Yes, you are right on. My friend has a 55 foot Nordhavn and even my own boat There is only one hydraulic rod/piston and it is ether controlled by the GPS, autopilot or manually. The GPS system and A.P. will control the hydraulic pump. Manual, you are turning the wheel which acts as a pump to move the rod which moves the rudder.A yacht of that size should have had redundancies built in AND a manual override.....