The reason we call(ed) ships 'she' is a hold over from when English
actually had grammatical gender (which is applied more-or-less
arbitrarily - i.e., has nothing to do with actual gender). We are
normally taught that in language, the genders are masculine,
femenine, and neuter. But linguistically speaking, they are really
animate and inanimate, and in some languages there is a modified
version of the animate - femenine. At some point, English began to
label inanimate objects that moved (thus becoming in some way
animate) or used for transportation with the femenine gender. The
same applies to other forms of transportation - in the old "She'll be
comin' 'round the mountain" song, the 'she' is a stagecoach.
So, one could say that it is a linguistic anachronism and thus should
be eliminated. But on the other hand, English is filled with
linguistic anachronisms, so why bother? I personally prefer to use
she - I think it sounds better, and it helps prevent confusion in the
sentence (which can fill up with many 'it's very quickly - for the
same reason, I have no objection to the conventional capitalization
of the word 'God" when referring to the Abrahamic deity.
Jamie