Those of you who read "Smoke Test: Once in a Blue Moon" will notice that Captain Lubbock is having a hard time balancing his watch duties with his other chores. You will also note that the Grendelsbane has more engineers than required by the ship design rules, and that no one person is classified as Electronics Officer. The extra engineer is needed so that regular maintenance can be performed each day. (And that's only for a ship purchased at 75% original price -- at 50% I'd have had to add on one or more mechanics.)
Before sitting down to design ships and establish crew berths I researched what current marine freighters carry as crew. Basically, your average ship has a captain and 3 mates, a Chief Engineer and 3 assistants, a Radio Operator, a half dozen deck hands, another half dozen mechanics for the Engineering Department, and a couple of cooks. That's 8 officers and maybe 15 crew. Whew!
Okay, so that's way too many for a 200-dton free trader. So I cut it down to a captain and 2 mates, a Chief Engineer and 2 assistants (that way they can rotate maintenance and watch duties) and one cook/medical technician. But what about larger ships?
Here's where I got clever. Most ship design systems -- whether they be some form of Traveller or Eaglestone's Hybrid Ship Design or whatever -- assign number of crew based on design requirements. That is, they suggest a pilot, navigator, comm/sensor operator and engineering crew based on how large your power plant and drives are (1 per 60 dtons, for example). What I do is to say that this crew requirement is for one watch only. Therefore, you actually need 3 pilots and three navigators (the latter being a mate who is watch commander), and 3 times the number of engineers design specs call for. Plus a Captain, however many stewards you want and one comm operator. The main function of communications is to listen for distress calls, so the comm operator need not be on the bridge at all times; alarms go off if a distress call comes in over the emergency frequency. Gunners are simply crew who are qualified to man the weapons systems on top of their other duties. Let's face it -- how often does a gunner have to shoot at something?
But what about sensors? This is where I cheat. Most pilots will spend their insystem transit watch staring at the compass to make sure course is maintained. They might as well be staring at a radar screen as well. The two instruments can be set one above the other. (A minor alarm will sound if a blip appears to make sure the pilot's attention is drawn to it. Remember the original Star Trek sensor alarm?) The pilot only spots the object and informs the navigator/watch commander who performs the analysis while the pilot goes back to staring at the compass and radar screens.
If this is unsatisfactory, you can always assign 3 sensor operators to the crew. This makes for a lot of NPCs, but the choice is yours. My GURPS Space (supplemented with Traveller books) 200-dton free trader, No Complaints, has a captain and 2 mates, 3 engineers, a maintenance technician, a steward/medical technician, one comm operator (also certified for electronics repair) and 2 pilots. The pilots work 6 hours on and 6 off during insystem transit. During FTL transit, the pilots and comm operator stand watches divided into 6 hours "fire watch" patrolling the ship, 6 hours scut work, and 6 hours rest time. The 3 engineers are organized to stand watch 6 hours, do maintenance work 6 hours, and have 6 hours rest time. No Complaints needs 36 man-hours of maintenance work each day, so the maintenance tech has to work 12 hours a day. Total crew for the ship is eleven: 6 officers, and 5 ratings. Seems like a lot for a 200-dton ship, but it feels more like a merchant ship, and "excess" crew can be NPCs. For a Traveller-designed ship, like Grendelsbane, I drop the 2 pilots from the roster. (My GURPS Space design is based on the Alcubierre-Van Der Broeck warp drive and allows for 60% of ship space for cargo, even with the larger crew, and room for 4 passenger cabins with 12 square feet each. Most of the crew share a cabin with another person.)
For warships, I have 2 sensor operators on each shift (one for PESA, and one for AESA) and 1 comm operator per shift. The battle stations for the 4 sensor operators and 2 comm operators who are off-duty will be in the Command Information Center. Off-duty pilots and navigators will be in Auxiliary Control.