That's what I'm thinking too, and furthermore that the mechanical advantage in that system means that the rudder can only be moved by hand very slowly.
There's probably no way to move it by hand on a ship of sufficient size, only hydraulically, but emergency steering would be a completely separate hydraulic system (separate pump, rams, and mechanical controls) powered by a separate generator or engine. The mode of operation is a person goes down into the steering gear room (as parent mentioned) and responds to instructions telephoned, shouted in person, radioed, or some other way communicated. E.g. "starboard 15°". So your "fly-by-wire" controls can be all kinds of messed up, so long as you can disconnect them and operate the backup system by hand you maintain control.
On a small boat we just have a small cover in the cockpit over the rudder pin where we can insert an emergency tiller and steer "by hand" (realistically need to quickly rig some lines for mechanical assistance but that's okay because the secondaries are right there).
I assume it would be a hydraulic system using hand-power. If it's got electrical/mechanical power and is intended to be an infrequently used emergency system, then you probably have to count on it being poorly maintained and still have a fully manual fallback.
From what I understand, these sort of systems on old 20th century warships ar least are all hand-crank powered.
