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Comment by mpyne | Hacker News Reader

Only 1 U.S. submarine has ever had 2 nuclear reactors (bonus points for those who know why it was designed with 2).

Soviet submarines often had 2 though.

For the U.S. submarines they frequently would test shutting down the 1 operational reactor at-sea and trying to recover from the casualty, just to prove that it could be done when you didn't have time to pre-plan.

Edit: U.S. subs do have diesels though. So next question: how do you bring up the diesel engine and its required auxiliaries without AC?

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Here's the black start procedure for the 1950's-era ship I worked on. No idea if this is at all similar to how they start diesels on a modern sub.

1. Hand-crank a small diesel engine connected to a small air compressor.

2. Use the small air compressor to build up pressure to start the emergency diesel generator.

3. Start the emergency diesel.

4. Using the emergency power, run one of the large air compressors to build up pressure for starting the main generators.

5. Start the main generators.

The emergency diesel was near the stern of the ship, away from the generator room, to ensure an generator room fire couldn't take out the emergency diesel.

I knew it! Generators all the way down!

It's actually similar on a submarine, except that there's no need to hand-crank an air compressor as we have tons of compressed air already available on a submarine.

Also, once the diesel is running it is used to power the electrical buses that provide the minimal pumps and other gear needed to recover the reactor and eventually restart (or emergency restart) the turbogenerators that provide ship's service power.

Unfortunately there's no room to have separate emergency generators and emergency diesel so they are co-located.

You skipped a step. LOLz.

I skipped quite a few in fact. I love getting people interested in submarines but I have no great desire to irritate my friends at NR by creeping past the rules regarding NNPI (whether of the U variety or otherwise).

I can appreciate that. And I was just having a little fun with you.

But I was simply referring to the part where you surface the boat before starting the diesels. I think some folks might be under the impression that you can run those while submerged which is most decidedly NOT the case.

What I think many people don't realize is that a reactor shutdown is likely to be a mission-over/career-ender type of deal for almost the entire officer corps onboard. It's not supposed to happen EVER. It's like forgetting your gun as you exit the helicopter.

BTW, It was "supposed to work" but didn't isn't an excuse. You (as an officer) are responsible. That's what maintenance and drills are for. Reactor shuts down and diesels won't come up? Wow. Major UNSAT. A dead-in-the-water carrier is almost as bad as running the damn thing aground.

I'm wondering how the CNO felt about that poodle-screw.

You can run the diesels underwater though. Obviously there is a limit, but surfacing the boat is neither required (sea state permitting) nor desired ("OH LOOK, A SUB!!").

DIW on a CVN is a big deal, that is true (though hardly a career killer by itself for O-gang, even the ones in Reactor Department). NR takes nuclear safety very seriously and the carrier won't sink just from loss of propulsion so the reactors will very much be configured to fail conservative if necessary.

Even on a submarine, which can flounder without propulsion and only has a single reactor, we do scram drills all the time. A scram can occur for no better reason than that reactor protection was feeling finicky that day, so the drills are designed to assume a scram will happen, and recover safely and efficiently.

On the other hand, an unplanned scram really is one of those things which may get someone disqualified from watchstanding, and possibly de-nuked completely, since those usually represent a crew that doesn't properly respect the power of the reactor.

I don't know that I'd call running with the snorkel up anything but non-submerged. Although I will give you that running at p-depth is almost the same thing. I'm sure you'll agree that anything other than underway on main propulsion is a far less preferable situation than normal ops.

BTW, I spent some time as a bubble-head, so I do understand what you're talking about here. Just keep in mind that not everything you've heard about subs is true and not everything I knew about subs is still true. A lot has changed since I was in.

USS Triton, needed high speed to shadow carrier groups

I would have also accepted: "needed two reactors because it was the only USN submarine with two shafts."

Technically, you mean the only USN SSN with two shafts, but even that is incorrect. Nautilus was a conventionally-driven submarine with counter-rotating screws just like its diesel-electric WWII-era forebears.

The first single-shaft U.S. submarine was a diesel research vessel, USS Albacore, which proved the feasibility of many innovations which were later ported over to the nuclear submarine fleet. USS Skipjack was the first nuclear submarine to include most of those features, including single-screw design.

Never been in the navy, so just guessing. Just kicking around ideas...

Option A: You hand-crank the beast somehow? To get the glow-plug going, you again use a hand generator? Hopefully enough to bootstrap the generator (maybe it's a smaller generator that runs a larger one)? Generators all the way down?

Option B: You blow ballast somehow and use the inrushing water to drive a turbine that runs the generator or gets it going?

Option C: You manually pull the control rods and switch the coolant loop to run a small turbine to prime the generator?

Option D: You mayday and get a jump from the Russian/Chinese/Iranian sub following you around?

Option E: You try something dumb and dangerous with hydrogen peroxide from the torpedoes (I think/hope that that's phased out now)?

I think it's mostly batteries, a sub operating at constant depth and in motion is negatively buoyant. If something goes wrong and it loses propulsion, power has to be available immediately to operate the systems that can handle the emergency - whether it's blowing ballast or restarting the reactor. This is a somewhat different constraint than the procedure described by the other reply - ships float without power, subs, not always.

I mentioned this upthread - USS Thresher[1] seems to have suffered a loss of both propulsion and ballast control while near test-depth with, unfortunately, tragic results for the vessel and all on board.

[1] http://en.wikipedia.org/wiki/USS_Thresher_(SSN-593)

Option F: Compressed air. Turns out mechanical systems are stupid simple to hand-power and yet can store a ton of energy usable without fancy equipment. Plus it turns out we might need compressed air for this no matter what depending on where the boat is at.

Ah, very cool. Oftentimes the crudest solutions are the best.

All merchant ships are required to have enough compressed air for several starts (and we're talking about much larger diesel engines). I'd assume it's the same for a nuclear sub.

With a storeable dc power source, just like a car or truck.

I suppose if that failed or had somehow discharged incorrectly, there should probably be a way to handcrank the diesel generator, like how early cars required hand cranking to start.

PS: I had to look it up, but that's an interesting reason why that us sub had 2 nuclear reactors.

Nice try, Ivan.

Remember, it's called the silent service for a reason. Those who know, don't tell; those who tell, don't know.

Water pressure?

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