A system and method of use for a marine vehicle to compensate for the effects of forward velocity of the vehicle and ambient currents of a water medium on lateral thrust from a lateral tunnel in the vehicle. A thruster in the tunnel has a variable pitch propeller rotated by a motor at a maintained constant speed to produce lateral thrust of flowing water through the tunnel. A power supply provides input power to the motor, and voltage and amp meters provide signals representative of the power. A computer generates pitch control signals from the representative signals, and a pitch actuator connected to the propeller and the computer is responsive to the pitch control signals to change the blade pitch of the propeller in order to maintain the lateral thrust at a predetermined level.