A boat propelling system capable of reducing electric power consumption includes an outboard engine main body, a swivel bracket arranged to allow the outboard engine main body to pivot in a right-left direction with respect to a hull, an electric motor arranged in the swivel bracket to pivot the outboard engine main body in the right-left direction, a transmission mechanism arranged in the swivel bracket to transmit a driving force of the electric motor to the outboard engine main body, a locking clutch arranged to lock the transmission mechanism so that the outboard engine main body will not be pivoted in the right-left direction by an external force acting on the outboard engine main body, a steering section arranged to steer the outboard engine main body, a steering angle sensor arranged to detect a steering angle of the steering section, a pivot sensor arranged to detect an actual pivot angle of the outboard engine main body, and an ECU arranged and programmed to control the electric motor based on a result of a comparison between a threshold value and an angle difference between a target pivot angle of the outboard engine main body based on the steering angle and an actual pivot angle. The threshold value can be set based on a boat speed and a trim angle.