Way too many people. Just like how subs are over manned.
Subs operate at really minimal manning, if you look at size. A Burke has 300something crew, while an Ohio only has ~150.
As I understand it, the Virginia-class still has a Chief of the Watch (as the person in charge of the watch section) and a single Helmsman, no Dive.
Subs are built around "One person per job to be done per watch." Which gives you something like 30-37 people on watch times 4 watches, plus 10-15 people outside the watchbill. (CO, XO, COB, yeoman, doc, Supply Officer, and cooks)
There's a few jobs that could be combined, sure. There's 4 people in Sonar, each one individually watching a different system plus a supervisor. And like you said, you don't need Dive, Helm, Planes, Messenger.
But you're still going to have both the sensor and shooter watches. In sub terms, both Sonar, Firecontrol Tech, and Torpedoman.
Even a tiny ship like the Rocinante or NR1 is going to have a person manning the sensors and the point defenses are going to be on "full auto" as long as they're away from a space station.
There isn't going be volume for "Roving". Spacecraft are not going be like the space station depicted here:
Roving watches give you bodies to respond to sudden holes in the ship. Not from battle damage, from debris and meteoroids.
But yes, it's probable that we could reduce some of the engineering watches by virtue of being able to put remote displays on those systems.
But spaceships will be
big when we get to nuclear-powered spacecraft that can handle continuous burns.
Even a minimal spaceship will need berthing, crews mess, and the actual work areas where the sensor consoles are and where the atmosphere control systems are. Which means there
will be space to wander.
Don't need helmsman, planesman and diving officer, one person can do that. Just as airliners got rid of radioman, navigators, engineers, etc, the vehicles don't need as crew. See B-2 vs B-1/B-52.
One person
is doing all that. The Helmsman/Pilot/Sailing Master is ONE position. The Lee Helm/Messenger is a second position, and they trade who is driving every hour or so. Lets the current driver get up and "dispose of used caffeine".
There's a whole
lot of
stuff in a ship, and the person keeping track of that
stuff needs to spend no more than 5-7 hours doing that. What I have read about the better operational cycle was 12 hour days, but each set of 12s was split into a 5hr and a 7hr watch, with everyone in that 12 awake all 12 and running drills etc. Only rarely would they run a drill that would require waking up the other 12s. So that's 4 watch sections. Plus a 5th watch section that's kinda screwed since they're the drill monitors and are doing drills for 14 hours, and in addition they're taking a kickout watch.
Large cruise ships have just one person standing engineering watch. And it is more than just propulsion, in addition to electrical power generation, it is also monitoring fresh water production, sewage treatment, trash incineration, etc.
Citation needed, please.
Because the USN would absolutely have one person on propulsion, one on power generation, one doing fresh water, one doing sewage treatment, etc ad nauseam.
And frankly I'm having a hard time seeing how they can keep all the stuff going with only one person.
Use the NR-1 manning and start subtracting from there.
400 ton vessel with a crew of 13.
That's probably broken down as 4 people per watch section times 3 watch sections, plus the actual Officer In Charge. Reactor Operator, Helmsman, Sonar, "Officer of the Deck" or maybe "Scientist". Nothing to take away.