Say that you have a ship with a crew rating of 30. What type of acquisition roll do you make to upgrade one's crew rating?

Does one use the rules for replenishing one's crew, but using the penalties assumed by Good or Best craftmanship items?

Or does one acquire it using the rules for acquiring ship components because (on pg. 193, Core Rulebook) the crew rating costs Ship Points?

It's... really really really hard. There are limited rules for doing this.

A few things you can do:

1.) Give a player character the job of Chief Bosun. Immediate +5 there.

2.) Crew improvements that can be added after game start are in into the storm page 163. Only the 'Best Quality' adds to Crew Rating, which adds +5... and it is unknown if this stacks with itself...

And that's about it. The core rules cost ship points, and as such can only be obtained prior to game start...

I vaguely recall the qualities for crew being in Battlefleet Koronus, but I don't have my PDFs handy.