Ship propulsion systems

Abstract

The present invention provides a ship propulsion system that can suppress the loss of stability of a ship when changes occur in the ship's navigation conditions while hump control is in place. [Solution] The ship's propulsion system comprises a drive source and a propulsion unit that generates thrust by power transmitted from the drive source, a propulsion machine installed on the hull, a trim angle adjustment unit that adjusts the trim angle of each propulsion machine on both the left and right sides relative to the hull, and a control unit that controls the trim angle adjustment unit, wherein the control unit is capable of performing hump control, which adjusts the trim angle of the propulsion machine with a preset trim angle lower limit as the lower limit, and when a preset condition is met while hump control is being performed, the system adjusts the trim angle of the propulsion machine so that the trim angle of the propulsion machine becomes a trim angle reference value set to be greater than the trim angle lower limit.

Description

Technical Field

[0001] The present invention relates to a marine vessel propulsion system.

Background Art

[0002] Conventionally, various technologies for automatically controlling marine vessel propulsion systems have been proposed in order to improve the stability, acceleration performance, maximum speed, fuel efficiency, and the like of a marine vessel during navigation. For example, when the bow is lifted significantly relative to the stern and the pitch angle of the hull with respect to the horizontal plane increases, a so-called hump state is reached, which may impair the forward visibility of the marine vessel.

[0003] For example, Patent Document 1 discloses that when the pitch angle of the hull with respect to the horizontal plane exceeds a set value, the trim angle of the propulsion unit is reduced to suppress the hump state of the hull.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Incidentally, if the trim angle of the propulsion unit is significantly reduced in order to more effectively suppress the hump state of the hull, there is a possibility that the stability of the marine vessel may be impaired or the operator may feel a sense of incongruity due to changes in the navigation state of the marine vessel or the like. The present invention has been made in view of the above circumstances, and an object thereof is to provide a marine vessel propulsion system capable of suppressing impairment of the stability of a marine vessel when a change in the navigation state of the marine vessel or the like occurs during hump control.

Means for Solving the Problems

[0006] (1) A marine vessel propulsion system according to one aspect of the present disclosure comprises: A propulsion system provided on the hull has a drive source and a propulsion unit that generates thrust by power transmitted from the drive source, A trim angle adjustment unit for adjusting the trim angle of the propulsion unit relative to the hull, A ship propulsion system comprising a control unit for controlling the trim angle adjustment unit, The control unit, In order to suppress the pitch tilt of the hull, a hump control is possible in which the trim angle of the propulsion system is adjusted by the trim angle adjustment unit, using a preset lower limit value for the trim angle. When the hump control described above is being performed and a preset condition is met, the trim angle adjustment unit adjusts the trim angle of the propulsion unit so that the trim angle of the propulsion unit becomes a trim angle reference value set to be larger than the lower limit of the trim angle in the direction in which the propulsion unit stands upright in front of the propulsion direction of the hull.

[0007] (2) In the propulsion system of a ship relating to the embodiment of (1) above, The aforementioned control unit, If it is determined that the hull is turning while the hump control is being performed, the trim angle adjustment unit may adjust the trim angle of the propeller so that the trim angle of the propeller becomes the trim angle reference value.

[0008] (3) In the propulsion system of a ship relating to the embodiment of (2) above, The control unit, If, while the hump control is being performed, it is determined that the hull is turning, and the trim angle of the propulsion engine is between the trim angle reference value and the trim angle lower limit, the trim angle of the propulsion engine at that time may be maintained.

[0009] (4) In a ship propulsion system relating to any one of the embodiments described in (1) to (3) above, The control unit, If the trim angle of the thruster reaches the lower limit of the trim angle while the hump control is being performed, the execution of the hump control may be stopped, and the system may be put into a standby state where the hump control can be performed again.

[0010] (5) In a ship propulsion system relating to any one of the embodiments described in (1) to (4) above, The system further includes a trim angle control unit that operates the trim angle adjustment unit via external input, The control unit, While the hump control is being performed, if the trim angle of the thruster is between the trim angle reference value and the trim angle lower limit when an operation input is received from the trim angle operation unit, the trim angle of the thruster may be adjusted by the operation input from the trim angle operation unit, with the trim angle reference value as the lower limit. [Effects of the Invention]

[0011] According to the embodiment of (1), when hump control is being performed and a preset condition is met, the trim angle of the propeller is adjusted so that the trim angle of the propeller becomes a trim angle reference value that is set to be greater than the lower limit of the trim angle. As a result, when the set condition is met, the effect of suppressing the hump state by hump control is reduced. Therefore, when hump control is being performed and a change in the ship's navigation state occurs, it is possible to suppress the loss of the ship's stability.

[0012] According to the embodiment of (2), if it is determined that the hull is turning, the trim angle of the propulsion system is set to the trim angle reference value. This suppresses the effect of hump control while the hull is turning and stabilizes the behavior of the hull while it is turning.

[0013] According to the aspect (3), when it is determined that the hull is turning, if the trim angle of the propulsion unit is between the trim angle reference value and the trim angle lower limit value, the trim angle of the propulsion unit at that point is maintained. Accordingly, when the hump control is executed with the trim angle of the propulsion unit set to be equal to or less than the trim angle reference value, the hull can be stably shifted to the turning state while maintaining the hump state suppression effect by the hump control when the hull shifts to the turning state.

[0014] According to the aspect (4), when the trim angle of the propulsion unit reaches the trim angle lower limit value while the hump control is being executed, the execution of the hump control is stopped, and a standby state in which the hump control can be executed is set. Accordingly, in a state where the trim angle of the propulsion unit reaches the trim angle lower limit value and the hump state suppression effect by the hump control is maximized, continuing the hump control suppresses frequent fluctuations in the trim angle of the propulsion unit, and the state where the hump state suppression effect is exerted can be stably maintained.

[0015] According to the aspect (5), when an operation input from the trim angle operation unit is received while the hump control is being executed, if the trim angle of the propulsion unit is between the trim angle reference value and the trim angle lower limit value, the trim angle reference value is set as the lower limit when the trim angle of the propulsion unit is adjusted by the operation input from the trim angle operation unit. Accordingly, when a mariner performs a manual operation, it is possible to prevent the trim angle of the propulsion unit from becoming equal to or less than the trim angle reference value due to the manual operation. As a result, it is possible to prevent the hump state suppression effect by the hump control from being strongly perceived during manual operation, and to prevent the mariner from feeling a sense of discomfort. Brief Description of the Drawings

[0016] [Figure 1] It is a plan view of the ship according to the present embodiment. [Figure 2] It is a functional block diagram of the propulsion system of the ship. [Figure 3] It is a side view of the propulsion unit of the above propulsion system. [Figure 4]In the above propulsion system, this is a diagram showing an example of trim support control, heel control, hump control, and bow control executed in accordance with the ship speed. [Figure 5] This is a diagram showing a state in which trim support control is performed by the above propulsion system. [Figure 6] In the above propulsion system, this is a diagram showing an example of set values of trim support angles in trim support control, heel control, and hump control executed in accordance with the ship speed. [Figure 7] This is a diagram showing a state in which heel control is performed while the above ship is tilted to the port side. [Figure 8] This is a diagram showing a state in which heel control is performed while the above ship is tilted to the starboard side. [Figure 9] This is a diagram showing a state in which the above ship is performing hump control. [Figure 10] This is a diagram showing an example of each threshold value of ship speed in hump control. [Figure 11] This is a flowchart showing an execution method of hump control during execution of trim support control. [Figure 12] This is a flowchart showing the flow of the control method of the propulsion system following Figure 11. [Figure 13] This is a timing chart showing an example of the operation of the above propulsion system. [Figure 14] This is a timing chart showing another example of the operation of the above propulsion system. [Mode for Carrying Out the Invention]

[0017] Hereinafter, embodiments of the present invention will be described based on the drawings. Note that the front-rear, up-down, and left-right directions in the following description are assumed to coincide with the orientation of the ship 1. In this case, the arrow FR in the drawings indicates the front of the ship 1, the arrow UP in the drawings indicates the upper side of the ship 1, and the arrow LH in the drawings indicates the left side of the ship 1. Further, the center line CL extends in the front-rear direction at the center position in the left-right direction (width direction) of the ship 1.

[0018] Figure 1 is a plan view of the vessel according to this embodiment. Figure 2 is a functional block diagram of the vessel's propulsion system. As shown in Figure 1, the ship 1 comprises a hull 2 ​​and a propulsion system 20 provided on the hull 2. As shown in Figures 1 and 2, the propulsion system 20 comprises a plurality of thrusters 3, an operating unit 7, a detection unit 6 (see Figure 2), and a control unit 8 (see Figure 2).

[0019] (propulsion machine) As shown in Figure 1, the propulsion system 3 includes a right propulsion system 3a located on the right side of the stern 2b, straddling the centerline CL, and a left propulsion system 3b located on the left side of the stern 2b, straddling the centerline CL. The two propulsion systems 3 (right propulsion system 3a and left propulsion system 3b) are located on both the left and right sides of the stern 2b of the hull 2, straddling the centerline CL. In other words, the vessel 1 of this embodiment is a so-called twin-propulsion small vessel. In the following description, unless it is necessary to distinguish between the propulsion systems 3a and 3b, they will be referred to collectively as the propulsion system 3.

[0020] Figure 3 is a side view of the propulsion system's thruster. As shown in Figure 3, the propulsion system 3 is, for example, an outboard motor. The propulsion system 3 comprises a casing 31, a drive source 32, a drive shaft 33, a propulsion unit 34, and a shift switching mechanism 35. The casing 31 is attached to a bracket 22 located at the stern 2b via a rudder shaft 36 (swivel shaft) that extends vertically. The propulsion unit 3 is mounted to the hull 2 ​​so as to be rotatable around the rudder shaft 36 by the operation of a rudder actuator 41 (see Figure 2).

[0021] The drive source 32 is, for example, an internal combustion engine. The drive source 32 is housed in the upper part of the casing 31 with the crankshaft aligned vertically. The power (engine speed) of the drive source 32 is set based on the opening of the throttle valve. The throttle valve is driven by the operation of the throttle actuator 42 (see Figure 2). The drive source 32 may also be an electric motor. The drive shaft 33 transmits power generated by the drive source 32 to the propulsion unit 34 via the shift switching mechanism 35. The drive shaft 33 extends vertically within the casing 31. The upper end of the drive shaft 33 is connected to the drive source 32.

[0022] The propulsion unit 34 comprises a propeller shaft 341 and a propeller 342. The propeller shaft 341 is rotatably mounted at the lower end of the casing 31 around an axis along the longitudinal direction. The front end of the propeller shaft 341 is connected to the shift switching mechanism 35 within the casing 31. The propeller 342 is mounted at the rear end of the propeller shaft 341, protruding outward from the casing 31. The propeller 342 rotates integrally with the propeller shaft 341.

[0023] The shift switching mechanism 35 includes a drive gear 351, a forward gear 352, a reverse gear 353, and a clutch 354. The drive gear 351 is located at the lower end of the drive shaft 33. The drive gear 351 is rotatable integrally with the drive shaft 33. The forward gear 352 and the reverse gear 353 are rotatably mounted on the propeller shaft 341, facing each other in the front-rear direction with the drive gear 351 in between. The forward gear 352 and the reverse gear 353 can mesh with the drive gear 351. The forward gear 352 and the reverse gear 353 rotate in opposite directions as the drive gear 351 rotates.

[0024] The clutch 354 switches the power connection or disconnection between the forward gear 352 or the reverse gear 353 and the propeller shaft 341. The clutch 354 is rotatably mounted integrally with the propeller shaft 341. The clutch 354 is movably mounted along the propeller shaft 341 in the forward and backward directions by the operation of the shift actuator 43. By selectively engaging with the forward gear 352 and the reverse gear 353, the clutch 354 switches the rotation direction of the propeller shaft 341 and the propeller 342, thereby switching the propulsion direction of the ship 1.

[0025] The propulsion unit 3 is supported by a bracket 22 attached to the stern 2b of the hull 2, so as to be rotatable around a support shaft 38 that extends in the left-right direction. This allows the propulsion unit 3 to rotate (oscillate) around the support shaft 38 with respect to a reference plane Fv. Here, the reference plane Fv is a virtual plane that lies along the vertical plane passing through the central axis of the support shaft 38 when the hull 2 ​​is simply floating on the water surface. Here, the trim angle θt is defined as the angle at which the direction in which the steering shaft 36 of the propulsion unit 3 extends is inclined in the longitudinal direction around the support shaft 38 with respect to the reference plane Fv. In this embodiment, the trim angle θt is expressed as positive when the lower end of the propulsion unit 3 moves away from the stern 2b, and negative when the lower end of the propulsion unit 3 moves towards the stern 2b. In this embodiment, rotating the propulsion unit 3 in the positive direction is expressed as increasing the trim angle θt, and rotating the propulsion unit 3 in the negative direction is expressed as decreasing the trim angle θt.

[0026] The thruster 3 has an adjustable trim angle θt via a trim angle adjustment unit 45. The trim angle adjustment unit 45 uses an actuator (not shown) to rotate the thruster 3 around the support shaft 38 within a preset angular range. The thruster 3 is restricted from rotating in the positive and negative directions by abutting against a stopper (not shown) provided on the bracket 22. In this embodiment, the trim angle θt when the thruster 3 is rotated to its most negative position is defined as the lower limit of the trim angle. In this embodiment, the bracket 22 is attached to the mounting surface 2f formed on the stern 2b via an intermediate member 37. The intermediate member 37 is sandwiched between the bracket 22 and the mounting surface 2f. The intermediate member 37 is formed in a wedge shape, with its thickness gradually decreasing in the front-rear direction from top to bottom. As a result, the bracket 22 is positioned at a greater rearward inclination compared to when it is directly attached to the mounting surface 2f without using the intermediate member 37. This configuration allows the propulsion unit 3 to be set to a larger negative rotation angle (rotation range).

[0027] (Operation unit) As shown in Figures 1 and 2, the control unit 7 is provided to allow the operator to input controls for steering the vessel 1. In this embodiment, the control unit 7 includes, for example, a steering angle input unit 71, a thrust input unit 72, a trim angle control unit 73, and an operation input unit 74.

[0028] The steering angle input unit 71 is located in the cockpit of the hull 2. The steering angle input unit 71 is, for example, a steering wheel that is rotatable in a reciprocating manner. The steering angle input unit 71 receives external input from the operator when changing the course of the vessel 1 (hull 2). That is, the steering angle input unit 71 receives operation by the operator to change the direction (steering angle) of the propulsion engine 3 around the steering axis 36. The steering angle is the angle of inclination of the propulsion engine 3 with respect to the centerline CL in a plan view. In this embodiment, the steering angle of the propulsion engine 3 when the course of the vessel 1 is in the straight direction is set as the reference value (0°). In addition to the steering wheel, the steering angle input unit 71 may also be a joystick, or it may be mounted as a switch on the operation input unit 74, etc.

[0029] The thrust input unit 72 is located in the cockpit of the hull 2. The thrust input unit 72 is, for example, a throttle lever. The thrust input unit 72 receives external input from the operator when changing the thrust of the propeller 3 or the shift position of the propeller 3. The thrust input unit 72 is configured to be able to move back and forth by rotation or sliding. The thrust input unit 72 can move back and forth within an operating area that has three shift areas: forward position F, neutral position N, and reverse position R. When the thrust input unit 72 is in the forward position F, the propeller 3 exerts thrust to move the ship 1 forward. When the thrust input unit 72 is in the reverse position R, the propeller 3 exerts thrust to move the ship 1 backward. When the thrust input unit 72 is in the neutral position N, the drive gear 351 shown in Figure 3 is disconnected from the forward gear 352 and the reverse gear 353, and the propeller 3 does not exert thrust to propel the ship 1.

[0030] As shown in Figure 1, a trim angle control switch is provided near the thrust input section 72 as a trim angle control section 73. The operator of the ship 1 can change the trim angle θt of the propulsion unit 3 by manually operating the trim angle control switch (trim angle control section 73).

[0031] The operation input unit 74 receives various operations on the vessel 1. The operation input unit 74 is configured to be manually operated by the operator, for example, an MFD (Multi Function Display). The operation input unit 74 may also be an external device such as a portable terminal connected to the vessel 1 by wire or wireless connection.

[0032] (Detection unit) The detection unit 6 shown in Figure 2 detects the state (navigation state) of the vessel 1. In this embodiment, the detection unit 6 includes a position sensor 61, a ship speed sensor 62, a steering angle sensor 63, an inertia sensor 64, a trim operation sensor 65, a trim angle sensor 66, and an actual steering angle sensor 67. The position sensor 61 detects the position of the thrust input unit 72. Based on the position of the thrust input unit 72, which is, for example, a throttle lever that indicates the lever opening, the position sensor 61 detects the lever opening of the thruster 3. The position sensor 61 outputs a detection signal based on the position of the thrust input unit 72 to the control unit 8.

[0033] As shown in Figure 2, the ship speed sensor 62 detects the ship speed V of the vessel 1. The ship speed sensor 62 is, for example, a GPS (Global Positioning System) and calculates the ship speed V based on positioning signals from positioning satellites. The ship speed sensor 62 may also be an acoustic or electromagnetic sensor that detects the ship speed (water speed) V of the vessel 1. The ship speed sensor 62 may also estimate the ship speed V based on the engine speed. The ship speed sensor 62 outputs a signal representing the detected ship speed V to the control unit 8.

[0034] The steering angle sensor 63 detects the amount of operation (steering instruction angle) caused by the rotational operation of the steering angle input unit 71. The steering angle sensor 63 outputs a detection signal based on the steering instruction angle of the steering angle input unit 71 to the control unit 8.

[0035] The inertial sensor 64 detects the tilt of the hull 2 ​​in the roll direction, i.e., the heel angle θh. The inertial sensor 64 also detects the tilt of the hull 2 ​​in the pitch direction, i.e., the pitch angle θp. The inertial sensor 64 outputs detection signals based on the detected tilt of the hull 2 ​​in the roll and pitch directions to the control unit 8.

[0036] The trim operation sensor 65 detects whether or not an operation input has been made to the trim angle operation switch, which is the trim angle operation unit 73. The trim operation sensor 65 outputs a detection signal to the control unit 8 indicating whether or not an operation input has been detected.

[0037] The trim angle sensor 66 is provided in the trim angle adjustment unit 45. The trim angle sensor 66 detects the actual trim angle θt adjusted by the trim angle adjustment unit 45. The trim angle sensor 66 outputs a detection signal indicating the detected trim angle θt to the control unit 8.

[0038] The actual steering angle sensor 67 is provided on the steering actuator 41. The actual steering angle sensor 67 detects the actual steering angle of the thruster 3 and outputs it to the control unit 8.

[0039] (Control Unit) The control unit 8 comprehensively controls the operation of the ship 1 (propulsion unit 3). The control unit 8 is one or more electronic control units provided by the ship 1. The control unit 8 is realized, for example, by a hardware processor such as a CPU (Central Processing Unit) executing a program (software) stored in a storage unit 80 such as a ROM (Read Only Memory) or RAM (Random Access Memory). Some or all of these components may be realized by hardware (including circuitry) such as an LSI (Large Scale Integration), ASIC (Application Specific Integrated Circuit), FPGA (Field-Programmable Gate Array), GPU (Graphics Processing Unit), or SOC (System On Chip), or by the cooperation of software and hardware.

[0040] The control unit 8 includes a storage unit 80, an acquisition unit 81, a determination unit 82, and a drive processing unit 83.

[0041] The memory unit 80 stores programs and various data necessary for the navigation of the ship 1, such as trim support control, heel control, hump control, and wedge control. The acquisition unit 81 acquires the detection results of the various sensors of the detection unit 6. The determination unit 82 determines the state of the ship 1 based on the information obtained by the acquisition unit 81 and the information stored in the storage unit 80.

[0042] The drive processing unit 83 controls the operation of various actuators based on the determination result from the determination unit 82 and the information stored in the storage unit 80 and the acquisition unit 81. In this embodiment, if the determination unit 82 determines that a predetermined condition has been met, the drive processing unit 83 controls the operation of the trim angle adjustment unit 45, the steering actuator 41, etc., to perform trim support control, heel control, hump control, and wedge control. In this embodiment, the drive processing unit 83 performs trim support control, heel control, hump control, and wedge control when the vessel 1 is in a straight-ahead state. In this embodiment, the drive processing unit 83 determines that the vessel 1 does not perform wedge control.

[0043] (Trim support control) Figure 4 shows an example of trim support control, heel control, hump control, and wedge control performed in a propulsion system according to the ship's speed. As shown in Figure 4, when the vessel 1 is moving straight, the determination unit 82 determines that in the areas of heel control, hump control, and wedge control, the drive processing unit 83 executes trim support control according to the settings of the operator, for example, based on input from the trim angle operation unit 73 and the operation input unit 74.

[0044] Figure 5 shows an example of trim support angle settings for trim support control, heel control, and hump control performed in the propulsion system according to ship speed. As shown in Figure 5, the trim support control adjusts the trim angle θt in the trim angle adjustment unit 45 so that the trim support angle θsp is set according to a preset ship speed V (or propeller rotation speed). In this embodiment, in the trim support control, the trim support angle θsp is set according to the ship speed V so that stability, acceleration, maximum speed, fuel consumption, etc. are optimized. The trim support angle θsp may also be set according to the propeller rotation speed. For this reason, the ship speed V (or propeller rotation speed) and the trim support angle θsp that optimizes stability, acceleration, maximum speed, fuel consumption, etc. are stored in the memory unit 80 in association with each other in advance. In the example in Figure 6, the trim support angle θsp is set in steps with respect to the ship speed V (or propeller rotation speed).

[0045] The drive processing unit 83 obtains the trim support angle θsp associated with the ship speed, which is acquired by the acquisition unit 81, from the storage unit 80. The drive processing unit 83 controls the trim angle adjustment unit 45 so that the trim angle θt of the thruster 3 approaches the acquired trim support angle θsp. Figure 6 shows the state in which trim support control is being performed by the propulsion system. As shown in Figure 6, when the drive processing unit 83 performs trim support control, it sets the trim support angles θsp of the thrusters 3a and 3b on both sides in the left-right direction to the same value.

[0046] (Heel control) As shown in Figure 4, if the determination unit 82 determines that the ship 1 is moving straight, the ship speed V is equal to or greater than the second threshold V2, and trim support control is being performed, and that the preset conditions are met, the drive processing unit 83 performs heel control in addition to trim support control. Specifically, the drive processing unit 83 performs heel control in addition to trim support control, that is, both trim support control and heel control, when the ship 1 is moving straight, trim support control is being performed, and the ship speed is equal to or greater than the second threshold V2. In this case, the drive processing unit 83 executes heel control when the heel angle θh, which is the inclination of the hull 2 ​​in the roll direction detected by the inertial sensor 64, is greater than or equal to a preset heel angle reference value θhs (for example, several degrees). In other words, if the heel angle θh is less than the heel angle reference value θhs, the drive processing unit 83 does not execute heel control and continues trim support control.

[0047] When the drive processing unit 83 performs heel control, it sets a target value for the heel suppression angle θd according to the heel angle θh of the hull 2. Here, the heel suppression angle θd is the trim angle of the propulsion units 3 on both the left and right sides to suppress the tilt of the hull 2 ​​in the roll direction. The drive processing unit 83 calculates a heel suppression angle θd that can effectively suppress the tilt of the hull 2 ​​in the roll direction according to the heel angle θh of the hull 2 ​​using a pre-set calculation formula.

[0048] The drive processing unit 83 sets the heel suppression angle θd based on the trim support angle θsp of the thruster 3 at that time. The drive processing unit 83 sets the heel suppression angle θd of one thruster 3 in the left-right direction to a value greater than the trim support angle θsp, and sets the heel suppression angle θd of the other thruster 3 in the left-right direction to a value smaller than the trim support angle θsp.

[0049] Figure 7 shows the state of heel control when the ship is tilting to port. Figure 8 shows the state of heel control when the ship is tilting to starboard. For example, as shown in Figure 7, when the hull 2 ​​is tilted to the port side, the drive unit 83 sets the heel suppression angle θd2 of the right-side propulsion engine 3a to a value greater than the trim support angle θsp, and the heel suppression angle θd1 of the left-side propulsion engine 3b to a value less than the trim support angle θsp. For example, as shown in Figure 8, when the hull 2 ​​is tilted to the starboard side, the drive unit 83 sets the heel suppression angle θd1 of the left-side propulsion engine 3b to a value greater than the trim support angle θsp, and the heel suppression angle θd2 of the right-side propulsion engine 3a to a value less than the trim support angle θsp.

[0050] (Hump control) Figure 9 shows a ship performing hump control. If the determination unit 82 determines that the preset conditions are met, the drive processing unit 83 executes hump control. If the determination unit 82 determines that the preset conditions are met while trim support control is being executed, the drive processing unit 83 can execute hump control in addition to trim support control. As shown in Figure 9, hump control is performed to suppress excessive lift of the bow 2a when the bow 2a is significantly lifted relative to the stern 2b and the pitch angle θp is large. When performing hump control, the drive unit 83 sets the trim angles θt of the propellers 3a and 3b on both sides in the left and right directions to the same value. When performing hump control, the drive unit 83 rotates the propeller 3 in a negative direction from the state where the trim angle θt = 0°. In hump control, the drive unit 83 adjusts the trim angle θt of the propeller 3 with the lower limit of the trim angle θtd as the lower limit.

[0051] Figure 10 shows examples of ship speed thresholds in hump control. As will be described in detail later, the drive processing unit 83 enables hump control when the ship speed V of the hull 2 ​​is within a preset speed range. Specifically, as shown in Figure 10, the drive processing unit 83 executes hump control when the ship speed V is within a set speed range if it is greater than or equal to a preset first threshold V1 and less than a preset second threshold V2 during the acceleration of the hull 2. The drive processing unit 83 enables hump control when the ship speed V becomes greater than or equal to a preset first threshold V1 during the acceleration of the hull 2. The drive processing unit 83 stops executing hump control when it is executing hump control during the acceleration of the hull 2 ​​and the ship speed V becomes greater than or equal to a second threshold V2 which is greater than the first threshold V1. Furthermore, the drive processing unit 83 enables hump control when the ship speed V is less than the first threshold V1 during acceleration of the hull 2, and the lever opening of the propulsion unit 3 is equal to or greater than a preset reference opening.

[0052] Furthermore, when the hull 2 ​​is decelerating, the drive processing unit 83 determines that the ship speed V is within the set speed range and executes hump control when the ship speed V is higher than a preset fourth threshold V4 and less than or equal to the third threshold V3. The drive processing unit 83 enables hump control when the ship speed V is less than or equal to the third threshold V3, which is less than the second threshold V2, during the deceleration of the hull 2. The drive processing unit 83 stops executing hump control when it is executing hump control during the deceleration of the hull 2 ​​and the ship speed V is less than or equal to the fourth threshold V4, which is less than the first threshold V1. Furthermore, the drive processing unit 83 enables hump control when the ship speed V is less than or equal to the fifth threshold V5, which is less than the second threshold V2 and greater than the third threshold V3, and the pitch angle θp of the ship 2 is greater than or equal to a preset third reference pitch angle, during the deceleration of the hull 2.

[0053] When the drive processing unit 83 is performing hump control and a preset condition is met, it causes the trim angle adjustment unit 45 to adjust the trim angle θt of the thruster 3 so that the trim angle θt of the thruster 3 becomes the trim angle reference value θts.

[0054] For example, if the drive processing unit 83 determines that the hull 2 ​​is turning while hump control is being performed, it causes the trim angle adjustment unit 45 to adjust the trim angle θt of the propulsion unit 3 so that the trim angle θt of the propulsion unit 3 becomes the trim angle reference value θts. Here, the determination of whether or not the hull 2 ​​is turning is made, for example, by the determination unit 82, by checking whether the steering instruction angle of the steering angle input unit 71 detected by the steering angle sensor 63 exceeds a preset steering angle threshold. Alternatively, the determination of whether or not the hull 2 ​​is turning may also be made, for example, by the determination unit 82, by checking whether the actual steering angle detected by the actual steering angle sensor 67 exceeds a steering angle threshold.

[0055] In this way, the drive unit 83 sets the trim angle θt of the propulsion unit 3 to the trim angle reference value θts while the hull 2 ​​is turning. This allows the hump control to exert its effect of suppressing the hump state during turning, and also prevents the propulsion unit 3 from tilting significantly in the negative direction when the trim angle θt is smaller than the trim angle reference value θts. However, when the drive unit 83 determines that the hull 2 ​​is turning while hump control is being performed, if the trim angle θt of the propulsion unit 3 is between the trim angle reference value θts and the trim angle lower limit value θtd, it will maintain the trim angle θt of the propulsion unit 3 at that time. In other words, if the hull 2 ​​transitions to a turning state while hump control is being performed, and at that time the trim angle θt of the propulsion unit 3 is tilted in the negative direction more than the trim angle reference value θts, the trim angle θt will not be returned to the trim angle reference value θts, but will be maintained at that time. This allows the hull 2 ​​to transition to a turning state while the effect of suppressing the hump state by hump control is fully exerted.

[0056] If the drive processing unit 83 is performing hump control and the trim angle θt of the thruster 3 reaches the lower limit of the trim angle, it stops the execution of hump control and then enters a standby state where hump control can be performed again. In this case, even after stopping the execution of hump control, the drive processing unit 83 maintains the trim angle θt of the thruster 3 at the lower limit of the trim angle θtd.

[0057] Furthermore, if the drive processing unit 83 receives an input from the trim angle control unit 73 while hump control is being performed, it stops the execution of hump control. This prevents the trim angle of the propulsion system from falling below the trim angle reference value due to manual operation, thereby reducing any discomfort the operator may feel. When the drive processing unit 83 receives an input from the trim angle control unit 73 while hump control is being performed, if the trim angle θt of the propulsion unit 3 is between the trim angle reference value θts and the trim angle lower limit value θtd, it allows the trim angle θt of the propulsion unit 3 to be adjusted by the input from the trim angle control unit 73, with the trim angle reference value θts as the lower limit. In other words, if the execution of hump control is stopped by the operator making an input from the trim angle control unit 73, and the operator subsequently adjusts the trim angle θt of the propulsion unit 3 by making an input from the trim angle control unit 73 after the execution of hump control has stopped, the lower limit of the adjustment range of the trim angle θt will be the trim angle reference value θts. This prevents the trim angle θt from being made smaller than the trim angle reference value θts when manually adjusting the trim angle θt of the propulsion unit 3 by making an input from the trim angle control unit 73 while hump control is being performed.

[0058] (Bogen control) The drive processing unit 83 performs wedge control when the ship speed V is less than the first threshold V1. Wedge control steers the multiple propulsion units 3 in the yaw direction in a direction that intersects the longitudinal direction of the hull 2. When the ship 1 is moving straight and the ship speed V is less than the first threshold V1, wedge control rotates the left and right propulsion units 3 around the swivel axis in opposite directions and by the same steering angle. Wedge control reduces the forward thrust acting on the entire hull 2 ​​compared to when the propulsion units 3 are arranged parallel to the longitudinal direction of the hull 2, making it possible to sail the hull 2 ​​at low speed or very low speed. In this embodiment, the specific details of wedge control are not limited in any way.

[0059] (Control method for the propulsion system) Next, the operation method of the propulsion system will be explained. The processes described below are executed repeatedly, for example, at a predetermined control cycle (e.g., several tens of milliseconds). Figure 11 is a flowchart showing the flow of the propulsion system control method. Figure 12 is a flowchart showing the flow of the propulsion system control method following Figure 11. The flowcharts shown in Figures 11 and 12 illustrate the processing flow when performing hump control, which is part of the control of the propulsion system 20 executed by the control unit 8. As shown in Figure 11, in step S11, the control unit 8 acquires the ship speed detection result from the ship speed sensor 62 using the acquisition unit 81. In step S11, in order to detect a change in ship speed, the control unit 8 acquires the ship speed detection result multiple times with a predetermined control cycle interval.

[0060] In step S12, the control unit 8 determines, based on the detection result of the ship speed sensor 62, whether the ship speed V of the hull 2 ​​is within a preset speed range. In this case, the control unit 8 determines that the ship speed V is within the set speed range when the ship speed V is greater than or equal to a preset first threshold V1 and less than a preset second threshold V2 during the acceleration of the ship hull 2. When the hull 2 ​​is decelerating, the control unit 8 determines that the ship speed V is within the set speed range if the ship speed V is higher than a preset fourth threshold V4 and less than or equal to the third threshold V3, and executes hump control. Here, the fourth threshold V4 is set, for example, 5 to 10 km / h lower than the first threshold V1. The third threshold V3 is set, for example, 5 to 10 km / h lower than the second threshold V2.

[0061] If the ship speed V is outside the set speed range and the result of the determination in step S12 is "No", proceed to step S13, which will be described later.

[0062] (If the ship speed is determined to be within the set range) If the ship speed V is within the set speed range and the result of the determination in step S12 is "Yes", the system skips to step S15, and the control unit 8 enters a standby state where it can perform hump control. In the following step S16, the control unit 8 determines whether the conditions for executing hump control when the ship speed V is within the set speed range are met.

[0063] Examples of conditions for executing hump control when the ship speed V is within the set speed range include the following conditions a1) and a2). Condition a1) The detected pitch angle θp acquired by the inertial sensor 64 is greater than the preset first reference pitch angle. Condition a2) Based on the steering angle indicated by the steering angle input unit 71 detected by the steering angle sensor 63, or the actual steering angle detected by the actual steering angle sensor 67, it is determined that the hull 2 ​​is turning. If the ship speed V is within the set speed range, in step S16, the control unit 8 determines that the hump control execution condition is satisfied if at least one of conditions a1) and a2) is satisfied.

[0064] If the result of the determination in step S16 is "No", the process ends, a predetermined control cycle is observed, and the process from step S11 is repeated. If the result of step S16 is "Yes", proceed to step S17.

[0065] (If the ship speed is determined to be outside the set range) If the ship speed V is outside the set speed range and the result of the determination in step S12 is "No", then in step S13, the control unit 8 determines whether or not the acceleration exception condition is satisfied. Examples of exceptions during acceleration include the following conditions b1) to b3). Condition b1) The hull 2 ​​is accelerating. Condition b2) The ship speed V is less than the first threshold V1. Condition b3) The lever opening of the thruster 3, as obtained by the position sensor 61, is greater than a preset reference opening. If the ship speed V is outside the set speed range and all of conditions b1) to b3) are satisfied, the control unit 8 determines in step S13 that the acceleration exception condition is satisfied.

[0066] If the result of step S13 is "Yes", the process skips to step S15, and the control unit 8 enters a standby state where it can perform hump control. In the following step S16, the control unit 8 determines whether the conditions for executing hump control are met when the acceleration exception conditions are satisfied.

[0067] When the ship speed V is outside the set speed range and the acceleration exception condition is satisfied in step S13, the following conditions c1) to c3) are examples of conditions for executing hump control. Condition c1) The lever opening of the thruster 3, as obtained by the position sensor 61, is greater than the preset first lever opening. Condition c2) The detected pitch angle θp acquired by the inertial sensor 64 is greater than the preset reference pitch angle. Condition c3) Based on the steering angle input unit 71 detected by the steering angle sensor 63, or the actual steering angle detected by the actual steering angle sensor 67, it is determined that the hull 2 ​​is turning. Here, the first lever opening may be the same value as the reference opening described above, or it may be a value slightly larger than the reference opening. If the ship speed V is outside the set speed range and the acceleration exception condition is satisfied, in step S16, if at least one of conditions c1) to c3) is satisfied, the control unit 8 determines that the hump control execution condition is satisfied.

[0068] If the result of the determination in step S16 is "No", the process ends, a predetermined control cycle is observed, and the process from step S11 is repeated. If the result of step S16 is "Yes", proceed to step S17.

[0069] (If the ship speed is determined to be outside the set range) If the ship speed V is outside the set speed range and the result of the determination in step S13 is "No", then in step S14, the control unit 8 determines whether or not the deceleration exception condition is satisfied. Examples of exceptions during deceleration include the following conditions d1) and d2). Condition d1) The hull 2 ​​is decelerating. Condition d2) The ship speed V is between the third threshold V3 and the fifth threshold V5. If the ship speed V is outside the set speed range and all conditions d1) and d2) are satisfied, the control unit 8 determines that the deceleration exception condition is satisfied.

[0070] If the result of the judgment in step S14 is "No", the process ends, a predetermined control cycle is observed, and the process from step S11 is repeated. If the result of the determination in step S14 is "Yes", the process proceeds to step S15, and the control unit 8 is put into a standby state where it can perform hump control. In the following step S16, the control unit 8 determines whether the conditions for executing hump control are met when the deceleration exception conditions are satisfied.

[0071] For example, the following condition e1) is an example of a condition for executing hump control when the ship speed V is outside the set speed range and the deceleration exception condition is satisfied. Condition e1) The detected pitch angle θp acquired by the inertial sensor 64 is greater than the preset third reference pitch angle. Here, the third reference pitch angle may be the same value as the first reference pitch angle, or it may be slightly larger than the first reference pitch angle. If the ship speed V is outside the set speed range and the deceleration exception condition is met, in step S16, if condition e1) is met, the control unit 8 determines that the hump control execution condition is met.

[0072] If the result of the determination in step S16 is "No", the process ends, a predetermined control cycle is observed, and the process from step S11 is repeated. If the result of step S16 is "Yes", proceed to step S17.

[0073] (Execution of hump control) In step S17, the control unit 8 performs hump control. In this case, the control unit 8 reduces the trim angle θt of all thrusters 3 to the lower limit of the trim angle.

[0074] (Transition to other states while hump control is in operation) After starting the hump control in step S17, the control unit 8 will transition to another state if a preset condition is met during the execution of the hump control. As shown in Figure 12, in step S18 following step S17, the control unit 8 determines whether the trim angle θt of the thruster 3 detected by the trim angle sensor 66 is greater in the positive direction than a preset lower limit of the trim angle θtd while hump control is being performed.

[0075] If the result of step S18 is "Yes", proceed to step S19. If the result of step S18 is "No," that is, if the trim angle θt of the thruster 3 reaches the lower limit of the trim angle θtd, proceed to step S21. In step S21, the control unit 8 stops the execution of hump control. After stopping the execution of hump control, the system returns to step S15 in Figure 11 and enters a standby state where hump control can be executed. In this case, even after stopping the execution of hump control in step S21 (while in hump control standby in step S15), the control unit 8 maintains the trim angle θt of the thruster 3 at the lower limit of the trim angle θtd. This allows the system to maintain a state in which the effect of suppressing the hump state by hump control is maximized while waiting for the execution of hump control.

[0076] In step S19, the control unit 8 determines whether the hull 2 ​​is in a turning state. To do this, the control unit 8 determines, for example, whether the steering instruction angle of the steering angle input unit 71 detected by the steering angle sensor 63 exceeds a preset steering angle threshold.

[0077] If the result of step S19 is "No", proceed to step S20. If the result of step S19 is "Yes," that is, if hull 2 ​​is turning, proceed to step S22.

[0078] In step S22, the control unit 8 determines whether the trim angle θt of the thruster 3 is less than or equal to the trim angle reference value θts. If the result of the determination in step S22 is "Yes," that is, if the trim angle θt of the thruster 3 is less than or equal to the trim angle reference value θts and is between the trim angle reference value θts and the trim angle lower limit value θtd, the control unit 8 maintains the trim angle θt of the thruster 3 at that point in step S23. This allows the vehicle to transition to a turning state while fully utilizing the effect of suppressing the hump state by the hump control.

[0079] If the result of the determination in step S22 is "No," that is, if the trim angle θt of the thruster 3 is greater in the positive direction than the trim angle reference value θts, the control unit 8 returns the trim angle θt of the thruster 3 to the trim angle reference value θts in step S24. This allows the hump control to exert its effect of suppressing the hump state, while preventing the trim angle θt from being smaller than the trim angle reference value θts and preventing the thruster 3 from tilting significantly in the negative direction.

[0080] In step S20, the control unit 8 determines whether or not it has received an operation input from the trim angle control unit 73 by the operator.

[0081] If the result of step S20 is "No", the process ends, a predetermined control cycle is observed, and step S11 is repeated. If the result of step S20 is "Yes," that is, if it is determined that a manual action was taken by the operator, the process proceeds to step S25 and the execution of the hump control is stopped.

[0082] Next, in step S26, the control unit 8 determines whether the trim angle θt of the thruster 3 is less than or equal to the trim angle reference value θts. If the result of step S26 is "No," that is, if the trim angle θt of the thruster 3 is greater than the trim angle reference value θts in the positive direction, proceed to step S27. If the result of the determination in step S26 is "Yes," that is, if the trim angle θt of the thruster 3 is less than or equal to the trim angle reference value θts, the control unit 8 returns the trim angle θt of the thruster 3 to the trim angle reference value θts in step S28, and then proceeds to step S27.

[0083] In step S27, the control unit 8 enables manual operation of the trim angle θt of the propulsion unit 3 based on the operator's input from the trim angle control unit 73. At this time, the control unit 8 sets the lower limit of the adjustment range of the trim angle θt to the trim angle reference value θts.

[0084] Figure 13 is a timing chart showing an example of the operation of the propulsion system. In Figure 13, for both the "Hump State Determination Flag" and the "Trim Operation Determination Flag," "0" indicates that the determination result in the control unit 8 is "No," and "1" indicates that the determination result in the control unit 8 is "Yes." As shown in Figure 13, for example, when the lever opening is increased by the operator's operation of the thrust input unit 72, the ship speed V increases. Subsequently, when the ship speed V exceeds the first threshold V1, the hump control enters a standby state.

[0085] When the operator operates the steering angle input unit 71 and begins steering, for example, to the left, the steering instruction angle (steering angle) detected by the steering angle sensor 63 increases to the left (time t1). When the steering angle exceeds the steering angle threshold (time t2) while the pitch angle θp of the hull 2, which increases with the increase in ship speed V, does not exceed the first reference pitch angle, the hump state determination flag changes from "0" to "1" in step S16, and hump control is initiated. At this time, the control unit 8 changes the trim operation determination flag from "0" to "1", and in step 24, changes the trim angle θt of all propulsion units 3 toward the trim angle reference value θts.

[0086] When the trim angle θt of all thrusters reaches the trim angle reference value θts (time t3), in step S18 the trim operation determination flag changes from "1" to "0", and the control unit 8 maintains the trim angle θt of thruster 3 at the trim angle reference value θts.

[0087] Subsequently, when the operator operates the steering angle input unit 71 and begins to return the steering to its original position, for example to the left, and the steering instruction angle (steering angle) detected by the steering angle sensor 63 becomes smaller than the steering threshold at the time of return (time t4), the control unit 8 returns the hump state determination flag from "1" to "0".

[0088] Figure 14 is a timing chart showing another example of the propulsion system's operation. As shown in Figure 14, when the lever opening is increased by the operator's operation of the thrust input unit 72, the ship speed V increases. Subsequently, when the ship speed V exceeds the first threshold V1 (time t11), the hump control enters standby mode.

[0089] As the ship speed V increases, when the pitch angle θp of the hull 2 ​​exceeds the first reference pitch angle (time t12), the hump state determination flag changes from "0" to "1" in step S16, and hump control is initiated. At this time, the control unit 8 changes the trim operation determination flag from "0" to "1" and, in accordance with the hump control, changes the trim angle θt of all propulsion units 3 toward the lower limit of the trim angle θtd. As a result, the pitch angle θp of the hull 2 ​​begins to decrease with a time lag.

[0090] Subsequently, when the trim angle θt of all thrusters reaches the lower limit of the trim angle θtd (time t13), the trim operation determination flag changes from "1" to "0" in step S18, and the control unit 8 stops executing the hump control in step S21.

[0091] When the helmsman operates the steering angle input unit 71 and begins to steer, for example, to the left, the steering instruction angle (steering angle) detected by the steering angle sensor 63 increases to the left. When the steering angle exceeds the steering angle threshold (time t14), the control unit 8 determines that the hull 2 ​​is in a turning state. At this point, since the trim angle θt of all propulsion units 3 has been at the lower limit of the trim angle θtd since time t13, the control unit 8 maintains the trim angle θt of all propulsion units 3 at the lower limit of the trim angle θtd.

[0092] Thus, in this embodiment, when the propulsion system 20 is performing hump control and a preset condition is met, it adjusts the trim angle θt of the propulsion unit 3 so that the trim angle θt of the propulsion unit 3 becomes a trim angle reference value θts which is set to be greater than the trim angle lower limit value θtd. As a result, when the set condition is met, the effect of suppressing the hump state by hump control is reduced. Therefore, when the navigation state of the ship 1 changes while hump control is being performed, it is possible to suppress the loss of stability of the ship 1.

[0093] Furthermore, in this embodiment, when the propulsion system 20 determines that the hull 2 ​​is turning, the trim angle θt of the propulsion unit 3 is set to the trim angle reference value θts. This suppresses the effect of hump control while the hull 2 ​​is turning, and stabilizes the behavior of the hull 2 ​​while it is turning.

[0094] Furthermore, in this embodiment, when it is determined that the hull 2 ​​is turning, the propulsion system 20 maintains the trim angle θt of the propulsion unit 3 at that time if the trim angle θt of the propulsion unit 3 is between the trim angle reference value θts and the trim angle lower limit value θtd. As a result, when hump control is performed with the trim angle θt of the propulsion unit 3 set to or below the trim angle reference value, when the hull 2 ​​transitions to a turning state, the hull 2 ​​can be stably transitioned to a turning state while maintaining the effect of suppressing the hump state by the hump control.

[0095] Furthermore, in this embodiment, when the hump control is being performed, if the trim angle θt of the thruster 3 reaches the lower limit of the trim angle, the thruster system 20 stops the execution of the hump control and enters a standby state where hump control can be performed. As a result, when the trim angle θt of the thruster 3 has reached the lower limit of the trim angle and the effect of suppressing the hump state by the hump control is being exerted to the fullest extent, continuing the hump control suppression prevents the trim angle θt of the thruster 3 from fluctuating frequently, and allows the state in which the effect of suppressing the hump state is exerted to be stably maintained.

[0096] Furthermore, in this embodiment, when the propulsion system 20 is performing hump control and receives an operation input from the trim angle operation unit 73, if the trim angle θt of the propulsion engine 3 is between the trim angle reference value θts and the trim angle lower limit value θtd, the trim angle θt of the propulsion engine 3 is adjusted by the operation input from the trim angle operation unit 73, with the trim angle reference value θts set as the lower limit. This prevents the trim angle θt of the propulsion engine 3 from falling below the trim angle reference value when the operator performs manual operation. This reduces the strong feeling of the hump suppression effect by hump control during manual operation, and prevents the operator from feeling any discomfort.

[0097] It should be noted that the present invention is not limited to the embodiments described above with reference to the drawings, and various modifications are conceivable within its technical scope. For example, in the above embodiment, various conditions for implementing hump control were illustrated, but these conditions can be changed as appropriate.

[0098] Furthermore, in the above embodiment, one thruster 3 is provided on each of the left and right sides, but multiple thrusters may be provided on each of the left and right sides, or one may be provided in the center. Furthermore, the control procedures and content executed by the control unit 8 can be modified as appropriate. Furthermore, the configuration in the above embodiment is just one example of the present invention, and various modifications are possible without departing from the spirit of the invention. [Explanation of Symbols]

[0099] 1 ship 2 hull 3 Propulsion machine 3a Right propulsion machine (propulsion machine) 3b Left propulsion machine (propulsion machine) 8 Control Unit 20 Propulsion System 32 Power source 34 Promotion Department 45 Trim angle adjustment section 73 Trim angle control section θt…Trim angle θtd…Lower limit of trim angle θts…Trim angle reference value

Claims

1. A propulsion system provided on the hull has a drive source and a propulsion unit that generates thrust by power transmitted from the drive source, A trim angle adjustment unit for adjusting the trim angle of the propulsion unit relative to the hull, A ship propulsion system comprising a control unit for controlling the trim angle adjustment unit, The control unit, In order to suppress the pitch tilt of the hull, a hump control is possible in which the trim angle of the propulsion system is adjusted by the trim angle adjustment unit, using a preset lower limit value for the trim angle. When the hump control described above is being performed and a preset condition is met, the trim angle adjustment unit adjusts the trim angle of the propeller so that the trim angle of the propeller becomes a trim angle reference value set to be larger than the lower limit of the trim angle in the direction in which the propeller stands upright in the direction forward of the ship's propulsion. A ship's propulsion system.

2. The control unit, If, while the hump control is being performed, it is determined that the hull is turning, the trim angle adjustment unit adjusts the trim angle of the propeller so that the trim angle of the propeller becomes the trim angle reference value. The propulsion system for a ship according to claim 1.

3. The control unit, When the hump control is being performed, and it is determined that the hull is turning, if the trim angle of the propeller is between the trim angle reference value and the trim angle lower limit, the trim angle of the propeller at that time is maintained. The propulsion system for a ship according to claim 2.

4. The control unit, If the trim angle of the thruster reaches the lower limit of the trim angle while the hump control is being performed, the execution of the hump control is stopped, and the system enters a standby state where the hump control can be performed again. A ship propulsion system according to claim 1 or 2.

5. The system further includes a trim angle control unit that operates the trim angle adjustment unit via external input, The control unit, While the hump control is being performed, if the trim angle of the thruster is between the trim angle reference value and the trim angle lower limit when an operation input is received from the trim angle operation unit, the trim angle of the thruster can be adjusted by the operation input from the trim angle operation unit, with the trim angle reference value as the lower limit. A ship propulsion system according to claim 1 or 2.

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