being relatively movable with respect to its element and slidable with respect thereto for one direction of movement of the element and movable therewith in the other direction of movement of its element application_number US 85706677 A description with reference to fig1 an actuator made according to the invention is utilized in a marine propulsion system and control therefor but it is to be understood that the actuator of the invention is not restricted to use in such systems but may find use in virtually any control system requiring a mechanical output which is responsive to plural inputs of the same or different mediums the marine drive includes an engine 10 contained in an engine room 12 in a ship or the like the engine 10 drives a propulsion shaft 14 connected to a propeller or the like not shown the shaft 14 receives rotational power from the engine 10 via a gear unit 16 the engine 10 is normally controlled from a pilot house 18 having a conventional speed control 20 connected via an air conduit 22 to a conventional air pressure controller 24 to an engine speed governor 26 the governor 26 may be for example a woodward ug 8 governor manufactured by woodward governor nederland b v of hoofdorp the netherlands and forms no part of the present invention the governor 26 may also be manually controlled within the engine room by means of a conventional mechanical actuator 28 the engine 10 is provided with a hydro mechanical sensor apparatus 30 of the type available from caterpillar tractor co the assignee of the present application as part no 3n5760 the sensor apparatus 30 will typically monitor the oil pressure of the engine 10 the water temperature in its cooling system and sense an.