the surface (30), the width being in a range of 6-20 mm, preferably from 9-17 mm, most preferably from 11-14 mm.

Propulsion device (1) according to one of the preceding claims, wherein the tip section (37) when viewed in a viewing direction along the plane extends from the first end (38) to the second end (39) according to a continuous increase curve.

Propulsion device (1) as claimed in any of the foregoing claims, wherein the tip section (37), when viewed in a viewing direction along the plane, extends from the first end (38) to the second end (39) according to a continuous increase curve which is proportional to a distance from the first end (38) of the tip section (37).

The propulsion device (1) of any one of claims 1 to 8, wherein the tip section (37), when viewed in a viewing direction along the plane, extends from the first end (38) to the second end (39) according to a curved line spaced from the first end (38) of the tip section (37).

Propulsion device (1) according to one of the preceding claims, further comprising: a second screw (12) mounted on the propeller shaft (13, 14) which is intended to be rotated during operation of the propulsion device (1) to thus being able to cause a further water flow downstream of the second screw (12), the second screw (12) being arranged downstream of the tubular housing portion (34); the motor (20) is adapted to drive the propeller shaft (13, 14); the drive assembly is adapted to couple the propeller shaft (13, 14) to the output shaft (22) of the motor (20), the propeller shaft (13, 14) being perpendicular to both the drive shaft (31) and the output shaft (22) of the engine; and the housing assembly is adapted to include the transmission portion (15) for accommodating the propeller shaft (13, 14).

Propulsion device (1) according to claim 12, wherein a tip of a blade of the first screw (11) is able to rotate along a first defined circle and a tip of a blade of the second screw (12) is capable of to rotate along a second described circle, the diameter of the second described circle being smaller than the diameter of the first described circle.

Vessel comprising at least one propulsion device (1) according to one of claims 1-13.