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Finally, a HN thread that I can contribute to and I'm 9 hours late to the party. I was serving in the engineering department on a USN aircraft carrier (non-nuc
by hudibras 14y ago
Finally, a HN thread that I can contribute to and I'm 9 hours late to the party.
I was serving in the engineering department on a USN aircraft carrier (non-nuclear) when a cascading casualty led to all boilers going off line. The ship had an emergency diesel generator aligned to automatically power up, but it failed to start due to a previously-unknown problem. So an 80,000 ton warship with 5,000 people on board slowly drifted to a stop, completely dark except for emergency 60's-era-battle lanterns that were already starting to dim.
No steam = no electricity (the normal ship's generators were steam-powered) and no electricity = no steam (because the start-up feedwater pumps and air blowers for the boilers were electric).
One of the other two EDGs was already down with a casualty which left a single diesel generator that had to be started with compressed air stored in two huge bottles--so basically had two chances to get the ship moving again. (No electricity = no air compressors to refill the bottles.) After a few hours of double- and triple-checking the alignment of the diesels, electrical systems, and boilers (the original steam plant casualty had to be diagnosed) using flashlights in temperatures well into the triple digits (no electricity = no air condi...you get the idea) we successfully started the one remaining diesel which provided AC to the boilers to start up.
By far the scariest day I ever had in the navy. Only saving grace was that we weren't flying planes at the time.
- scrumper 14y agoInteresting story, thanks for sharing. Glad I'm reading about it and not living it. I don't know much about this sort of thing, so I'll ask the obvious dumb question: why no batteries to start the diesel generator? Was it too big? Edit: Reading on, it seems like compressed air is the norm. Is it more space efficient than a battery big enough to start a large generator?
- hudibras 14y agoI think it was because the system was simpler and more reliable with no moving parts besides valves, just a giant air bottle with pipes leading to each of the cylinders. No motor to worry about or lead-acid batteries to maintain. The whole system probably took up way more room than a starter motor would but excessive space or weight is not a big concern on an aircraft carrier.
- cobrausn 14y agoI think it also had something to do with age - newer vessels (submarines, at least) use a large lead acid battery array for emergency power when needed... and by emergency power, I mean enough power to start the emergency diesel generator.
- mpyne 14y agoSubmarines do have a large lead-acid battery for emergency power. In fact, the WWII-era boats had bigger and better batteries. However the battery isn't there to start the Emergency Diesel Generator. Submarine EDGs are air started, for many very good reasons. We still need the batteries since it's possible to suffer a loss of all AC power while the boat is submerged far beyond feasible snorkel depth, and have to recover from it without broaching.
- VLM 14y agoSquare/cube law strikes again. You can only run an automotive starter continuously like a minute or so (at absolute best) before something melts down and the system is scrap. Scaling the power cube up by a factor of a thousand or so and the cooling square surface area up by a hundred or less and suddenly you get like one revolution of the motor before the starter windings and relay/contactor melt down. Not pretty. Of course you could make everything unimaginably immense but that starts making air tanks and air compressors look cheap.
- rdl 14y agoCould you have hacked something up using a starter cart or even an aircraft or APU or something (or a launch or cable to an escort), if the two tries had failed, but for some otherwise-corrected problem so a third try would work? Or I guess just transported some compressed air from an escort, too -- I'm not sure what volumes you're talking about, and if the other gas cylinders a warship probably has on board would be suitable)
- sneak 14y agoPresumably they have more than one of the same class of ship, which (further presumably) has the same emergency start tanks (and air pumps + power to refill them for additional tries). Could be a loooong wait, though. I guess that's why they have two.