Control device for vessel equipped with a turbocharger engine

A first target air quantity, by which a requested torque can be achieved by an operation of a variable in relation to a Ansaugeigenschaft actuator is calculated using a first parameter. A second target air quantity with which the required torque can be achieved by an operation of a variable with respect to a turbo charging property actuator is calculated using a second parameter. A value of a first parameter changes in response to a decrease of the required torque at or below a first value to a value that reduces an efficiency of a conversion of an air amount into torque. Further, a value of the second parameter starts in response to that the required torque down is lowered to or a second reference value which is greater than the first reference value to change in a direction in which the conversion efficiency is reduced, and gradually changes in a direction in which the conversion efficiency is lowered, according to the further lowering of the required torque from the second reference value to the first reference value. The set air ratio is set in a period in which the required torque is larger than the first reference value to a first air ratio and is switched in response to a decrease of the required torque to the first reference value or below a second air ratio that is leaner than the first air ratio.