METHOD AND APPARATUS IN AN ELECTRIC PROPULSION ARRANGEMENT OF A SAILING VESSEL

Abstract

The object of the invention is a method and an apparatus in an electric propulsion arrangement of a sailing vessel, wherein the sailing vessel has a traction device provided with an electric motor and with a propeller mechanism, the electric motor of traction device is arranged to be used, if necessary, in forward drive and reverse drive as well as during sailing as a generator for charging the accumulators of the sailing vessel. The propeller mechanism comprises a propeller hub with blades, a hollow propeller shaft fixed at its first end to the propeller hub, a shaft controlling the pitch angles of the propeller blades, said control shaft rotating inside the propeller shaft, and a servomotor rotating the control shaft. The servomotor is fixed to the second end of the propeller shaft to be rotatable along with the propeller shaft.

Claims

1. Method in an electric propulsion arrangement of a sailing vessel, wherein the sailing vessel has a traction device provided with an electric motor and with a propeller mechanism, the electric motor of which traction device is used, if necessary, in forward drive and reverse drive as well as during sailing, if necessary, as a generator for charging the accumulators of the sailing vessel, and which the propeller mechanism of the traction device comprises a propeller hub with blades, a hollow propeller shaft fixed at its first end to the propeller hub, and a shaft controlling the pitch angles of the propeller blades, said control shaft being inside the propeller shaft, and an actuator, such as a servomotor, changing the position of the control shaft in relation to the propeller shaft, and in which method the propeller shaft is supported and rotated around its center axis from a section between the first and the second end of the propeller shaft, wherein the pitch angles of the propeller blades are adjusted by means of the actuator fixed by its frame to the second end of the propeller shaft to be rotatable along with the propeller shaft by rotating with the actuator the control shaft that is inside the propeller shaft in relation to the propeller shaft.

2. Method according to claim 1, wherein the pitch angles of the propeller blades are adjusted between 0-360 degrees via the adjustment mechanism in the propeller hub by rotating the control shaft by means of the actuator inside the propeller shaft, and in that when using the electric motor of the traction device as a generator the pitch angle of the propeller blades is adjusted with the actuator to an adjustment angle that is between 120-270 degrees, e.g. 180-220 degrees, suitably between 190-210 degrees and preferably approx. 200 degrees.

3. Method according to claim 1, wherein the adjustment position of the pitch angles of the propeller blades is measured with a position sensor, the adjustment position identification data provided by which is delivered to the control system of the recovery apparatus for the kinetic energy of the sailing vessel, said apparatus being in the sailing vessel.

4. Method according to claim 1, wherein the adjustment angles of the blades are optimized by means of the actuator fixed to the propeller shaft separately for a) forward drive, b) reverse drive, c) free sailing, in which case the propeller resistance is as small as possible, and d) for recovery of the kinetic energy of the sailing boat, in which case the pitch angles of the propeller blades are adjusted in such a way that the efficiency ratio of kinetic energy recovery is as high as possible and the amount of the capacity of the kinetic energy recovered and being charged into the accumulators of the sailing vessel during a sailing journey of normal duration is at least equal to, or greater than, the amount of electrical energy needed by the sailing boat during a sailing journey of normal duration.

5. Apparatus in an electric propulsion arrangement of a sailing vessel, wherein the sailing vessel has a traction device provided with an electric motor and with a propeller mechanism, the electric motor of which traction device is arranged to be used, if necessary, in forward drive and reverse drive as well as during sailing, if necessary, as a generator for charging the accumulators of the sailing vessel, and which the propeller mechanism of the traction device comprises a propeller hub with blades, a hollow propeller shaft fixed at its first end to the propeller hub, and a shaft controlling the pitch angles of the propeller blades, said control shaft being inside the propeller shaft, as well as an actuator, such as a servomotor, arranged for changing the position of the control shaft in relation to the shaft of the propeller, and in which apparatus the propeller shaft is supported and arranged to be rotatable around its center axis from a section between the first and the second end of the propeller shaft, wherein the actuator is fixed by its frame to the second end of the propeller shaft to be rotatable along with the propeller shaft and the drive shaft of the actuator is connected to the second end of the control shaft to move the control shaft in relation to the shaft of the propeller.

6. Apparatus according to claim 5, wherein the first end of the control shaft is disposed inside the hub of the propeller and locked to be immobilized in the axial direction in relation to the hub, and in that the second end of the control shaft is connected to the drive shaft of the actuator inside the second end of the hollow shaft of the propeller, the speed of rotation of which drive shaft is reduced by means of a reduction gear, functioning as a reduction gear and connected to the actuator, to be suitable for adjusting the pitch angles of the propeller blades.

7. Apparatus according to claim 5, wherein inside the propeller hub is a mechanism for controlling the pitch angles of the blades, with which mechanism the pitch angle of the blades is arranged to be adjusted between 0-360 degrees by rotating the control shaft by means of the actuator, and in that when using the electric motor of the traction device as a generator the pitch angle of the blades is adjusted to be between 120-270 degrees, e.g. 180-220 degrees, suitably between 190-210 degrees and preferably approx. 200 degrees.

8. Apparatus according to claim 5, wherein the adjustment mechanism for the pitch angles of the blades comprises a first bevel gear fixed to the first end of the control shaft and a second bevel gear fixed to the fixing shaft of each blade, the second bevel gear meshing with the first bevel gear.

9. Apparatus according to claim 5, wherein the arrangement comprises a position sensor detecting the adjustment position of the pitch angles of the propeller blades being adjusted with the actuator, the position sensor being adapted to rotate along with the propeller shaft, which actuator and position sensor are connected to the electrical system of the sailing vessel and to the control system of the recovery apparatus for the kinetic energy of the sailing vessel via a slip-ring stack and brushes or corresponding transmission arrangement.

10. Apparatus according to claim 5, wherein both the hollow shaft of the propeller as well as the control shaft inside it are divided into a first part and a second part, which parts are connected to each other with a bevel gear transmission in such a way that on the first end of the first part of the propeller shaft is a bevel gear that is connected to mesh with a bevel gear that is on the second end of the second part of the propeller shaft, and correspondingly on the first end of the first part of the control shaft is a bevel gear that is connected to mesh with a bevel gear that is on the second part of the control shaft.

11. Method according to claim 2, wherein the adjustment position of the pitch angles of the propeller blades is measured with a position sensor, the adjustment position identification data provided by which is delivered to the control system of the recovery apparatus for the kinetic energy of the sailing vessel, said apparatus being in the sailing vessel.

12. Method according to claim 2, wherein the adjustment angles of the blades are optimized by means of the actuator fixed to the propeller shaft separately for a) forward drive, b) reverse drive, c) free sailing, in which case the propeller resistance is as small as possible, and d) for recovery of the kinetic energy of the sailing boat, in which case the pitch angles of the propeller blades are adjusted in such a way that the efficiency ratio of kinetic energy recovery is as high as possible and the amount of the capacity of the kinetic energy recovered and being charged into the accumulators of the sailing vessel during a sailing journey of normal duration is at least equal to, or greater than, the amount of electrical energy needed by the sailing boat during a sailing journey of normal duration.

13. Method according to claim 3, wherein the adjustment angles of the blades are optimized by means of the actuator fixed to the propeller shaft separately for a) forward drive, b) reverse drive, c) free sailing, in which case the propeller resistance is as small as possible, and d) for recovery of the kinetic energy of the sailing boat, in which case the pitch angles of the propeller blades are adjusted in such a way that the efficiency ratio of kinetic energy recovery is as high as possible and the amount of the capacity of the kinetic energy recovered and being charged into the accumulators of the sailing vessel during a sailing journey of normal duration is at least equal to, or greater than, the amount of electrical energy needed by the sailing boat during a sailing journey of normal duration.

14. Apparatus according to claim 6, wherein inside the propeller hub is a mechanism for controlling the pitch angles of the blades, with which mechanism the pitch angle of the blades is arranged to be adjusted between 0-360 degrees by rotating the control shaft by means of the actuator, and in that when using the electric motor of the traction device as a generator the pitch angle of the blades is adjusted to be between 120-270 degrees, e.g. 180-220 degrees, suitably between 190-210 degrees and preferably approx. 200 degrees.

15. Apparatus according to claim 6, wherein the adjustment mechanism for the pitch angles of the blades comprises a first bevel gear fixed to the first end of the control shaft and a second bevel gear fixed to the fixing shaft of each blade, the second bevel gear meshing with the first bevel gear.

16. Apparatus according to claim 7, wherein the adjustment mechanism for the pitch angles of the blades comprises a first bevel gear fixed to the first end of the control shaft and a second bevel gear fixed to the fixing shaft of each blade, the second bevel gear meshing with the first bevel gear.

17. Apparatus according to claim 6, wherein the arrangement comprises a position sensor detecting the adjustment position of the pitch angles of the propeller blades being adjusted with the actuator, the position sensor being adapted to rotate along with the propeller shaft, which actuator and position sensor are connected to the electrical system of the sailing vessel and to the control system of the recovery apparatus for the kinetic energy of the sailing vessel via a slip-ring stack and brushes or corresponding transmission arrangement.

18. Apparatus according to claim 7, wherein the arrangement comprises a position sensor detecting the adjustment position of the pitch angles of the propeller blades being adjusted with the actuator, the position sensor being adapted to rotate along with the propeller shaft, which actuator and position sensor are connected to the electrical system of the sailing vessel and to the control system of the recovery apparatus for the kinetic energy of the sailing vessel via a slip-ring stack and brushes or corresponding transmission arrangement.

19. Apparatus according to claim 8, wherein the arrangement comprises a position sensor detecting the adjustment position of the pitch angles of the propeller blades being adjusted with the actuator, the position sensor being adapted to rotate along with the propeller shaft, which actuator and position sensor are connected to the electrical system of the sailing vessel and to the control system of the recovery apparatus for the kinetic energy of the sailing vessel via a slip-ring stack and brushes or corresponding transmission arrangement.

20. Apparatus according to claim 6, wherein both the hollow shaft of the propeller as well as the control shaft inside it are divided into a first part and a second part, which parts are connected to each other with a bevel gear transmission in such a way that on the first end of the first part of the propeller shaft is a bevel gear that is connected to mesh with a bevel gear that is on the second end of the second part of the propeller shaft, and correspondingly on the first end of the first part of the control shaft is a bevel gear that is connected to mesh with a bevel gear that is on the second part of the control shaft.

Description

[0013] In the following, the invention will be described in greater detail by the aid of some embodiments and by referring to the attached simplified drawings, wherein

[0014] FIG. 1 presents a simplified side view of one sailing boat provided with a typical traction device,

[0015] FIG. 2 presents a simplified side view of a sailing boat provided with a another type of traction device,

[0016] FIG. 3 presents a simplified and partially sectioned side view, shortened in length, of one propeller shaft with fittings, according to the invention, of a traction device of a sailing boat.

[0017] FIG. 4 presents a simplified, partially cross-sectioned and magnified side view of a part of a propeller shaft with fittings, according to FIG. 3, of a traction device of a sailing boat,

[0018] FIG. 5 presents a simplified and partially sectioned side view, shortened in length, of one second traction device, according to the invention, of a sailing boat, wherein the propeller shaft is of two parts in such a way that the bottom part forms a 90-degree angle in relation to the top part,

[0019] FIG. 6 presents a simplified, partially sectioned and magnified side view of the shaft arrangement of the bottom part of the traction device according to FIG. 5, and

[0020] FIG. 7 presents a simplified, partially cross-sectioned and magnified side view of one propeller hub of a traction device of a sailing boat.

[0021] FIGS. 1 and 2 present a side view of a sailing boat, in which is a traction device that is partly inside the hull, the propeller mechanism 1 of which device is under the bottom of the boat. The traction device has e.g. an electric motor disposed inside the hull of the sailing boat, which motor is driven with the accumulators of the sailing boat, if necessary, for forward drive and also for reverse drive. In addition, the sailing boat is provided with an apparatus 1a for recovering the kinetic energy of the sailing boat when the boat is traveling by means of the sails and the travel motion rotates, via the propeller mechanism 1, the electric motor as a generator. The kinetic energy recovery apparatus 1a comprises, in addition to the propeller mechanism 1 and electric motor, at least a control system, an adjustment system and a set of accumulators comprising one or more rechargeable accumulators.

[0022] FIG. 3 presents a simplified and partially sectioned side view of one propeller mechanism 1 of a traction device of a sailing boat, the mechanism comprising e.g. a propeller hub 3 with propeller blades 3a and a hollow shaft 4 rotating the hub 3, which shaft is fixed at its first end to the hub 3, and to which propeller shaft 4 a belt wheel 5 or corresponding transmission means is fixed between the ends of the propeller shaft 4, which transmission means transfers the rotational movement of the electric motor of the traction device to the propeller shaft 4. The propeller mechanism 1 is fixed to the frame 2 of the traction device of the sailing boat, which frame 2 can be a plate-type element or e.g. an enclosure-type element. The propeller shaft 4 is rotated with the electric motor of the traction device disposed inside the hull of the sailing boat, e.g. via a toothed belt 6 and a belt wheel 5. The electric motor is not presented in the drawings. Instead of a toothed belt 6 and a belt wheel 5 also a direct-drive motor can be used, in which case the propeller shaft 4 is fixed inside the hollow rotor shaft of the direct-drive motor between the ends of the propeller shaft 4 in such a way that the servomotor 8, as described hereinafter, can be disposed on the second end of the propeller shaft 4.

[0023] An actuator, such as a reduction gear 8c, such as a servomotor 8 provided with a planetary gear, adjusting the pitch angles of the propeller blades 3a is fixed via a coupling mechanism 7 to the second end of the propeller shaft 4, which servomotor is connected to rotate along with the propeller shaft 4 in the direction of rotation of the shaft 4. A control shaft 9 concentric with the shaft 4 is inside the hollow shaft 4 of the propeller, said control shaft being described in more detail in conjunction with the descriptions of the figures hereinafter. The control shaft 9 is connected at its first end to a pitch angle adjustment mechanism in the propeller hub 3 and at its second end to the drive shaft 8a of the reduction gear 8c of the servomotor 8, the drive shaft rotating the control shaft 9 around its center axis inside the hollow shaft 4 of the propeller. The reduction gear 8c reduces the speed of rotation of the drive shaft 8a in such a way that the control shaft 9 rotates, rotated by the servomotor 8, in the speed of rotation range of approx. 2-40 rpm, e.g. in the range of 5-20 rpm, suitably in the range of 8-12 rpm and preferably e.g. at the revolutions per minute speed of N, where N has e.g. the values 8, 10, 11 and the decimal values between them.

[0024] FIG. 4 presents a simplified, partially sectioned and magnified side view of a part of a propeller shaft 4, with fittings, of the traction device of a sailing boat. As stated above, the shaft 4 of the propeller is hollow and inside it is a control shaft 9, which is fixed at its 10 second end via a wedge 10 to the drive shaft 8a of the reduction gear 8c of the servomotor 8.

[0025] The coupling mechanism 7 on the second end of the propeller shaft 4 comprises a ring-shaped coupling means 7a, which is fixed to the second end of the shaft 4 by means of a locking means 15, such as a locking bushing, or directly fixed to the belt wheel or some other power transmission wheel 5 in such a way that the coupling means 7a is not able to move in the axial or radial directions in relation to the shaft 4. The fixing flange 8b on the frame of the reduction gear 8c of the servomotor 8 is fixed to the end of the coupling means 7a by means of fixing screws. Inside the coupling means 7a is a sensor arrangement, which comprises e.g. a disc-shaped positioning flange 12 and a position sensor 11 detecting the position of the positioning flange 12, which sensor is connected to the control system of the kinetic energy recovery apparatus 1a. The positioning flange 12 is adapted to rotate via a wedge 10 along with the control shaft 9. In this way the angular position of the control shaft 9 is detected with the sensor arrangement and, on the basis of the angular position, the adjustment position of the pitch angles of the propeller blades 3a. The adjustment position detection data measured with the position sensor 11 and sent to the control system of the kinetic energy recovery apparatus 1a is sent onwards from the control system, as control data and position change data, to the servomotor 8 for changing the adjustment position, until the desired adjustment position has been achieved.

[0026] The propeller shaft 4 is mounted on a bearing 19 to the frame 2 of the traction device, which bearing 19 is in a bearing housing, which is composed of a first ring-shaped half 16 and a second ring-shaped half 17, which are fixed to each other with fixing means 18, such as screws, through a bracket element 2. The bearing housing is locked into its position in the axial direction on the shaft 4 of the propeller by means of locking means 15, such as retainer bushings. Also the belt wheel 5 is locked into its position in the axial direction on the shaft 4 of the propeller by means of the locking means 15. Alternatively, the shaft 4 of the propeller is fixed in a direct drive motor onto the hollow rotor shaft of the electric motor of the traction device.

[0027] The propeller mechanism 1 further comprises a slip-ring stack 13 fixed onto the propeller shaft 4 to rotate along with the shaft 4, and brushes 14 or corresponding elements on the slip rings, which brushes are fixed e.g. to the bracket element 2 or to some other suitable location. The servomotor 8 and sensor 11 are connected to the electrical system and to the control system of the kinetic energy recovery apparatus 1a of the boat via the slip-ring stack and brushes 14 or corresponding transmission arrangement.

[0028] FIG. 5 presents a simplified and partially sectioned side view of one second traction device of a sailing boat, the traction device having a kinetic energy recovery arrangement, according to the invention, for a sailing boat. Only the top end and bottom end of the traction device are seen in the figure, because a part of the vertical shaft and body 22 is cut away. In addition, the body 22 is presented diagrammatically and for the sake of clarity parts are omitted from inside the body. In this solution there is a direct drive motor, such as an electric motor 6a, instead of a belt wheel 5, the electric motor rotating the hollow shaft of the propeller, which shaft is now disposed to travel through the electric motor 6a in the same way as it travels through the belt wheel 5 in the solution presented by FIG. 3. Instead of an electric motor 6a, in this solution there could also be a belt wheel on the propeller shaft 4, in which case the actual electric motor would be farther away.

[0029] The propeller shaft 4 and the control shaft 9 inside it are, in this solution, divided into two parts, the first of which, i.e. the upper part, is essentially vertical when the traction device is in its drive position, and the 20 second, i.e. lower part is at a right angle to the first part. The first and second parts of the shafts 4 and 9 are connected to each other with a bevel gear transmission 20 that is an angular gear in such a way that when driving with the traction device the first part of the propeller shaft 4 rotates the second part of the propeller shaft 4 and the first part of the control shaft 9 rotates the second part of the control shaft 9. Correspondingly, when using the electric motor of the traction device as a generator, the second part of the propeller shaft 4 rotates the first part of the propeller shaft 4 and the second part of the control shaft 9 rotates the first part of the control shaft 9.

[0030] On the second end of the first part of the propeller shaft 4, i.e. on the free end or on the top end, is a similar coupling mechanism 7 and servomotor 8 with slip-rings 13 as in the solution according to FIG. 3. The servomotor 8 is attached to the first end of the second part of the propeller shaft 4, in the same way as in the solution according to FIGS. 3 and 4. Likewise the servomotor 8 and the position sensor 11 of the control shaft 9 are connected to the electrical system and control system of the kinetic energy recovery apparatus 1a of the boat in the same way as in the solution according to FIGS. 3 and 4.

[0031] The biggest difference with respect to the solution according to FIGS. 3 and 4 is the division of the shafts 4 and 9 into two parts. FIG. 6 presents in more detail a magnified view of the shaft arrangement of the bottom part of the traction device according to FIG. 5 at the point of the bevel gear transmission 20. On the first end, i.e. on the bottom end, of the first part of the propeller shaft 4 is a bevel gear 25 that is connected to mesh with a bevel gear 27 that is on the second end of the second part of the propeller shaft 4. Correspondingly, on the first end, i.e. on the bottom end, of the first part of the control shaft 9 is a bevel gear 26 that is connected to mesh with a bevel gear 28 that is near the second end of the second part of the control shaft 9. The first end of the second part of the propeller shaft 4 is fixed to the propeller hub 3 by means of a fixing flange 4a and the first end of the control shaft 9 is fixed to the pitch angle adjustment mechanism 23 that is in the propeller hub 3, the adjustment mechanism being described in more detail in connection with FIG. 7. The first end of the first part of the propeller shaft 4 is mounted on a bearing to the frame 22 of the traction device by means of the bearing 21, and the second part is mounted on a bearing to the frame 22 of the traction device by means of the bearing 29. Correspondingly, the second end of the second part of the control shaft 9 is mounted via a sliding bearing inside the second end of the second part of the propeller shaft 4, and the first end, i.e. the bottom end, of the first part of the control shaft 9 is mounted via a sliding bearing inside the first end, i.e. the bottom end, of the first part of the propeller shaft 4.

[0032] FIG. 7 presents a partially cross-sectioned and magnified view of one propeller hub 3, according to the invention, of a traction device of a sailing boat. The hub 3, and its components, can be similar in both the traction drive applications presented, and generally in all the traction drive solutions according to the present invention. Likewise the propeller and its hub 3 can be any commercially available propeller whatsoever. In any reference in the description of FIG. 7 hereinafter, the propeller shaft 4 or control shaft 9 refers also to the second part, i.e. bottom part, of the propeller shaft and control shaft of the solution according to FIG. 5. The propeller shaft 4 is fixed to the hub 3 of the propeller by means of a fixing flange 4a in such a way that when the propeller shaft 4 rotates, the propeller hub 3 rotates along with the shaft 4.

[0033] The first end of the control shaft 9 is connected to the adjustment mechanism 23 of the propeller blades 3a, which mechanism is inside the hub 3 and comprises e.g. a locking ring 9c of the control shaft 9, a first bevel gear 24a on the first end of the control shaft 9 and a bevel gear 24 on each fixing arm of a propeller blade 3a, the bevel gear 24 being disposed inside the hub 3, which bevel gears 24a and 24b function as an angular gear. The first end of the control shaft 9 is locked to be immobilized in the axial direction inside the hub 3. On the first end of the control shaft 9 is a thread for the locking, on which thread is a locking nut 9b, which is adapted to press the locking ring 9c inside the hub 3 in such a way that the control shaft 9 is not able to move in the axial direction in relation to the hub 3.

[0034] The first bevel gear 24a belonging to the adjustment mechanism 23 for the pitch angles is fixed onto the locking ring 9c, which is in turn locked to rotate along with the control shaft 9 via a wedge 9a. Thus the bevel gear 24a also rotates along with the rotational movement of the control shaft 9. The second bevel gear 24b that is on the fixing arm of each blade 3a of the propeller and is disposed inside the hub 3 meshes with the bevel gear 24a that is on the end of the control shaft 9 in such a way that when rotating the control shaft 9 inside the propeller shaft 4, the pitch angle of all the blades 3a changes at the same time and by the same amount, between 0-360 degrees, depending on the angle of rotation or number of rotations of the control shaft 9.

[0035] With the solution according to the invention it is therefore possible to adjust the pitch angle of the propeller blades 3a more than in solutions that are known in the art. For achieving a sufficiently good efficiency ratio in the recovery of kinetic energy, the pitch angles of the propeller blades 3a are adjusted in the solution according to the invention with the servomotor 8 approx. 120-270 degrees, e.g. approx. 180-220 degrees, suitably between 190-210 degrees and preferably approx. 200 degrees. The adjustment angles of the blades 3a are thus optimized with the solution according to the invention separately and, if necessary, both for forward drive and for reverse drive as well as for free sailing, in which case the propeller resistance is as small as possible, and finally for recovery of the kinetic energy of the sailing boat, in which case the pitch angles of the propeller blades 3a are adjusted in such a way that the efficiency ratio of kinetic energy recovery is as high as possible.

[0036] In this case the kinetic energy of the sailing boat is recovered with the recovery arrangement according to the invention with an efficiency ratio whereby the amount of energy being charged into the accumulators of the sailing boat during a sailing journey of normal duration is at least equal to, or greater than, the amount of electrical energy needed by the sailing boat during a sailing journey of normal duration. The accumulators of the sailing boat can thus be fully charged during a sailing journey of normal duration. In this way a sailing vessel can function also for long periods of time fully self-sufficiently when receiving the electrical energy it needs for recharging accumulators via the electric motor of the traction device when moving by means of the sails.

[0037] It is obvious to the person skilled in the art that different embodiments of the invention are not only limited to the examples described above, but that they may be varied within the scope of the claims presented below. Thus, for example, the adjustment mechanism that is inside the propeller hub can also be different to what is presented in the preceding. In this case, instead of the bevel gear transmission, there can be some other type of gear transmission mechanism or a completely other type of mechanism, which transfers the rotational movement of the control shaft into a movement adjusting the pitch angle of the propeller blades.

[0038] It is further obvious to the person skilled in the art that the mechanism for connecting the servomotor to the shaft of the propeller can also be different to what is presented in the preceding. A good point from the viewpoint of the simplicity of the construction is, however, that the servomotor is fixed as simply as possible to the propeller shaft, in which case it rotates along with the propeller shaft, and that the control shaft rotated by the servomotor rotates when adjusting the pitch angle inside the hollow propeller shaft in relation to the rotational movement of the propeller shaft itself. In this case the servomotor that is fixed to the second end of the propeller shaft and rotates along with the shaft changes the radial interpositioning of the control shaft and the propeller shaft, thus changing the position of the propeller blades fixed to the first end of the propeller shaft.

[0039] It is further obvious to the person skilled in the art that instead of an electric servomotor being the actuator for adjusting the blades, the actuator can also be a hydraulic or pneumatic actuator, or even a mechanical actuator.

[0040] It is also obvious to the person skilled in the art that instead of toothed-belt gearing, also other power transmission solutions can be used between the shaft and the propulsion motor, such as V-belt transmission and gear wheel transmission.

[0041] It is also further obvious to the person skilled in the art that the propeller can also have, instead of the two blades presented, a number of controllable blades, e.g. 3, 4, 5, 6 or even more.