Method for controlling the propulsion of a marine vessel

Abstract

To disclose a method for controlling a propulsion system of a sea vessel.SOLUTION: A controller forms data regarding a pitch angle of at least two foils attached to be capable of rotation to a foil wheel based on angle variable eccentricity of each of at least two foils and a rotational angle of the foil wheel. The variable eccentricity is restricted in one portion of the rotational angle of the foil wheel. An actuator device receives the data from the controller and sets at least two foils to the pitch angle based on the data.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for controlling a propulsion system of a marine vessel. [Background technology]

[0002] A marine vessel may move relative to the water around it using thrust from a propulsion system that includes one or more rotating foil wheels with foils extending perpendicularly from the wheel. Foil wheel propulsion systems generate thrust through the combined action of a fixed rotation about a central axis and the oscillating motion of the foils. With individual foil pitch control, a typical propulsion system operates at a trochoidal pitch angle that is optimal for torque loads at maximum speed. However, with realistically limited foil motor torque, such a propulsion system may not be optimal under bollard pull conditions.

[0003] Therefore, it would be beneficial to find a pitch angle function that has improved bollard pull thrust in a propulsion system with realistically limited foil motor torque. Summary of the Invention

[0004] According to one aspect, the subject matter of the independent claims is provided. The dependent claims define some embodiments.

[0005] Some example embodiments will now be described with reference to the accompanying drawings. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 illustrates an example of a seagoing vessel. [Figure 2] FIG. 2 illustrates an example of a propulsion system. [Figure 3] FIG. 3 illustrates an example coordinate system. [Figure 4] FIG. 4 is a flow chart illustrating an example function. [Figure 5]FIG. 5 is a flow chart illustrating example functionality. [Figure 6] FIG. 6 illustrates an example of the derivative of the pitch angle. [Figure 7] FIG. 7 illustrates an example of the derivative of the pitch angle. [Figure 8] FIG. 8 illustrates an example of a foil motor rotor angle curve. [Figure 9] FIG. 9 illustrates an example of a foil motor torque curve. [Figure 10] FIG. 10 illustrates an exemplary embodiment of the device. DETAILED DESCRIPTION OF THE INVENTION

[0007] The following embodiments are illustrative. Although the specification may refer to "an," "one," or "some" embodiment(s) in some places, this does not necessarily mean that each such reference is to the same embodiment(s) or that a feature applies only to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments. Furthermore, the terms "comprising" and "including" should not be understood to limit the described embodiments / examples to only those features referenced; such embodiments may also include features / structures not specifically referenced. Furthermore, terms containing ordinal numbers, such as "first," "second," etc., may be used to describe various elements, but structural elements are not limited by these terms. These terms are used solely to distinguish one element from another. For example, a first element could be referred to as a second element, and similarly, a second element could be referred to as a first element, without departing from the scope of the present disclosure.

[0008] The method embodiments and examples described herein may be implemented in any foil wheel propulsion system having individually controllable foils.

[0009] It should be noted that while the figures illustrate various embodiments, they are simplified diagrams showing only some structural and / or functional entities. The connections shown in the figures may refer to logical or physical connections. It is clear to those skilled in the art that the described devices and / or systems may also have functions and structures other than those shown in the figures and text. It should be understood that the details of some functions, structures, and signaling used for measurement and / or control are irrelevant to the actual invention. Therefore, they need not be described in greater detail herein.

[0010] FIG. 1 illustrates an example of a marine vessel 100 (the marine vessel is partially shown in FIG. 1 ) having a propulsion system 102 with one or more propulsion subsystems 104, 104′. Marine vessels may include transport vessels and passenger ships, and the terms marine vehicle or marine vessel may generally refer to, for example, any vessel designed for waterborne transportation. Transport vessels may include, for example, cargo ships and container ships. Additionally, marine vessels may refer to fishing vessels, service vessels such as tugboats and supply ships, and warships. Furthermore, marine vessels may be used as ferries and submarines. Those skilled in the art will appreciate that marine vessels may include any number of the illustrated elements, other equipment, other functions, and other structures not illustrated. These, as well as the protocols used, are well known to those skilled in the art and are irrelevant to the actual invention. Therefore, they need not be described in greater detail herein.

[0011] In the illustrated example, the propulsion subsystems 104, 104' are cyclorotor propellers that may be capable of generating both cycloidal and trochoidal pitch angles depending on the propeller's advance rate. Advance rate may be understood as the ratio of free-stream fluid velocity to the propeller's tip speed. Each exemplary propulsion subsystem 104, 104' includes a foil wheel 106, 106'. The foil wheel 106, 106' includes at least two foils 108, 108'. The foils 108, 108' are blades that may extend from the wheel 106, 106' perpendicular to the plane of rotation of the wheel 106, 106'. The foils 108, 108' are rotatably attached to the foil wheel 106, 106'. All foils 108, 108' of the foil wheel 106, 106' may be individually rotatably controllable relative to the foil wheel 106, 106', so that a desired pitch angle can be obtained completely independently for each of the foils 108, 108'. Alternatively, the foils 108, 108' may be jointly controllable and coupled to the foil wheel, for example mechanically through suitable joints and / or gears, so that a desired pitch angle can be obtained for each of the foils 108, 108'. For example, the foils 108, 108' may be coupled to achieve a constant phase difference between the rotation of the individual foils.

[0012] 1, the wheel engine system 120 may be common to multiple propulsion subsystems 104, 104' through mechanical power transmission. Alternatively, each or some of the propulsion subsystems 104, 104' may have a separate wheel engine system 120.

[0013] FIG. 2 illustrates an example in which the propulsion system 102 includes one foil wheel 106 with individually controllable foils 108. That is, the propulsion system 102 may correspond to one of the propulsion subsystems 104, 104′. Additionally, the example propulsion system 102 includes an actuator arrangement 110 and a controller 112. The actuator arrangement 110 is operatively coupled to the foils 108 and configured to rotate the foils. The controller 112 may be common to the propulsion subsystems 104, 104′ (see FIG. 1), or the controller 112 may include multiple sub-controllers, one sub-controller for each of the propulsion subsystems 104, 104′ (although such a possibility is illustrated in FIG. 2, the controller 112 of FIG. 2 may also exist for multiple foil wheels).

[0014] According to one embodiment, the controller 112 comprises one or more memories 116 and one or more processors 114 containing computer program code. The one or more memories 116 and the computer program code cause the controller 112, using the one or more processors 114, to calculate an angle of rotation θ of the foil wheel 106 to which at least two foils 108 are mechanically connected, and an angularly variable eccentricity r of each of the at least two foils 108. + Based on this, the pitch angles γ(θ, r + ) which can be expressed mathematically as: γ(θ,r + )=J(θ,r + (θ)), where J is the pitch angle γ(θ,r + ) and the angle of rotation θ of the foil wheel 106 and the angular variable eccentricity r + (θ) is its argument. The pitch angle of the foil γ(θ,r + ) can also be called the foil pitch trajectory because it is a function of the rotation angle θ of the foil wheel and typically forms a curve.+ is limited at a portion of the rotation angle of the foil wheel 106 to limit the peak torque of the foil 108.

[0015] According to one embodiment, the controller 112 then controls the pitch angle γ(θ,r + ) to the actuator device 110, which, based on the data generated by the controller 112, controls the at least two foils 108 to rotate at a pitch angle γ(θ,r + ) from the control device 112. The data may include a pitch angle parameter and / or at least one value of the pitch angle. The actuator device 110 may comprise an electric motor device AR for each of the at least two foils 108, the electric motor device AR being operably coupled to the respective foil 108. The electric motor device AR may be configured to rotate each foil 108 about the longitudinal axis of the foil, as illustrated in the example of FIG. 2. The electric motor device AR may comprise a regulator and an electric motor (foil motor), which receives, for example, a pitch angle γ(θ,r + ) to rotate the foils to which it is mechanically coupled. The functionality of the foil wheel 106 and the at least two foils 108 described in FIG. 2 can be similarly applied to the foil wheel 106′ and foils 108′ of FIG.

[0016] The control device 112 may also control the drive device 118 of the wheel engine system 120. The wheel engine system 120 may include an engine (motor), which may include an electric engine, a combustion engine such as a diesel engine, a gasoline engine, or a gas engine, and potentially a mechanical gearbox. The configuration of the drive device 118 may depend on the type of engine. If the wheel engine system 120 includes one or more electric engines (electric motors), the drive device 118 may include, for example, an electric drive device configured to control the electric engine(s). The control device 112 may send commands to the drive device 118, which may then control the rotational speed and / or rotational direction of the engine of the wheel engine system 120. The wheel engine system 120 may rotate the foil wheel 106, for example, directly or through a gearbox. However, the details of the wheel engine system are not relevant to the actual invention, and those skilled in the art are familiar with various wheel engine systems 120 themselves. Therefore, they need not be described in more detail herein. As illustrated in the example of FIG. 2, each of the propulsion subsystems 104, 104' may have its own wheel engine system 120.

[0017] In one embodiment, the pitch angle is:

[0018]

number

[0019] where γ is the foil pitch angle relative to the x-axis (current direction of travel), θ is the rotation angle of the foil wheel 106 measured counterclockwise relative to the negative y-axis, and r + is the eccentricity, and tan -1is the inverse tangent function (also known as the arctangent function). An example of the coordinate system and central angle definition of the foil 108 is illustrated in Figure 3, where X and Y represent the coordinate axes of the foil wheel relative to the direction of travel, and X' and Y' represent the coordinate axes of the foil relative to the foil wheel. Five foils 108 are attached to a foil wheel (not shown in Figure 3), arranged with an equal angle of 72° between adjacent foils. In this case, the angular velocity of the foil motor is

[0020]

number

[0021] where ω wheel is the angular velocity of the foil wheel 106. The angular acceleration of the foil motor is

[0022]

number

[0023] where the angular velocity ω of the foil wheel 106 wheel is assumed to be constant. Therefore, the behavior of the first and second derivatives of the pitch angle γ determines the behavior of the angular velocity and angular acceleration of the foil motor, respectively. The required foil motor torque depends on the angular velocity for the hydrodynamic load and the angular acceleration for the inertial load. The angular velocity and angular acceleration peak near an angle θ=180° with respect to the negative y-axis, and therefore the foil experiences the highest load near that angle.

[0024] Variable angle eccentricity for limited torque

[0025]

number

[0026] is also a function of the rotation angle θ. In one example, it is

[0027]

number

[0028] where:

[0029]

number

[0030] is the optimum constant eccentricity obtained with unconstrained foil motor torque, A is the limit amplitude parameter, and n is the steepness parameter. The limit amplitude parameter and steepness parameter define lower values ​​of the eccentricity for a portion of the rotation angle around a first rotation angle where the foil 108 experiences the highest load. The first rotation angle may be an angle θ=180° with respect to the negative y-axis. The limit amplitude parameter and steepness parameter may be selected as desired. The limit amplitude defines how much the eccentricity is reduced from the eccentricity used outside the portion around the angle θ=180°. A large steepness parameter creates a narrow limit portion (with respect to θ), while a small steepness parameter creates a wider limit portion.

[0031] Another example is variable angular eccentricity for limited torque.

[0032]

number

[0033] can be written symbolically as a partial sum of different functions, for example a Fourier series.

[0034] FIG. 4 illustrates an example of a control method.

[0035] 4, data regarding the pitch angles of the at least two foils is formed by a controller in block 401 based at least on the angular variable eccentricity of each of the at least two foils and the rotation angle of the foil wheel. The at least two foils are individually controllable and rotatably attached to the foil wheel. The variable eccentricity is limited to a portion of the rotation angle of the foil wheel. The at least two foils are set to a pitch angle based on the data in block 402 by an actuator device that receives the data from the controller.

[0036] FIG. 5 illustrates an example of determining the parameters for the variable angular eccentricity of the control method.

[0037] Referring to FIG. 5 , in block 501, a first eccentricity is determined. The first eccentricity is an optimal constant eccentricity for unlimited torque. In block 502, a second eccentricity is determined. The second eccentricity is the maximum constant eccentricity that the foil motor can tolerate. In block 503, a limit amplitude parameter is determined as the deviation between the first eccentricity and the second eccentricity. For example, if the first eccentricity is 0.7 and the second eccentricity is 0.5, the limit amplitude parameter is 0.2. Thus, the limit amplitude parameter is a positive constant. In block 504, a steepness parameter is determined so that the first and second derivatives of the data relating to the pitch angle with respect to the rotation angle are smooth. The steepness parameter may be determined iteratively. The steepness parameter may also be determined by more advanced optimization methods.

[0038] An example of the first derivative is presented in Figure 6 and an example of the second derivative is presented in Figure 7. The first and second derivatives of the pitch function for limited torque eccentricity are compared to the first and second derivatives of the pitch function for constant eccentricity.

[0039] 6 and 7, the dashed lines indicate the rotational speed at a constant eccentricity r + = 0.7, and the dashed line indicates a constant eccentricity r += 0.5, and the solid line represents the torque limit eccentricity ratio.

[0040]

number

[0041] The figures in Figures 6 and 7 are merely examples to show that the first and second derivatives of the limited torque related to eccentricity can be drawn close to the curve obtained with a constant eccentricity of 0.7 for most of the rotation angle θ, but around θ = 180° the curve can be shifted closer to the curve obtained with a constant eccentricity of 0.5 in order to avoid high loads on the foil motor.

[0042] Figure 8 illustrates a corresponding example of the foil motor rotor angle relative to the stator, which can be determined by subtracting the rotation angle θ from the pitch angle γ, i.e., γ - θ. The dashed line indicates the angle of rotation for a given eccentricity r + = 0.7, and the dashed line indicates a constant eccentricity r + = 0.5, and the solid line represents the torque limit eccentricity ratio.

[0043]

number

[0044] The figures in Figure 8 are merely an example to show that the rotor angle associated with limited torque eccentricity can be brought close to the curve obtained with a constant eccentricity of 0.7 for most of the rotation angle θ, but around θ = 180° the curve can be shifted closer to the curve obtained with a constant eccentricity of 0.5 to avoid high loads on the foil motor.

[0045] The advantage of shaping the pitch angle of the foil trajectory as a function of the variable eccentricity angle can be to obtain higher bollard pull thrust while the maximum foil motor torque can be somewhat reduced. Foil-wise eccentricity adjustment is made possible by individually controllable foils. The presented method can be used to optimize the pitch function to suit the selected foil motor torque specification, or to select foil motors for a required bollard pull thrust without oversizing them.

[0046] An example of foil wheel bollard pull performance simulation is shown in Table 1. A speed of 55 RPM is used in the simulation. A constant eccentricity r + = 0.5 is considered to be at the foil motor torque limit, i.e., the bollard pull thrust cannot be increased by increasing the constant eccentricity, the angle variable torque limit eccentricity

[0047]

number

[0048] can result in a 33% higher bollard pull thrust, while the maximum foil motor torque is reduced from 61 kNm to 56 kNm.

[0049] [Table 1]

[0050] Figure 9 illustrates a corresponding example of the resulting foil motor torque. The thin solid line represents the torque at constant eccentricity r + = 0.7, and the solid circle indicates a constant eccentricity r + =0.5, and the thick solid line indicates the torque limit eccentricity ratio.

[0051]

number

[0052] The numbers in Figure 9 are merely an example to show that the maximum foil motor torque associated with a limited torque eccentricity is even smaller than that obtained with a constant eccentricity of 0.5.

[0053] 4 and 5 are not in an absolute chronological order, and some of the blocks may be performed simultaneously or in an order different from the predetermined order. Other functions may also be performed between or within the blocks. Some of the blocks or portions of the blocks may also be excluded or replaced by corresponding blocks or portions of blocks, for example, determining the first eccentricity and the second eccentricity may be excluded or replaced by each other.

[0054] The techniques described herein may be implemented by various means, such that an apparatus implementing one or more functions / operations described above using the embodiments / examples, e.g., according to any of Figures 1-5 and any combination thereof, may include not only prior art means but also means for implementing one or more functions / operations of the corresponding functions described using the embodiments, e.g., according to any of Figures 1-5 and any combination thereof, which may include separate means for each separate function / operation, or a means may be configured to perform two or more functions / operations. For example, one or more of the means for one or more functions / operations described above may be software and / or software-hardware and / or hardware and / or firmware components (indelibly recorded on a medium such as a read-only memory or embodied in hardwired computer circuitry), or a combination thereof. The software code may be stored in any suitable processor / computer-readable data storage medium(s) or memory unit(s) or article(s) of manufacture and executed by one or more processors / computers, hardware (one or more devices), firmware (one or more devices), software (one or more modules), or any combination thereof. In the case of firmware or software, implementation may be through modules (e.g., procedures, functions, etc.) that perform the functions described herein.

[0055] 10 is a simplified block diagram illustrating some units of an apparatus (device, equipment) 1000 configured to perform at least some of the functions described above for controlling the propulsion of a marine vessel, e.g., according to Figures 1 to 5 and any combination thereof. In the illustrated example, the apparatus 1000 comprises one or more interface (IF) entities 1001, such as one or more user interfaces, and one or more processing entities 1002 connected to the various interface entities 1001 and one or more memories 1003.

[0056] The one or more interface entities 1001 are entities for receiving and transmitting information, such as a communication interface comprising hardware and / or software for providing communication connectivity according to one or more communication protocols, for storing and fetching data, or for providing user interaction via one or more user interfaces, such as those described above in the description of the example illustrated by FIG. 1.

[0057] The processing entity 1002 is capable of performing calculations and is configured to implement at least some of the functions / operations described above, e.g., according to any of Figures 1-5 and any combination thereof, using corresponding algorithms 1004 stored in memory 1003. The entity 1002 may include one or more processors, controllers, control units, microcontrollers, etc., that are configurable to perform the embodiments / examples / implementations or operations described above, e.g., according to any of Figures 1-5 and any combination thereof. Typically, a processor is a central processing unit, but the processor entity 1002 may be an additional computing processor or a multi-core processor or microprocessor.

[0058] The memory 1003 can be used to store computer program code, i.e., algorithms 1004, necessary for one or more of the functions / operations described above, for example, according to any of Figures 1-5 and any combination thereof. The memory 1003 can also be used to at least temporarily store other possible information necessary for one or more of the functions / operations described above, for example, according to any of Figures 1-5 and any combination thereof. The memory 1003 can comprise, for example, a data buffer that can at least temporarily store measurement data and / or information received as user input.

[0059] In summary, the methods described herein, for example, according to any of Figures 1-5 and any combination thereof, may be configured as a computer or processor, or a microprocessor such as a single-chip computer element, including at least a memory for providing storage areas used for arithmetic operations and an arithmetic processor for performing arithmetic operations, or as a chipset or one or more logic gates. For example, according to any of Figures 1-5 and any combination thereof, each or some or one of the algorithms for the functions / operations described above may be included in one or more computer processors, application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), graphics processing units (GPUs), and / or other hardware components that will be and / or have been programmed by downloading computer program code (one or more algorithms) to perform one or more functions of one or more embodiments / examples.

[0060] One embodiment provides a computer program embodied on any client-readable distribution / data storage medium or memory unit(s) or article(s) of manufacture, comprising program instructions executable by one or more processors / computers, which, when loaded into an apparatus (device, equipment), constitute an entity providing the corresponding function or at least a portion of the corresponding function. The program, also referred to as a program product, including software routines, program fragments constituting a "program library," applets, and macros, can be stored in any medium, including a non-transitory computer-readable storage medium, and downloaded to the apparatus. In other words, for example, each or some or one of the algorithms for one or more functions / operations described above, according to any of Figures 1-5 and any combination thereof, can be included in an element comprising one or more arithmetic logic units, several special registers, and control circuitry.

[0061] It will be obvious to those skilled in the art that as technology advances, the concept of the present invention can be implemented in various ways. The present invention and its embodiments are not limited to the examples described above, but may be modified within the scope of the claims. The original claims of the present application are set forth below. [1] A method for controlling a propulsion system of a marine vessel, the propulsion system comprising a foil wheel, at least two foils rotatably mounted on the foil wheel, an actuator device, and a controller, the method comprising: generating, by the control device, data relating to pitch angles of the at least two foils based at least on the angular variable eccentricity of the at least two foils and a rotation angle of the foil wheel, wherein the variable eccentricity is limited within a portion of the rotation angle of the foil wheel; setting the at least two foils to the pitch angle based on the data by the actuator device receiving the data from the controller; A method comprising: [2] The method according to [1], wherein the at least two foils are individually controllable. [3] The method according to [1], wherein the portion of the rotation angle of the foil wheel is located near a first rotation angle, and the foil is subjected to the highest load at the first rotation angle. [4] determining the portion of the rotation angle of the foil wheel using at least a limit amplitude parameter and a steepness parameter; The method according to any one of [1] to [3], further comprising: [5] determining a first eccentricity, wherein the first eccentricity is an optimum constant eccentricity for unlimited foil motor torque; determining a second eccentricity, wherein the second eccentricity is a maximum constant eccentricity that can be tolerated by the foil; determining the limit amplitude parameter as a deviation between the first eccentricity and the second eccentricity; determining the steepness parameter such that first and second derivatives of the data relating to the pitch angle with respect to the roll angle are smooth; The method according to [4], further comprising: [6] determining the portion of the rotation angle of the foil wheel using parameters of a Fourier series. The method according to any one of [1] to [3], further comprising: [7] A computer-readable medium comprising program instructions that, when executed by an apparatus, cause the apparatus to perform at least one of the methods described in [1] to [3]. [8] The computer-readable medium according to [7], wherein the computer-readable medium is a non-transitory computer-readable medium. [9] A propulsion system for a marine vessel, comprising: a foil wheel, at least two foils rotatably mounted on the foil wheel, an actuator device, and a control device; the controller comprising one or more memories containing computer program code and one or more processors; the one or more memories and the computer program code are configured, using the one or more processors, to cause at least the control device to at least form data regarding a pitch angle of the at least two foils based on an angular variable eccentricity of the at least two foils and a rotation angle of the foil wheel, wherein the variable eccentricity is limited within a portion of the rotation angle of the foil wheel, and communicate the data regarding the pitch angle to the actuator device; The actuator device is configured to set the at least two foils to the pitch angle based on the data.

[10] The propulsion system of [9], wherein the at least two foils are individually controllable.

[11] The propulsion system described in [9], wherein the portion of the rotation angle of the foil wheel is located near a first rotation angle, and the foil is subjected to the highest load at the first rotation angle.

[12] The propulsion system described in any one of [9] to

[11] , wherein the one or more memories and the computer program code are configured to further cause the control device, using the one or more processors, to determine the portion of the rotation angle of the foil wheel using at least a limit amplitude parameter and a steepness parameter.

[13] The one or more memories and the computer program code are configured to cause the controller, using the one or more processors, to: determining a first eccentricity, wherein the first eccentricity is an optimum constant eccentricity for unlimited foil motor torque; determining a second eccentricity, wherein the second eccentricity is a maximum constant eccentricity that can be tolerated by the foil; determining the limit amplitude parameter as a deviation between the first eccentricity and the second eccentricity; determining the steepness parameter such that first and second derivatives of the data relating to the pitch angle with respect to the roll angle are smooth;

[12] The propulsion system according to

[12] , further configured to:

[14] A propulsion system as described in any one of [9] to

[11] , wherein the one or more memories and the computer program code are configured to use the one or more processors to further cause the control device to determine the portion of the rotation angle of the foil wheel using parameters of a Fourier series.

[15] A marine vessel equipped with at least one propulsion system according to any one of [9] to

[11] .

Claims

1. 1. A method for controlling a propulsion system of a marine vessel, the propulsion system comprising a foil wheel, at least two foils rotatably mounted on the foil wheel, an actuator device, and a controller, the method comprising: forming, by the control device, data relating to pitch angles of the at least two foils based at least on the angular variable eccentricity of the at least two foils and a rotation angle of the foil wheel, wherein the variable eccentricity is limited at a portion of the rotation angle of the foil wheel, the portion of the rotation angle of the foil wheel being located near a first rotation angle, and foils are subjected to the highest load at the first rotation angle; receiving the data from the controller, and setting the at least two foils to the pitch angle based on the data by the actuator device; A method comprising:

2. The method of claim 1 , wherein the at least two foils are individually controllable.

3. determining the portion of the rotation angle of the foil wheel using at least a limit amplitude parameter and a steepness parameter; The method of any one of claims 1 to 2, further comprising:

4. determining a first eccentricity, wherein the first eccentricity is an optimum constant eccentricity for unlimited foil motor torque; determining a second eccentricity, wherein said second eccentricity is a maximum constant eccentricity that can be tolerated by said foil; determining the limit amplitude parameter as a deviation between the first eccentricity and the second eccentricity; determining the steepness parameter such that first and second derivatives of the data relating to the pitch angle with respect to the roll angle are smooth; The method of claim 3 further comprising:

5. determining the portion of the rotation angle of the foil wheel using parameters of a Fourier series; The method of any one of claims 1 to 2, further comprising:

6. A computer readable medium comprising program instructions which, when executed by an apparatus, cause said apparatus to perform at least the method of any one of claims 1-2.

7. The computer-readable medium of claim 6 , wherein the computer-readable medium is a non-transitory computer-readable medium.

8. 1. A propulsion system for a marine vessel, comprising: a foil wheel, at least two foils rotatably mounted on the foil wheel, an actuator device, and a control device; the controller comprising one or more memories containing computer program code and one or more processors; the one or more memories and the computer program code are configured to cause, using the one or more processors, at least the control device to form data regarding a pitch angle of the at least two foils based at least on an angular variable eccentricity of the at least two foils and a rotation angle of the foil wheel, wherein the variable eccentricity is limited at a portion of the rotation angle of the foil wheel, the portion of the rotation angle of the foil wheel being located near a first rotation angle, and foils are subjected to a highest load at the first rotation angle; and communicate the data regarding the pitch angle to the actuator device; the actuator device is configured to set the at least two foils to the pitch angle based on the data.

9. 9. The propulsion system of claim 8, wherein the at least two foils are individually controllable.

10. 10. The propulsion system of claim 8, wherein the one or more memories and the computer program code are configured, using the one or more processors, to further cause the control device to determine the portion of the rotation angle of the foil wheel using at least a limit amplitude parameter and a steepness parameter.

11. The one or more memories and the computer program code are configured to cause the controller, using the one or more processors, to: determining a first eccentricity, wherein the first eccentricity is an optimum constant eccentricity for unlimited foil motor torque; determining a second eccentricity, wherein said second eccentricity is a maximum constant eccentricity that can be tolerated by said foil; determining the limit amplitude parameter as a deviation between the first eccentricity and the second eccentricity; determining the steepness parameter such that first and second derivatives of the data relating to the pitch angle with respect to the roll angle are smooth; The propulsion system of claim 10 further configured to:

12. 10. The propulsion system of claim 8, wherein the one or more memories and the computer program code are configured, using the one or more processors, to further cause the controller to determine the portion of the rotation angle of the foil wheel using parameters of a Fourier series.

13. A marine vessel equipped with at least one propulsion system according to any one of claims 8 to 9.

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