One time, we lost propulsion because a 24v supply wire hidden in a control cubicle had a terminal that had vibrated loose. Since all the relays and controls in that row were wired in series, this caused the rest downstream of it to lose power, too. This, in turn, caused that generator to become completely uncontrollable. As in, the controls at the EOS could neither shut it down nor open the breaker to it. Even the E-stop mushroom button at the engine's control panel wasn't working.
Because it was no longer operating at the correct RPM due to the electronic governor losing power (this caused it to revert to a mechanical governor on the engine itself), the output frequency on the generator was incorrect, which caused it to trip the other generators offline on reverse power trips. Since it was a diesel-electric vessel, which now had one generator online which was malfunctioning and wasn't even recognized by the drive motor controllers as being online and closed to the bus, the pilothouse lost their handles and we started drifting in a circle.
Our ship had four mains feeding into a single 4160V electrical bus, with three normally online and one as a backup. The engines were 16-cylinder EMDs turning AC alternators, and they were controlled using Siemens SIMATIC S5/SIMADYN D PLCs, a bit older and more obsolete than the SIMATIC S7s involved in the Stuxnet incident with Iran's nuclear centrifuges at Natanz.
The Chief Engineer on watch had a great deal of familiarity with the vessel class, and he did two things pretty much immediately:
- Ran out into the panel room and started yanking on wires in the control cubicle until he saw one spark, pretty much identifying the fault immediately.
- Opened the bus tie breaker in the middle of the bus to isolate the malfunctioning main engine to one end of the vessel (it's a double-ended RORO and everything is double-redundant, basically a ship mirrored at both ends).
We regained propulsion pretty quickly, but by then, the tugs had already pulled alongside and were hooking up. We didn't ram into anything and no one was hurt, luckily.
Time taken to identify the problem and regain propulsion? About three to five minutes, and that was with an experienced chief who knew the plant inside and out. Now, imagine that you're two minutes away from an allision or collision, on a giant container ship where all the major equipment is spread over an area the size of a football field, and there are alarms going off and pajeets running around in circles flailing and cursing and shitting everywhere. It literally doesn't matter what you do. You're fucked.
