Patent Publication Number: US-2022234701-A1

Title: Rescue system

Description:
TECHNICAL FIELD 
     The present invention relates to a rescue system for a watercraft. 
     BACKGROUND ART 
     JP6605363B2 discloses an emergency stop apparatus of a watercraft such as a small boat. The emergency stop apparatus includes a transmitter held by a person of the watercraft to transmit a radio signal, a receiver installed on the boat to receive the radio signal transmitted by the transmitter, and a control device that, based on the received radio signal, stops the engine of the watercraft in emergency. The control device stops the engine when it is determined that the person having the transmitter has fallen overboard from the watercraft based on the strength of the received radio signal. According to the emergency stop apparatus disclosed by JP6605363B2, when a person (a crew member or a passenger of the watercraft) falls overboard from the watercraft, it is possible to prevent the watercraft from moving away from the person in the water. 
     However, even though the engine is stopped in emergency, the watercraft keeps moving forward due to the inertia, and therefore, the distance between the watercraft and the person who has fallen overboard from the watercraft (hereinafter referred to as the “overboard person”) may widen. To quickly rescue the overboard person, it is preferred to keep the watercraft positioned near the overboard person. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing background, a primary object of the present invention is to provide a rescue system for a watercraft which enables quick rescue of an overboard person. 
     To achieve the above object, one aspect of the present invention provides a rescue system ( 1 ) for a watercraft ( 2 ), comprising: a control device ( 3 ) provided in the watercraft; a portable device ( 4 ) held by a person on board the watercraft and communicating with the control device; and a position detection device ( 17 ) that detects a position of the watercraft, wherein the control device detects a fall of the person from the watercraft based on a signal from the portable device, stores the position of the watercraft indicated by a signal from the position detection device when the fall of the person from the watercraft is detected as an overboard event detection position, and controls at least one of a propulsion device ( 7 ) and a steering device ( 8 ) of the watercraft based on the overboard event detection position and a current position of the watercraft such that the current position of the watercraft approaches the overboard event detection position. 
     According to this aspect, since the control device of the rescue system detects an overboard person based on the signal from the portable device and makes the watercraft approach the overboard person, quick rescue of the overboard person can be achieved. 
     In the above aspect, preferably, when the fall of the person from the watercraft is detected, the control device performs a stop control to stop the propulsion device or to make a speed of the propulsion device extremely low and thereafter controls the propulsion device and the steering device to make the watercraft automatically navigate toward the overboard event detection position. 
     According to this aspect, it is possible to make the watercraft approach the overboard person. 
     In the above aspect, preferably, the control device stops the propulsion device when a distance between the overboard event detection position and the current position of the watercraft is less than or equal to a prescribed determination value. 
     According to this aspect, it is possible to prevent the overboard person from being caught in the propulsion device. 
     In the above aspect, preferably, the rescue system further comprises a rescue equipment ejection device that ejects rescue equipment from the watercraft to an outside, wherein the control device causes the rescue equipment ejection device to eject the rescue equipment when a distance between the overboard event detection position and the current position of the watercraft is less than or equal to a prescribed determination value. 
     According to this aspect, it is possible to quickly provide the overboard person with the rescue equipment. 
     In the above aspect, preferably, the control device transmits a rescue request signal when a return switch ( 13 ) is not operated by a time when a prescribed time has elapsed from when the fall of the person from the watercraft was detected. 
     According to this aspect, when it is taking time to rescue the overboard person, the control device can automatically transmit the rescue request signal. 
     In the above aspect, preferably, the control device acquires a distance between the control device and the portable device based on the signal from the portable device and determines that the person has fallen from the watercraft when the distance between the control device and the portable device is greater than or equal to a prescribed determination value. 
     According to this aspect, the control device can detect the fall of the person from the watercraft. 
     In the above aspect, preferably, the control device determines that the person has fallen from the watercraft when the control device cannot receive the signal from the portable device. 
     According to this aspect, the control device can detect the fall of the person from the watercraft. 
     In the above aspect, preferably, the portable device has a water detection sensor ( 52 ) that detects contact with water, and transmits or stops a water detection signal to the control device according to a detection state of water, and the control device determines that the person has fallen from the watercraft based on the water detection signal. 
     According to this aspect, the control device can detect the fall of the person from the watercraft. 
     In the above aspect, preferably, the portable device acquires the position of the portable device based on a GNSS signal and transmits a rescue signal containing the position of the portable device. 
     According to this aspect, even when the watercraft which the person was on board does not perform rescue work for some reason, the portable device can request rescue to other watercraft or the control station. 
     According to the foregoing configuration, it is possible to provide a rescue system for a watercraft which enables quick rescue of an overboard person. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an explanatory diagram of a rescue system according to an embodiment of the present invention; 
         FIG. 2  is a block diagram of the rescue system; 
         FIG. 3  is a block diagram of a portable device; 
         FIG. 4  is a flowchart showing a procedure of an overboard event detection process; and 
         FIG. 5  is a flowchart showing a procedure of an automatic navigation process. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following, a rescue system for a watercraft according to an embodiment of the present invention will be described with reference to the drawings. 
     As shown in  FIGS. 1 and 2 , a rescue system  1  includes a control device  3  provided in a watercraft  2  and a portable device  4  which is held by a person on board the watercraft  2  and communicates with the control device  3 . The rescue system  1  preferably includes multiple portable devices  4  in accordance with the number of persons on board. The control device  3  is constituted of one or more electronic control units (ECUs) each including a CPU, a ROM, a RAM, etc. The control device  3  is provided in the hull  6  of the watercraft  2 . 
     The hull  6  is provided with a propulsion device  7 , a steering device  8 , a rescue equipment ejection device  9 , a steering wheel  11 , an acceleration/deceleration lever  12 , a return switch  13 , a camera  14 , a surroundings sensor  15 , a touch panel display  16 , and a position detection device  17 . The propulsion device  7 , the steering device  8 , the rescue equipment ejection device  9 , the steering wheel  11 , the acceleration/deceleration lever  12 , the return switch  13 , the camera  14 , the surroundings sensor  15 , the touch panel display  16 , and the position detection device  17  are connected with the control device  3 . 
     In the present embodiment, the propulsion device  7  is an outboard motor  21  mounted on the stern of the hull  6 . The outboard motor  21  includes a vertically extending case  22 , a drive source  23  consisting of an engine or an electric motor and accommodated in the case  22 , a propeller  24  provided on a lower portion of the case  22  so as to be rotated by a driving force of the drive source  23 , and an outboard motor ECU  25  that controls the drive source  23 . the outboard motor ECU  25  is constituted of an electronic control unit (ECU) including a CPU, a ROM, a RAM, etc. In the case where the drive source  23  is an electric motor, the outboard motor ECU  25  preferably includes an inverter circuit. The outboard motor ECU  25  receives a control signal from the control device  3  and accordingly controls the drive source  23 . 
     The steering device  8  includes a stern bracket  27  that supports the outboard motor  21  on the hull  6  so as to be pivotable about a vertical axis and a steering actuator  28  for pivoting the outboard motor  21  about the vertical axis relative to the hull  6 . 
     The steering wheel  11  receives a steering operation of a person on board and outputs a signal according to the steering operation to the control device  3 . The acceleration/deceleration lever  12  receives an acceleration/deceleration operation of the person on board and outputs a signal according to the acceleration/deceleration operation to the control device  3 . 
     The rescue equipment ejection device  9  is a device that ejects the rescue equipment from the watercraft  2  to the outside. Preferably, the rescue equipment is a lifebuoy connected to the hull  6  by a rope, for example. The rescue equipment ejection device  9  is configured to fling the rescue equipment a prescribed distance by using the driving force of the electric motor or the explosive power of gunpowder, for example. Preferably, the rescue equipment ejection device  9  can change the ejection direction of the rescue equipment relative to the hull  6 . For example, the rescue equipment ejection device  9  is provided to be pivotable about a vertical axis relative to the hull  6  and is caused to pivot relative to the hull  6  by the driving force of the electric motor. Also preferably, the rescue equipment ejection device  9  can change the flying distance of the rescue equipment by adjusting the output. 
     The camera  14  captures images of the surroundings of the hull  6 . The camera  14  may be a digital camera using a solid imaging element such as a CCD or a CMOS, for example. At least one camera  14  is provided at an appropriate position on the hull  6 . The camera  14  includes at least a front camera configured to capture images in front of the hull  6 , and preferably includes a rear camera configured to capture images behind the hull  6  and a pair of side cameras configured to capture images on the left and right sides of the hull  6 . The camera  14  preferably is a stereo camera, for example. 
     The surroundings sensor  15  may be a sonar, radar, lidar, or the like. The sonar, radar, lidar, or the like emits sound waves or electromagnetic waves to the surroundings from the hull  6  and captures the waves reflected by an object around the hull  6  thereby to detect the position (distance and direction) of the object. At least one surroundings sensor  15  is provided at an appropriate position on the hull  6 . Preferably, multiple surroundings sensors  15  are provided on the front, rear, left, and right sides of the hull  6 . 
     The return switch  13  is provided on the hull  6  to receive an operation of a person on board. Based on the signal from the return switch  13 , the control device  3  ends the later-described rescue control. The touch panel display  16  outputs images and receives a touch operation of the person on board. 
     The position detection device  17  includes a GNSS (Global Navigation Satellite System) receiver and acquires the position of the watercraft  2  based on a received GNSS signal. 
     The control device  3  includes a communication device  31 , a navigation unit  32 , a rescue control unit  34 , a hull control unit  35 , and an automatic navigation control unit  36 . The communication device  31 , the navigation unit  32 , the rescue control unit  34 , the hull control unit  35 , and the automatic navigation control unit  36  may be realized by a single electronic control unit or may be realized by multiple electronic control units that are connected to each other. 
     The communication device  31  includes a receiver and a transmitter and wirelessly communicates with the control station  41 , multiple other watercraft  42  in the surroundings, a marine information database (DB) server  43 , and multiple portable devices  4  held by respective persons on board. 
     The navigation unit  32  acquires the position of the watercraft  2  from the position detection device  17 . In addition, the navigation unit  32  communicates with the marine information DB server  43  via the communication device  31  to acquire marine information. The navigation unit  32  includes marine map data and creates a route to the destination based on the position of the own watercraft  2  and the destination. The destination is preferably input by a person on board via the touch panel display  16 . The navigation unit  32  creates a navigation image including the position of the watercraft  2 , a marine map around the watercraft  2 , and the route to the destination and displays the navigation image on the touch panel display  16 . 
     The hull control unit  35  controls the steering actuator  28  of the steering device  8  in accordance with the signal from the steering wheel  11 . Thereby, the hull control unit  35  changes the angle of the outboard motor  21  relative to the hull  6 , namely, the steering angle. Also, the hull control unit  35  generates an acceleration/deceleration request for the outboard motor  21  in accordance with the signal from the acceleration/deceleration lever  12 , and outputs the acceleration/deceleration request to the outboard motor ECU  25 . The outboard motor ECU  25  controls the drive source  23  based on the acceleration/deceleration request. Thereby, the hull control unit  35  changes the acceleration of the hull  6 . The outboard motor ECU  25  may be configured integrally with the control device  3  as a part of the hull control unit  35 . Also, the hull control unit  35  controls the steering device  8  and the outboard motor  21  in accordance with the signal from the automatic navigation control unit  36 . 
     The rescue control unit  34  detects a fall of a person from the watercraft  2  (hereinafter may be referred to as an “overboard event”) based on the signal from the portable device  4  carried by each person on board. As shown in  FIG. 3 , the portable device  4  includes a transmitter  51  that transmits a radio signal, a water detection sensor  52  that detects contact with water, a rescue request switch  53 , a GNSS receiver  54 , a control circuit  55 , and a battery  56 . The water detection sensor  52  is preferably constituted of an electric circuit that becomes short circuited so that the voltage is lowered when contacting with water, for example. The control circuit  55  normally makes the transmitter  51  transmits a first radio signal of a prescribed strength. Also, the control circuit  55  preferably makes the transmitter  51  transmit or stop a second radio signal (water detection signal) according to a detection state of water indicated by a signal from the water detection sensor  52 . For example the control circuit  55  transmits the second radio signal when the water detection sensor  52  detects water and stops the transmission of the second radio signal when the water detection sensor  52  does not detect water. Alternatively, the control circuit  55  may transmit the second radio signal when the water detection sensor  52  does not detect water and stops the transmission of the second radio signal when the water detection sensor  52  detects water. In the present embodiment, the control circuit  55  transmits the second radio signal when the water detection sensor  52  detects water. The control circuit  55  continues transmission of the first radio signal regardless of presence or absence of transmission of the second radio signal. Also, based on the signal from the rescue request switch  53 , the control circuit  55  makes the transmitter  51  transmit a rescue radio signal when the rescue request switch  53  is pressed. The portable device  4  is preferably formed in a card shape or a tag shape. Also, the portable device  4  may be incorporated in the equipment worn by the person, such as a wrist band or a belt. 
     In accordance with an overboard event detection process shown in  FIG. 4 , the rescue control unit  34  detects an overboard event based on the signal from the portable device  4 , and when an overboard event is detected, stores the position of the watercraft  2  indicated by the signal from the position detection device  17  as an overboard event detection position. 
     The rescue control unit  34  executes the overboard event detection process shown in  FIG. 4  at a prescribed time interval. First, the rescue control unit  34  determines whether the strength of the first radio signal received by the communication device  31  from the portable device  4  is less than or equal to a prescribed first determination value (S 1 ). When the strength of the first radio signal is less than or equal to the prescribed determination value, it can be inferred that the person holding the portable device  4  has fallen overboard and is apart from the control device  3  by a distance greater than or equal to a prescribed distance. 
     When the strength of the first radio signal is less than or equal to the determination value (the determination result in S 1  is Yes), the rescue control unit  34  determines whether the second radio signal is received (S 2 ). When the water detection sensor  52  detects water, the portable device  4  transmits the second radio signal. Therefore, when the rescue control unit  34  receives the second radio signal, it can be inferred that the person holding the portable device  4  is in the water. 
     When the second radio signal is received (the determination result in S 2  is Yes), the rescue control unit  34  determines that the person has fallen into the water and sets an overboard event detection flag F 1  to 1 (S 3 ). Note that the initial value of the overboard event detection flag F 1  is set to 0. Subsequently, the rescue control unit  34  starts measurement of an elapsed time from when the overboard event detection flag F 1  is set to 1 (S 4 ). 
     Subsequently, based on the signal from the position detection device  17 , the rescue control unit  34  stores the position of the watercraft  2  as an overboard event detection position (S 5 ). Then, the rescue control unit  34  generates an alarm to notify that a person has fallen into the water (S 6 ). The rescue control unit  34  preferably displays the alarm on the touch panel display  16  and/or outputs from a speaker, for example. 
     Next, the rescue control unit  34  determines whether the return switch  13  has been pressed (S 7 ). The return switch  13  is configured to be operated by a person on board the watercraft  2 . A person on board operates the return switch  13  when the rescue control by the control device  3  should be stopped. When the return switch  13  has been operated (the determination result in S 7  is Yes), the rescue control unit  34  sets the overboard event detection flag F 1  back to 0 (S 8 ) and stops the alarm (S 9 ). Thereafter, the rescue control unit  34  repeats the process from S 1 . 
     When the return switch  13  has not been pressed (the determination result in S 7  is No), the rescue control unit  34  determines whether the elapsed time is greater than or equal to a prescribed second determination value (S 10 ). As the case where the elapsed time becomes greater than or equal to the second determination value, it is assumed that the overboard event of a person is not noticed by the other persons on the hull  6  or that the persons on the hull  6  noticed the overboard event of the person but the rescue work is taking time, for example. When the elapsed time is greater than or equal to the second determination value (the determination result in S 10  is Yes), the rescue control unit  34  transmits a rescue request signal via the communication device  31  (S 11 ). The rescue request signal preferably contains information related to the overboard event detection position. The rescue request signal is received by other watercraft  2  traveling around the own watercraft  2  and the control station  41 . The other watercraft  2  and the control station  41  which received the rescue request signal start rescue actions. When the elapsed time is less than the second determination value (the determination result in S 10  is No), the rescue control unit  34  executes the process in step S 7  again. 
     When the rescue control unit  34  detects an overboard event of a person, the automatic navigation control unit  36  controls at least one of the propulsion device  7  and the steering device  8  of the watercraft  2  based on the overboard event detection position and the current position of the watercraft  2  such that the current position of the watercraft  2  approaches the overboard event detection position. Preferably, the automatic navigation control unit  36  controls at least one of the propulsion device  7  and the steering device  8  in accordance with an automatic navigation process shown in  FIG. 5 . 
     In the automatic navigation process, the automatic navigation control unit  36  first determines whether the overboard event detection flag F 1  is 1 (S 21 ). As described above, the overboard event detection flag F 1  is set by the rescue control unit  34  such that, when the rescue control unit  34  detects an overboard event of a person, the overboard event detection flag F 1  is set to 1. 
     When the overboard event detection flag F 1  is 1 (the determination result in S 21  is Yes), the automatic navigation control unit  36  outputs a stop command to the hull control unit  35  to stop the propulsion device  7  (S 22 ). Upon receipt of the stop command, the hull control unit  35  stops the propulsion device  7 . Thereby, the watercraft  2  stops. In another embodiment, the automatic navigation control unit  36  may conduct control to drive the propulsion device  7  at an extremely low speed such that the influence of ocean current is cancelled and the position of the watercraft  2  is maintained. 
     Next, the automatic navigation control unit  36  creates an action plan for making the watercraft  2  automatically navigate from the current position of the watercraft  2  to the overboard event detection position (S 23 ). The action plan includes a time schedule of increase and decrease of the output of the propulsion device  7  and a time schedule of increase and decrease of the output of the steering actuator  28  of the steering device  8 . 
     Next, the automatic navigation control unit  36  controls the propulsion device  7  and the steering device  8  according to the action plan (S 24 ). The automatic navigation control unit  36  sets the required control amount of the propulsion device  7  and the required control amount of the steering device  8  at each point in time based on the action plan, and outputs the required control amount of the propulsion device  7  and the required control amount of the steering device  8  to the hull control unit  35 . The hull control unit  35  controls the propulsion device  7  and the steering device  8  according to the required control amount of the propulsion device  7  and the required control amount of the steering device  8 . Thereby, the watercraft  2  travels toward the overboard event detection position. The process of step S 24  may be executed after a prescribed standby time has elapsed from when the process of step S 22  is executed. 
     Next, the automatic navigation control unit  36  determines whether the distance between the current position of the watercraft  2  acquired by the position detection device  17  and the overboard event detection position has become less than or equal to a prescribed third determination value (S 25 ). When the distance between the current position of the watercraft  2  and the overboard event detection position is greater than the third determination value (the determination result in S 25  is No), the automatic navigation control unit  36  executes the process of step S 24  again. 
     When the distance between the current position of the watercraft  2  and the overboard event detection position is less than or equal to the third determination value (the determination result in S 25  is Yes), the automatic navigation control unit  36  outputs a stop command the hull control unit  35  to stop the propulsion device  7  (S 26 ). Upon receipt of the stop command, the hull control unit  35  stops the propulsion device  7 . Thereby, the watercraft  2  stops. 
     Subsequently, the automatic navigation control unit  36  outputs an activation command to the rescue equipment ejection device  9  to activate the rescue equipment ejection device  9  (S 27 ). Upon receipt of the activation command, the rescue equipment ejection device  9  ejects the rescue equipment to the outside of the hull  6 . Preferably, the activation command contains a target ejection angle of the rescue equipment relative to the hull  6  and the rescue equipment ejection device  9  sets the ejection angle of the rescue equipment relative to the hull  6  based on the target ejection angle. Preferably, the automatic navigation control unit  36  acquires the position of the person who has fallen overboard from the hull  6  (hereinafter may be referred to as the “overboard person”) relative to the hull  6  based on at least one of the image data acquired by the camera  14  and the signal from the surroundings sensor  15  and decides the ejection angle based on the position of the overboard person. 
     When it is determined in step S 21  that the overboard event detection flag F 1  is 0 (the determination result in S 21  is No), the automatic navigation control unit  36  executes normal navigation control (S 28 ). In the normal navigation control, preferably, the automatic navigation control unit  36  creates an action plan for making the watercraft  2  automatically navigate from the current position of the watercraft  2  to the destination, sets the required control amount of the propulsion device  7  and the required control amount of the steering device  8  at each point in time based on the action plan, and outputs the required control amount of the propulsion device  7  and the required control amount of the steering device  8  to the hull control unit  35 . The destination is preferably input by a person on board via the touch panel display  16 . 
     Preferably, the automatic navigation control unit  36  cancels the automatic navigation process of  FIG. 5  when the signal from the return switch  13  indicates that the return switch  13  is operated. 
     The control device  3  of the rescue system  1  according to the embodiment detects an overboard person based on the signal from the portable device  4  and makes the watercraft  2  approach the overboard person. Therefore, quick rescue of the overboard person can be achieved. In addition, since the control device  3  determines an overboard event of a person based on the distance between the watercraft  2  and the overboard person and the presence or absence of detection of water by the water detection sensor  52 , erroneous detection of an overboard event of a person can be avoided. 
     The control device  3  stores the position indicated by the signal from the position detection device  17  when an overboard event of a person is detected as the overboard event detection position, and therefore, the position of the overboard person can be identified. Also, the control device  3  makes the watercraft  2  automatically navigate toward the overboard event detection position even though a person on the watercraft  2  does not manually operate. Therefore, even in such cases as when the fall of a person into the water is not noticed by the other persons on the watercraft  2  or when the persons on board cannot perform rescue actions for some reason, quick rescue of the overboard person can be performed. 
     When an overboard event of a person is detected, the control device  3  executes the stop control to stop the propulsion device  7  (S 22 ), and this prevents the watercraft  2  from moving away from the overboard person. Also, after the stop control, the control device  3  makes the watercraft  2  automatically navigate toward the overboard event detection position (S 23 , S 24 ), thereby to make the watercraft  2  approach the overboard person. In addition, since the control device  3  stops the propulsion device  7  when the distance between the overboard event detection position and the current position of the watercraft  2  is less than or equal to the third determination value (S 25 , S 26 ), it is possible to prevent the overboard person from being caught in the propulsion device  7 . Further, since the control device  3  makes the rescue equipment ejection device  9  eject the rescue equipment when the distance between the overboard event detection position and the current position of the watercraft  2  is less than or equal to the third determination value, it is possible to quickly provide the overboard person with the rescue equipment. 
     The control device  3  transmits the rescue request signal when the return switch  13  is not operated by the time when the prescribed time has elapsed from when an overboard event of a person was detected (S 7 , S 10 , S 11 ). Thereby, when it is taking time to rescue the overboard person, the control device  3  can automatically transmit the rescue request signal. 
     The portable device  4  acquires the position of the portable device  4  based on the GNSS signal and transmits the rescue signal containing the position of the portable device  4 . Thereby, even when the watercraft  2  which the person was on board does not perform rescue work for some reason, the portable device  4  can request rescue to other watercraft  2  or the control station  41 . 
     Concrete embodiments of the present invention have been described in the foregoing, but the present invention is not limited to the above embodiments and may be modified or altered in various ways. For example, in another embodiment, the GNSS receiver  54  and the rescue request switch  53  of the portable device  4  may be omitted. In this case, the configuration of the portable device  4  can be simplified and the size of the portable device  4  can be reduced. 
     In another embodiment, the rescue equipment ejection device  9  may be omitted from the rescue system  1 . In this case, the process of step S 27  in the automatic navigation process preferably is omitted. 
     In another embodiment, the processes of steps S 23 , S 24 , S 25 , and S 26  in the automatic navigation process may be omitted. In this case, when an overboard event of a person is detected, the rescue system  1  stops the propulsion device  7  (S 22 ) and does not cause the watercraft  2  to move toward the overboard event detection position. According to this aspect, the configuration of the control device  3  can be simplified. 
     In another embodiment, the processes of step S 4 , S 10 , and S 11  in the overboard event detection process may be omitted. 
     In another embodiment, the rescue control unit  34  may determine that a person has fallen into the water when at least one of the two conditions that the strength of the first radio signal is less than or equal to the first determination value (S 1 ) and that the second radio signal is received (S 2 ) is satisfied. Also, the rescue control unit  34  may determine that a person has fallen into the water when the first radio signal transmitted from the portable device  4  cannot be received. 
     In another embodiment, the determination condition of step S 7  may be replaced by a condition that the strength of the first radio signal received by the communication device  31  has become greater than or equal to a prescribed determination value. Also, the determination condition of step S 7  may be replaced with a condition that the communication device  31  no longer receives the second radio signal. 
     Instead of the outboard motor  21 , the propulsion device  7  may be a propeller or a water jet provided at the bottom of the watercraft. Also, the steering device  8  may be configured by a rudder pivotably provided on the hull  6  and an actuator for pivoting the rudder. Also, the size of the watercraft  2  is not limited, and the watercraft  2  may be any watercraft of various sizes, such as a fishing boat, a tanker, and so on.