Abstract: A method of operating a thruster apparatus involves causing a first propeller to rotate in response to pressure of a first flow of pressurized hydraulic fluid, and causing a second propeller to rotate in response to pressure of a second flow of pressurized hydraulic fluid separate from the first flow of pressurized hydraulic fluid. Thruster apparatuses are also disclosed.

Abstract: A fluid power apparatus is connected to a pressurized fluid supply and a conventional helm pump controlled by the helm of a vessel to shift the rudder. The apparatus comprises an actuator cylinder connectable to the rudder, and a servo cylinder and a main valve connected to the helm pump to pass fluid therebetween and between the actuator cylinder. The actuator cylinder and servo cylinder have respective bodies and piston rods, and portions of the servo cylinder and actuator cylinder are connected together for concurrent simultaneous movement along respective longitudinal axes. Valve shifting structure is responsive to a change in fluid signal from the helm pump applied to the servo apparatus. Fluid diverting structure is responsive to a threshold supply pressure so as to actuate the valve to stop flow of supply fluid when supply pressure drops below the threshold pressure.

Abstract: A fluid power apparatus is connected to a pressurized fluid supply and a conventional helm pump controlled by the helm of a vessel to shift the rudder. The apparatus comprises an actuator cylinder connectable to the rudder, and a servo cylinder and a main valve connected to the helm pump to pass fluid therebetween and between the actuator cylinder. The actuator cylinder and servo cylinder have respective bodies and piston rods, and portions of the servo cylinder and actuator cylinder are connected together for concurrent simultaneous movement along respective longitudinal axes. Valve shifting structure is responsive to a change in fluid signal from the helm pump applied to the servo apparatus. Fluid diverting structure is responsive to a threshold supply pressure so as to actuate the valve to stop flow of supply fluid when supply pressure drops below the threshold pressure.