Late to the game... But my two bits,
I agree with what folks have been speculating regarding the Core Crystal as the likely vessel that contains the ship's identity. But I think what makes up that identity encompasses every aspect of the ship, it' crew and the crystal's history. The main hint I base that on is the way Grimm describes the Itasca as a storied ship. The Itasca has a history and reputation that makes it a high value target/trophy. Perhaps that logic could also be applied to the strength of the ship's personality. Also, Grimm mentioned that a ship's performance was seemed to be enhanced when it's captain treated it as a living thing.
What defines the ship's personality? My thinking is that the personality is defined as the Core absorbs meaning from the ship's name and purpose, as well as the crew's expectations and beliefs regarding the ship, especially the captain's. Plus, based on Lady Lancaster's comment about the crystals at the vattery behaving differently, perhaps the crystals already have an intrinsic personality that develops as they are formed? So my guess is that the personality is built on the crystal + The ship (design and name) + the commander and crew + history.
Random supporting observations:
The Preddy and Grimm seemed to be in sync such that Preddy claimed that he heard her the best and Folly noted that Grimm and the ship were one in the same. My guess is that there is a symbiotic connection between ship and commander. And also with the crew to a lesser extent.
Each ship has a unique "battle cry" that seems to correlate to it's name and/or personality. No mention was made whether or not the name is given before or after it's maiden voyage. So if the name influences the personality or if the personality drives the naming is not yet defined.
When the Preddy's dive song kicks in, the crew is almost compelled to join in.
Journeyman's weirdly intimate relationship with Preddy may be more important to the fact that he can squeeze more performance out of her systems than his technical skills.
Random thought... How messed up must the Glorious be considering how incompetent it's commander is?
-DavicusPrime