Watercraft and watercraft control system

A watercraft control system is configured to track and follow a lead watercraft cruising ahead of a host watercraft. The watercraft control system basically includes a detector and a digital controller. The watercraft control system can be integrated with a main watercraft control system of the host watercraft, or can be an add-on watercraft control system that supplements the main watercraft control system of the host watercraft. The detector is configured to detect the lead watercraft in front of the host watercraft. The digital controller is configured to communicate with the detector's processor to receive a detection signal from the detector. The digital controller is configured to output at least one control command related to a propulsion direction of the host watercraft and a propulsion force of the host watercraft to at least a propulsion unit of the host watercraft to track and follow the lead watercraft.

BACKGROUND

Technical Field

The present disclosure generally relates to the field of watercrafts. More particularly, the present disclosure relates to a host watercraft that is configured to track and follow a lead watercraft.

Background Information

Some watercrafts are equipped with a cruise control system. Typically, for the basic cruise control system, a driver manually attains a desired speed and then initiates the cruise control system to maintain the watercraft at the cruising speed set by the driver. The watercraft then travels at the selected speed relieving the driver regulating the throttle, while the watercraft steers automatically by following a path manually predefined by the user. This path is defined by what is commonly known as waypoints in the marine industry.

SUMMARY

Generally, the present disclosure is directed to any watercraft such as an outboard motor boat, a personal watercraft, a jet boat, a pontoon boat, etc., or a watercraft control system that is configured to track and follow a lead watercraft cruising ahead of the host watercraft. Thus, such a watercraft is equipped with object sensing technology and an autopilot capable of full throttle control, shifting control and steering control.

In accordance with one aspect of the present disclosure, a watercraft is provided that is configured to track and follow a lead watercraft cruising ahead of the host watercraft. The host watercraft basically comprises a watercraft body, a propulsion unit, a detector and a digital controller. The propulsion unit is provided to the watercraft body. The detector is configured to detect the lead watercraft. The digital controller is configured to communicate with the detector to receive a detection signal from the detector. The digital controller is configured to output at least one control command related to a propulsion direction of the watercraft and a propulsion force of the watercraft to at least the propulsion unit to track and follow the lead watercraft.

In accordance with another aspect of the present disclosure, a watercraft control system is provided that is configured to track and follow a lead watercraft cruising ahead of a host watercraft. The watercraft control system basically comprises a detector and a digital controller. The detector is configured to detect the lead watercraft in front of the host watercraft. The digital controller is configured to communicate with the detector to receive a detection signal from the detector. The digital controller is configured to output at least one control command related to a propulsion direction of the host watercraft and a propulsion force of the host watercraft to at least a propulsion unit of the host watercraft to track and follow the lead watercraft.

Also, other features, aspects and advantages of the disclosed watercraft and the disclosed watercraft control system will become apparent to those skilled in the watercraft field from the following detailed description, which, taken in conjunction with the annexed drawings, discloses several illustrative embodiments of a watercraft and a watercraft control system with various features.

It should be noted that these figures are intended to illustrate the general characteristics of methods, structures and/or materials utilized in certain illustrative embodiments and to supplement the written description provided below. These drawings are not, however, to scale and may not precisely reflect the precise structural or performance characteristics of any given embodiment, and should not be interpreted as defining or limiting the range of values or properties encompassed by illustrative embodiments. The use of similar or identical reference numbers in the various drawings is intended to indicate the presence of a similar or identical element or feature.

DETAILED DESCRIPTION OF EMBODIMENTS

Selected embodiments will now be explained with reference to the drawings. It will be apparent to those skilled in the watercraft field from this disclosure that the following descriptions of the embodiments are provided for illustration only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents. Like reference numerals in the drawings denote like similar or identical elements or features, and thus the descriptions of the similar or identical elements or features may be omitted in later embodiments.

Referring initially toFIGS. 1 and 2, a watercraft10is illustrated in accordance with a first embodiment. The watercraft10is configured to track and follow a lead watercraft W that is cruising ahead of the watercraft10. More specifically, the watercraft10includes a watercraft control system12that is configured to automatically track and follow the lead watercraft W that is cruising ahead of the watercraft10once the lead watercraft W is selected by the driver or user for tracking and following. The watercraft control system12can be integrated with a main watercraft control system of the watercraft10, or can be an add-on watercraft control system that supplements the main watercraft control system of the watercraft10. In either case, the watercraft10is equipped with the watercraft control system12such that the watercraft10constitutes a host watercraft with respect to the lead watercraft W.

Here, in the first embodiment, the watercraft control system12of the watercraft10includes a detector14that is configured to detect the lead watercraft W in front of the watercraft10. Preferably, the detector14includes an image recognition device as shown in the first embodiment. However, the detector14can include optical sensors such as one or more cameras, and/or one or more camera active sensors such as lasers, lidar, or millimeter-wave radars. In the first embodiment, the detector14is a stereo camera which is basically two cameras in a single unit that is mounted to the watercraft10.

The watercraft10is configured to be driven in either an autopilot mode or a manual mode. Here, the watercraft10is provided with a drive-by-wire system that operates the watercraft10, and that is configured to perform various operations of the watercraft10. Specifically, the watercraft10is provided with a cockpit that has a steering wheel or helm16(e.g., a manual steering device) and a remote control18(e.g., a manual throttle-shift device). The steering wheel16is used by a driver or user to manually turn the watercraft10, and thus, manually change a propulsion direction of the watercraft10. The remote control18is used by a driver or user to manually control a propulsion force of the watercraft10. In the autopilot mode, the driver set a cruising speed for the watercraft10and a travel path defined by waypoints in a conventional manner. It will be apparent from disclosure that the autopilot mode is an optional feature that is not necessary for the track and follow mode described herein.

As seen inFIG. 1, the watercraft control system12can be set by a user to move along a host watercraft path PH that tracks and follows in a lead watercraft path PL of the lead watercraft W. On the other hand, a user can set the watercraft control system12to move along the host watercraft path PH that tracks and follows the lead watercraft path PL of the lead watercraft W with a predetermined lateral offset amount OS with respect to the lead watercraft path PL of the lead watercraft W as seen inFIG. 2. Preferably, the predetermined lateral offset amount OS is adjustable by the user. The predetermined lateral offset amount OS can be adjusted by the user to one of a plurality of preset distances or can be infinitely adjusted by the user to any desired distances within the tracking capabilities of the watercraft control system12.

Also, as seen inFIG. 1, the watercraft10tracks and follows the lead watercraft W by a target following distance Zdes. This target following distance Zdescan be adjusted by the user to one of a plurality of preset target following distances or can be infinitely adjusted by the user to any desired target following distance within the tracking capabilities of the watercraft control system12(e.g., the detector14). The target following distance Zdescan be set by the user in both cases of the watercraft10following in the lead watercraft path PL of the lead watercraft W and the watercraft10being offset from the lead watercraft path PL of the lead watercraft W. Instead of the watercraft control system12using a target following distance for maintaining the target following distance Zdes, the watercraft control system12can be configured to track and follow the lead watercraft W within a predetermined target following range. In other words, the watercraft control system12can be configured so that a following distance of the watercraft10from the watercraft control system12can vary within a target following range while the watercraft10tracks and follows the lead watercraft W to maintain the target following distance Zdes. Stated differently, the watercraft control system12can be configured to maintain the target following distance Zdesby either maintaining a target following distance or a target following range. Thus, as used herein, the term “target following distance” does not require a single following distance to be maintained.

As explained later in more detail, upon the watercraft control system12detecting the lead watercraft in the host watercraft path PH, the watercraft control system12notifies the host watercraft driver of the watercraft10of the lead watercraft W and provides the host watercraft driver with an option to activate an auto-track & follow mode. If the auto-track & follow mode is activated, then the watercraft control system12engages an automatic steering control such that the watercraft10tracks the lead watercraft W and also engages an automatic throttle control such that the watercraft10maintains the target following distance Zdesbehind the lead watercraft W while also tracking the lead watercraft W. After the auto-track & follow mode is activated, the host watercraft driver does not need to input any control commands (i.e., hands free driving) unless the watercraft control system12experiences a failure or the host watercraft driver wants to deactivate the watercraft control system12from the auto-track & follow mode. The watercraft control system12can also be set with a maximum following speed such that the watercraft10does not exceed the maximum following speed in the event that the lead watercraft W is traveling above the maximum following speed. Thus, the watercraft10will continue to track the lead watercraft W but the distance between the watercraft10and the lead watercraft W will be allowed to increase above the target following distance Zdes. At some point, the lead watercraft W may be at a distance from the watercraft10such that the watercraft control system12can no longer track the lead watercraft W. In this case, the watercraft control system12will automatically deactivate from the auto-track & follow mode and will alert driver that the auto-track & follow mode has been deactivate. If the watercraft10was previously traveling in a cruise control mode at a preset speed or an autopilot mode, then the normal cruise control or the normal autopilot mode will resume. Otherwise, the watercraft10will return to the manual mode.

Referring toFIG. 3, a simplified top view of the watercraft10is illustrated, and some of the parts of the watercraft10will now be discussed. In the first embodiment, the watercraft10basically includes a watercraft body20and a plurality of propulsion units22. The detector14is preferably mounted to the watercraft body20near the front end of the watercraft10. Preferably, the detector14is disposed on a centerline CL of the watercraft body20. However, the location of the detector14is not limited to the illustrated location.

Here, the watercraft10is illustrated as an outboard motor boat that is equipped with the watercraft control system12. However, the watercraft control system12is not limited to being used with an outboard motor boat. Rather, as explained later, the watercraft control system12can be applied to practically any watercraft that includes a propulsion system and a steering system.

Here, the watercraft body20basically includes a hull20aand a deck20b. The deck20bis provided on the hull20ain a conventional manner. Preferably, the hull20aand the deck20bare integrated to form a unit. The hull20a, the deck20band the other parts of the watercraft10are made of suitable materials that are typically used in watercrafts for a marine environment, and thus, the materials of the various parts of the watercraft10will not be discussed herein. However, the watercraft body20is not limited to the illustrated hull and deck construction. Rather, the construction of the watercraft body depends on the type of watercraft. For example, a watercraft body of a pontoon boat typically includes two or more pontoons that support a deck. Also, for example, the watercraft body may not have a deck.

The propulsion unit22is provided to propel the watercraft10in a conventional manner. In the first embodiment, three of the propulsion units22are provided in the form of three outboard motors as seen inFIG. 3(only one of the propulsion units22is shown inFIG. 4). However, the propulsion units22are not limited to this illustrated configuration of the first embodiment. It is acceptable for the propulsion units to be inboard motors or water jet propulsion devices instead of outboard motors. Basically, the term “propulsion unit” as used herein is a machine that produces a thrust to push a watercraft. The propulsion unit can also be referred to as a propulsion device or a propulsion system. A propulsion unit or device typically includes a drive source (e.g. an engine or an electric motor) and a propulsor (e.g. a propeller or an impeller) that provide a thrust to the watercraft.

While the watercraft10is illustrated as having three of the propulsion units22, it will be apparent from this disclosure that the watercraft10can have only a single propulsion unit, two propulsion units, or more than three propulsion units, as needed and/or desired, depending on the particular design of the watercraft. Also, the watercraft10can be provided with one or more other types of propulsion units such as one or more water-jet drives and/or inboard motors. In other words, the auto-track & follow mode of the watercraft control system12can be used with other types of propulsion systems other than the propulsion system illustrated in the first embodiment. In any case, the watercraft10comprises at least one propulsion unit that is provided to the watercraft body20, and more preferably further comprises an additional propulsion unit22that is provided to the watercraft body20.

The propulsion units22are controlled by the driver using the steering wheel16to manually turn the watercraft10, and using the remote control18to manually control a propulsion force (thrust) of the watercraft10. The remote control18is also used by the driver or user reverse the direction of the thrusts of the propulsion units22. Preferably, the propulsion units22can be independently turned with respect to each other. Also, the thrust of the propulsion units22can be independently controlled by the driver or user. Here, the steering system of the watercraft10is a steer-by-wire system in which the steering wheel16is not mechanically connected to the propulsion units22. However, the watercraft control system12can be adapted to a mechanical steering system. Likewise, the remote control18is not mechanically connected to the propulsion units22. However, the watercraft control system12can be adapted to a watercraft having a mechanical throttle system. Since the steering systems and throttle systems are not well known and the auto-track & follow mode of the watercraft control system12can be adapted to those known systems, the steering system and throttle system of the watercraft10of the first embodiment will only be briefly discussed herein.

As seen inFIG. 5, a block diagram of selected components of the watercraft10. As schematically illustrated inFIG. 5, the watercraft10is provided with a central digital controller24that is connected to a network of the watercraft10, and the watercraft control system12includes a digital controller25that is connected to the network of the watercraft10. For example, the network of the watercraft10can be Controller Area Network (CAN bus) that allow microcontrollers and devices to communicate with each other. The central digital controller24can be also referred to as a boat control unit (BCU), while the digital controller25can be also referred to as a graphics processing unit (GPU). InFIG. 5, the watercraft control system12is illustrated as an add-on component of the watercraft10. However, some or all of the functions of the digital controller25(GPU) could be integrated into the central digital controller24(BCU). Thus, the term “digital controller” is not limited to a single controller having one or more processors, but rather includes one controller as well as two or more controllers that are physically separated from each other. Thus, for example, the term “digital controller” can include a GPU by itself, the BCU by itself or both the GPU and the BCU.

Also as seen inFIG. 5, the watercraft10is provided with an electrical power supply BT (e.g., a battery) for supplying electrical power the central digital controller24and the digital controller25as well as to the various electrical components of the watercraft10. Of course, the digital controller25can have its own electrical power supply (e.g., a battery) if desired.

The central digital controller24can be a microcomputer. The central digital controller24includes a processor24a, such as a CPU (Central Processing Unit) and memory24b(computer storage) such as a ROM (Read Only Memory) and a RAM (Random Access Memory). The central digital controller24can also include other conventional components such as an input interface circuit and an output interface circuit. The processor24aof the central digital controller24is programmed to control the various components of the boat10such as adaptive cruise control, autopilot control, satellite positioning control, etc. The memory24bof the central digital controller24stores processing results, detection results and control programs such as ones for controlling the watercraft10. For example, the RAM stores statuses of operational flags and various control data, while the ROM stores the control programs for various operations.

In the illustrated embodiment, the central digital controller24is programmed to control the propulsion units22in accordance with operation signals from the steering wheel16and the remote control18as well as control signals from the watercraft control system12. The basic controls of the propulsion units22in accordance with the operation signals from the steering wheel16and the remote control18are relatively conventional, and thus, the basic controls of the propulsion units22will not be discussed in detail herein. The central digital controller24is also programmed to automatically control the at propulsion units22based on detection results of sensors or detectors.

While the central digital controller24and the watercraft control system12are illustrated as separate components in which the watercraft control system12is connected to the network of the watercraft10, the watercraft control system12can be integrated with the central digital controller24. In other words, here, the watercraft control system12is an add-on component that is plugged into the network of the watercraft10. Thus, as illustrated inFIG. 5, the watercraft control system12includes its own digital controller25having at least one processor25a, such as a CPU (Central Processing Unit) and memory25b(computer storage) such as a ROM (Read Only Memory) and a RAM (Random Access Memory). On the other hand, if the watercraft control system12is fully integrated into the watercraft10, then the watercraft control system12can use the central digital controller24to carry out the auto-track & follow mode.

The digital controller25is configured to communicate with the detector14to receive a detection signal from the detector14. Here, for example, the digital controller25is provided with a communication interface25cthat is used to communicate with the detector14either wirelessly or via a wired connection to the network of the watercraft10. Thus, the digital controller25can also communicate with the onboard computer system of the watercraft10via the communication interface25c. Here, for example, the digital controller25is plugged into a network interface controller NIC (e.g., a MicroAutoBox by dSpace), and the detector14is plugged into a USB port of the communication interface25cof the digital controller25. The processor25aof the digital controller25(the GPU25) communicates with the digital controller24(the BCU). In this way, the digital controller25can communicate with the central digital controller24and the propulsion units22to control the propulsion force of the watercraft10as well as communicate with the other components of the watercraft10that are connected to the network of the watercraft10.

Here, the detection signal from the detector14is a pair of images since the detector14includes a stereo camera. By using a stereo camera as the detector14can detect the presence of the lead watercraft W as well as be used to determine the distance between the lead watercraft W and the watercraft10. Also, the images captured by the detector14can be used to provide the predetermined lateral offset amount OS.

Using the detection results of the detector14, the digital controller25then controls a propulsion direction of the watercraft10and a propulsion force of the watercraft10so that the watercraft10tracks and follows the lead watercraft W at the target following distance Zdes. In the first embodiment, the digital controller25is configured to selectively carry out at least one of differential steering and rudder steering to change the propulsion direction of the watercraft10in order to track and follow the lead watercraft W, as discussed later.

In the case in which a stereo camera is utilized for the detector14, the digital controller25(GPU) is provided with an image detection program. The processor25aof the digital controller25is connected to the detector14(e.g., the camera) and receives the image data of the camera view in front of the watercraft10. From the image data, the processor25aof the digital controller25detects the lead watercraft W within the image that is captured by the detector14, and determines lateral and longitudinal positions of the lead watercraft W relative to the host watercraft10. The lateral and longitudinal positions of the lead watercraft W are then communicated from the digital controller25(GPU) to the digital controller24(BCU).

The image detection program can use any detection method available. The detection method that is used will depend on the types of devices used as the detector14. For example, the image detection program of the digital controller25can use either (1) a hypothesis generation methodology where the locations of potential objects in an image are hypothesized by using watercraft information such as symmetry, color, shadow, corners, horizontal/vertical edges, texture, and watercraft lights; or (2) a hypothesis verification methodology that verifies the presence of an object in an image by analyzing differences between the images observed and known object models or templates. If a stereo camera is utilized for the detector14, then a disparity map process can be used to process the corresponding pixels in the two (right and left) images to find the differences for determining the presence of a watercraft in the images. Alternatively, when using a stereo camera for the detector14, then an inverse perspective mapping process can be used for determining the presence of a watercraft in the images. Since these methodologies for determining the presence of an object in an image are known, these methodologies will not be discussed in further detail herein.

Also, the lead watercraft W can be further provided with a marker that assists in identifying the presence of the leading watercraft by the detector14. For example, the marker can be a plurality of LED light sources that are position so that the light from LED light sources can be viewed from a rear side of the lead watercraft W in the longitudinal direction. Alternatively, the marker can be a balloon or a disk that is provided with a particular shape or pattern. In this way, the marker can contribute to the detector14easily locating the leading watercraft W. Moreover, the detection method utilized for determining the presence of a leading watercraft is not limited to these methodologies. In any case, the digital controller25has a watercraft detection program that detects a presence of the lead watercraft W based on a detection result of the detector14.

Still referring toFIG. 5, each of the propulsion units22basically includes an internal combustion engine26(i.e., a drive source) and a propeller28(i.e., a propulsor). Here, each of the propulsion units22further includes an engine control unit30(ECU). Alternatively, for example, the engine control units36can be omitted and the control of the internal combustion engines26(hereinafter “the engines26”) can be performed by the central digital controller24. Here inFIG. 5, the engines26are referred to as first engine, second engine and third engine to distinguish the engines26. Likewise, inFIG. 5, the propellers28are referred to as first propeller, second engine and third propeller. Also, inFIG. 5, the engine control units36are referred to as first ECU, second ECU and third ECU. Each of the engine control units30is a digital controller similar in configuration to the configuration of the central digital controller24that is previously discussed. Each of the engine control units30is programmed to control its respective propulsion unit22to independently generate the propulsion forces of the propulsion units22, respectively, and to independently steer or turn the propulsion units22, respectively, in order to propel and steer the watercraft10.

Referring back toFIG. 4, one of the propulsion units22is illustrated in more detail. Since the construction of the propulsion units22are the same, the description of the propulsion unit22illustrated inFIG. 4also applies to the other propulsion units22. The propulsion unit22is mounted to a rear portion20cof the hull20in a conventional manner. The engine26is connected to the propeller28via a drive shaft31and a propeller shaft32. The propeller shaft32is connected to the drive shaft31through a drive transmission33. The engine26rotates the propeller28via the drive shaft31and the propeller shaft32to generate a thrust for propelling the watercraft10. The drive transmission33switches the rotational direction of the power to be transmitted from the drive shaft31to the propeller shaft32. The drive transmission33includes, for instance, a plurality of gears and a clutch that changes meshing of the gears. The drive shaft31is operatively connected to a crankshaft34of the engine26so that rotation of the crankshaft34is transmitted to the drive shaft31which in turn transmits rotation to the propeller shaft32to rotate the propeller28. The engine26, the drive shaft31, the propeller shaft32and the drive transmission33are provided in a housing36.

The propulsion unit22is provided with a shift actuator38that is electrically connected to the engine control unit30as seen inFIG. 4. The shift actuator38includes, for example, an electric motor or other types of actuators that is configured to switch an operating position of the drive transmission33of the propulsion unit22to a forward position to generate a forward propulsion force, a reverse position to generate a reverse propulsion force, or a neutral position. Thus, the shift actuator38is configured to operate the drive transmission33to change rotational direction of the propeller shaft32and the propeller28between a forward drive thrust and a reverse drive thrust. Preferably, the shift actuator38is an electric actuator that is electrically controlled by the engine control unit30. The engine control unit30is programmed to operate the shift actuator38to control the drive transmission33based on a control signal received from the central digital controller24and/or the digital controller25of the watercraft control system12. In this way, the central digital controller24and/or the digital controller25can carry out differential steering and switching between a forward propulsion and a reverse propulsion.

The propulsion unit22is also provided with a throttle actuator40that is electrically connected to the engine control unit30as seen inFIG. 4. The throttle actuator40includes, for example, an electric motor or other types of actuators for change the output of the engine26. Namely, the throttle actuator40changes an opening degree of a throttle valve to adjust the output or speed of the engine26. Preferably, the throttle actuator40is an electric actuator that is electrically controlled by the engine control unit30. The propulsion unit22is also provided with an engine speed sensor42that detects a rotational speed of the crankshaft34of the engine26to determine an engine rotational speed of the engine26. The detection signal of the engine speed sensor42is transmitted to the engine control unit30, the central digital controller24and/or the digital controller25. The engine control unit30is programmed to operate the throttle actuator40to control the speed of the engine26based on a control signal received from the central digital controller24and/or the digital controller25of the watercraft control system12. In this way, the central digital controller24and/or the digital controller25can carry out throttle control of the engine26.

The propulsion unit22is also provided with a steering actuator44that is electrically connected to the engine control unit30as seen inFIG. 4. The steering actuator44includes, for example, a hydraulic or electric cylinder, or other types of actuators that is provided to turn the propulsion unit22relative to the watercraft10. The propulsion unit22is also provided with a steering angle sensor46that detects a steering angle of the propulsion unit22. The steering angle sensor46can be, for example, a stroke sensor of the hydraulic cylinder of the steering actuator44. The steering angle sensor46transmits the detection result to the engine control unit30, the central digital controller24and/or the digital controller25. The engine control unit30is programmed to operate the steering actuator44to control the propulsion direction of the watercraft10.

Referring again toFIG. 5, with this configuration of the watercraft10, the propulsion units22can be operated to carry out rudder control (i.e., turning the propulsion unit as a rudder) and/or differential control (i.e., operating at least one of the propulsion units with a different thrust output with respect to at least one other of the propulsion units) for changing the propulsion direction of the watercraft10. Thus, the watercraft10has three steering units48with each of the steering units48having one of the steering actuator44for carrying out rudder control. Alternatively, with certain watercrafts, either the rudder control or the differential control can be omitted from the auto-track & follow mode of the watercraft control system12as needed and/or desired.

In the first embodiment, a driver input provided to the steering wheel16is electronically communicated through the central digital controller24. A steering sensor (not shown) is in communication with at least one of the steering wheel16and a steering shaft that is associated with the steering wheel16. The steering sensor46is arranged to provide a signal indicative of a rotational position, angular position, input force, or input torque applied to at least one of the steering wheel16or a steering shaft (not shown) associated with the steering wheel16to the central digital controller24. The central digital controller24is arranged to receive the signal and provide commands or signals to the engine control units30of the propulsion units22and/or the steering actuator44to move the propulsion units22as a rudder. However, when the watercraft control system12is in the auto-track & follow mode, the driver inputs are not needed, and the propulsion units22and/or the steering actuator44are controlled by the central digital controller24and/or the digital controller25based on detection signals from various sensors.

As seen inFIG. 5, for example, the watercraft10can be provide with a running speed detector50(e.g., a GPS speedometer, a pitot speedometer, etc.), a satellite navigation receiver52(e.g., a Global Positioning System (GPS) receiver, a Navigation Satellite System (NSS) receiver, or a Global Navigation Satellite System (GNSS) receiver), and a heading sensor54(e.g., on-board gyro and tilt sensors). The running speed detector50, the satellite navigation receiver52and the heading sensor54can be integrated into a single unit that provides speed data, heading data and position data. The running speed detector50, the satellite navigation receiver52and the heading sensor54are connect to the digital controller25by the network of the watercraft10so that signals are communicated to the digital controller25via the network of the watercraft10. The speed of the watercraft10can be provided to the digital controller25by a detection signal from the running speed detector50, or can be provided to the digital controller25a GNSS signal that is received by the satellite navigation receiver52. The position of the watercraft10can be provided to the digital controller25based on the GNSS signal that is received by the satellite navigation receiver52. The heading of the watercraft10can be provided to the digital controller25based on the heading sensor54. Thus, the digital controller25receives the speed of the watercraft10, the relative position of the watercraft10, and the relative heading of the watercraft10based on detection results from various receivers, detectors and/or sensors.

Preferably, as seen inFIG. 6, the watercraft control system12further comprises a user interface such as a Multi-Function Display, a wireless tablet56and/or a joystick58that communicates with the digital controller25. The tablet56preferably has a processor that communicates with the processor25aof the digital controller25and a display screen, such that the tablet56displays the current image from the detector14as well as other information related to the auto-track & follow mode such as the distance between the watercraft10and the lead watercraft W, the speed of the watercraft10, the heading of the watercraft10, etc.

Here, the joystick58is provided on the watercraft body20and programmed to be used to operate with the wireless tablet56and the digital controller25. In this way, the user can use the wireless tablet56and/or the joystick58to activate and deactivate the auto-track & follow mode. In the first embodiment, the wireless tablet56(i.e., the user interface) includes a touch screen56a(i.e., a user input) that is used to select the lead watercraft W. Thus, the digital controller25is configured to track and follow the lead watercraft based on a selection of the lead watercraft W in response to an input from a user input (e.g., the touch screen56aand/or the joystick58).

Alternatively, the watercraft control system12can use a user interface60that is built into the watercraft10instead of or in conjunction with the wireless tablet56. The user interface60is often referred to as a Multi-Function Display. The user interface60of the watercraft10can be a touch screen display, or a display without a touch screen, and one or more knobs and/or buttons.

The auto-track & follow mode executed by the digital controller25will now be discussed with reference toFIGS. 6 to 16. As seen inFIG. 6, a state transition logic is illustrated for the watercraft control system12. When the watercraft10is started, the central digital controller24and the digital controller25are initialized and various other components are automatically activated including the detector14. Before the user selects a lead watercraft W to track and follow, the watercraft control system12will enter a standby mode. In standby mode, the watercraft control system12waits for the user to select a watercraft to track and follow, but the digital controller25has not yet taken over the controls from the user. For the digital controller25to take over, a user must select a lead watercraft on the tablet56, or using the joystick58. Alternatively, the digital controller25can be woken up by using the user interface60of the watercraft10.

Once the user selects a lead watercraft (e.g., the lead watercraft W), the digital controller25activates the lateral and longitudinal control systems which allow for the automatic watercraft tracking and following process (i.e., the user engage the auto-track & follow mode). While in the auto-track & follow mode, there are no necessary inputs required from the driver of the watercraft10, unless the watercraft control system12experiences a failure or the driver of the watercraft10requests the auto-track & follow mode to be disengaged. While in the auto-track & follow mode, the control processes ofFIGS. 12 and 13are simultaneously executed to control both the steering (propulsion direction) and the throttle (propulsion force and/or propulsion direction).

Referring toFIGS. 7 and 8, lateral control of the watercraft10during the auto-track & follow mode will be discussed. As mentioned above, lateral control of the watercraft10can be achieved by differential thrust control and rudder control. During nominal forward speed operation, the watercraft10employs a pure-pursuit tracking method by modifying its rudder based on a difference between a target tracking azimuth angle and an actual azimuth angle. As seen inFIG. 7, a font landscape view is illustrated looking forward from the watercraft10at the lead watercraft W that includes a field of view of the detector14(e.g., the stereo camera). From the image (camera frame) obtained by the detector14(e.g., the stereo camera), the digital controller25can both detect the lead watercraft W and determine the distance of the watercraft10from the lead watercraft W.

Also, the host watercraft10can track the lead watercraft W at a predetermined lateral offset amount OS of the host watercraft path PH from the lead watercraft path PL based on a default setting or a user setting. Basically, the user can choose to a track and follow path using the camera image. For example, the number of pixels can be normalized such that the middle or center of the camera image is set to “0%”, and the pixel at each edge of the camera image is set to −100% and 100%. In short, the user specifies to the digital controller25at which percentage of the frame to track the lead watercraft W. In this way, the user sets the predetermined lateral offset amount OS of the host watercraft path PH from the lead watercraft path PL. For example, the default setting for the host watercraft path PH to track the lead watercraft W can be set to 50%, which would result on the host watercraft10tracking to the left of the lead watercraft W.

As illustrated inFIG. 8, lateral feedback control is employed based on the detection results from the image inFIG. 7to control a rudder angle δRof the host watercraft10. More specifically, as seen inFIG. 8, the digital controller25regulates the heading of the watercraft10through slight adjustments on the rudder angle δRbased on the current location of the lead watercraft W, which is measured using the camera's coordinate system. In other words, feedback control is employed to control the heading of the host watercraft10by providing a desired heading point xdesand comparing this value with an estimated current heading point x(t), which varies at each point in time because it depends on the location of the lead watercraft10.

In the case of the desired heading point xdesaligning with the desired heading point xdes, the goal of the lateral feedback control is to drive the resulting error elatto zero (i.e., elat=xdes−x(t)), even in the presence of disturbances such as wind, wave and currents which may act to drive the watercraft10away from the desired tracking point. In the case of the watercraft path PH being offset from the lead watercraft path PL, the goal of the lateral feedback control is to drive the resulting error to the amount of the desired offset, even in the presence of disturbances such as wind, wave and currents which may act to drive the watercraft10away from the desired tracking point. Furthermore, as seen inFIG. 8, the digital controller25controls the propulsion direction using either rudder control or differential control such that the desired heading point xdesaligns with the estimated current heading point x(t). In this way, the watercraft path PH of the watercraft10tracks and follows in the lead watercraft path PL of the lead watercraft W as seen inFIG. 1.

Alternatively, the digital controller25controls the propulsion direction using either rudder control or differential control such that the desired heading point xdesis not zero (or in the middle of the camera frame) as seen inFIG. 7. In this case, the host watercraft path PH will be offset from the lead watercraft path PL by the predetermined lateral offset amount OS which can be either a default setting or set by the user. In this way, the watercraft path PH of the watercraft10is offset from the lead watercraft path PL of the lead watercraft W during tracking and following the lead watercraft W as seen inFIGS. 2 and 7. Also, preferably, the user can twist or tilt the joystick58to temporarily offset the watercraft path PH from the lead watercraft path. Thus, the watercraft path PH will remain offset from the lead watercraft path PL as long as the user twists or tilts the joystick58from its rest or neutral position. Alternatively, the desired azimuth angle can be determined from the desired heading point xdesand can be controlled by the user from the touch screen56aand/or the user interface60(Multi-Function Display) of the watercraft10. Of course, it will be apparent from this disclosure that the watercraft path PH with respect to the lead watercraft path PL can be controlled and/or set by the user in a variety of ways and is not limited to the above mentioned ways.

Referring toFIGS. 10 and 11, longitudinal control of the watercraft10during the auto-track & follow mode will be discussed. As mentioned above, longitudinal control of the watercraft10can be achieved by adjusting the propulsion forces of the propulsion units22. The longitudinal control process employed in the auto-track & follow mode allows for the watercraft10to follow the lead watercraft W at some target following distance Zdes, which can also be referred to as a target or desired following distance of the watercraft10, as long as the speed of the tracking host watercraft is never higher than some threshold specified by the user. If the speed of the lead watercraft W is ever greater than the maximum allowable speed set by the user, then the digital controller25automatically disengages the auto-track & follow mode and returns to a cruise control mode, where steering is handed back to the driver of the host watercraft10, but speed is regulated by the digital controller25. This transition is preferably indicated by a beep to alert the user.

On the other hand, while the speed of the lead watercraft W remains lower the maximum allowable speed set by the user for the watercraft10, the digital controller25will regulate the target following distance Zdesto the lead watercraft W by making gentle automatic modifications to the throttle based on the difference between the actively calculated target following distance Zdesand the estimated current distance as perceived by the detector14. This actively calculated target following distance Zdesis preferably set by a prescribed constant time-headway rule. The constant time-headway rule is nothing more than the time to take for the watercraft10to contact with the lead watercraft W if the lead watercraft W were to suddenly stop with the watercraft10maintaining its instantaneous speed. If the target following distance Zdesis calculated such that the time-headway remains constant, the string stability is guaranteed. This guarantees that multiple watercraft can operate behind each other, each becoming the lead watercraft to the watercraft behind. The target following distance Zdesis given by the follow formula:
Zdes=τ*ν+dz

Note that the target following distance Zdesis a function of the velocity ν of the host watercraft10. If the velocity ν of the watercraft10becomes zero, then the target following distance Zdesbecomes equal to a separation distance dz (i.e., Z=dz). The user has the ability to change the value of the constant τ as needed and/or desired. However, if the constant τ is changed too fast, then undesirable accelerations of the watercraft10may occur. To solve this issue, a rate limiter may be used to prevents the value of the target following distance Z from changing too fast, despite a user input.

As seen inFIG. 10, feedback control is employed based on the estimated following distance Δz(t) provided by the detector14, where the output of the digital controller25becomes the prescribed throttle level δTto the throttle actuators40of the engines26of the watercraft10in order to properly maintain the target following distance Zdes. More specifically, as seen inFIG. 10, the digital controller25regulates the propulsion force of the watercraft10to obtain the following condition: Δz(t)=Zdes, even in the presence of disturbances such as wind, waves, and current.

Instead of the longitudinal control of the watercraft10by the digital controller25being based mainly on the target following distance Zdes, the longitudinal control of the watercraft10by the digital controller25can be a based on a balance between the set speed (maximum velocity νdes) and the target following distance Zdes. As seen inFIG. 11, a balance between the set speed (maximum velocity νdes) and the target following distance Zdescan be easily performed using two feedback controls by a comparison of the two output throttles. In either case, the minimum throttle is always selected as the active throttle. An anti-windup scheme can be employed on each of the feedback controls since they each have an integrator to minimize steady state errors. This keeps each of the corresponding throttles from running away to infinity while one of the feedback controls is active vs the other. When the lead watercraft W moves faster than our maximum speed, throttle demand for the distance feedback control approaches toward its limit, and hence the throttle demand for the velocity feedback control becomes the active throttle. Similarly, when the lead watercraft W is moving slower than our maximum speed, the throttle demand for the velocity feedback control approaches toward its limit, making the throttle demand for the distance feedback control the active throttle.

Also, if the auto-track & follow mode is started while the watercraft10is too far from the desired tracking distance, then the auto-track & follow mode can result in an uncomfortable accelerations of the watercraft10. This happens because there is an immediate large error on the distance feedback control when the auto-track & follow mode is first engaged, and therefore the distance feedback control reacts aggressively to minimize this situation. Through the introduction of input shaping logic, the digital controller25is able to suppress the distance feedback control to slowly move towards the target following distance Zdesthrough an exponential decaying function, yielding a smooth transient.

The goal of the digital controller25is to minimize the error between the target following distance Zdesand the estimated current distance Δz(t) to the lead watercraft. The digital controller25samples the image data from the detector14at a prescribed interval, and the digital controller25then increases or decreases the throttles of the engines26based on whether the watercraft10is closer or farther from the target following distance Zdesat that point in time.

Referring now toFIG. 12, one example of a throttle (longitudinal) control flow chart is illustrated that is executed by the digital controller25of the watercraft control system12during the auto-track & follow mode. More specifically, the digital controller25is configured to output at least one control command related to a propulsion force of the watercraft10to at least one of the propulsion units22maintain the target following distance Zdesbehind the lead watercraft W. Thus, the digital controller25controls the throttles of the engines26of the propulsion units22to maintain the target following distance Zdesbehind the lead watercraft W while also performing the steering control to allow the watercraft10to track the lead watercraft W as explained later. As mentioned above, the target following distance Zdescan be adjusted using the tablet56, the joystick58and/or the user interface60of the watercraft10.

In step S1, the processor25aof the digital controller25determines the distance to the lead watercraft W. In the first embodiment, the digital controller25receives an estimated distance signal from the detection system (the detector14and the processor25a), which first calculates the estimated current distance z(t) from the watercraft10to the lead watercraft W using the detection signal from the detector14. Then, the throttle control process proceeds to step S2.

In step S2, the digital controller25determines whether the estimated current distance z(Q) from the watercraft10to the lead watercraft W is greater than the target following distance Zdes. If the digital controller25determines the estimated current distance z(t) from the watercraft10to the lead watercraft W is greater than the target following distance Zdes, then the throttle control process proceeds to step S3. If the digital controller25determines the estimated current distance z(t) from the watercraft10to the lead watercraft W is equal to or less than the target following distance Zdes, then the throttle control process proceeds to step S5.

In step S3, the digital controller25outputs a signal to the engine control units30of the propulsion units22to increase the thrust of the propulsion units22. This is accomplished by the throttle actuator40increasing the opening degrees of the throttle valves of the engines26by a predetermined amount. Then, the throttle control process proceeds to step S4.

In step S4, the digital controller25determines whether the estimated current distance z(t) from the watercraft10to the lead watercraft W is decreasing or not. In other words, the digital controller25determines if the watercraft10is getting closer to the lead watercraft W or not. If the digital controller25determines the estimated current distance z(t) from the watercraft10to the lead watercraft W is decreasing, then the throttle control process proceeds to step S5. If the digital controller25determines the estimated current distance z(t) from the watercraft10to the lead watercraft W is not decreasing, then the throttle control process proceeds back to step S3to further increase the opening degrees of the throttle valves40of the engines26by a predetermined amount.

In step S5, the digital controller25determines whether the estimated current distance z(t) from the watercraft10to the lead watercraft W is less than the target following distance Zdes. If the digital controller25determines the estimated current distance z(t) from the watercraft10to the lead watercraft W is less than the target following distance Zdes, then the throttle control process proceeds to step S6. If the digital controller25determines the estimated current distance z(t) from the watercraft10to the lead watercraft W is equal to or greater the target following distance Zdes, then the throttle control process repeats step S5until the estimated current distance z(t) from the watercraft10to the lead watercraft W becomes less than the target following distance Zdes.

In step S6, the digital controller25outputs a signal to the engine control units30of the propulsion units22to decrease the thrust of the propulsion units22. This is accomplished by the throttle actuator40decreasing the opening degrees of the throttle valves of the engines26by a predetermined amount. Then, the throttle control process proceeds back to step S2.

In parallel to the previously discussed on-board longitudinal control system, the digital controller25also runs an on-board lateral control system whose sole goal is to steer the host watercraft10behind the lead watercraft. This lateral control system is configured to selectively switch between rudder control and differential control based on a predetermined traveling condition (e.g., the speed of the watercraft10, the speed of the engines26, etc.), for example, as indicated inFIGS. 13 and 14. This switching function is desirable since at low speeds the effectiveness of the rudder reduces to zero for some watercrafts at zero speed.

Here inFIG. 13, the predetermined traveling condition includes a first traveling threshold Th1and a second traveling threshold Th2that is smaller than the first traveling threshold Th1(i.e., Th2<Th1). For example, the first traveling threshold Th1can be an upper watercraft cruising speed or an upper engine speed (rpm), while the second traveling threshold Th2can be a lower watercraft cruising speed or a lower engine speed (rpm). The digital controller25is configured to switch the control from the differential mode to the steering mode upon determining a current traveling condition of the watercraft exceeds the first traveling threshold Th1, and to switch the control from steering mode to the differential mode upon determining the current traveling condition of the watercraft falling below the second traveling threshold M2. This hysteresis logic allows for smooth transitions while operating near a desired switching point (e.g., a desired cruising speed or a desired engine speed).

Referring now toFIG. 13, one example of a steering (lateral) control logic diagram flow chart of the steering control is illustrated that is executed by the digital controller25of the watercraft control system12during the auto-track & follow mode. Here, the digital controller25controls the shift actuators38, the throttle actuators40and/or the steering actuators44to turn or steer the watercraft10while also performing the above mentioned throttle control to allow the watercraft10to follow and maintain some distance to the lead watercraft W. The tracking function can be adjusted by the user such that the watercraft10either follows in the lead watercraft path PL of the lead watercraft W as seen inFIG. 1, or follows the lead watercraft path PL of the lead watercraft W with the predetermined lateral offset amount OS with respect to the lead watercraft path PL of the lead watercraft W as seen inFIG. 2. Preferably, the predetermined lateral offset amount OS is adjustable by the user using the tablet56, the joystick58and/or the user interface60of the watercraft10.

Here inFIG. 13, as mentioned above, the digital controller25is configured to switch the control from the differential mode to the steering mode upon determining the current traveling condition of the watercraft exceeds the first traveling threshold Th1, and to switch the control from steering mode to the differential mode upon determining the current traveling condition of the watercraft falling below the second traveling threshold M2. This hysteresis logic allows for smooth transitions while operating near a desired switching point (e.g., a desired cruising speed or a desired engine speed).

In step S11, the digital controller25receives the current traveling state (e.g., a current cruising speed or a current engine speed) of the watercraft10. In the first embodiment, for example, the digital controller25receives a cruising speed signal indicative a current cruising speed of the watercraft10from the running speed detector50or an engine speed signal indicative a current engine speed from one or more of the engine speed sensors42. Then, the steering control process proceeds to step S12.

In step S12, the digital controller25determines whether the current traveling state of the watercraft10exceeds the first traveling threshold Th1. If the digital controller25determines the traveling state of the watercraft10exceeds the first traveling threshold Th1, then the steering control process proceeds to step S13. If the digital controller25determines the current traveling state of the watercraft10has fallen below the second traveling threshold Th2, then the steering control process proceeds to step S15.

In step S13, the digital controller25executes a rudder control mode to steer the watercraft10and track the lead watercraft W. This type of steering is called rudder steering because at least one of the propulsion units22is turned as a rudder to turn the watercraft10. In the case of rudder steering, the digital controller25is configured to output the at least one control command to at least one of the steering actuators44to turn at least one of the propulsion units22. One example a rudder control process carried out while in the rudder control mode is illustrated inFIG. 15. Then, the steering control process proceeds to step S14.

In step S14, while in the rudder control mode, the digital controller25determines whether the current traveling state of the watercraft10has fallen below the second traveling threshold Th2. If the digital controller25determines the current traveling state of the watercraft10has fallen below the second traveling threshold Th2, then the steering control process proceeds to step S15. If the digital controller25determines the current traveling state of the watercraft10has not fallen below the second traveling threshold Th2, then the steering control process repeats step S14to monitor when or if the steering control should be switched from rudder control to differential control.

In step S15, the digital controller25executes a differential control mode to steer the watercraft10and track the lead watercraft W. This type of steering is called differential steering because different propulsion forces are outputted between at least two of the propulsion units22to turn the watercraft10. In the case of differential steering, the digital controller25is configured to output at least one control command to the propulsion units22to generate different propulsion forces between the propulsion units22. In other words, the digital controller25is configured to selectively output the at least one control command to the propulsion units22to generate different propulsion forces (differential control) based on a predetermined traveling condition (e.g., the speed of the watercraft10, the speed of the engines26, etc.). One example of a differential control process carried out while in the differential control mode is illustrated inFIG. 16. Then, the steering control process proceeds back to step S12to monitor when or if the steering control should be switched from differential control back to rudder control.

Thus, the digital controller25is configured to switch control from the differential mode in which the propulsion units22generates different propulsion forces to steer the host watercraft10to the steering mode in which the direction of propulsion forces changes based on the location of the leading vehicle W. While in the steering mode, the propulsion forces generated by the propulsion units22can be the same.

Referring now toFIG. 14, a graph illustrates a mode switching process that occurs during the steering control executed by the watercraft control system12during the auto-track & follow mode according to the flow chart ofFIG. 13. Namely, the switching between rudder control mode and differential control mode is based on the speed of the watercraft10to achieve a smooth and noiseless mode switch. More specifically, a hysteresis mode switching process is used based on the speed of the watercraft10to achieve a smooth and noiseless mode switch. For example, the first traveling threshold Th1can be set to 1.8 m/s and the second traveling threshold Th2can be set to 1.2 m/s. Thus, at speeds higher than the first traveling threshold Th1(e.g., 1.8 m/s), the watercraft10will operate in a rudder steering mode using the turning of the rudder for lateral control of the watercraft10. At speeds lower than the second traveling threshold Th2(e.g., 1.2 m/s), the watercraft10will operate in differential mode using differential thrust to control the lateral dynamics of the watercraft10. This mode switching type allows for less changes, while maintaining the same performances regarding maneuverability and tracking. All parameters relating to the hysteresis mode switching process are, of course, watercraft specific and should be treated accordingly.

With the steering control process ofFIGS. 13 and 14, the first traveling threshold Th1and the second traveling threshold Th2are preferably different values such that the watercraft10maintains the target following distance Zdeswithout the engines26being adjusted too frequently. Alternatively, a steering mode switch can be provided for switching between steering by differential control and steering by rudder control.

Referring now toFIG. 15, one example of the rudder control mode of step S13inFIG. 13is illustrated. In the rudder control mode, the digital controller25controls the steering actuators44to turn or steer the watercraft10while also performing the throttle control to allows the watercraft10to follow and track the lead watercraft W.

In step S21, the digital controller25receives the images from the detector14which indicates the estimated current heading point x(t) (the estimated current watercraft propulsion direction of the watercraft10) with respect to the desired heading point xdes(the target propulsion direction of the watercraft10). Then, the steering control process proceeds to step S22.

In step S22, based on the difference between the estimated current azimuth angle of the lead watercraft W and the desired azimuth angle of the lead watercraft W, the digital controller25calculates the desired/target propulsion direction that is needed to track the lead watercraft W along the desired tracking path. The estimated current azimuth angle can be determined from the estimated current heading point x(t) by the processor25aof the digital controller25. If the digital controller25determines that a starboard correction is needed, then the steering control process proceeds to step S23. If the digital controller25determines that a starboard correction is not needed, then the steering control process proceeds to step S24.

In step S23, the digital controller25outputs a signal to one or more of the steering actuators44to turn or steer the watercraft10towards the target direction computed in step S22. The angle sensors46detects the current steering angles of the propulsion units22and the digital controller25determines the amount that one or more of the propulsion units22should be turned to the target propulsion direction in order to correct the direction of the watercraft10. Then, the steering control process proceeds to step S24.

In step S24, based on the difference between the estimated current azimuth angle of the lead watercraft W and the desired azimuth angle of the lead watercraft W, the digital controller25calculates the desired/target propulsion direction that is needed to track the lead watercraft W along the desired tracking path. If the digital controller25determines that a port correction is needed, then the steering control process proceeds to step S25. If the digital controller25determines that a port correction is not needed, then the steering control process repeats step S24.

In step S25, the digital controller25outputs a signal to one or more of the steering actuators44to turn or steer the watercraft10towards the target propulsion direction using the angle sensors46to detect the current steering angles of the propulsion units22. Then, the steering control process proceeds back to step S22to monitor when or if additional steering is needed to maintain the target propulsion direction.

Referring now toFIG. 16, one example of the differential control mode of step S15inFIG. 13is illustrated. In the differential control mode, the digital controller25controls the shift actuators38and/or the throttle actuators40to turn or steer the watercraft10while also performing the throttle control to allow the watercraft10to follow and track the lead watercraft W. By operating the shift actuators38, the digital controller25can switch between a forward thrust and a rearward thrust to effectuate a change in the propulsion direction. Also, the propulsion direction can be changed by controlling the throttle actuators40such that the forward thrust is different in at least two of the propulsion units22. This type of steering using the propulsion units22to turn the watercraft10is called differential steering because different propulsion forces are outputted between at least two of the propulsion units22to turn the watercraft10.

In step S31, the digital controller25receives the images from the detector14which indicates the estimated current heading point x(t) (the estimated current watercraft propulsion direction of the watercraft10) with respect to the desired heading point xdes(the target propulsion direction of the watercraft10). Then, the steering control process proceeds to step S32.

In step S32, based on the difference between the estimated current azimuth angle of the lead watercraft W and the desired azimuth angle of the lead watercraft W, the digital controller25calculates the desired/target propulsion direction that is needed to track the lead watercraft W along the desired tracking path. If the digital controller25determines that a starboard correction is needed, then the steering control process proceeds to step S33. If the digital controller25determines that a starboard correction is not needed, then the steering control process proceeds to step S34.

In step S33, the digital controller25outputs a signal to one or more of the shift actuators38and/or the throttle actuators40to turn or steer the watercraft10towards the target direction computed in step S22. The heading sensor54detects the current heading rate of the watercraft10and the digital controller25determines the differential amount to be generate by the propulsion units22in order to correct the current heading or propulsion direction of the watercraft10to the target propulsion direction. Then, the steering control process proceeds to step S34.

In step S34, based on the difference between the estimated current azimuth angle of the lead watercraft W and the desired azimuth angle of the lead watercraft W, the digital controller25calculates the desired/target propulsion direction that is needed to track the lead watercraft W along the desired tracking path. If the digital controller25determines that a port correction is needed, then the steering control process proceeds to step S35. If the digital controller25determines that a port correction is not needed, then the steering control process repeats step S34.

In step S35, the digital controller25outputs a signal to one or more of the shift actuators38and/or the throttle actuators40to turn or steer the watercraft10towards the target propulsion direction using the heading sensor54to detect the current propulsion direction of the watercraft10. Then, the steering control process proceeds back to step S32to monitor when or if additional steering is needed to maintain the target propulsion direction.

In summary, as mentioned above, the steering control can be accomplished by rudder control and/or differential control. In the case of rudder control, the digital controller25is configured to output the at least one control command to one of the steering units50to change the propulsion direction of the watercraft10. In the case of differential control, the digital controller25is configured to output the at least one control command to the propulsion units22to generate different propulsion forces between the propulsion units22.

Thus, in summary, the digital controller25is configured to output at least one control command related to a propulsion direction of the watercraft10and a propulsion force of the watercraft10to at least one of the propulsion units22to track and follow the lead watercraft W in accordance with the on-board longitudinal control system and the on-board lateral control system. Thus, the digital controller25controls the throttle actuators40of the engines26of the propulsion units22to maintain the target following distance Zdesbehind the lead watercraft W while also performing either rudder control or differential control to steer to the watercraft10such that the watercraft10follows and tracks the lead watercraft W.

Referring now toFIGS. 17 to 19, a watercraft210is illustrated in the form of a jet propulsion boat that is equipped with a watercraft control system212. The watercraft control system212is the same as the watercraft control system12, discussed above, except that the watercraft control system212is adapted to a jet propulsion boat. Basically, the watercraft210includes a watercraft body220and a pair of propulsion units222. The watercraft body220is provided with the propulsion units222in a conventional manner. The propulsion units222are steerable in a conventional manner. Each of the propulsion units222includes an engine226as seen inFIG. 18. Each of the engines226drives an impeller228as seen inFIG. 19in a conventional manner. Since jet propulsion boats are well known, the watercraft210will not be discussed in more detail.

The watercraft control system212is configured to execute the auto-track & follow mode in the same way as the watercraft control system12. Thus, the watercraft210is provided a detector214for tracking and following a lead watercraft. Like, the first embodiment, the detector214is a stereo camera that is used to detect a lead watercraft and determine a distance of the watercraft210from the lead watercraft. In this way, the watercraft control system212can execute the auto-track & follow mode in the same way as the watercraft control system12such that the watercraft210can track and follow a lead watercraft.

Referring now toFIG. 20, a watercraft310is illustrated in the form of a personal watercraft that is equipped with a watercraft control system312. The watercraft310is a saddle seat type of personal watercraft that is well known. The watercraft control system312is the same as the watercraft control system12, discussed above, except that the watercraft control system312is adapted to a personal watercraft. Basically, the watercraft310includes a watercraft body320and a single propulsion unit322. The watercraft body320is provided with the propulsion unit322in a conventional manner. The propulsion unit322is a jet propulsion device similar to the one illustrated inFIG. 19. The watercraft control system312of the watercraft310is configured to carry out the auto-track & follow mode in the same manner as discussed above, except that the watercraft control system12does not utilize the differential mode control. In other words, since the watercraft310only has a single propulsion unit322, the steering control is solely carry out using rudder control during the auto-track & follow mode. Since personal watercrafts are well known, the watercraft310will not be discussed in more detail.

Other than omitting differential steering control, the watercraft control system312is configured to execute the auto-track & follow mode in the same way as the watercraft control system12. Thus, the watercraft310is provided a detector314for tracking and following a lead watercraft. Like, the first embodiment, the detector314is a stereo camera that is used to detect a lead watercraft and determine a distance of the watercraft310from the lead watercraft. In this way, the watercraft control system312can execute the auto-track & follow mode in substantially the same way as the watercraft control system12such that the watercraft310can track and follow a lead watercraft.

In understanding the scope of the present invention, the term “comprising” and its derivatives, as used herein, are intended to be open ended terms that specify the presence of the stated features, elements, components, groups, integers, and/or steps, but do not exclude the presence of other unstated features, elements, components, groups, integers and/or steps. The foregoing also applies to words having similar meanings such as the terms, “including”, “having” and their derivatives. Thus, as used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Also, the terms “part,” “section,” “portion.” “member” or “element” when used in the singular can have the dual meaning of a single part or a plurality of parts. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which illustrative embodiments of the inventive concepts belong. It will be further understood that terms, such as those defined in commonly-used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled”” to another element, there are no intervening elements present. As used herein the term “and/or” includes any and all combinations of one or more of the associated listed items. Additionally, similar words used to describe the relationship between elements or layers should be interpreted in a like fashion (e.g., “between” versus “directly between”, “above” versus “directly above”, “below” versus “directly below”, “adjacent” versus “directly adjacent,” “on” versus “directly on”). Thus, components that are shown directly connected or contacting each other can have intermediate structures disposed between them unless specified otherwise.

It will be understood that, although the terms “first”, “second”, etc. may be used herein to describe various elements, components, regions, layers, positions and/or sections, these elements, components, regions, layers, positions and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer, position or section from another element, component, region, layer, position or section. Thus, a first element, component, region, layer, position or section discussed above could be termed a second element, component, region, layer, position or section without departing from the teachings of illustrative embodiments.

Spatially relative terms, such as “forward”, “rearward”, “above”, “below”, “beneath”, “downward”, “vertical”, “horizontal”, and “transverse” as well as any other similar spatial terms may be used herein for the ease of description to describe one element or feature's relationship to another element(s) or feature(s) of the above embodiments. These terms, as utilized to describe the present invention should be interpreted relative to a watercraft floating in calm water.

The terms of degree such as “substantially”, “about” and “approximately” as used herein mean an amount of deviation of the modified term such that the end result is not significantly changed.