1. Field of the Invention
The present invention relates to a navigation control system for a ship including a ship body having an operator seat and at least one outboard motor containing an engine, and specifically, to a navigation control system including constant velocity navigation control of the ship.
2. Description of the Related Art
In JP2008-87736A or JP2004-142538A, a navigation control system for a ship including a ship body having an operator seat and at least one outboard motor containing an engine is disclosed. The ship is a small type ship, for example, such as a motorboat. In JP2008-87736A, the outboard motor has a throttle actuator that controls a throttle opening of the engine, a shift actuator that controls a shift position, and an engine control module, and the engine control module controls the throttle actuator and the shift actuator. Further, near the operator seat of the ship body, operation amount computing means is provided. The operation amount computing means detects an operation state based on an operation input from an operator and computes control command values containing start and stop of the outboard motor, the throttle opening, and the shift position. The operation amount computing means transmits the control command values to the outboard motor via communication means, and the outboard motor controls the start and stop of the engine, the throttle opening, and the shift position based on the received control command value. However, JP2008-87736A does not disclose constant velocity navigation control of the ship.
JP2004-142538A discloses a propulsion control apparatus containing constant velocity navigation control of a ship. JP2004-142538A discloses switching from a constant velocity navigation mode to a normal navigation mode, and, at the switching from the constant velocity navigation mode to the normal navigation mode, the constant velocity navigation control is cancelled and switched to the normal navigation control.
Since the navigation control system disclosed in JP2008-87736A does not contain constant velocity navigation control, even when the engine revolution speed of the outboard motor is constant, the ship velocity against to the ground is continuously affected by water flow and waves and changes in traveling on water, the ship velocity changes due to slight turn by steering, and thus, the constant velocity is not sustainable. Under the circumstances, when navigation is performed while the constant velocity is sustained, it is necessary for the operator to adjust the ship velocity by operating an operation lever corresponding to the outboard motor and adjusting the engine revolution speed of the outboard motor based on information from a ship velocity meter. Thus, the operation by the operator becomes complex and the proficiency of the operator is necessary. Since the navigation control system disclosed in JP2008-87736A does not contain constant velocity navigation control, when accurate navigation of a predetermined distance is performed in a predetermined time, as described above, there are problems that the complex operation of the operation lever is necessary for the operator and the arrival may be late for a predetermined time due to the influence of water flow at navigation with the amount of lever operation of the operation lever fixed constant. Further, in a small type ship such as a motorboat, sometimes the boat tows a water ski or a wakeboard while turning or slaloming at a fixed velocity, and a skilled operation technique for the operation lever of the operator is necessary. Thus, there is a problem that the operation of the motorboat is difficult for a beginner having a poor operation technique.
According to the constant velocity navigation control disclosed in JP2004-142538A, the operation of the operation lever at constant velocity navigation can be simplified. However, in the propulsion control apparatus of JP2004-142538A, for example, when the constant velocity navigation mode is switched to the normal navigation mode for dealing with an emergency that a player of water ski or wakeboard towed by the ship falls into the water or the like, the constant velocity navigation mode is cancelled, and therefore, it is difficult to easily perform the control of returning from the normal navigation mode to the constant velocity navigation mode. If the ship velocity is excessively increased by the operation lever in the normal navigation mode, the ship may be in danger of runaway.