Propulsion Device Control Apparatus

This invention relates to a propulsion device control apparatus configured to control a propulsion device of a boat.

Conventionally, there has been known a device that controls three propulsion devices mounted on a boat according to the operation of two right and left levers. Such a device is described, for example, in JP 2008-128138 A and JP 2006-035884 A. In the device described in JP 2006-035884 A, a right propulsion device is controlled according to a lever position of a right lever, a left propulsion device is controlled according to a lever position of a left lever, and a virtual lever position between the lever position of the right lever and an operation position of the left lever is calculated, and a middle propulsion device is controlled according to the calculated virtual lever position. In the device described in JP 2008-128138 A, when a main switch of only the right propulsion device is turned off, the middle propulsion device is controlled according to the operation by the right lever, and when a main switch of only the left propulsion device is turned off, the middle propulsion device is controlled according to the operation by the left lever.

However, as in the device described in JP 2008-128138 A, when the middle propulsion device is controlled according to the virtual lever position between the lever position of the right lever and the operation position of the left lever, it is difficult to efficiently use the middle propulsion device when one lever fails. Further, as in the device described in JP 2006-035884 A, when a lever for operating the middle propulsion device is automatically changed according to a situation, there is a possibility that the lever is operated against the intention of a boat operator.

An aspect of the present invention is a propulsion device control apparatus configured to control a propulsion device of a boat. The apparatus includes: a lever configured to instruct a propulsion direction of forward, neutral, or rearward and a target propulsion force of the propulsion device; and a controller including a processor and a memory coupled to the processor and configured to control the propulsion device based on an instruction from the lever. The propulsion device includes: a right propulsion device provided on a starboard side of the boat; a left propulsion device provided on a port side of the boat; and at least one middle propulsion device provided between the right propulsion device and the left propulsion device. The lever includes: a right lever corresponding to one of the right propulsion device and the left propulsion device; and a left lever corresponding to other of the right propulsion device and the left propulsion device. The controller is configured to switch between: a normal mode in which the middle propulsion device is controlled based on the instruction from the right lever and the instruction from the left lever; and a preset mode in which the middle propulsion device is controlled based on the instruction from a preset lever of the right lever and the left lever. The controller controls the middle propulsion device in the normal mode when both the right lever and the left lever are normal, while limits a propulsion force of the propulsion device corresponding to the one and switches from the normal mode to the preset mode when the one fails.

Hereinafter, an embodiment of the present invention will be described with reference to.is a block diagram schematically illustrating an example of an overall configuration of a propulsion device control apparatus (hereinafter, the apparatus)according to the embodiment of the present invention. The apparatusis applied to a boaton which three or more propulsion devicesare mounted, and controls each of the propulsion devices. Each propulsion devicemay be an engine-driven propulsion device or a motor-driven propulsion device.

As illustrated in, the apparatusmainly includes a plurality of the (for example, three) propulsion devicesmounted on the boat, and two leversthat are provided in a steering seat of the boatand instruct a propulsion direction of any one of “forward”, “neutral”, and “rearward” of each propulsion deviceand target propulsion force. The plurality of propulsion devicesinclude a right propulsion deviceR provided on the starboard side of the boat, a left propulsion deviceL provided on the port side of the boat, and one or more (for example, one) middle propulsion devicesM provided between the right propulsion deviceR and the left propulsion deviceL. The two leversinclude a right leverR corresponding to one (usually the right propulsion deviceR) of the right propulsion deviceR and the left propulsion deviceL, and a left leverL corresponding to the other one (usually the left propulsion deviceL) of the right propulsion deviceR and the left propulsion deviceL.

The right propulsion deviceR is connected to a right ECUR, and the right propulsion deviceR is controlled by the right ECUR. The middle propulsion deviceM is connected to a middle ECUM, and the middle propulsion deviceM is controlled by the middle ECUM. The left propulsion deviceL is connected to a left ECUL, and the left propulsion deviceL is controlled by the left ECUL. Hereinafter, the right ECUR, the middle ECUM, and the left ECUL may be collectively referred to as a propulsion device ECU.

The right leverR and the left leverL are connected to a lever ECU. The lever ECUis connected to each of the right ECUR, the middle ECUM, and the left ECUL. Instructions from the right leverR and the left leverL are transmitted to the right ECUR, the middle ECUM, and the left ECUL via the lever ECU. Hereinafter, the right ECUR, the middle ECUM, the left ECUL, and the lever ECUmay be collectively referred to as a controller.

is a diagram illustrating an example of a correspondence relationship between a lever position of each leverand a propulsion direction of each propulsion deviceinstructed according to the lever position. As illustrated in, each leveris provided to be swingable, for example, in the forward-and-rearward direction of the boat. When the lever position of each leveris in the neutral position, “neutral” is instructed as the propulsion direction of each propulsion device, in which the boatis not propelled forward or rearward in the neutral position. When the lever position of each leveris in the forward position on the front side of the neutral position, “forward” for propelling the boatforward is instructed as the propulsion direction of each propulsion device. When the lever position of each leveris in the rearward position behind the neutral position, “rearward” for propelling the boatrearward is instructed as the propulsion direction of each propulsion device.

The center lever position of the neutral position is set to 0%, and the foremost and rearmost lever positions are set to 100%. The lever position of each leveris detected as a voltage value by a potentiometer (not illustrated) and is input to the lever ECU.

The lever ECUincludes a computer including a processor such as a CPU, a memory such as a ROM and a RAM, and other peripheral circuits. The lever ECUconverts a voltage value [V] indicating the lever position input from each leverinto a propulsion direction (forward, neutral, rearward) and a lever position [%], and transmits the propulsion direction and the lever position to each propulsion device ECU.

is a diagram illustrating an example of a correspondence relationship between the lever position of each leverand target propulsion force of each propulsion deviceinstructed according to the lever position. When each propulsion deviceis an engine-driven propulsion device, the propulsion force of each propulsion deviceis adjusted by, for example, an opening degree or a position (hereinafter, a throttle position TH) of a throttle valve that adjusts an intake amount of an engine. When each propulsion deviceis a motor-driven propulsion device, the propulsion force of each propulsion deviceis adjusted by a motor rotation speed. Hereinafter, as an example, a case in which each propulsion deviceis the engine-driven propulsion device will be described. Therefore,illustrates the throttle position TH (target value) as the target propulsion force of each propulsion device.

As illustrated in, when the lever position inis in front of 0%, the throttle position TH corresponding to the lever position is set as the target value based on a characteristic at the time of forward movement. When the lever position is behind 0%, the throttle position TH corresponding to the lever position is set as the target value based on a characteristic at the time of rearward movement, which is gentler than the characteristic at the time of forward movement.

Each propulsion device ECUincludes a computer having a processor such as a CPU, a memory such as a ROM and a RAM, and other peripheral circuits. Each propulsion device ECUconverts the lever position [%] of each levertransmitted from the lever ECUinto the throttle position TH (0% to 100%) based on the characteristic ofstored in advance.

Each propulsion device ECUswitches the propulsion direction of each propulsion deviceamong “forward”, “neutral”, and “rearward” by controlling a shift mechanism (actuator) connecting an engine to a propeller. When the propulsion direction of each of the propulsion devicesis “neutral”, the engine and the propeller are disconnected via the shift mechanism, the propeller does not rotate, and each propulsion devicedoes not propel the boat. When the propulsion direction of each of the propulsion devicesis “forward” or “rearward”, the engine and the propeller are connected to each other via the shift mechanism, and the propeller rotates according to the engine speed, whereby each of the propulsion devicespropels the boatforward or rearward.

In addition, each propulsion device ECUcontrols the throttle valve (actuator) to adjust the throttle position TH, thereby adjusting the engine speed of each propulsion deviceand the rotation speed of the propeller. As a result, propulsion force by which each propulsion devicepropels the boatis adjusted.

The right ECUR controls the right propulsion deviceR according to the propulsion direction and the throttle position TH corresponding to the lever position of the right leverR transmitted from the lever ECU. The left ECUL controls the left propulsion deviceL according to the propulsion direction and the throttle position TH corresponding to the lever position of the left leverL transmitted from the lever ECU.

On the other hand, the middle ECUM controls the middle propulsion deviceM in a “normal mode” or a “preset mode”. In the normal mode, the middle ECUM controls the middle propulsion deviceM based on the propulsion direction and the throttle position TH corresponding to the lever position of the right leverR and the propulsion direction and the throttle position TH corresponding to the lever position of the left leverL, which are transmitted from the lever ECU. In the preset mode, the middle ECUM controls the middle propulsion deviceM according to the propulsion direction and the throttle position TH corresponding to a lever position of a preset lever of the right leverR and the left leverL transmitted from the lever ECU.

is a flowchart illustrating an example of propulsion force determination processing of the middle propulsion deviceM executed by the middle ECUM, and illustrates an example of propulsion force determination processing of the middle propulsion deviceM in the normal mode. When both the right leverR and the left leverL are normal, the middle ECUM controls the middle propulsion deviceM in the normal mode. The processing inis started when the middle ECUM starts, and is repeatedly performed at a predetermined cycle.

As illustrated in, first, in S(S: processing step), it is determined whether the propulsion direction corresponding to the lever position of the right leverR coincides with the propulsion direction corresponding to the lever position of the left leverL. When affirmative determination is made in S, the processing proceeds to S, and the middle propulsion deviceM is controlled according to the propulsion direction and the throttle position TH corresponding to the lever position of the preset lever of the right leverR and the left leverL. On the other hand, when negative determination is made in S, the processing proceeds to S, and the middle propulsion deviceM is controlled so that the propulsion direction becomes “neutral” and the throttle position TH becomes 0%. The preset lever is one leverwhich is selected in advance by a user of the boat(that is, a boat operator) from the right leverR and the left leverL and is preset. Information indicating whether the preset lever is the right leverR or the left leverL is stored in advance in the middle ECUM.

is a diagram illustrating propulsion force of the middle propulsion deviceM when the same propulsion direction is instructed by the right leverR and the left leverL. In the example in, since “forward” is instructed by the right leverR and the left leverL, the propulsion direction of the middle propulsion deviceM is also controlled to become “forward”. Although not illustrated in the drawing, when “rearward” is instructed by the right leverR and the left leverL, the propulsion direction of the middle propulsion deviceM is also controlled to become “rearward”. When “neutral” is instructed by the right leverR and the left leverL, the propulsion direction of the middle propulsion deviceM is also controlled to become “neutral”.

In the case of “forward” or “rearward”, the propulsion force of the middle propulsion deviceM is controlled according to the throttle position TH corresponding to the lever position of the preset lever (right leverR in). In the case of “neutral”, the throttle position TH is controlled to become 0%.

Such control of the propulsion direction and the propulsion force of the middle propulsion deviceM is automatically performed corresponding to the lever position of the preset lever, but since the preset lever is the leverthat is selected by the boat operator himself or herself and is preset, it does not violate the intention of the boat operator.is a diagram illustrating the propulsion force of the middle propulsion deviceM when different propulsion directions are instructed by the right leverR and the left leverL. In the example of, since “forward” is instructed by the right leverR and “rearward” is instructed by the left leverL, the middle propulsion deviceM is controlled so that the propulsion direction becomes “neutral” and the throttle position TH becomes 0%. Although not illustrated herein, when the right leverR instructs “forward” and the left leverL instructs “neutral”, when the right leverR instructs “neutral” and the left leverL instructs “forward”, when the right leverR instructs “neutral” and the left leverL instructs “rearward”, when the right leverR instructs “rearward” and the left leverL instructs “forward”, and when the right leverR instructs “rearward” and the left leverL instructs “neutral”, respectively, similarly, the middle propulsion deviceM is controlled so that the propulsion direction becomes “neutral” and the throttle position TH becomes 0%.

For example, for the purpose of turning the boaton the spot, the right leverR and the left leverL may be tilted to the same extent in opposite directions. When the right leverR and the left leverL instruct different propulsion directions, the middle propulsion deviceM is set to “neutral” and, as such, the boat operator's intention to turn the boaton the spot is not violated.

is a flowchart illustrating another example of the propulsion force determination processing in. In the processing of, when affirmative determination is made in S, the processing proceeds to S, and the propulsion force of the middle propulsion deviceM is controlled according to an average value of the throttle position TH corresponding to the lever position of the right leverR and the throttle position TH corresponding to the lever position of the left leverL.

is a diagram illustrating the propulsion force of the middle propulsion deviceM determined in the propulsion force determination processing in. In the example in, since “forward” is instructed by the right leverR and the left leverL, the propulsion direction of the middle propulsion deviceM is also controlled to become “forward”. The propulsion force of the middle propulsion deviceM is controlled according to the average value of the throttle position TH corresponding to the lever position of the right leverR and the throttle position TH corresponding to the lever position of the left leverL. Although not illustrated herein, when “rearward” is instructed by the right leverR and the left leverL, the propulsion direction of the middle propulsion deviceM is also controlled to become “rearward”, and the propulsion force of the middle propulsion deviceM is controlled according to the average value of the throttle position TH corresponding to the lever position of the right leverR and the throttle position TH corresponding to the lever position of the left leverL.

is a flowchart illustrating still another example of the propulsion force determination processing in. In the processing in, when affirmative determination is made in S, the processing proceeds to S, and the propulsion force of the middle propulsion deviceM is controlled according to a smaller throttle position TH of the throttle position TH corresponding to the lever position of the right leverR and the throttle position TH corresponding to the lever position of the left leverL.

is a flowchart illustrating still another additional example of the propulsion force determination processing in. In the processing in, when affirmative determination is made in S, the processing proceeds to S, and the propulsion force of the middle propulsion deviceM is controlled according to a larger throttle position TH of the throttle position TH corresponding to the lever position of the right leverR and the throttle position TH corresponding to the lever position of the left leverL.

is a diagram illustrating the propulsion force of the middle propulsion deviceM determined in the propulsion force determination processing in. In the example in, since “forward” is instructed by the right leverR and the left leverL, the propulsion direction of the middle propulsion deviceM is also controlled to become “forward”. In addition, the propulsion force of the middle propulsion deviceM is controlled according to the smaller throttle position TH of the throttle position TH corresponding to the lever position of the right leverR and the throttle position TH corresponding to the lever position of the left leverL. Although not illustrated herein, when “rearward” is instructed by the right leverR and the left leverL, the propulsion direction of the middle propulsion deviceM is also controlled to become “rearward”, and the propulsion force of the middle propulsion deviceM is controlled according to the smaller throttle position TH of the throttle position TH corresponding to the lever position of the right leverR and the throttle position TH corresponding to the lever position of the left leverL.

Since the normal mode described above is based on the premise that both the right leverR and the left leverL are normal, the middle propulsion deviceM may not be efficiently used in a state where one of the leversfails.

The failure of the leverincludes a failure (a sensor failure) of the potentiometer of the leverthat detects the lever position and a communication failure between the lever ECUand the propulsion device ECU. When the sensor failure occurs on the leverside, for example, the lever ECUgradually decreases a lever position of the failed leverup to 0% by a predetermined amount (for example, 1%) for each control cycle, and transmits the lever position to the propulsion device ECU. When the communication failure occurs between the lever ECUand the propulsion device ECU, for example, each propulsion device ECUcontrols each propulsion deviceby gradually decreasing the throttle position TH corresponding to the lever position of the failed leverup to 0% by a predetermined amount (for example, 1%) for each control cycle. In other words, the propulsion force of each propulsion deviceis limited.

When such a failure of the leveroccurs, and for example, when the propulsion force of the middle propulsion deviceM is controlled according to the average value of the throttle position TH corresponding to the lever position of the right leverR and the throttle position TH corresponding to the lever position of the left leverL, the middle propulsion deviceM cannot be efficiently used. That is, since the throttle position TH corresponding to the lever position of the failed leverconstantly becomes 0%, the throttle position TH of the middle propulsion deviceM can be used only up to 50%.

Therefore, in the present embodiment, the apparatusis configured as follows so that the middle propulsion deviceM can be efficiently used without violating the intention of the boat operator even when one of the leversfails by switching to the preset mode for controlling the middle propulsion deviceM according to an instruction from the preset lever.

is a flowchart illustrating an example of propulsion force determination mode switching processing of the middle propulsion deviceM executed by the middle ECUM. The processing inis started when the middle ECUM starts, and is repeatedly performed at a predetermined cycle. As illustrated in, first, in S, it is determined whether both the right leverR and the left leverL are normal, that is, whether neither the right leverR nor the left leverL fails. When the affirmative determination is made in S, the processing proceeds to S, and the control mode of the middle propulsion deviceM is switched to the normal mode (when the mode is already the normal mode, control in the normal mode is continued).

On the other hand, when negative determination is made in S, the processing proceeds to S, and it is determined whether the middle propulsion deviceM is in “neutral”. When affirmative determination is made in S, the processing proceeds to S, and it is determined whether the lever position of the preset lever is in the neutral position and the “neutral” propulsion direction is instructed from the preset lever. When the affirmative determination is made in S, the processing proceeds to S, and the control mode of the middle propulsion deviceM is switched to the preset mode (when the mode is already the preset mode, control in the preset mode is continued). On the other hand, when negative determination is made in Sor S, the processing proceeds to S, and the control mode of the middle propulsion deviceM is set to the normal mode.

are time charts illustrating a change in the propulsion force (throttle position TH) of each propulsion devicewhen the normal mode is switched to the preset mode. In the drawings, a solid line indicates the current throttle position TH of the middle propulsion deviceM, a two-dot chain line indicates the throttle position TH corresponding to the lever position of the right leverR, and a one-dot chain line indicates the throttle position TH corresponding to the lever position of the left leverL. In the examples of, the right leverR is preselected and preset as the preset lever. Until t(t: time point), in the normal mode corresponding to, the propulsion force of the middle propulsion deviceM is controlled according to the smaller throttle position TH of the throttle position TH corresponding to the lever position of the right leverR and the throttle position TH corresponding to the lever position of the left leverL. More specifically, the throttle position TH corresponding to the lever position of the right leverR is maintained at 80%, the throttle position TH corresponding to the lever position of the left leverL is maintained at 20%, and the throttle position TH of the middle propulsion deviceM is maintained at 20% according to the smaller throttle position TH.

In such a state, when the left leverL, which is not the preset lever, fails at t(negative determination in Sin), the throttle position TH corresponding to the lever position of the left leverL gradually decreases from 20% to 0%, and the propulsion force of the left propulsion deviceL decreases (is limited). At this time, as illustrated in, when the throttle position TH (target value) of the middle propulsion deviceM is simply changed from 20% of the failed left leverL to 80% of the right leverR which is the preset lever, the propulsion force of the middle propulsion deviceM rapidly increases, and the boatis rapidly accelerated.

As in Sto Sin, only when the current propulsion direction of the middle propulsion deviceM is “neutral” and the propulsion direction of the right leverR, which is the preset lever, is “neutral”, switching from the normal mode to the preset mode is permitted, whereby such sudden acceleration (or sudden deceleration) can be prevented.

That is, as illustrated in, at t, neither the propulsion direction of the middle propulsion deviceM nor the propulsion direction of the right leverR, which is the preset lever, is “neutral”, and thus switching to the preset mode is not permitted (No in Sand Sin), and the normal mode is continued (S). In this case, the throttle position TH corresponding to the lever position of the failed left leverL decreases from 20% to 0%, the throttle position TH of the middle propulsion deviceM also decreases from 20% to 0%, and the propulsion force of the left propulsion deviceL and the middle propulsion deviceM decreases (is limited). Thereafter, when the boat operator operates the right leverR to set the lever position to 0% at t(YES in Sand Sin), switching from the normal mode to the preset mode is permitted at t(S). Thereafter, the propulsion direction and the propulsion force of the right propulsion deviceR and the middle propulsion deviceM are controlled according to the operation of the right leverR by the boat operator. In this case, although the middle propulsion deviceM cannot be used until the boat operator operates the right leverR, which is the preset lever, to set the lever position to 0%, the operation of the middle propulsion deviceM according to the intention of the boat operator can be implemented.

It is noted that, in the preset mode in a case where the preset lever fails, since the throttle position TH corresponding to the lever position of the failed preset lever decreases up to 0%, the throttle position TH of the middle propulsion deviceM according to the instruction from the preset lever also decreases up to 0%, and the propulsion force of the middle propulsion deviceM decreases (is limited).

Although not illustrated in the drawing, even if the current propulsion direction of the middle propulsion deviceM is “neutral” (YES in S), when the propulsion direction of the preset lever is not “neutral” (NO in S), switching to the preset mode is not permitted, so that it is also possible to prevent the propulsion force of the middle propulsion deviceM from being suddenly generated. For example, as illustrated in, when the right leverR and the left leverL are operated in opposite directions to turn the boaton the spot, it is possible to prevent the propulsion force of the middle propulsion deviceM from being suddenly generated when the leverfails.

is a flowchart illustrating another example of the propulsion force determination mode switching processing in. In the processing in, when negative determination is made in S, the processing proceeds to S, and it is determined whether a difference between the current throttle position TH of the middle propulsion deviceM and the throttle position TH corresponding to the lever position of the preset lever is equal to or less than a predetermined value a. When affirmative determination is made in S, the processing proceeds to S, and the control mode of the middle propulsion deviceM is set to the preset mode. On the other hand, when negative determination is made in S, the processing proceeds to S, and the control mode of the middle propulsion deviceM is set to the normal mode.

In this case, as illustrated in, when the boat operator operates the right leverR, which is the preset lever, at tand the lever position after the operation approaches the current throttle position TH of the middle propulsion deviceM, switching from the normal mode to the preset mode is permitted at t. In this case, although the middle propulsion deviceM cannot be used until the boat operator operates the right leverR which is the preset lever, the operation of the middle propulsion deviceM according to the intention of the boat operator can be implemented without rapidly changing the propulsion force of the middle propulsion deviceM.

is a flowchart illustrating still another example of the propulsion force determination mode switching processing in. In the processing in, when negative determination is made in S, the processing proceeds to S, and the control mode of the middle propulsion deviceM is set to the preset mode. Next, in step S, it is determined whether the difference between the current throttle position TH of the middle propulsion deviceM and the throttle position TH corresponding to the lever position of the preset lever is equal to or less than a predetermined value p. When affirmative determination is made in S, the processing proceeds to S, the throttle position TH corresponding to the lever position of the preset lever is set as a target value as it is, and the middle propulsion deviceM is controlled.

On the other hand, when negative determination is made in S, the processing proceeds to S, and the middle propulsion deviceM is controlled so that the current throttle position TH gradually changes up to the throttle position TH instructed by the preset lever. For example, the target value is calculated by adding, to the current throttle position TH, a value obtained by multiplying a difference between the current throttle position TH and the throttle position TH of the preset lever by a predetermined coefficient k (k<1), thereby controlling the middle propulsion deviceM. The coefficient k may be a constant or, for example, a variable determined according to the difference between the current throttle position TH and the throttle position TH of the preset lever. For example, the coefficient k is set to a smaller value as the difference between the current throttle position TH and the throttle position TH of the preset lever is larger. In the normal mode, when a change amount of the throttle position TH (target value) per unit time is set as a predetermined value 7 (for example, 10% per 10 msec), such a predetermined value 7 may be multiplied by the coefficient k.

is a time chart similar towhen the normal mode is switched to the preset mode by the processing in. As illustrated in, when the left leverL, which is not the preset lever, fails at t, switching from the normal mode to the preset mode is immediately permitted (from Sto Sin). Then, when a difference between the current throttle position TH of the middle propulsion deviceM when switching to the preset mode is permitted and the throttle position TH of the right leverR, which is the preset lever, is larger than the predetermined value p, the propulsion force of the middle propulsion deviceM is controlled so as to gradually change up to the throttle position TH of the preset lever (from Sto S).

In this case, immediately after the failure of one of the levers, the middle propulsion deviceM is controlled according to the preset lever that does not fail, so that the middle propulsion deviceM can be efficiently used without violating the intention of the boat operator. Further, when the current throttle position TH and the throttle position TH of the preset lever deviate from each other, the propulsion force of the middle propulsion deviceM is controlled to gradually change and, as such, the propulsion force of the middle propulsion deviceM is not suddenly changed.

The preset mode described above is also used when the right propulsion deviceR or the left propulsion deviceL is not operating normally. A case in which the propulsion deviceis not operated normally includes a case in which the propulsion deviceis not operated because the propulsion deviceor the propulsion device ECUis turned off, and a case in which the propulsion deviceand the propulsion device ECUare turned on but the propulsion deviceor the propulsion device ECUis not operated normally due to a failure.

The middle ECUM determines whether both the right propulsion deviceR and the left propulsion deviceL are normally operating. Thereafter, when negative determination is made, the middle ECUM determines that the right propulsion deviceR or the left propulsion deviceL is not normally operating, and switches the control mode of the middle propulsion deviceM to the preset mode (when the current mode is already the preset mode, control in the preset mode is continued).

For example, in a case where the right leverR is preselected and preset as the preset lever, when it is determined that the right propulsion deviceR is not operating normally, the middle ECUM controls the middle propulsion deviceM according to an instruction from the right leverR which is the preset lever, and the left ECUL controls the left propulsion deviceL according to an instruction from the left leverL. When it is determined that the left propulsion deviceL is not normally operated, both the right ECUR and the middle ECUM control the right propulsion deviceR according to the instruction from the right leverR. Even when the right propulsion deviceR or the left propulsion deviceL is not operated normally, the middle propulsion deviceM can be efficiently used without violating the intention of the boat operator by controlling the middle propulsion deviceM in the preset mode.