I imagine you may prefer to start naming your basses something - not necessarily a woman's name - when you've got more than one of the same type, e.g. fretted 4. Unless they all have different model names which you can remember, that is.
As I said above, my first three basses initially had male names. Why male? For the same reason that you guys think of your basses as female: you get into some sort of cosy physicality with your instrument, and you often describe it as looking sexy, so thinking of a bass as somehow belonging to the opposite sex probably comes reasonably natural to a straight musician, I imagine. I've never been able to refer to any bass as "he", though, unless in a tongue-in-cheek way.
The reason why I stopped that naming thing is that, at least at the moment, each of my basses is different from all the others, with no doubles except my student bass ("Barry"), so I don't need names to tell them apart, saying "the fretted 5" will suffice.