Beyond that, assigning gender to oceans or ships is a romantic conceit you find in poetry, but there are different reasons behind this enculturation.

Seamen who have a relationship with ships and the sea often call the ocean she. I think extending this personification is how cars become/became female to men as in your example “She’s a great little car.” In fact, if you set up the item (like a car) as a metaphor, and go through traits one by one, you can see how this concept can build. (Everything from color to shape to handling to physical details, etc…)

The moon whose cycles are monthly is often related to females–whose cycles are monthly.

But the origin is more or less impossible to pin down. After all, metaphor and personification begin in the eye of the beholder.

As for the sun and moon – the former has traditionally been seen as masculine,the latter feminine – don’t ask me why!

http://www.poetry-chaikhana.com/F/FrancisofAss/CanticleofBr.htm

Add – my son says the Greek Goddess of the Earth is feminine and she is also the Goddess of fertility so that explains “Mother Earth” – I think!