I have read through the book several times, and while I have found what stats I should give them, and how many can fit on a class of ship, I have never been able to find where it tells you how many crew members you should place on an GM controlled opposing ship. I'm certain it's in there somewhere, so if someone could tell me where the information is, I would really appreciate it.
If you go by the sample ships on the CRB, as many crew as there is complement.
I'd either agree with The Ragi, and go for the full compliment (unless you feel some story-driven reason to make it less) or alternatively, match the player's crew assuming they're roughly the same size of ship. This way you're balancing the action economy.
I'm not really sure how it works when say, a medium player ship faces a big NPC ship (like say, a cruiser). The action economy could get pretty strange. But if you're talking an explorer class (i.e. sunrise maiden) PC ship vs a similar ship, if there were only 4 players, I'd hesitate to put 6 on the npc ship.
Probably safe to say that, barring unusual circumstances, most enemy ships should have a full crew compliment.
Hmm, I'm not sure I like the idea of always maxing it. As Wingblaze said, once you got into a large ship vs a small one, things would get rough. It also doesn't look like Paizo sticks with that either. Looking at the ships in the AP's, temple of the twelve has a freighter with 6 crew, but then splintered worlds has an explorer with 4, and the ruined clouds has an explorer with 2. I thought there was a system that told you how many crew members to use based on CR and party size, but I guess I was wrong. I may just have to test it, and wing it for a while.
That would suck.
If I remember correctly, no matter how many people are onboard, they can't take more starship actions than they have roles, except where noted otherwise (I think engineers and gunners are an exception to the general rule).
I know you can only have one Captain and one Pilot, but I believe you can have multiple Science Officers. It's the multiple gunners that worries me, when I ran a fight where my four players fought a ship with a full 6 crew members, the NPC's ability to fire twice as many weapons was super rough to deal with, even after I started making them overconfident.
I would run use the minimal crew count for a ship and if this means the enemy has more gunners then the players, the players have to deal with it (maybe stand in an arc with less weapons or outside of weapon range).
Four PCs is the default assumption in most of the APs and balance considerations. That makes it easier.
You can have one captain, one pilot, and multiple of everything else until you get to the max crew limit. This isn't really about the number of warm (or not warm) bodies on board; it's about the number of crew actions.
A four PC vs six NPC fight is going to be a little ugly for the PCs and the enemy ship tier better reflect that if you want balance. I'd say off hand that a two crew action advantage is probably equivalent to +1 ship tier as a guess for these level of numbers. Obviously the first few actions matter a lot more than the 5th/6th.
It'll also depend on the enemy ship. If the ship has multiple unlinked gun mounts, that can be very bad for the players if the enemy has the gunners to man them. If they only have two weapons per arc (a turret and one arc weapon) then more gunners is irrelevant.
Thanks for the help everyone. I'll have to do more experimentation to figure out what works best, but I really agree that is the NPC's have a crew advantage, that should affect CR. I'll also have to think about how I design their ships, and try not to overarm them with guns if they already have extra gunners. I really like the starship rules, but this question has been on my mind since I read the AP, and saw the vastly varying amount of crews.
You are wise to think carefully Morganator.
Let's face facts - people have been playing D&D/Pathifnder/etc for many years. We know to playtest, balance, etc. and there's years worth of what worked and what didn't. Starfinder gets a lot of "free" quality with this legacy.
But starship combat ain't that. It is in effect a completely new mini-game and it's barely been tested compared to the legacy that supports the rest of the game. Everything about it is open to review and re-evaluation. It may work well when it stays in its proverbial lane but fall apart if it drifts outside of it. Or not. Who knows. Time will tell. Personally I feel like the balance is off somewhere with the DCs and the npc crews. (I suspect there was a mistake in development, they fixed the DCs in errata, but never adjusted the NPC crews. Just my hunch.) But I'm sure everyone has their own peeve.
Games are supposed to be fun. Games that don't feel "fair" are usually not fun, so encounter balance is key, and your caution is wise. And you can always own it with your players - "Hey, I'm not sure how this is supposed to work, so I may need to tweak it as we go"