Why do we refer to a ship, plane or train as she when sexing is clearly inappropriate?

Herman Melville did not reveal why Cap'n Ahab referred to the great white whale as Moby Dick when it could just as easily have been Moby Mabel. Perhaps he got a really close look upon his first encounter?

Educated viewing of Erithacus rupecula will not separate the humble robin for a start - unless observed laying eggs.
Resort to the DNA element and you still have a 20% chance of error.