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Comment by philip1209 | Hacker News Reader

Is max torque on an typical nuclear submarine limited by the max reactor output, or can they rely on batteries to exceed this temporarily?

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Generally it’s just various design parameters. Until the newest (and not-yet-built) Columbia-class, boats are all steam propulsion, and you can hit various pressure limits for components without maxing the reactor out. That said, yes, with nominal conditions generally All Ahead Flank will have the reactor output at 100%. All Back Emergency usually hits some other limit first.

Columbia-class is electric drive, which is absolutely wild to me. Those are monstrous motors.

Source: I ran a reactor on a Virginia-class (not USS Virginia, the subject of the article, but in the same class).

Thanks for the detailed answer!

My understanding is the electric motors have in general gotten scary-powerful. I know some cruise ships have switched over to them because it simplifies the overall mechanical architecture (fewer moving parts, fewer high-pressure fluid circuits). Some of the Royal Carribean fleet has "azipods" that can be angled 360 degrees to provide arbitrary thrust for simplifying docking and undocking.

Totally, and the controls for the motors have to be crazy now. Imagine trying to reliably switch and vary that amount of power to turn on and off, and control speed at that level of power

Electric drives are nothing new on submarines in general; the _Gato_ class were diesel-electric, and the French and Chinese apparently prefer nuclear-electric. But I think this is the US Navy's first nuclear-electric ship

Nah, we’ve had two nuclear-electric boats before: Tullibee and Glenard P. Lipscomb. They just weren’t successful (Tullibee was to some extent, but she was also quite small).

From first principles I'd expect the functional limit not to be one of power generation but of energy transfer. The limit probably manifests as wiring and motors overheating in a full electric drive (I don't think any subs are...) or as sound, heat and fatigue in reduction gears and gear shafts.

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