Technical Field

[0001] The invention relates to a controllable pitch propeller for a propulsion and power regeneration arrangement in a vessel. Furthermore, the invention relates to a propulsion and power regeneration arrangement comprising such controllable pitch propeller and to a vessel comprising such propulsion and power regeneration arrangement.

Background Art

[0002] Controllable pitch propellers (CPPs) have been used for many years in vessels, e.g., sailing ships, motor boats, as an alternative to fixed pitch propellers or constant pitch propellers. In a CPP, the angle or pitch of the blades can be adjusted to suit the changing operating conditions of the propulsion system. This has several benefits such as easing the start of a vessel from a stationary position and making the vessel more manoeuvrable at low speed, or allowing for an optimization of the pitch angle to reduce fuel use. In such cases, the pitch may be varied over a relatively small range of angles within the range of forward operating modes.

[0003] Nowadays, there is an increasing interest in self-sustainable vessels with hybrid drive systems. The thought for vessels, and especially sailing vessels, is that energy may be recovered while sailing, for instance to power onboard systems or charge accumulators. Even at anchor, power may be generated if a sufficient current flowing over the propeller is present.

[0004] A known solution is to attach, in addition to a propeller, a separate turbine to the vessel. The turbine may be configured to retrieve energy efficiently, yet has as negative side-effects that drag is increased during drive mode, that additional maintenance is required, and moreover, that the system is expensive. It would therefore be desirable to design a CPP system that may be used both as a propeller and as a turbine. Wind turbines are also known for generating energy on board a vessel but have other disadvantages, in particular that they may interfere with the rigging of a sailing vessel.

[0005] Known in the art, are CPP systems wherein the blade angle can be adjusted to provide optimal pitch during modes of forward drive and reverse drive. Also known in the art, are CPPs used in sailing vessels, which in addition to forward and reverse mode can be used in a feathering mode when the vessel is travelling solely under the force of the sails and support from the engine is not desired. In the feathering mode, the blades assume a minimum drag position, wherein the blades are angled to a position where they are approximately parallel to the fluid flow. Such a system is disclosed in patent document WO 2005/012078 A1 . As a consequence of minimizing the drag, that system is not able to recover energy efficiently.

[0006] It would be desirable to provide an improved controllable pitch propeller that enables the efficient conversion of energy during sailing. It would further be desirable to provide an improved controllable pitch propeller system that allows for pitch angle adjustment to generate a user-defined amount of power.

Summary of Invention

[0007] According to the invention, a controllable pitch propeller for a vessel is provided comprising: a propeller hub, connectable to a drive shaft for rotating the hub about a longitudinal axis; a travelling member arranged at least partially within the propeller hub to be moved in a direction along the longitudinal axis, and connectable to an actuating device for creating movement of the travelling member along the longitudinal axis; a plurality of propeller blades each having a propeller blade base, mounted on the propeller hub, wherein each propeller blade has a blade angle that is adjustable through at least 140 degrees by rotating the propeller blade about a respective pivot axis, each pivot axis being oriented transversely with respect to the longitudinal axis; and a linkage arranged between the travelling member and the respective blade bases for adjusting the blade angle of each propeller blade by converting the movement of the travelling member into rotation of each propeller blade over a range of at least 140 degrees.

[0008] The resulting propeller is able to adopt the full range of angles required to allow optimised driving in both forward and reverse directions and feathering mode. Moreover, the blade angle may be used for the generation of power due to a flow of water over the propeller blade surfaces.

[0009] A variable pitch propeller with adjustable blade angle over a range of at least 140 degrees can assume pitch angles outside the range for which conventional CPPs have been designed. Such ranges have historically been designed to allow for suitable positions for forward drive, reverse drive, and minimum drag position and do not allow for a suitable position for power regeneration. By accurately adjusting the blade angle within a range of positions beyond the minimum drag position and opposite to a position suitable for forward drive, the propeller can generate power more efficiently.

[0010] This control is furthermore achievable by actuation in a longitudinal direction of the drive shaft, enabling a more precise control of the blade angle within a system that is itself subject to rotation around that longitudinal axis. It will be understood each blade must move over a total angle of at least 140 degrees but must have high accuracy at the position of operation. This requires a robust mechanism that is not subject to backlash or creep and can accurately maintain a given blade angle once selected.

[0011] The skilled person will be well aware that the precise geometric design of the propeller and its blades may vary and will depend on the particular vessel configuration. For the blades, each pivot axis will be generally transverse to the longitudinal axis, but not necessarily perpendicular to the longitudinal axis. In a preferred embodiment, the longitudinal axis will be perpendicular to each pivot axis. Furthermore, in preferred embodiments each pivot axis may intersect the longitudinal axis.

[0012] In general, the blade angle or angle of pitch of a propeller blade is defined as the angle between the plane of rotation around the drive shaft and a chord of the propeller blade. The chord is the imaginary straight line joining a leading edge and trailing edge of the hydrofoil-shaped cross- sectional area of the propeller blade. Since a blade is usually twisted, the value of the blade angle usually varies along the span of the blade, decreasing from the root to the tip. It will however be understood that, independent of the absolute angle a chord makes, each chord of the propeller blade is adjustable through a range of at least 140 degrees.

[0013] The invention is also applicable to any number of blades. In preferred embodiments, the variable pitch propeller may comprise 4 or 5 propeller blades, yet also variable pitch propellers having 2 or 3 or more than 5 propeller blades are included in the present invention.

[0014] In preferred embodiments of the invention, the blade angle is adjustable through an angle of at least 180 degrees. In embodiments wherein the blade angle is adjustable through an angle of at least 180 degrees, the blade angle may be adjusted within a range of positions far beyond the minimum drag position and opposite to a position suitable for forward drive. In such positions, the propeller can generate power more efficiently.

[0015] In more preferred embodiments of the invention, the blade angle is adjustable through an angle of at least 193 degrees. An optimal angle for regeneration of power is approximately 193 degrees relative to a design pitch in forward drive mode. The 193 degrees are measured by turning the propeller blades backward, where the term turning backward is used to indicate movement of the tip of the blade from a position optimal for forward drive, through a position optimal for reverse drive and through the feathering position, toward the position suitable for power regeneration. The design pitch in forward drive mode is an optimal blade position in forward drive given certain design parameters such as a design vessel speed, and a number of rotations per minute of the drive shaft that is needed to obtain such vessel speed provided design conditions for the environment like wind and water velocities.

[0016] The skilled person will understand that in an arbitrary set of conditions, different from the design conditions, the optimal pitch of forward drive may differ by several degrees. Therefore adjustability through a range larger than 193 degrees is preferable. In preferred embodiments, the blade angle is adjustable through an angle of at least 195 degrees, preferably at least 205 degrees, and more preferably at least 225 degrees. The margins are required to allow for optimum positions during all modes. The position for maximum power regeneration may depend on various factors, such as the speed of the vessel, characteristics of the propulsion and power regeneration arrangement whereto the controllable pitch propeller is attached, or the shape of the propeller blades. Apart from the additional margins to find optimal pitch for the different modes, adjustability over larger ranges may support other functions. For example, in motorized sailing vessels when using the propeller for motor sailing, i.e. , sailing using both the sails and the motor simultaneously, an additional 10 degrees in addition to the normal range may be required.

[0017] In an embodiment, the blade angle is continuously adjustable. Here the term continuously adjustable is used to indicate that the propeller blade angle can assume any position within the range through which the blade angle can be adjusted. Optimum power regeneration can thus be precisely achieved for any speed of the vessel. The angle of pitch associated with optimum energy regeneration is dependent on the speed of the vessel. Similarly, an optimal angle of pitch during forward drive may be achieved for any speed of the vessel. For vessels with a hybrid propulsion arrangement, an angle of optimal pitch may also be dependent on the type of motor used, e.g., an electric motor or diesel motor require a different blade angle for optimized forward drive. It will be understood that the actual adjustment is dependent upon the actuating device that acts on the travelling member. Nevertheless, the controllable pitch propeller itself including the linkage that converts the movement of the travelling member into rotation of the propeller blade is preferably not limited to specific settings or otherwise limited to incremental adjustment.

[0018] The blade angle may be adjusted to an accuracy of within a few degrees or even less to optimize the various drive modes dependent on the speed of the vessel and other factors. In addition, the opportunity to adjust the blade angle to any desired position within the range increases the flexibility of the system. Accurate adjustment may be available over the full range of angles of the propeller blade or may be limited to primary operating regions such as the forward drive and power generation regions. Between these regions, the movement of the blades may be subject to coarser adjustment.

[0019] In some conditions it may be desirable to configure the blade angle in such a way that maximum power is generated during sailing. However, as this will increase the drag, it will also slow down the vessel. In other conditions, optimum power generation may involve generating less power and maintaining more speed. This may for instance result in the desire to configure the position of the propeller blade to attain a blade angle wherein enough electrical energy is retrieved to recharge accumulators, or to power the on-board systems. A suitable controller as discussed below may monitor the actuating device and/or the blade angle and compare it with drag and generated power or energy. This data may be used by the controller to adjust the blade angle automatically.

[0020] As noted above, the travelling member is arranged at least partially within the propeller hub and is arranged to be moved in a direction along the longitudinal axis. This may be limited to movement only in the longitudinal direction but may also include a component of movement in the circumferential direction should this be required by the linkage. In this context, it is understood that the travelling member rotates along with the propeller hub and the mentioned longitudinal movement and circumferential movement is with respect to the hub.

[0021] In a preferred embodiment, the travelling member is located completely within the hub. In particular, the travelling member may comprise a member that is mounted entirely within the propeller hub and arranged to be rotatable therewith. This configuration ensures that the travelling member is not exposed to external influences or damage and that the hub itself can be optimised from a hydrodynamic perspective. It also allows for disconnecting the controllable pitch propeller from the vessel without having to detach the linkage from the travelling member. The travelling member may be arranged within a bearing assembly in the propeller hub to guide its motion such as within an interior channel or cavity within the hub.

[0022] In certain embodiments, the travelling member will have rotational symmetry of at least an order n around the longitudinal axis, wherein n is the number of propeller blades. Thus a three blade propeller may be associated with a travelling member of generally triangular cross-section, while a four blade propeller may have a travelling member of square cross-section.

[0023] The skilled person will be aware that various forms of linkage may be capable of providing the given conversion of linear movement into rotation of the respective blade. In a simple configuration, the travelling member may engage directly with an element of the blade base and the linkage may comprise gear teeth or cam surfaces on the respective parts that achieve the required rotation. Nevertheless, it has been found that achieving the necessary range of movement and required accuracy requires that the linkage comprises at least an additional member. The additional member may be a common linkage that is common to all of the blades, such as a ring or annular member that is engaged by the travelling member and acts on the respective blade bases. [0024] In a preferred embodiment, each propeller blade comprises an individual linkage for converting the movement of the travelling member into rotation of the respective blade base. Such a configuration may be more versatile in design and manufacture than a common linkage. In embodiments where the travelling member has rotational symmetry around the longitudinal axis and each propeller blade has an individual linkage, the entire propeller hub may then be constructed in a rotationally symmetric manner.

[0025] In one preferred embodiment described in greater detail below, each individual linkage directly converts the movement of the travelling member into rotation of a rotatable member in a plane normal to the respective pivot axis of the blade. In this manner linear motion is converted into rotation directly in a plane normal to the pivot axis. This may be the rotational plane of the base of the propeller blade or a plane parallel thereto. In this context, reference to direct conversion is intended to mean that there is no rotation in a plane perpendicular to the blade base. This has the beneficial effect that the dimensions of each individual linkage may be relatively small, in particular, in the radial direction. This can mean that the dimensions of the propeller hub may also remain limited, preventing the propeller hub from generating an unnecessary amount of drag.

[0026] In an embodiment, each individual linkage comprises a rotatable member, a first mechanism, and a second mechanism. The rotatable member is arranged within the propeller hub and is rotatable about a pivot point having a second axis of rotation oriented parallel to and spaced from the respective pivot axis. This pivot point, or centre of rotation of the rotatable member, is preferably rotatably connected to an inner wall of the propeller hub. In other embodiments, the rotatable member may also be connected to another element that does not move with reference to the propeller hub.

[0027] The first mechanism is configured to convert linear motion of the travelling member along the longitudinal axis into rotation of the rotatable member over a first angle about the second axis of rotation. The skilled person will understand that in embodiments where the first mechanism is arranged such that the travelling member pushes or pulls the rotatable member at a point that travels in a direction parallel to the longitudinal axis, the required force to rotate the rotatable plate will be least. Therefore in preferred embodiments, the first angle is smaller than 120 degrees, preferably less than 80 degrees.

[0028] The second mechanism is configured to convert the rotation of the rotatable member over the first angle into rotation of the propeller blade over a second angle about the pivot axis, wherein the second angle is larger than the first angle. In a preferred embodiment, the second angle is the same as the angle of propeller blade adjustment.

[0029] The combination of the first and second mechanism leads to the application of a two- stage rotation stroke, which is meant to indicate that the first mechanism allows for rotation of an intermediate member over a first angle, and the second mechanism uses this rotation to adjust the propeller blade over the second angle. By application of this two-stage rotation stroke, it is possible to achieve the desired adjustment of the blade angle with an input longitudinal movement of the actuating device that is significantly reduced in comparison to a situation wherein only a single rotation stroke would be applied. Additionally, the force required in use to achieve the desired rotation may also be reduced, allowing for a lighter construction of the individual elements of the linkage. The skilled person will understand that the presently described arrangement of first and second mechanism is just one possibility for applying a two-stage rotation stroke and that further stages may also be contemplated.

[0030] In preferred embodiments that apply a double rotation stroke, the ratio between the first angle and the second angle is between 0.15 and 0.5, preferably between 0.24 and 0.4. It will be understood by the skilled person which ratio is most preferred given the specific characteristics of an embodiment and the intended use of the controllable pitch propeller. In embodiments, the ratio may be optimized to make the linkages compact. In embodiments, the ratio may also be optimized in a manner that the force to adjust the blade angle in various positions of the range is approximately evenly spread throughout the entire range. It will be understood by the skilled person how the distance that the travelling member travels is related to the distance between the second axis and pivot axis.

[0031] In preferred embodiments, the travelling member travels over a maximum distance between 0.5 and 1 times the radius of the propeller blade base. In further preferred embodiments, the distance between the second axis and pivot axis is between 0.3 and 0.7 times the radius of the propeller blade base. These dimensions prevent the propeller hub from becoming too large and generating unnecessary drag.

[0032] In a preferred embodiment, each rotatable member is a flat plate having the second axis of rotation generally perpendicular to a plane of the plate. Here the term flat plate is used to indicate that a length and a width of the rotatable member are larger than the thickness of the rotatable member. A flat rotatable plate contributes to relatively small dimensions of each individual linkage, in particular, in the radial direction. As explained above, this means that the dimensions of the propeller hub may also remain limited, preventing the propeller hub from generating an unnecessary amount of drag.

[0033] In an embodiment, each first mechanism comprises a pin slot arranged within the travelling member. A first sliding shoe is arranged within that pin slot, and is moveable in a direction transverse to the longitudinal axis when the travelling member moves along the longitudinal axis. The first sliding shoe has an opening for receiving a pin, and the first mechanism further comprises a pin having a first end that is arranged within the first sliding shoe, and a second end connected with the rotatable member at a position offset with respect to the pivot point. This mechanism is well suited for enduring high loads. In addition, little maintenance is generally required.

[0034] In an embodiment, each second mechanism comprises a crank slot arranged within the rotatable member, and a second sliding shoe arranged within the crank slot, and arranged to be moveable along an axis that extends radially outward from the pivot point of the rotatable member. The second sliding shoe has an opening for receiving a crank pin, and the second mechanism further comprises a crank pin having a first end engaging in the second sliding shoe, and a second end that is eccentrically engaged with a propeller blade base or an element connected therewith. This mechanism is similarly well suited for enduring high loads. In addition, little maintenance is generally required.

[0035] According to a second aspect of the invention, and in accordance with the advantages and effects described herein above, there is also provided a controllable pitch propeller system for a vessel, comprising a controllable pitch propeller as described above, and an actuating device for creating motion of the travelling member along the longitudinal axis.

[0036] The actuating device is connected to the travelling member and configured to create motion thereof along the longitudinal axis. The skilled person will understand that any actuator that can create a controlled motion of the travelling member along the longitudinal axis can suffice, it being understood that this controlled motion must take place through the drive train of the propeller, acting in the hostile environment that is typical of such propellers. Exemplary embodiments include for instance hydraulic actuation, or actuation by a screw jack or ball screw. Preferably, the actuating device is connected to the travelling member through a longitudinally actuated rod. In preferred embodiments, the actuating device is electric.

[0037] In further preferred embodiments, the actuating device comprises a control motor driving a planetary roller screw. A planetary roller screw allows for high-precision, high-speed, heavy-load, long-life and heavy-use applications. An accurate blade angle adjustment may therefore be performed quickly. Moreover, a planetary roller screw is maintenance friendly. In preferred embodiments, the control motor is an electric motor such as a stepper motor or servomotor.

[0038] According to a further aspect of the invention, and in accordance with the advantages and effects described herein above, there is provided a propulsion and power regeneration arrangement for a vessel, comprising a controllable pitch propeller system having a propeller hub, and a drive shaft that is connected to the propeller hub. The propulsion and power regeneration arrangement further comprises a power source arranged to drive the drive shaft, an energy consuming device or energy accumulator, a central control unit, and a pitch control unit that is configured to control the actuating device. The energy consuming device or energy accumulator is configured to receive energy regenerated by the controllable pitch propeller in power regeneration mode. The central control unit is configured to control the power source and the energy consuming device or energy accumulatorto operate in different modes comprising at least a forward drive mode, a reverse drive mode, and a power regeneration mode. The power source may be a motor or another device suitable to drive the drive shaft.

[0039] In embodiments, the propulsion and power regeneration arrangement is electric, and the power source comprises at least an electric motor. In embodiments, the electric motor is designed to also be used as a generator. In other embodiments, the propulsion and power regeneration arrangement is hybrid, comprising at least two different power sources.

[0040] In embodiments, the drive shaft is between 3 meters and 20 meters long. In embodiments, the diameter of the drive shaft is between 50 mm and 500 mm. In preferred embodiments, the drive shaft is hollow and a rod, which connects to the travelling member, extends through the drive shaft. This rod may be concentrically arranged within the drive shaft and configured to rotate along with the drive shaft. The rod may have any cross sectional area, yet is preferably rotationally symmetric, having for example a circular, triangular, squared, pentagonal, or hexagonal cross sectional area. [0041] In embodiments wherein a rod extends through a hollow drive shaft, a first end of the rod may be connected to the travelling member within or outside of the propeller hub, whereas the actuating device on board of the vessel may be connected to the other end of the rod.

[0042] The drive shaft is configured to receive torque to rotate the propeller hub from the power source in drive mode and vice-versa to provide energy to the energy consuming device or energy accumulator in regeneration mode. Preferably, the power source has a capacity of at least 20 kW, preferably at least 100 kW, and more preferably at least 250 kW. In general, the capacity will be less than 20000 kW and mostly less than 10000 kW. The person skilled in the art will recognize that such motors are customary for vessels of approximately 20 meters or more, preferably 30 meters or more.

[0043] In preferred embodiments, the power source comprises an electric motor that is designed to also run as an electric generator. Consequently, the electric generator may be used to convert rotational energy into electrical energy, which can be easily stored by an accumulator. The energy that is retrieved by the electric motor may be used to drive the same electric motor. In embodiments wherein the electric generator and electric motor are the same device, the vessel needs to be equipped only with a single motor that can serve both as motor and as an electric generator.

[0044] In further embodiments, the power source comprises a motor arrangement having a plurality of motors. Preferably, the motor arrangement comprises both an electric motor that can be used as a generator and a fuel-based engine that can serve as back-up during long periods without sufficient wind. The electric motor that functions as electric generator, or the separate electric generator is connected to the accumulator. In embodiments, the accumulator may for instance comprise one or multiple rechargeable batteries.

[0045] The variable pitch propeller system may form part of a propulsion and power regeneration arrangement that can automatically control the propeller blade angle. A request for sailing in a certain mode, e.g., forward drive, reverse drive, or a certain amount of desired power regeneration, is processed by the central control unit and/or the pitch control unit. These control units monitor the actuating device and/or the blade angle and compare it with drag and generated power or energy. This data may be used by the pitch control unit to adjust the blade angle automatically.

[0046] In embodiments, the propulsion and power regeneration arrangement may comprise one or more sensors that can be mounted below the vessel, within the hull of the vessel, or on deck, to monitor data associated with the performance of the vessel such as speed of the vessel, experienced drag, used electricity, or generated electricity. Other sensors may also monitor environmental conditions, and collect data on for instance wind conditions, water temperature, or data on currents. Further sensors may monitor the status of the vessel, such as the status of the accumulator and the time that is required until it is fully recharged.

[0047] In embodiments, the electric propulsion and power regeneration arrangement may also comprise a control panel, and the pitch control unit may be configured to control the adjustment of the propeller blade angle based on data entered through a control panel that is accessible by a captain or another operator of the vessel. Through this controller, operator demands may be entered by the captain, such as a user-defined energy recovery rate, which may for example be entered in terms of a desired speed of the vessel, a percentage of maximum speed that may be compromised for regenerating energy, a desired absolute energy recovery rate, or a number of hours during which an accumulator should be recharged to full. It will be understood that there are many other user-defined energy recovery output variables that may be used by a control unit to define an appropriate blade angle.

[0048] The control panel provides the user of the system with a user-friendly interface that automatically translates desired user-defined input into protocols to be followed by the pitch control unit and/or central control unit. Especially in embodiments wherein the controllable pitch propeller has a blade angle that is continuously adjustable, it is highly valuable if an operator of the vessel can input specific desires.

[0049] According to a further aspect of the invention, and in accordance with the advantages and effects described herein above, there is provided a vessel comprising an electric propulsion and power regeneration system according to the invention. In embodiments, the vessel is a sailing vessel since the invention is particularly suited for application in a sailing vessel. Nevertheless, the skilled person will understand that the electric propulsion and power regeneration system may be used in any situation wherein an external current is present, and for which power regeneration is desired. In embodiments, the vessel may also be a motorized vessel that uses currents when anchored to regenerate electrical energy. In embodiments, the vessel may also be a motorized vessel that comprises at least two propellers, wherein at least one of the propellers is a controllable pitch propeller that may regenerate energy when the vessel is being propelled by the other propeller.

Brief Description of Drawings

[0050] Embodiments will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts. In the drawings, like numerals designate like elements. Multiple instances of an element may each include separate letters appended to the reference number. For example, two instances of a particular element “20” may be labelled as “20a” and “20b”. The reference number may be used without an appended letter (e.g. “20”) to generally refer to an unspecified instance or to all instances of that element, while the reference number will include an appended letter (e.g. “20a”) to refer to a specific instance of the element.

[0051] Figure 1 A schematically shows a sailing vessel with a propulsion and power regeneration arrangement and controllable pitch propeller according to the invention;

[0052] Figure 1 B schematically shows the components of the propulsion and power regeneration arrangement of the vessel of Figure 1 A;

[0053] Figure 1C shows an enlarged side view of the controllable pitch propeller system of Figure 1 A;

[0054] Figure 2A shows an exploded isometric view of the linkage within the propeller hub according to an embodiment of the invention;

[0055] Figure 2B shows a cross-sectional plan view along cross-section MB as indicated in Figure 2A;

[0056] Figure 2C shows a cross-sectional front view along cross section IIC as indicated in Figure 2A; and

[0057] Figure 3 presents a simplified cross-sectional view of the pitch control unit, controlling the linkage.

[0058] The figures are meant for illustrative purposes only, and do not serve as a restriction of the scope or the protection as laid down by the claims.

Description of Embodiments

[0059] The following is a description of certain embodiments of the invention, given by way of example only and with reference to the figures.

[0060] Figure 1A schematically shows the side view of a sailing vessel 1 of approximately 45 meters in length, having a bow 3 and a stern 4, between which a hull 2 with a keel 5 and a rudder

6 extend. The sailing vessel 1 is provided with a propulsion and power regeneration arrangement

7 that can be used to generate thrust or recover energy during sailing.

[0061] The propulsion and power regeneration arrangement 7 comprises a drive shaft 8 that extends through the hull 2. During forward or reverse drive, the drive shaft 8 is operated by a motor and drives a controllable pitch propeller 9 to generate thrust. Dependent on the configuration of the propeller blades 12, this leads to forward travel or backward travel.

[0062] When the vessel 1 is travelling by means of the sails 10, the propeller 9 may be used to provide auxiliary support, or electricity may be retrieved by operating the vessel 1 in a power generation mode. In power generation mode, the controllable pitch propeller 9 functions as a turbine, and kinetic energy retrieved from a current powers the rotation of the controllable pitch propeller 9. The drive shaft 8 rotates along with the controllable pitch propeller 9. During power generation mode, the rotation direction of the drive shaft 8 is opposite to the direction during forward and reverse drive mode.

[0063] Figure 1 B schematically shows the propulsion and power regeneration arrangement 7 of the vessel 1 of Figure 1A. Part of the arrangement 7 is located within the hull 2 of the vessel 1 , and part of it in the water. The drive shaft 8 extends with one end into the water and with the other end into the hull 2. A hollow stern tube 19 seals the connection.

[0064] In propulsion mode, the drive shaft 8 receives rotational power through a transmission system 20. This transmission system 20 is fixed between the ends of the drive shaft 8 and transfers rotational power of a motor arrangement 22 to the drive shaft 8.

[0065] The motor arrangement 22 may have one or more motors 21a, b. In this embodiment, the motor arrangement has two motors, the first motor being a diesel motor 21 a, and the second motor being an electric motor 21 b. The electric motor 21 b is designed to also function as an electric generator, and therefore the propulsion and power regeneration arrangement 7 does not include a separate electric generator. However, in other embodiments a separate electric generator could be provided. In other embodiments, also another type of energy consuming device or energy accumulator may be used that directly uses or stores the rotational energy provided by the propeller and drive shaft in power regeneration mode.

[0066] In this specific embodiment, the propulsion and power regeneration is electric. The skilled person will understand that a different type of motor may also be included, and that motors may also comprise a motor system instead of a single motor, e.g., a diesel motor working in combination with a hydropump. In addition, the skilled person will understand that also more than one motor of the same type may be provided within the motor arrangement 22, such as two diesel motors and one electric motor.

[0067] The motor arrangement 22 is controlled by a central control unit 23. The central control unit 23 regulates which motor 21a, 21 b should be used, and controls the power supply to the motor arrangement 22. For example, during forward or reverse drive mode, the central control unit 23 may route a controlled amount of electricity from a rechargeable accumulator 24 to the electric motor 21 b. Alternatively, the central control unit 23 may regulate a switch to the diesel motor 21a, when for instance the rechargeable accumulator 24 is almost empty.

[0068] During power regeneration mode, the system works oppositely. A current in the water exerts pressure on the propeller blades 12. Consequently, the controllable pitch propeller 9 forces the drive shaft 8 to rotate, which torque via the transmission system 20 reaches the electric generator 21 b. Central control unit 23 distributes the retrieved electrical energy to the rechargeable accumulator 24 for storage, and/or distributes it directly to power on-board electrical systems 29. [0069] The rechargeable accumulator 24 may be one device, but may also comprise for instance multiple batteries in series or parallel. These batteries may all be rechargeable, or only several of them. In addition, the accumulator 24 may also, via the central control unit 23, be connected to an additional on-board charging system 25 which uses power from another source to recharge the accumulator 24, such as power received from on deck solar panels, or dockside electricity. [0070] The central control unit 23 is further connected to a pitch control unit 26 that controls an actuating device 27. The actuating device 27 is connected to a linkage 50 that is included, at least partially, within the controllable pitch propeller 9. In other embodiments, the central control unit 23 and pitch control unit 26 may also be combined.

[0071] The electric propulsion and power regeneration arrangement 7 is operated by a control panel 28 that is easily accessible for an operator of the vessel 1 , for instance on the deck of the sailing vessel 1 . The control panel 28 allows the operator of the vessel 1 to enter operator demands, which are forwarded to the central control unit 23. Operator demands may for instance comprise controls on speed, the mode of driving such as forward/reverse drive, or a preferential amount of energy that is being recharged while sailing.

[0072] In this embodiment, energy regeneration allows for an efficiency ratio of approximately 25%, which means that at maximum power regeneration approximately 25% of the power that is needed to sail using the motor arrangement 22 at a certain speed may be retrieved when sailing with the same speed using the sails 10. This is a lower efficiency rate than an individual turbine or hydrogenerator would achieve, yet there are other benefits of a combined arrangement. For example, a combined propeller and turbine is relatively cheap since the controllable pitch propeller 9 is already available below the vessel 1. As such, unnecessary drag while sailing in full sailing mode without retrieving power is avoided.

[0073] The power and regeneration arrangement 7 may be operated by an operator of the vessel 1 through control panel 28. The operator may select predefined operating modes such as forward drive, reverse drive, minimum drag position, or power regeneration, and/or enter more specific operator demands such as during power regeneration mode requesting a certain minimum velocity to be maintained, a certain amount of power to be stored, or a certain percentage of the maximum retrievable amount of power to be stored.

[0074] Figure 1C shows an enlarged side view of the drive shaft 8 and controllable pitch propeller 9 of Figures 1 A and 1 B. The controllable pitch propeller 9 has a propeller hub 11 that is connected to the drive shaft 8. The drive shaft 8 is approximately 7 meters long, has a diameter of 125 mm, and extends in a straight line defining a longitudinal axisX. At one end, the drive shaft 8 is connected to a back part 83 of the propeller hub 11 of the controllable pitch propeller 9. The other end extends through the stern tube 19 into the hull 2. The drive shaft 8 is hollow, and a rod 33 having a diameter of approximately 60 mm is concentrically arranged within the drive shaft 8. The rod 33 rotates along with the drive shaft and is used to connect the actuating device 27 with the controllable pitch propeller 9.

[0075] In forward or reverse drive mode, the drive shaft 8 receives rotary power from the motor arrangement 22 disposed inside the hull 2. The propeller hub 11 and four propeller blades 12 that are mounted on the propeller hub 11 rotate along with the drive shaft 8, generating thrust and allowing the vessel 1 to propel forward or backward dependent on the propeller blade angle. The skilled person will understand how the blade angle affects the generated thrust. Moreover, the skilled person will understand that the number of propeller blades 12 may be different in other embodiments, such as two blades, three blades, or five blades.

[0076] The propeller hub 11 has a back part 83 to which the drive shaft is attached, and a front part 82. The propeller blades 12 each have a circular blade base 13 that is retained between the front part 82 and the back part 83. The propeller hub 11 has a diameter of approximately 40 cm. [0077] The propeller blades 12 rotate along with the propeller hub 11 about the longitudinal axis X, and in addition are also rotatable with respect to the propeller hub 11 about a respective pivot axis P. Each pivot axis P is oriented in a plane normal to the longitudinal axis X. Rotation of the propeller blade base 13 and the respective propeller blade 12 about the respective pivot axis P allows for adjustment of the blade angle of the propeller blade 12.

[0078] In this embodiment, the pivot axis Pa of a first propeller blade 12a and the pivot axis Pc of a second propeller blade 12c opposite to the first propeller blade 12a coincide. Nevertheless, a person skilled in the art will understand that this is not necessarily the case in other embodiments also. In other embodiments, the pivot axes P may not be perpendicular to the longitudinal axis X. [0079] The controllable pitch propeller 9 is equipped with a linkage 50 that enforces the rotation of each propeller blade 12 about its respective pivot axis P. The linkage 50 is positioned inside the propeller hub 11 and only indicated schematically in Figure 1c. The linkage 50 can be used to adjust the blade angle of each propeller blade 12 to suitable positions for forward drive, reverse drive, minimum drag position, and power regeneration mode. The blade angle of the propeller blade 12 is defined as the angle between a chord 14 of the propeller blade 12, i.e., an imaginary straight line that joins the leading edge 15 and the trailing edge 16 of the propeller blade 12, and a plane perpendicular to the longitudinal axis X. The skilled person will understand that since the propeller blades 12 are typically twisted, the angle that a chord 14 makes will change from the root 17 to the tip 18 of a propeller blade 12. Here we discuss relative positions and measure the blade angle from a position, termed the design pitch, which is considered to be optimal for forward drive mode provided certain design conditions.

[0080] The skilled person will understand that from a design pitch for forward drive, the blades may be rotated over an angle of approximately 110 degrees to be placed in a position wherein all blades are mostly parallel to the flow and pointing toward the drive shaft with theirtip 18. From this position, the blade can be turned further to obtain a situation in which more drag is generated. By turning the blade further, the drag is gradually adjusted until an amount of drag is attained between a blade angle of -185 and -200 degrees from the design pitch for forward drive that allows for maximum power regeneration.

[0081] The angle that allows for retrieval of most energy depends amongst other things on the speed of the vessel 1 and external currents in the water. It is therefore important that the linkage 50 also allows for adjustment of the position by just a few degrees. Otherwise, the system would be optimized for a certain speed and work sub-optimally at any other speed. Therefore preferably the controllable pitch propeller 9 is equipped with a linkage 50 that allows for a continuous adjustment throughout the full range of blade angles that can be attained. [0082] Figure 2A shows in exploded view a linkage 50 within the propeller hub 11 according to a first embodiment. This linkage 50 allows for a continuous adaptation of the blade angle through a range of 210 degrees. Figure 2B shows a cross-sectional top view along cross-section IIA of Figure 2A and Figure 2C shows a cross-sectional side view along cross section MB.

[0083] The linkage 50 is activated by the actuating device 27 (not shown) that displaces an assembly of a rod 33 connected by a rod nut 34 to travelling member 51 . When the rod 33 is moved by the actuating device 27, the travelling member 51 is forced to displace along the longitudinal direction X within the propeller hub 11 .

[0084] In this embodiment, the rod 33 and rod nut 34 are individual elements that are removably connected to each other and to the travelling member 51 . In other embodiments, the rod 33 and/or rod nut 34 may also be formed as an integral part of the travelling member. Moreover, one or more of the elements may be absent.

[0085] The linkage 50 is connected to the travelling member 51. The travelling member 51 is substantially shaped as a rectangular cuboid having a top surface 71 facing the front of the propeller hub 12, a bottom surface 72 opposite to it, and four essentially identical side surfaces 73, each of which is facing a respective propeller blade base 13.

[0086] The linkage 50 includes an individual linkage or individual conversion device 54 for each propeller blade 12, i.e., four conversion devices 54 in total. To each of the four side surfaces 73 of the travelling member 51 , an individual conversion device 54i is attached. Figure 2a only shows the conversion device 54a of one propeller blade 12a for reasons of clarity.

[0087] Each conversion device 54a comprises a first mechanism to convert the linear motion of the travelling member 51 along the longitudinal axis into rotation of a rotatable plate 58a. This conversion is directly achieved in a plane parallel to the propeller blade base 13, and does not require the motion of an element along the vertical direction Z. In this embodiment, a pin-in-slot mechanism is used. The pin-in-slot mechanism comprises a pin slot 55a in the side surface 73a of the travelling member 51 . The pin slot 55a is configured to receive a first pin 56a, and provide the first pin 56a with freedom to move in a transverse direction along transverse axis Y, which is perpendicular to the longitudinal axis X and also perpendicular to the pivot axis P of the propeller blade 12a. Hence the first pin 56a can move in the longitudinal direction X when the travelling member 51 is displaced along the longitudinal axis X, and it can move in the transverse direction Y because of the freedom provided by the pin slot 55a.

[0088] The pin 56a is provided in pin slot 55a within a sliding shoe 57a to reduce the resistance and prevent the pin 56a from damaging. The sliding shoe 57a receives a first end of the first pin 56a. The second end of the first pin 56a engages with a rotatable plate 58a.

[0089] The rotatable plate 58a is rotatable about a pivot point on a second axis of rotation Q. The second axis of rotation Q is parallel to and spaced from the pivot axis P. The rotatable plate 58a is rotatably connected to the sidewall (not shown) of the propeller hub 11 using a rotation pin 65a. [0090] When the travelling member 51 is moved along the longitudinal axis X, the rotatable plate 58a will rotate over a first angle y. The pin 56a is pushed/pulled along the longitudinal direction X, and moves within the pin slot 55a along the transverse direction, forcing the pin 56a to describe a first arc 60a with the pivot point 59a as center. The first arc 60a is indicated only in Figure 2b, which shows a cross-sectional top view along cross-section I as indicated in Figure 2a.

[0091] A person skilled in the art will understand that this first mechanism can only provide rotation of the rotatable plate 58 through a limited angle as the forces to push or pull the rotatable plate 58 and all weight that is directly or indirectly connected thereto need to be exerted along the direction of the first arc 60a.

[0092] The conversion device 54a further comprises a second mechanism to convert the rotation of the rotatable plate 58a into a rotation of the propeller blade base 13 and propeller blade 12 through an angle larger than the first angle. The second mechanism includes a crank slot 61a provided within the rotatable plate 58a. This crank slot 61a is positioned in such a way that a crank pin 62a that is received therein is provided with freedom of motion closer to and further away from the pivot point 59a. To that end, a second sliding shoe 63a is mounted within the crank slot 61a. The second sliding shoe 63a is configured for receiving the first end of a crank pin 62a. The second end of crank pin 62a is eccentrically engaged with the propeller blade base 13a.

[0093] The first and second mechanism work simultaneously. When the travelling member 51 is displaced, the first mechanism induces rotation of the rotatable plate 58, and simultaneously the crank pin 62 starts describing a second arc 64 over a second angle Q as shown in Figure 2b. The crank pin 62, being eccentrically engaged to the propeller blade base 13, forces the propeller blade 12 to also rotate through angle Q. The pivot axis P is at the centre of the propeller blade base 13. [0094] The travelling member 51 is arranged to be displaced along the longitudinal axis over a distance of maximum 10 cm. Displacement over the maximum 10 cm leads to a situation wherein the rotatable member 58 is rotated over the first angle y of 55 degrees, and wherein the propeller blade 12 is rotated over the second angle Q of 210 degrees. Displacing the travelling member over a smaller distance leads to a smaller adjustment of the blade angle. Therefore, if the travelling member 51 can be positioned arbitrarily within its approximate range of 10 centimetres, the blade angle can be continuously adjusted through the entire range also.

[0095] In this embodiment, no locking mechanism is included to provide the travelling member 51 from displacement. Other embodiments, however, may be equipped with a locking mechanism to lock the position of the travelling member 51.

[0096] The blade angle is adjusted by application of a two-stage rotation. This two-stage rotation allows adjustment of the blade angle over an angle larger than the one that could be achieved using a single rotation stage. In terms of a gear ratio, the second mechanism has a gear ratio of 55:210, which is approximately 0.26. In other embodiments, the gear ratio may also be between 0.15 and 0.5, and preferably between 0.24 and 0.4. The skilled person will understand how to change the relative positions of the pin slot 55, crank slot 61 , and rotation pin 65 relative to the pivot axis P to adjust these ratios. In this embodiment, the positions have been optimized to limit the dimensions of the hub. [0097] In embodiments, the application of the two-stage rotation in the linkage 50 may also allow for a reduction in the forces that are applied on all elements, and/or a more equal distribution of the forces on the elements during adjustment of the blade angle from or to an angle in the middle of the range versus an angle near one of the endpoints of the range.

[0098] The skilled person will understand that a two-stage rotation may also be achieved using a different mechanism as first mechanism, such as a rack and pinion mechanism, a slider-crank mechanism, or a system using a chain and belt to convert linear motion into rotation. Similarly, the skilled person will recognize that there may be alternatives for the second mechanism that allow for conversion of the small angular displacement of the rotatable plate or another member, into a larger angular displacement of the propeller blade or propeller blade base. For example, a gear train. The skilled person will further understand that the distinction between a first mechanism and second mechanism should in no means be considered as limiting the scope of the invention.

[0099] Figure 2c shows a cross-sectional side view of the linkage 50 according to the same embodiment. In contrast to Figures 2a and 2b, Figure 2c shows a complete cross sectional view including all four individual conversion devices 54.

[00100] The cross-sectional view, as shown is rotationally symmetric about the longitudinal axis X, that extends through the centre of the rod 33. The travelling member 51 is rotationally symmetric, and in connection to each of its side surfaces 73, an individual conversion device 54 is constructed. Only individual conversion device 54a is fully shown. For the other conversion devices 54b, 54c, 54d only the pin slot 55b, 55c, 55d is shown.

[00101] The propeller blades 12 are clamped in between the front part 82 and back part 83 of the propeller hub 11 . Figure 2c only shows the back part 83, whereas the front part 82 is removed for clarity. The front part 82 is configured to be connected to the back part 83.

The linkage 50 is compact. The travelling member 51 is mounted at the centre of the propeller, around rod 33. Between each of the side surfaces 73 and the respective adjacent propeller blade base 12, an individual conversion device 54 is arranged. The rotatable plate 58 is only a few centimetres thick and generally thinner than the propeller blade base 13. The ratio between the hub diameter and the diameter of the entire controllable pitch propeller is approximately 0.3. This rather low ratio can be achieved because of the compactness of the linkage 50. Each of the individual conversion devices 54 converts the axial displacement of the travelling member 51 into rotary motion directly in a plane parallel to the blade base 13.

[00102] The controllable pitch propeller 9 is activated through the travelling member 51 , which is coupled to the rod 33 and rod nut 34 that are displaced by the actuating device 27. Figure 3 presents a simplified cross-sectional top view of an embodiment of an actuating device 27. The cross-section is taken through the centre of the centre of a hollow shaft 47 in the actuating device 27.

[00103] The actuating device 27 is positioned between the controllable pitch propeller 9 and the motor arrangement 22. Through the actuating device 27, a hollow central shaft 47 extends that connects a first flange 38 and a second flange 39. To the first flange 38, the controllable pitch propeller 9 can be connected via the drive shaft 8, while the second flange part 39 is facing the motor arrangement 22.

[00104] The actuating device 27 further comprises a control motor 30, which is preferably an electric motor such as a stepper motor or servomotor for providing precise control over the rotation, but may also be a hydraulic system or any other suitable motor. In this embodiment, the control motor 30 is a servomotor that drives a planetary roller screw 31 . Such planetary roller screws are generally known in the art and the present description is limited to those aspects required to understand its implementation in the present context. The control motor 30 is also only indicated schematically. [00105] The planetary roller screw 31 is positioned within a housing 40, and has a nut 41 , twelve planetary rollers 42, and an inner housing 43 with screw threads 45 along part of its outer surface. The control motor 30 drives rotation of the nut 41 . The nut 41 engages with the planetary rollers 42, which spin in contact with, and serve as low-friction transmission elements between the nut 41 and the inner housing 43. When activated, the planetary rollers 42 rotate around their own central axis, and orbit around the inner housing 43. The screw threads 44 of the planetary rollers 42 and the screw threads 45 of the inner housing 43 are arranged such that driven rotation of nut 41 leads to a displacement of the inner housing 43 in a direction along the longitudinal axis X. In this embodiment, the inner housing 43 is arranged to be moved over a distance of approximately 10 centimetres. The inner housing is shown in its extreme position close to the second flange 39, and may from this position be moved towards the first flange 38.

[00106] A yoke 46 is positioned within the inner housing 43, and the yoke 46 is arranged to be displaced within a slit 49 in the actuating device 27. The yoke 46 is positioned in a slit 49 of the central shaft 47 that extends through the actuating device 27. Upon displacement of the inner housing 43, the yoke 46 travels along the longitudinal direction with the inner housing 43, through the slit 49. The edge 37 of the slit 49 indicates to which position the yoke 46 may be moved. [00107] The yoke 46 is connected to a coupling member 48, which engages with the rod 33. This engagement may take place either inside the actuating device 27 or outside through an additional rod connecting the coupling member 48 and the rod 33. The actuating device 27 is thus configured to displace the rod 33 along the longitudinal axis X when the inner housing 43 is moved. When connected to the controllable pitch propeller 9 as described in Figure 2, also the travelling member 51 is displaced along the longitudinal axis X over the same distance as the inner housing 43. [00108] The actuating device 27 is a linear actuating device. This has as a benefit that it allows for higher accuracy in actuating the linkage 50. When a rotary actuation device would be used for linkage 50, the torque applied by the rotary actuating device would lead to torsion of the rod 33. The rod 33 is extending from both ends of the drive shaft 8, and therefore the rod 33 has a length of more than 7 metres in this embodiment. This would lead to a non-negligible angle of twist of the rod 33 when enough torque would be applied to adjust the blade angle.

[00109] Specifically beneficial of using a planetary roller screw 31 driven by a control motor 30 is that a planetary roller screw 31 has a high load carrying capacity and that a high accuracy may be achieved. Besides that, the planetary roller screw 31 has a relatively long lifetime in comparison to other linear actuators and it can operate with minimal maintenance and at high efficiency. For example, in comparison to hydraulic cylinders that may start leaking at some moment, planetary roller screws 31 are more reliable.

[00110] Moreover, the displacement of the inner housing 43 can be done continuously, i.e., the planetary roller screw mechanism allows for a very precise adjustment of the position of the inner housing 43. This position of the inner housing 43 can be maintained accurately, which means that the position of the travelling member 51 and therefore the blade angle position can be maintained accurately as well.

[00111] Although this actuating device 27 certainly has its benefits, the skilled person will understand that any other actuating device that leads to a controlled axial displacement of the rod 33 or another travelling member could also be used as actuating device.

[00112] For example, the actuating device as described in WO 2005/012078 A1 could also be the controllable pitch propeller 9. Also other variants of that system wherein mechanically a rod is pushed through a hollow drive shaft would suffice. Another category of possible embodiments for an actuating device involves devices that use hydraulic actuation. Such hydraulic actuation may either take place on board of the vessel or within or near the propeller hub. In yet other embodiments, the actuating device may include using a screw jack or a ball screw. The skilled person will understand that there are also several other possibilities for an actuating device that allow for a controlled axial movement of the rod or another member activating the linkage.

[00113] Moreover, it will be understood by a person skilled in the art that in some embodiments, for instance when hydraulic actuation takes place inside the propeller hub, the coupling mechanism of the actuator to the linkage may look different. For instance, a rod may be absent if the actuation is effective directly in the propeller hub.

[00114] Also a travelling member as illustrated in our exemplary embodiment may be absent or have a different shape. Exemplary alternatives include a claw with fingers, or preferably other shapes with a discrete rotational symmetry or with more general polygonal or curved cross-sectional shapes. The skilled person will understand that any shape suffices, provided that there is at least a travelling member that is displaced along the direction of the drive shaft and is able to pass this linear motion to a conversion device that converts linear motion into rotation. Therefore the skilled person will also understand that if the blade pitch adjustment system can be activated directly by for instance the rod directly, an additional travelling member is not needed. Similarly, the travelling member may also not be just one element, but may also consist of a number of individual elements, e.g., one element for each propeller blade.

[00115] The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. It will be apparent to the person skilled in the art that alternative and equivalent embodiments of the invention can be conceived and reduced to practice. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

[00116] Those skilled in the art and informed by the teachings herein will realize that the invention is applicable in any situation wherein an external current is present, and for which power generation is desired. This may for example include situations wherein the vessel is equipped with other propulsion means that propel the vessel, or a situation wherein the vessel is anchored and a current in the water may be used to generate power. In this case, the propeller may function as a turbine to power electrical circuits on board, to recharge the batteries overnight, or to drive other systems that can make a direct use of the rotational power produced by the controllable pitch propeller. The invention is therefore applicable to any motorized vessel that is considered to be exposed to external currents that allows for power regeneration, including both sailing vessels and regular motorized vessels.

[00117] In addition, those skilled in the art will for instance also realize that this invention is also applicable to multi-hull vessels such as a catamaran or trimaran. Such vessels may be equipped with more than one propeller, wherein one or more of the propellers may have controllable pitch according to the invention.