What is the origin of the tradition of say "her" to a ship?

According to my marine friends, they refer a ship as her because it's like a lady for them.as for our culture,we take care of the ladies very much. And they apply it to ships. They take good care of their ships to the extent that they almost treat it like a living thing. Their ship is very precious to them.

Among the theories as to why ships are referred to as female, one claims that crews believed the ship represented their mother, another that it is because early ships were dedicated to a goddess.