Abstract:
A small watercraft and outboard motor are configured so that operator-activated command signals are communicated from a control unit in the hull of the watercraft via a local area network to engine component actuators in the outboard motor. The local area network enables a simplified connection to be used between the watercraft hull and the outboard motor to provide communication of the command signals as well as to provide communication of navigational and engine parameter information. The local area network enables the user to operate the watercraft with increased reliability. Because of the small number (e.g., one) of control connections required between the hull and the outboard motor, the process for installing the outboard motor onto the watercraft hull is greatly simplified, which reduces the time and the cost initial installation and the cost of repair.

Description:
PRIORITY INFORMATION 
   This application is based on and claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2001-326813, filed on Oct. 24, 2001, the entire contents of which are hereby expressly incorporated by reference herein. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to a local area network (LAN) system for communicating control signals and other information in a small watercraft having an outboard motor. 
   2. Description of the Related Art 
   Watercraft (e.g., personal watercraft or boats) typically incorporate internal combustion engines along with propulsion units to provide power and propel the watercraft in a variety of popular applications. The internal combustion engines and propulsion units are outboard motors on many watercraft. In a conventional watercraft, cables, wires, and hoses are used to manage and operate the watercraft and the outboard motor. The number of cables, wires and hoses needed to interconnect the hull and the outboard motor often introduce complications and delays when mounting the outboard motor to the hull. 
   For example, cables and wires are conventionally used to control a throttle that regulates the opening of an engine throttle valve of the outboard motor, to control a shift device that switches a transmission to provide forward, reverse and neutral operational modes of a propulsion unit of the outboard motor, and to control a steering mechanism that translates a driver&#39;s steering requests into directional movements of the propulsion unit. Hoses supply fuel from a fuel tank to the outboard motor and supply oil from an oil tank to the outboard motor. A wiring harness enables communication between the outboard motor and the hull. For example, navigational information, engine parameters and watercraft parameters are communicated via the wiring harness to a display to be viewed by the operator. A battery cable supplies electrical energy from a battery disposed in the hull to the outboard motor. 
   An arrangement utilizing electrically controlled throttle and transmission activation was proposed in the Japanese Patent JP 3065369. A remote control unit is disposed proximate to the operator&#39;s seat in the hull to enable the operator to perform the shifting and throttling operations via electrical signals communicated from the remote control unit. The electrical signals are communicated to electric motors mounted in the hull that operate actuators and other devices. The actuators and other devices in the hull move wires in response to the operation of various levers of the electronic remote control unit by the operator to cause the shifting and throttling operations. Thus, the outboard motor is controlled according to the movement of the control levers without requiring direct mechanical interconnections from the control levers to the outboard motors. Yet, wires are used to transmit forces mechanically from the actuators and other devices mounted in the hull to the outboard motor to control the engine throttle, transmission shifting, and steering. The actuator wires must be connected between the actuators and the outboard motor when the outboard motor is installed on the hull of the watercraft. 
   Recently, local area network (LAN) systems and developing information technology have been used in watercraft to interconnect the hull and the outboard motor. Known LAN systems communicate with the outboard motor and the watercraft to receive parameters representing the operation of the outboard motor and the watercraft. Information responsive to the parameters are displayed to the watercraft operator. Although such LAN systems reduce the number of wire harnesses in the watercraft, conventional LAN techniques are used only to communicate watercraft and outboard motor parameters to the operator&#39;s display, and the LAN systems are not used to communicate control information from the remote throttle and shifting control unit and from the steering device to actuate the motors that operate the throttle, shifting, and steering mechanisms. Therefore, the number of wires used to control a drive-by-wire system in known watercraft has not been significantly reduced. 
   SUMMARY OF THE INVENTION 
   In accordance with aspects of embodiments of the present invention, a local area network (LAN) system interconnects a watercraft and an outboard motor with minimal connections and wiring to improve the reliability of the interconnections and to simplify the installation time of the outboard motor. The time required to mount the outboard motor to the hull is reduced because of the significant reduction in the number of wires and cables that need to be installed and connected. The LAN system communicates control signals and other information between the hull and the outboard motor. The LAN system enables operation of throttle and transmission actuation and informs the watercraft operator of various watercraft and outboard motor engine parameters. 
   In particular, a watercraft incorporating the embodiments described herein comprises a hull with an outboard motor attached to the rear part of the hull. The watercraft includes a plurality of operator-input systems disposed proximate to the operator&#39;s seat in the hull. The operator-input systems enable operations of the watercraft such as, for example, throttling, shifting, and steering. Response actuators are disposed in the outboard motor. The response actuators control engine parameters in accordance with the operator&#39;s requests as applied to the operator-input systems. The operator requests are communicated from the operator-input systems to the response actuators via a LAN communication system. Using the LAN communication system increases the performance and reliability of the watercraft and simplifies the mounting of the outboard motor to the hull of the watercraft. 
   One aspect of an embodiment in accordance with the present invention is a watercraft that includes an outboard motor mounted on a hull and that includes an operator-controlled navigational unit positioned in the hull. The navigational unit comprises at least one engine operation control unit that receives throttle and shift commands and that generates throttle and shift command signals. The navigational unit further comprises a control unit that receives steering commands and that generates steering command signals. A trim selection control unit receives trim selection commands and generates trim selection command signals. The outboard motor includes actuators that are responsive to control signals to operate a throttle body, a transmission, a steering system, and a trim system in the outboard motor. A control system in the outboard motor is connected via a communication system to the navigational unit. The control system receives the command signals from the control units in the navigational unit via the communication system and generates the control signals to the actuators in the outboard motor. 
   Another aspect of an embodiment in accordance with the present invention is a watercraft that includes an outboard motor. The outboard motor includes an engine that produces a propulsion force through a transmission mechanism. The watercraft comprises an operator-controlled navigational system. The navigational system includes at least one engine operation control unit that receives throttle and shift command inputs, a steering control unit that receives steering command inputs, and a trim control unit that receives trim selection command inputs. The control units generate respective control signals responsive to operator inputs applied to the control units. A display system is located proximate to the navigational system. Actuators in the outboard motor operate a throttle body, a transmission, a steering system, and a trim system in response to respective actuator signals. Sensors detect operating conditions of the watercraft. A control system in the outboard motor communicates with the sensors and with the actuators. The control system is connected via a communication system to the navigational system to receive the control signals from the control units. The control system responsive to the control signals to generate the actuator signals to the actuators. The control system further generates signals to the display system to cause the display system to display information responsive to the detected operating conditions of the watercraft. 
   Another aspect of an embodiment in accordance with the present invention is an outboard motor mounted on a watercraft. The watercraft includes a navigation system that receives control inputs from an operator. The outboard motor includes an engine that produces a propulsion force through a transmission mechanism. The outboard motor comprises actuators that operate a throttle body, a transmission, a steering system, and a trim system. A control system communicates with the navigation system of the watercraft via a communication system. The control system controls the actuators in response to commands received from the navigation system. 
   Another aspect of an embodiment in accordance with the present invention is an outboard motor mounted on a watercraft. The outboard motor includes an engine that produces a propulsion force through a transmission mechanism. The outboard motor comprises actuators in the outboard motor that operate a throttle body, a transmission, a steering system, and a trim system. A control system communicates with a navigation system located in the watercraft. The control system operates actuators in the outboard motor in response to commands received via a communication system from the navigation system. The control system further generates information signals responsive to operating conditions of the outboard motor and the watercraft, and the control system communicates the information signals to a display associated with the navigation system. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments in accordance with aspects of the present invention will be described below in connection with the accompanying drawing figures in which: 
       FIG. 1  is a pictorial illustration of an exemplary watercraft that includes an outboard motor mounted on a hull and that further includes a local area network (LAN) installed between the hull and the outboard motor to enable communication of operator requests from controls in the hull to an electronic control unit that provides actuator signals to a plurality of actuators in the outboard motor; 
       FIG. 2  illustrates a block diagram of the watercraft and outboard motor of  FIG. 1 , which shows a plurality of engine feedback systems, engine controls and engine components connected electronically through a single local area network; and 
       FIG. 3  illustrates a diagram of a local area network connector that advantageously enables communication between various controls on a watercraft and an outboard motor. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   As illustrated in  FIG. 1 , a watercraft  10  comprises a hull  11  for carrying passengers. An outboard motor  12  is attached to the rear part of the hull  11 . In preferred embodiments, communication between the hull  11  and the outboard motor  12  is provided by a controllable area network compatible (CAN-compatible) LAN cable  14  constructed in accordance with the controllable area network specification for vehicles. The cable  14  can also be constructed and operated in accordance with work specifications. 
   The hull  11  comprises an oil tank  15  that stores and supplies oil to the outboard motor  12 . An oil sensor  16  detects the amount of oil in the oil tank  15 . A battery  17  supplies electrical energy to components in the hull  11  and to the outboard motor  12 . A battery sensor  18  detects the voltage of the battery  17 . A control unit  20  is located proximate an operator&#39;s seat and is thus located remotely from the outboard motor  12 . The control unit  20  includes a control lever  24  that is operable by an operator to enable the operator to perform throttling and shifting operations. 
   As illustrated in  FIG. 2 , the control unit  20  includes a start-stop switch  21 , a lever position sensor  22  that senses the position of the control lever  24 , and a trim-tilt switch  23 . The hull  11  also includes a steering wheel  30  positioned proximate to the operator&#39;s seat. The steering wheel  30  includes a steering wheel angle sensor  31 . The control unit  20  and the steering wheel  30  enable the operator to control the direction and velocity of the watercraft  10  and are referred to as “navigation-related” devices. 
   An active monitor  41 , a global positioning system (GPS)  42 , a wireless transmitter  13 , a fuel level meter  51 , and a fuel flow rate meter  52  are also positioned proximate to the operator&#39;s seat so that the devices can be readily observed by the operator. The active monitor  41  advantageously comprises a cathode-ray tube (CRT) or a liquid crystal display (LCD). As discussed below, the active monitor  41  provides the operator and other persons in the watercraft with information regarding the operation of the watercraft. The GPS  42  receives signals transmitted from a plurality of satellites and processes the signals to determine the position of the watercraft  10 . 
   As further illustrated in  FIG. 2 , a fuel hose  54  connects the outboard motor  12  to a fuel tank  53  positioned on the bottom of the hull  11 . Similarly, an oil hose  54  connects the outboard motor  12  to the oil tank  15 . A power cable  56  provides electrical energy from the battery  17  to electrical components in the hull  11  and to the outboard motor  12 . 
   The outboard motor  12  comprises an engine  62  that generates rotational torque by combustion of the fuel from the fuel tank  53  in combination with atmospheric air introduced into combustion chambers at a predetermined air/fuel ratio. The engine  62  transfers the rotational torque to a transmission mechanism  63 , which selectively transmits the rotational torque to a thrust generator (e.g., a propeller)  64  in accordance with the enabled shifting operation (e.g., forward, reverse or neutral). The propeller  64  interacts with the surrounding water and converts the rotational torque into a propulsion force to move the watercraft  10  on the water surface. 
   The outboard motor  12  further comprises an engine control unit (ECU)  61 . As discussed below, the ECU  61  controls the operating parameters of outboard motor  12 . Although not shown in  FIG. 2 , the ECU  61  advantageously comprises a central processing unit (CPU), memory devices (ROM, RAM, etc.), auxiliary memory devices (nonvolatile RAM, hard disk, CD-ROM, magneto-optic disk, etc.), and a clock. 
   The ECU  61  communicates with a plurality of feedback sensors, such as, for example, a throttle opening sensor  71 , a shift position sensor  72 , a steering angle sensor  73 , and an engine speed sensor  74 . The sensors inform the ECU  61  of the operating parameters of the engine  62 . For example, the engine speed sensor  74  detects the speed of the engine  62  and transmits the detected engine speed information to the ECU  61 . 
   The ECU  61  controls the operating characteristics of the outboard motor  12  via a plurality of actuators such as, for example, a throttle actuator  81 , a shift actuator  82 , a steering actuator  83 , and a trim controller  84 . As described herein, the transmission mechanism  63  includes performs a plurality of functions related to the control and the conversion of the rotational torque produced by the engine  62 . In particular, the transmission mechanism  63  includes a gear mechanism (not shown), a clutch mechanism (not shown), a throttle valve (not shown), a shifter (not shown) and a turning mechanism. 
   The throttle actuator  81  opens and closes the throttle valve of the engine  62  according to the lever angle signal from the lever position sensor  22 . The throttle valve regulates the amount of an air/fuel mixture supplied to the combustion chambers of the engine in accordance with the degree to which it is opened by the throttle actuator  81 . The speed of the engine  62  is responsive to the amount of the air/fuel mixture. Thus, the speed of the engine  62  varies in response to the angle of the control lever  24 . The throttle opening sensor  71  detects the opening state (e.g., the percentage or angle of opening) of the throttle valve of the engine  62  and outputs throttle opening information to the ECU  61 . 
   The shifter and the clutch mechanism operate in response to the shift actuator  82  to change the operational mode between the forward, neutral and reverse modes. 
   The turning mechanism operates in response to the steering actuator  83  to change the direction of the thrust generated by the propeller  64 . 
   The start/stop switch  21  operates as an on-off switch that communicates an engine start signal and an engine stop signal to the ECU  61  in response to manual activation by the watercraft operator. The engine  62  may be started from a non-running still state and may be stopped from a running state based on start and stop signals communicated to the ECU  61  from the start-stop switch  21 . The ECU  61  triggers a starter (not shown) to start the engine  62  when a start signal is received. When an engine stop signal is received by the ECU  61 , the ECU  61  stops the ignition to the engine  62 , stops the fuel delivery to the engine  62 , or stops both the ignition and the fuel delivery. 
   The shift position sensor  72  detects the various states (position) of the transmission mechanism  63 , whether it is in the neutral, forward, or reverse position, and outputs the detected shift position information to the ECU  61 . 
   The lever position sensor  22  detects the position angle of the control lever  24  of the remote throttle  20 . The lever position sensor communicates an output signal to the ECU  61  to control the throttle actuator  81  and the shift actuator  82 . The shifter (not shown) in the transmission mechanism  63  changes the state of rotation of the propeller  64  in response to the power generated by the engine  62 . The rotational states of the propeller include a neutral state (non-rotation of the propeller  64 ), a forward state (rotation of the propeller  64  in a direction that propels the watercraft  10  in the forward direction), and a reverse state (rotation of the propeller  64  in a direction to propel the watercraft  10  in the reverse direction). 
   For example, when the control lever  24  is moved toward the bow or stern of the watercraft  10 , a signal is communicated via the LAN to the ECU  61 . When the control lever  24  is moved from a neutral position towards the bow by more than a predetermined angle, the ECU  61  signals the shift actuator  82  to shift the transmission mechanism  63  to the forward state to drive the propeller in the direction that propels the watercraft  10  forward. Likewise, when the control lever  24  is moved from a neutral position towards the stern by more than a predetermined angle, the ECU  61  signals the shift actuator  82  to shift the transmission mechanism  63  to the reverse state to drive the propeller in the direction that propels the watercraft  10  backward. 
   In addition to controlling the direction of rotation of the propeller  64 , when the control lever  24  is tilted toward the bow or toward the stern by more than a predetermined angle, the ECU  61  gradually opens the throttle valve of the engine  62  to allow more air/fuel mixture into the engine  62 . Opening the throttle valve results in an increase in propeller speed to thereby increase the velocity of the watercraft. 
   As fuel is supplied from the fuel tank  53  to the engine  62 , the fuel level meter  51  detects the remaining fuel amount in the fuel tank  53  and outputs a fuel amount signal to the ECU  61 . The fuel flow rate meter  52  detects the flow rate of fuel flowing from the fuel tank  53  to the engine  62  by measuring the amount of fuel flowing out of the fuel tank  53  per unit time. The fuel flow rate meter  52  outputs the fuel flow rate (fuel consumption rate) information to the ECU  61 . 
   The steering wheel angle sensor  31  detects a turning angle of the steering wheel  30  and outputs a steering angle control signal to the ECU  61 . The ECU  61  controls the steering actuator  83  according to the signal from the steering wheel angle sensor  31 . For example, when the steering wheel  30  is turned, the ECU  61  signals the steering actuator  83  to actuate the turning mechanism of the transmission mechanism  63 . The turning mechanism changes the direction of the outboard motor  12  with respect to the hull  11  and changes the direction of the watercraft  10 . 
   The steering angle sensor  73  detects the direction (angle) of the outboard motor  12  relative to the hull  11  and outputs the detected steering angle information to the ECU  61 . 
   The trim control device varies the horizontal plane surface of the watercraft  10  with respect to the surface of the water in the direction of travel of the watercraft  10 . The trim-tilt switch  23  enables the operator to adjust the trim and tilt of the outboard motor  12  with respect to the stern of the hull  11  to allow the operator to optimize the performance and fuel economy of the watercraft  10 . The trim-tilt switch provides the ECU  61  with signals representing an operator request, and the ECU  61  controls the trim controller according to the signals from the trim-tilt switch  23 . For example, when the watercraft  10  is moving forward, setting the trim-tilt switch  23  in the upward direction increases the inclination of the outboard motor  12  toward the tilt range, which raises the bow of the watercraft  10 . Similarly, setting the trim-tilt switch in the downward direction decreases the inclination of the outboard motor  12  toward the trim range, which lowers the bow of the watercraft  10 . The trim/tilt adjustment enables the operator to choose the most efficient (in terms of fuel economy), stabilized, and well-balanced operational state of the watercraft  10 . 
   When the bow rises too high, performance and fuel economy deteriorate due to the increase in the water resistance against the bottom of the hull  11 . When the bow lowers too much, although watercraft acceleration from the standing state improves, the watercraft  10  can become unstable or difficult to maneuver at high speeds. Fuel efficiency and stability at a particular velocity improve when the bow is raised by a predetermined angle measured between a keel line and the water surface. 
   How much the bow is raised or lowered to achieve optimal efficiency depends not only on the trim angle but also on the watercraft speed and load (number of people and amount of equipment in the watercraft). Therefore, an efficient watercraft operating state is realized by choosing a trim angle that correctly corresponds to watercraft speed and load. 
   As illustrated in  FIG. 2 , the LAN cable  14  comprises a hull-side LAN cable  141  with a connector  142  and a motor-side LAN cable  144  with a connector  143 . The connector  142  and the connector  143  are mechanically engaged to electrically or optically interconnect the hull-side LAN cable  141  and the motor-side LAN cable  144 . 
   The hull-side LAN cable  141  is connected to the start-stop switch  21 , the lever angle sensor  22 , the trim-tilt switch  23 , and the steering wheel angle sensor  31  to receive the control signals responsive to the operator commands. The control signals from each sensor or switch are transmitted from the hull-side LAN cable  141  to the ECU  61  via the connectors  142  and  143  and the motor-side LAN cable  144 . The ECU  61  is responsive to the control signals to generate the signals applied to the actuators of the outboard motor  12 , as discussed above. 
   The hull-side LAN cable  141  is also connected to the GPS device  42 , to the fuel level meter  51 , and to the fuel flow rate meter  52 . The feedback signals from the GPS device  42 , the fuel level meter  51  and the fuel flow meter  52  are transmitted to the ECU  61  via the hull-side LAN cable  141 , the connectors  142 ,  143 , and the motor-side LAN cable  144 . Similarly, information to be displayed on the active monitor  41  is transmitted from the ECU  61  to the active display  41  via the motor-side LAN cable  144 , the connectors  143 ,  142  and the hull-side LAN cable  141 . 
   The LAN cable  14  (comprising the LAN cables  141  and  144 ) serves as a control information transmission path to communicate control signals to the outboard motor  12 . The LAN cable  14  also serves as an information transmission path to communicate information to the active display  41  to inform the operator of the operating conditions of the watercraft  10 , such as, for example, parameter information from the sensors and navigational information. 
   Unlike previously known watercraft, the hull  11  and the outboard motor  12  of the watercraft  10  of  FIGS. 1 and 2  are interconnected via a single communication cable such as the LAN cable  14 . Thus, no moving actuator wires or actuator cables are needed between the hull  11  and the outboard motor  12  to communicate control forces from actuators in the hull  11  to components in the outboard motor  12 . Therefore, control signals (e.g., information related to the control of the outboard motor  12 ) and display information (e.g., signals representing operating conditions that are not related to the control of the outboard motor  12 ) can be sent through the single cable  14 . 
     FIG. 3  illustrates the connectors  142  and  143  of the LAN cable  14  in more detail. As discussed above in connection with  FIG. 2 , the hull-side LAN cable  141  originates in the hull  11 , and the motor-side LAN cable  144  originates in the outboard motor  12 . When the outboard motor  12  is mounted to the hull  11 , the connector  142  of the hull-side LAN cable  141  and the connector  143  of the motor-side  143  are mechanically engaged in one simple operation to quickly interconnect the cables  141  and  144  and thereby enable communication of control signals and information between the hull  11  and the outboard motor  12 . 
   In the illustrated embodiment, the connector  142  has a female (recessed) shape, and the connector  143  has a male (projecting) shape. The outside diameter of the male connector  143  has a size and shape corresponding to the inside diameter of the connector  142 . In preferred embodiments, the connector  142  is mounted at a fixed location on the side of the hull  11 . After the outboard motor  12  is mounted to the stern of the hull  11 , the LAN cable  14  is connected by inserting the connector  143  of the motor-side LAN cable  144  from the outboard motor  12  into the connector  142  of the hull-side LAN cable  141 . In particularly preferred embodiments, the connectors  142  and  143  are provided with a quick-fit (e.g., a push and turn) type of locking mechanism. 
   In preferred embodiments, the outside diameter of the hull-mounted connector  142  has a dimensional limit of, for example, 40 millimeters to enable easy installation of the connector  142  into the hull  11 . The hull-side LAN cable  141  is usually inserted into a preformed passage in the side of the hull  11 . Thus, the outside diameter of the connector  142  should be sufficiently smaller than the inside diameter of the preformed passage. Preferably, the dimensions of the motor-side LAN cable  144  are also selected to be of similar size and shape as the hull-side LAN cable  141 . 
   The active monitor  41  displays many types of useful information to the watercraft operator, including, for example, boat speed S, fuel consumption E, fuel consumption rate F, fuel amount FA, navigation range L, navigation time T, a return-to-port warning, an optimum trim position (angle), and engine conditions. 
   The ECU  61  performs a plurality of calculations (described below) based on position information from the GPS device  42 , the fuel amount from the fuel level meter  51 , and the fuel flow rate from the fuel flow rate meter  52 . The ECU  61  transmits the calculated results via the LAN cable  14  to the active monitor  41  to show the results to the watercraft operator. 
   The boat speed S (in km/h or knots (nautical miles/h)) is calculated as the traveled distance of the watercraft  10  divided by the travel time. In the preferred embodiment, the traveled distance is based on the position information from the GPS device  42 . 
   The fuel consumption E (in liters/km or liters/nautical mile, etc.) represents the amount of fuel consumed per unit of distanced traveled. The fuel consumption E is calculated from the watercraft speed S using the following equation:
 
 E=F/S ,  (1) 
 
where F represents the amount of fuel consumed per unit time (fuel consumption rate in liters per hour).
 
   The fuel consumption rate F is determined according to the fuel flow rate information from the fuel flow rate meter  52  and the watercraft speed S. The fuel consumption E depends on the speed of the watercraft  10 . The fuel consumption E generally decreases as the speed of the watercraft  10  approaches the most efficient speed of the watercraft  10 . The most efficient watercraft speed can be defined as a speed where the outboard motor trim angle is set to allow the watercraft to travel in the water with the least possible resistance. 
   The fuel amount FA is the amount measured as a unit of volume of fuel remaining in the fuel tank  53 . The fuel amount FA can be calculated from the fuel amount information from the fuel level meter  51 . The fuel amount FA can also be calculated from the following equation:
 
 FA =V0− V   1={umlaut over ( A )}V,   (2) 
 
where V0 is the maximum capacity (in liters) of the fuel tank  53 , and where V1 is the amount of fuel (in liters) consumed by the engine  62 . V1 can be calculated from the fuel flow rate based on the fuel flow rate information from the fuel flow rate meter  52 .
 
   The navigation range L is the maximum distance that can be traveled from the current position and can be calculated from the residual fuel amount FA and the fuel consumption E using the following equation:
 
 L=FA×E=ÄV×E.   (3) 
 
   Since the fuel consumption E varies with the boat speed S, the navigation range L calculated using the equation L=ÄV×E depends on the watercraft speed S. For example, the navigational range L represents the distance that can be reached when the watercraft  10  is assumed to maintain the current boat speed for a predetermined amount of time. 
   The navigation time T is the period of time that the watercraft can navigate at a current watercraft speed S. The navigational time T can be calculated from the navigation range L and the watercraft speed S using the equation:
 
 T=L/S.   (4) 
 
   The trim angle is closely related to watercraft efficiency. Displaying an optimum trim angle corresponding to a watercraft speed that enables maximum efficiency is convenient for the operator. The operator can operate the trim-tilt switch  23  to set the trim angle of the outboard motor  12  to the displayed optimum trim angle. 
   A conversion table showing the relationship between the watercraft speed S, watercraft load, and the optimum trim angle can be provided in the auxiliary memory device of the ECU  61 . If the conversion table is provided in the auxiliary memory device of the ECU  61 , the optimum trim angle can be found by referring to the conversion table and to a parameter such as the watercraft speed S. 
   When parameters cannot be measured automatically within the watercraft  10 , the parameters can be entered manually by the operator while referring to the optimum trim angle displayed. Finding an optimal operating setting for various possible watercraft parameters can also be accomplished, for example, by using tables or graphs showing the relation between the watercraft load and the optimum trim angle corresponding to watercraft designs. 
   Optimum trim angles corresponding to watercraft speeds can be obtained by a boat builder or by the operator through watercraft testing. These tests can involve operating the watercraft  10  to measure fuel consumption and stability compared to other watercraft with different trim angles, operational speeds, and loads. 
   Engine parameters can also be displayed on the active monitor  41  to inform the operator of engine condition. For example, the displayed parameters advantageously include engine speed from the engine speed sensor  74 , fuel flow rate information from the fuel flow rate meter  52 , and cooling water temperature from an engine coolant temperature sensor (not shown). 
   If the engine  62  experiences a malfunction, the specific malfunction along with a repair suggestion can be displayed on the active monitor  41 . A malfunction of the engine  62  can be detected when the engine parameters representing the state of the engine  62  are outside the boundaries of respective normal ranges. 
   Parameters requiring maintenance and attention can be displayed by referring to a corresponding table showing an engine maintenance schedule. The engine maintenance schedule can include specific service areas of the engine  62  along with repair suggestions to possible engine problems stored in the auxiliary memory device of the ECU  61 . For example, if the cooling water temperature rises due to a cooling water suction port being blocked, a high cooling temperature can be sensed by a engine coolant temperature sensor (not shown) and displayed on the active display  41  to assist the operator in diagnosis and prevent watercraft damage. 
   When plural outboard motors are provided, the individual operating states of each engine  62  may collectively be displayed on the screen of the single active monitor  41 . 
   The above-described information may be displayed not only with characters but also with graphics of the engine  62  to provide easier understanding by the operator. The operator can also be informed of the state of the watercraft by audible aids in addition to the visual information. 
   In accordance with the embodiments described above, a plurality of actuators such as, for example, the throttle actuator  81 , the shift actuator  82 , and the steering actuator  83 , are disposed in the cowling of the outboard motor  12 . The operation system and sensors in the hull  11  along with the engine sensors are connected through the LAN cable  14  to the ECU  61  in the outboard motor  12 . As a result, the conventional wires and cables for the throttle device, shifting device, and steering device interconnecting the hull and the outboard motor in previously known watercraft configurations can may be eliminated so that the work of attaching the outboard motor can be accomplished easily and quickly using the embodiments described herein. 
   According to the present invention as described above, actuators for driving various mechanisms that function in response operator requests such as throttling, shifting, and steering are disposed in the outboard motor. The operation system and sensors in the watercraft are connected through a communication cable to the ECU  61  controlling the actuators of the outboard motor  12 . The configuration of the LAN connection between the watercraft  10  and the outboard motor  12  provides a significant reduction in the number of wires and cables between the hull  11  and the outboard motor  12  in comparison to a conventional watercraft and outboard motor. Therefore, mounting of the outboard motor  12  to the hull  11  is simplified and improved. 
   Although the present invention has been described in terms of a certain preferred embodiments; other embodiments apparent to those of ordinary skill in the art also are within the scope of this invention. Thus, various changes and modifications may be made without departing from the spirit and scope of the invention. Moreover, not all of the features, aspects and advantages are necessarily required to practice the present invention. Accordingly, the scope of the present invention is intended to be defined only by the claims that follow.